Catalyst and base-free, direct oxidation of chitin to lactic acid with hydrogen peroxide

Catalyst and base-free, direct oxidation of chitin to lactic acid with hydrogen peroxide | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Catalyst and base-free, direct oxidation of chitin to lactic acid with hydrogen peroxide Xiao Du, Tengfei Li, Lumei Wang, Dezhang Ren, Zhibao Huo This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4495093/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Jul, 2024 Read the published version in Carbohydrate Research → Version 1 posted You are reading this latest preprint version Abstract In recent years, the research on the conversion of chitin to high value-added chemicals has attracted more and more attention. At present, the method of preparing lactic acid from chitin mostly uses strong base or catalyst. These reaction systems have disadvantages such as corrosion of containers and harm to human body. Herein, a simple and effective method to convert chitin to organic acids in catalyst and base-free conditions is developed. The use of H 2 O 2 only can efficiently convert chitin to organic acids in the absence of bases and catalysts. Under the optimal conditions of 30 mg chitin, 2.1 mL water, 0.9 mL H 2 O 2 at 230 o C for 1.5 h, the lactic acid yield of chitin can reach 58.2% and the total organic acid yield can reach 84.0%. This work provides an efficient method for the resource utilization of chitin biomass. chitin catalyst and base-free organic acids H2O2 lactic acid Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction With the rapid development of global industrialization, traditional non-renewable fossil raw materials are rapidly consumed. The development of renewable energy is of great significance. However, even today, fossil fuels still account for a large share of energy consumed [ 1 , 2 ] . Chitin, a polysaccharide extracted from the shells of marine crustaceans, is the second most abundant biopolymer after cellulose and is the main component of crustacean shells such as crabs and shrimp [ 3 , 4 ] . Shrimp shells contain up to 50–60% chitin, and much of this marine shell material is discarded and not used effectively as a resource. According to the statistics of China Fishery Yearbook, China's shrimp production has increased since 2013, and has reached 6.3073 million tons by 2020 [ 5 , 6 ] (Fig S1 ). If the waste shrimp shells can be used effectively, it is of great significance for the utilization of biomass resources. In 2007, Mahlous et al [ 7 ] have proposed a relatively perfect mechanism of shrimp shell preparation of chitin. These shell wastes produce less nitrogen oxides and sulfur oxides than chemicals prepared from fossil raw materials. The carbon dioxide produced also comes from the fixation of atmospheric carbon dioxide by the shellfish themselves, thus forming a certain carbon cycle [ 8 ] . In recent years, the concept of "shell biorefinery" has been put forward to contrast with biorefinery. The biorefinery concept aims to convert lignocellulosic biomass into chemicals. In the concept of shell biorefining, chitin is a potential resource for the production of high value-added compounds [ 9 , 10 ] . Lactic acid is considered to be a cheap, readily available and sustainably renewable biomass resource. It has a strong preservative and fresh-keeping effect, and can be used in food processing, extending shelf life and other functions [ 11 , 12 ] . In addition, lactic acid can be converted into a variety of other chemicals, including propylene glycol and acrylic acid [ 13 , 14 ] . At present, most lactic acid on the market comes from biological fermentation, which has some shortcomings such as unstable yield and long fermentation time. Thus, most of the researches is using cellulose and glycerol to prepare lactic acid [ 15 – 20 ] . In recent years, some progress has been made in the preparation of organic acids from chitin. Gao et al [ 21 ] , in the environment of NaOH, used CuO as the catalyst to oxidize chitin biomass to produce acetic acid with a yield of 38.1% and a small amount of pyrrole at the same time, and directly reacted with shrimp shells to obtain 47.9% acetic acid. Su et al [ 22 ] studied the low temperature pretreatment of chitin with hydroxide/urea as solvent, and finally obtained a large number of organic compounds including oxalic acid, malonic acid, formic acid and 31.0% acetic acid. Qi et al [ 23 ] used V 2 O 5 as catalyst and O 2 as oxidant to catalyze the conversion of N-acetyl-D-glucosamine (NAG) to acetic acid under the condition of no alkali, and the yield reached 33.4%. Kun et al [ 24 ] explored the process of producing lactic acid from chitin by different metal oxides. When the amount of MgO catalyst was 0.5 g and the reaction time was 6 h, the highest yield of 10.8% of the lactic acid was obtained. This is the first report of catalytic conversion of chitin to lactic acid. However, the use of alkali and toxic catalyst such as V 2 O 5 will cause environmental problems. Therefore the development of new methods for the conversion of chitin to lactic acid without alkali and/or catalysts is highly desired. In previous works, we reported a series of researches on the conversion of biomass and wastes into useful chemicals and fuels such as Preparation of sustainable Aviation Fuel (SAF) from algae, useful chemicals from biomass and so on [ 25 – 29 ] . Herein, we develop a catalyst and base-free, oxidative system for efficient convertion of chitin biomass to lactic acid and other organic acids with hydrogen peroxide (H 2 O 2 ) under relatively mild conditions, which has not been reported before. The obtained acidic products can be separated by simple and mature techniques such as solvent extraction (Scheme 1 ). 2. Experimental section 2.1 Chemicals and Materials Chitin was purchased from TCI. CuO, Ru/C and Pt/C were purchased from Energy Chemical. Co 2 O 3 was purchased from Macklin Chemical, CaO was purchased from General-Reagent, Al 2 O 3 was purchased from Greagent, ZrO 2 and H 2 O 2 (30%) were purchased from Aladdin Chemical. 2.2 General reaction procedures. The conversion of chitin was generally carried out in a small steel tube reactor (inner volume was 5.7 mL). In a typical experiment, chitin and additives were added to the reactor, and then heated in a muffle furnace preset to the reaction temperature and quenched with cold water after the reaction time was reached. The solid product after the reaction was collected by filtration, washed with deionized water and dried, and the liquid sample was collected by filtration with a 0.22 um filter head. Liquid samples were measured using HPLC (Agilent 1260) with SB-AQ columns and UV detectors. 2.3 Calculation of organic acid yield. The yields of all products were calculated on a carbon basis using the following formula. $$\text{The yield of organic acid = }\frac{\text{moles of carbon in product }}{\text{moles of carbon in initial reactant }}\text{×100\%}$$ 3. Results and Discussion 3.1 Catalyst screening In previous studies, metal oxides as catalysts played an important role in the conversion of chitin to organic acids. In this experiment, we selected several metal oxides to test their catalytic performance for the transformation. Due to some precious metals often had good catalytic effects, thus precious metal catalysts were also chosen for performance testing. The experiments were carried out under the initial conditions, 30 mg of chitin as the substrate, 0.09 mmol metal oxide catalysts, 2.66 mL deionized water, 0.34 mL H 2 O 2 , 220 o C, 2 h. By observing the high performance liquid chromatography (HPLC) of the product in Fig. 1 after the reaction, organic acids including formic acid, acetic acid, and lactic acid along with some unknown compounds were formed. The results of catalyst screening were shown in Table 1 . First, the catalysts combined with H 2 O 2 for the reaction were investigated. Among the catalysts tested, it could be found that the selectivity of ZrO 2 and Al 2 O 3 catalysts for the preparation of organic acid from chitin was higher than that of other metal oxides, and formic acid was the main product with 25.4% and 24.9% yield, respectively (entries 3 and 5). The use of other metal oxide catalysts gave the lactic acid as the main product (entries 1, 2 and 4). However, precious metal catalysts Ru/C and Pt/C were uneffective to give the low yield of lactic acid, and 6.6% and 1.5% were obtained, respectively (entries 6 and 7). This might be because metal oxides with the certain oxidation promoted the decomposition of chitin to organic acids. Next, when only H 2 O 2 was added, an interested result was obtained in the highest 38.7% yields of lactic acid and total organic acids of 58.0%, respectively (entry 8). The results were better than the use of metal oxides and H 2 O 2 together, indicating that metal oxides could promote not only the decomposition of chitin but also the decomposition of lactic acid to reduce the yield of lactic acid, it could be explained the role of CuO in mechanism study later. In addition, chitin could also be converted into organic acids to a certain extent when both catalyst and H 2 O 2 were not added, which might be due to the acidity and alkalinity of the hot water itself under hydrothermal conditions. Therefore, only H 2 O 2 was chosen for subsequent experiments. Table 1 Effects of catalysts on the yield of organic Acids a Entry Catalyst Catalyst loading (mg) Oxidizing agent AA Yields (%) LA Yields (%) FA Yields (%) Total yields (%) 1 CuO 7.2 H 2 O 2 2.0 20.5 9.4 31.9 2 Co 2 O 3 6.7 H 2 O 2 2.1 13.6 3.6 19.3 3 Al 2 O 3 9.2 H 2 O 2 2.5 20.0 25.4 47.9 4 CaO 5 H 2 O 2 2.8 17.9 8.5 29.2 5 ZrO 2 11.1 H 2 O 2 2.5 22.9 24.9 50.3 6 b Ru/C 8 H 2 O 2 1.3 6.6 2.2 10.1 7 b Pt/C 8 H 2 O 2 1.2 1.5 0.8 3.5 8 - - H 2 O 2 0.4 38.7 18.9 58.0 9 - - - 6.4 11.2 12.8 30.4 a Reaction Conditions: chitin 30 mg, 0.09 mmol metal oxide catalysts, 2.66 mL water, 0.34 mL H 2 O 2 , 220 o C, 2 h. b Precious metal catalysts Ru/C and Pt/C were fixed 8 mg. By comparing the phenomena before and after the reaction of chitin in Fig S2, the color of the liquid did not change much. It could be seen that chitin could not dissolve in the liquid and still kept a solid precipitation state before the reaction (Sample a). But no solid was observed after the reaction, indicating that chitin should be completely converted into organic acids (Sample b). 3.2 The effect of different parameters on the reaction 3.2.1 Effect of H 2 O 2 amount Although H 2 O 2 can produce oxygen in the reaction and cooperatively oxidize itself, considering its extremely corrosive and oxidizing properties, it might corrode the catalyst or decompose the target product, so the total liquid volume is always set at 3 mL, and the amount of H 2 O 2 is optimized from 0.1 mL to 1 mL, and results were shown in Fig. 2 . With the increase of the amount of H 2 O 2 , the yield of lactic acid gradually increases, and the yield of formic acid decreased slowly while that of acetic acid increased gradually. When the amount of H 2 O 2 was 0.9 mL, the lactic acid yield reached the maximum of 42.8%. When exceeded 0.9 mL, the decrease of Lactic acid, acetic acid and formic acid yield might be due to the strong oxidation of H 2 O 2 , resulting in decomposition of organic acids. 3.2.2 Effect of temperature and time Generally, reaction temperature would affect the conversion of chitin. 160 o C as the initial temperature was set for the transformation. As shown in Fig. 3 , yield of formic acid gradually decreased with the increase of temperature, which might be due to the instability of formic acid, while the increase of acetic acid and lactic acid yields indicated that the temperature could promote the conversion of chitin. At 230 o C, the lactic acid yield reached a maximum of 46.4%, and the subsequent yield began to reduce, which might be due to the decomposition of lactic acid caused by excessive temperature. During the reaction, reaction time was also an influencing factor for the yield of the product. The initial time was set 1 h. In Fig. 4 , with the increase of time, lactic acid first increases and then decreases, 1.5 h was the suitable to give a good yield of 58.2%. After 1.5 h, the yield of lactic acid decrease might be because lactic acid gradually decomposed during a long reaction time. 3.2.3 Effect of water filling In a fixed reactor, water filling would change the pressure and had a certain influence on the reaction. The conversion of chitin was conducted under the conditions of 0.2 mL H 2 O 2 at 230 o C for 1.5 h, the water filling was increased from 1.5 mL to 2.7 mL. As shown in Fig. 5 , the yield of organic acids increased with the increase of water filling to reach the maximum value at 2.1 mL, and then gradually decrease, indicating that high pressure benefited chitin and lactic acid decomposition. Under the optimal conditions, the yields of lactic acid and total organic acid reached 58.2% and 84.0% were achieved, respectively. 3.3 Mechanism study Based on the results above and previous work [ 30 ] , it was found that lactic acid might be an intermediate to decompose into acetic acid and formic acid under the optimal conditions, and also metal oxides such as CuO with the certain oxidation could promote the decomposition of lactic acid. To verify these possibility, the experiments were carried out under the optimal conditions. 3.3.1 Investigation of lactic acid as an intermediate As shown in Fig. 6 and Fig. 7 , lactic acid with 0.4 mol/L as raw material was conducted under the optimal conditions of 2.1 mL water, 0.9 mL H 2 O 2 and 230 o C for 1.5 h. When the reaction time was from 0 to 10 min, the concentration of lactic acid was greatly reduced to be almost completely transformed at 10 min, and the concentration of formic acid and acetic acid was increased up to the maximum value, which proved that lactic acid was an intermediate and could be decomposed into formic acid and acetic acid. The specific oxidation mechanism of lactic acid could be referred to our previous study on the oxidation mechanism of levulinic acid [ 30 ] . 3.3.2 Investigation of role of CuO In general, the use of oxidant could promote the conversion of chitin to produce lactic acid and organic acids, but the obtained yields of lactic acid and total yields were lower when CuO was used in entry 1 than that of the use of only H 2 O 2 in entry 8 of Table 1 , it was speculated that the reason might be that CuO as an oxidant promoted the decomposition of the lactic acid as an intermediate. To investigate the effect of CuO for the reaction without H 2 O 2 , the reaction of the organic acid mixture as substrate after the conversion of chitin was carried out with 1 mmol CuO at 220 o C for 2 h. As a result in Fig S3, the yield of lactic acid decreased from 58.2–22.7%, the yield of acetic acid increased from 23.4–36.4%, and the yield of formic acid increased from 2.4–7.2%. The results indicated that CuO could also oxidize lactic acid to produce acetic acid and formic acid. SEM images of CuO showed no change before and after the reaction in Fig S4, which proved that CuO was very stable during the decomposition of lactic acid into acetic acid and formic acid. 3.4 Application of shrimp shell as actual material for organic acids In order to explore the application of shrimp shell as actual material for organic acids. Firstly, shrimp shell was pretreated by immersing in 1 mol/L NaOH solution and stirred at 85 o C for 1 h to remove proteins, and then took out and added 1 mol/L hydrochloric acid solution to stir for 3 h to remove the salt. Finally, washed it with pure water, and then dried it to get chitin (Fig S5). Compared to commercial chitin, chitin prepared from shrimp shell could still achieve 48.7% yield of lactic acid and total organic acids of 68.0%, respectively (Table 2 ). This showed that the conversion of shrimp shell was effective in the actual substance and provided a new method for the transformation of actual shrimp and crab shells. Table 2 The acid-producing effects of different chitin resource a Ingredients AA Yields (%) LA Yields (%) FA Yields (%) Total acid yields (%) Chitin (shrimp shell preparation) 0.4 48.7 18.9 68.0 Chitin (Purchase TCI) 2.4 58.2 23.4 84.0 a Reaction Conditions: chitin 30 mg, 2.1 mL water, 0.9 mL H 2 O 2 , 230 o C, 1.5 h. 4. Conclusions We have developed a catalyst and alkali-free oxidation system of H 2 O 2 that can efficiently convert chitin biomass to lactic acid under relatively mild conditions. Under the optimal conditions, the maxmum yield of lactic acid reached 58.2% along with the total organic acids yield of 84.0%. In addition, in practical application, H 2 O 2 catalyzes the production of lactic acid and total organic acid from chitin prepared from shrimp shells with high yield. This research group is further studying the conversion of chitin biomass into organic acids, nitrogen-containing compounds and other useful products. This study provides an economic and environmental protection method for the resource utilization of chitin biomass. Declarations Author Contribution CRediT Author StatementXiao Du: Conceptualization, Methodology, Software, Investigation, Formal Analysis, Writing - Original Draft;Tengfei Li: Data Curation, Writing - Original Draft;Lumei Wang: Visualization, Investigation;Dezhang Ren: Resources, Supervision;Zhibao Huo: Conceptualization, Writing - Review & Editing, Supervision. Acknowledgements The author gratefully acknowledge the financial support from Shanghai Pujiang Program (20PJ1404800). We thank the all reviewers and editors for reviewing the manuscript and providing valuable comments. References Looney, B, Bp. 69, 66 (2020) Yolcan, O.O, Innovation and Green Development. 2, 100070 (2023) El Knidri, H., Belaabed, R., Addaou, A., Laajeb, A., Lahsini, A.J.I. j.o.b.m , Int. J. Biol. Macromol. 120, 1181–1189 (2018) Hamed, I., Özogul, F., Regenstein, J.M, Trends Food Sci. Technol. 48, 40–50(2016) Chen, X., Sun, Z., Di, Q., Liang, C, Ecol Inform. 80, 102478 (2024) Zhou, H, Mar Policy. 147, 105344 (2023) Mahlous, M., Tahtat, D., Benamer, S., Nacer Khodja, A, Nucl. Instrum. Methods Phys. Res., Sect. B. 265, 414–417 (2007) Drover, M.W., Omari, K.W., Murphy, J.N., Kerton, F.M.J.R.A, RSC Adv. 2, 4642–4644 (2012) Chen, X., Yang, H., Yan, N.J.C.A.E.J, Chem. Eur. J. 22, 13402–13421 (2016) Yan, N., Chen, X.J.N, Nature. 524, 155–157 (2015) Abdel-Rahman, M.A., Tashiro, Y., Sonomoto, K, Biotechnol. Adv. 31, 877–902 (2013) Mazzoli, R., Bosco, F., Mizrahi, I., Bayer, E.A., Pessione, E, Biotechnol. Adv. 32, 1216–1236 (2014) Datta, R., Henry, M.J.J.o.C.T, J. Chem. Technol. Biotechnol. 81, 1119–1129(2006) Maki-Arvela, P., Salmi, T., Holmbom, B., Willfor, S., Murzin, D.Y.J.C.r, Chem. Rev. 111, 5638–5666 (2011) Arcanjo, M.R.A., Silva, I.J., Rodríguez-Castellón, E., Infantes-Molina, A., Vieira, R.S, Catal. Today. 279, 317–326 (2017) Li, L., Shen, F., Smith, R.L., Qi, X.J.G.c, Green Chem. 19, 76–81 (2017) Palacio, R., Torres, S., Lopez, D., Hernandez, D, Catal. Today. 302, 196–202 (2018) Purushothaman, R.K.P., van Haveren, J., van Es, D.S., Melián-Cabrera, I., Meeldijk, J.D., Heeres, H.J, Appl. Catal., B. 147, 92–100 (2014) Wattanapaphawong, P., Reubroycharoen, P., Yamaguchi, A, RSC Adv. 7, 18561–18568 (2017) Yang, G.-Y., Ke, Y.-H., Ren, H.-F., Liu, C.-L., Yang, R.-Z., Dong, W.-S, Chem. Eng. J. 283, 759–767 (2016) Gao, X., Chen, X., Zhang, J., Guo, W., Jin, F., Yan, N.J.A.S.C, ACS Sustain Chem Eng. 4, 3912–3920 (2016) Su, H., Wang, J., Yan, L.J.A.S.C, ACS Sustain Chem Eng. 7, 18476–18482(2019) Qi, M., Chen, X., Zhong, H., Wu, J., Jin, F, Base-Free, ACS Sustain Chem Eng. 8, 18661–18670 (2020) Kun-asa, K., Reubroycharoen, P., Yamazaki, K., Mimura, N., Sato, O., Yamaguchi, A.J.C, ChemistryOpen. 10, 308–315 (2021) Du, Y., Zhang, C., Li, Y., Zhang, N., Ren, D., Huo, Z.J.K. J.o.C.E , Korean J. Chem. Eng. 40, 1912–1918 (2023) Ren, D., Jiang, X., Zhang, N., Duo, J., Norinaga, K., Huo, Z.J.B.C., Biorefinery, Biomass Convers Bior. 1–7 (2023) Ren, D., Zhao, C., Zhang, N., Norinaga, K., Zeng, X., Huo, Z, J. Environ. 10, 107188 (2022) Wang, J., Ren, D., Zhang, N., Lang, J., Du, Y., He, W., Norinaga, K., Huo, Z, Renewable Energy. 202, 952–960 (2023) Zhang, M., Jiao, X., Ren, D., Huang, C., Li, Y., Chen, D., Huo, Z, Fuel. 363, 131006 (2024) Fang, Y., Zeng, X., Yan, P., Jing, Z., Jin, F.J.I., research, e.c, Ind. Eng. Chem. Res. 51, 4759–4763 (2012) Scheme Schemes 1 is available in the Supplementary Files section Additional Declarations No competing interests reported. Supplementary Files Scheme1.png Scheme 1. Concept of the formation of organic acids from chitin. 6.SupplementaryMaterial.docx Cite Share Download PDF Status: Published Journal Publication published 01 Jul, 2024 Read the published version in Carbohydrate Research → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4495093","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":311422887,"identity":"64863d79-aa39-4fbd-8045-a18a0a319523","order_by":0,"name":"Xiao Du","email":"","orcid":"","institution":"Shanghai Ocean University","correspondingAuthor":false,"prefix":"","firstName":"Xiao","middleName":"","lastName":"Du","suffix":""},{"id":311422888,"identity":"719beacc-bd6d-4c39-bbb8-b22b93c4b470","order_by":1,"name":"Tengfei Li","email":"","orcid":"","institution":"Shanghai Ocean 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19:32:07","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":18249,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of time on lactic acid yield\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-4495093/v1/60bee8e66d69c4526549dcdb.png"},{"id":58149133,"identity":"05899ad5-a69e-443e-a658-09326aa72d92","added_by":"auto","created_at":"2024-06-11 19:24:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":19780,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of H\u003csub\u003e2\u003c/sub\u003eO dosage on lactic acid yield\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-4495093/v1/1046d336afe963c63601948f.png"},{"id":58149139,"identity":"b5879f06-3238-452d-9fdf-ae5c0ed0b030","added_by":"auto","created_at":"2024-06-11 19:24:07","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":33937,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Lactic acid is converted to formic acid and acetic acid, (b) Effect of time on lactic acid conversion.\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-4495093/v1/3d45aba099afbe1a733dcc7f.png"},{"id":58149137,"identity":"24f08d19-7290-46ca-9754-a512076bac48","added_by":"auto","created_at":"2024-06-11 19:24:07","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":55966,"visible":true,"origin":"","legend":"\u003cp\u003eProposed pathway for the conversion of chitin to organic acids.\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-4495093/v1/19a60ad517fb5e05e47b0528.png"},{"id":60773070,"identity":"5e861da6-b1ba-4730-8760-bfa51f8cff4f","added_by":"auto","created_at":"2024-07-21 15:32:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":730611,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4495093/v1/74dddd66-e791-4994-b613-7bef4a5290d8.pdf"},{"id":58149681,"identity":"affca165-8dd6-4557-8310-abac0754f220","added_by":"auto","created_at":"2024-06-11 19:40:07","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":201986,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1. \u003c/strong\u003eConcept of the formation of organic acids from chitin.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-4495093/v1/041e6de047a001852c6134f4.png"},{"id":58149140,"identity":"1f830063-04e4-40d2-8512-189e267c5200","added_by":"auto","created_at":"2024-06-11 19:24:07","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":933605,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"6.SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-4495093/v1/2e8bd051da9a0866cd7f8234.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Catalyst and base-free, direct oxidation of chitin to lactic acid with hydrogen peroxide","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the rapid development of global industrialization, traditional non-renewable fossil raw materials are rapidly consumed. The development of renewable energy is of great significance. However, even today, fossil fuels still account for a large share of energy consumed \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. Chitin, a polysaccharide extracted from the shells of marine crustaceans, is the second most abundant biopolymer after cellulose and is the main component of crustacean shells such as crabs and shrimp \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. Shrimp shells contain up to 50\u0026ndash;60% chitin, and much of this marine shell material is discarded and not used effectively as a resource. According to the statistics of China Fishery Yearbook, China's shrimp production has increased since 2013, and has reached 6.3073\u0026nbsp;million tons by 2020 \u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e (Fig \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). If the waste shrimp shells can be used effectively, it is of great significance for the utilization of biomass resources. In 2007, Mahlous et al\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e have proposed a relatively perfect mechanism of shrimp shell preparation of chitin. These shell wastes produce less nitrogen oxides and sulfur oxides than chemicals prepared from fossil raw materials. The carbon dioxide produced also comes from the fixation of atmospheric carbon dioxide by the shellfish themselves, thus forming a certain carbon cycle \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. In recent years, the concept of \"shell biorefinery\" has been put forward to contrast with biorefinery. The biorefinery concept aims to convert lignocellulosic biomass into chemicals. In the concept of shell biorefining, chitin is a potential resource for the production of high value-added compounds \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eLactic acid is considered to be a cheap, readily available and sustainably renewable biomass resource. It has a strong preservative and fresh-keeping effect, and can be used in food processing, extending shelf life and other functions\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. In addition, lactic acid can be converted into a variety of other chemicals, including propylene glycol and acrylic acid\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. At present, most lactic acid on the market comes from biological fermentation, which has some shortcomings such as unstable yield and long fermentation time. Thus, most of the researches is using cellulose and glycerol to prepare lactic acid\u003csup\u003e[\u003cspan additionalcitationids=\"CR16 CR17 CR18 CR19\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. In recent years, some progress has been made in the preparation of organic acids from chitin. Gao et al\u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e, in the environment of NaOH, used CuO as the catalyst to oxidize chitin biomass to produce acetic acid with a yield of 38.1% and a small amount of pyrrole at the same time, and directly reacted with shrimp shells to obtain 47.9% acetic acid. Su et al\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e studied the low temperature pretreatment of chitin with hydroxide/urea as solvent, and finally obtained a large number of organic compounds including oxalic acid, malonic acid, formic acid and 31.0% acetic acid. Qi et al\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e used V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e as catalyst and O\u003csub\u003e2\u003c/sub\u003e as oxidant to catalyze the conversion of N-acetyl-D-glucosamine (NAG) to acetic acid under the condition of no alkali, and the yield reached 33.4%. Kun et al\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e explored the process of producing lactic acid from chitin by different metal oxides. When the amount of MgO catalyst was 0.5 g and the reaction time was 6 h, the highest yield of 10.8% of the lactic acid was obtained. This is the first report of catalytic conversion of chitin to lactic acid. However, the use of alkali and toxic catalyst such as V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e will cause environmental problems. Therefore the development of new methods for the conversion of chitin to lactic acid without alkali and/or catalysts is highly desired.\u003c/p\u003e \u003cp\u003eIn previous works, we reported a series of researches on the conversion of biomass and wastes into useful chemicals and fuels such as Preparation of sustainable Aviation Fuel (SAF) from algae, useful chemicals from biomass and so on\u003csup\u003e[\u003cspan additionalcitationids=\"CR26 CR27 CR28\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e. Herein, we develop a catalyst and base-free, oxidative system for efficient convertion of chitin biomass to lactic acid and other organic acids with hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) under relatively mild conditions, which has not been reported before. The obtained acidic products can be separated by simple and mature techniques such as solvent extraction (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Chemicals and Materials\u003c/h2\u003e \u003cp\u003eChitin was purchased from TCI. CuO, Ru/C and Pt/C were purchased from Energy Chemical. Co\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e was purchased from Macklin Chemical, CaO was purchased from General-Reagent, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e was purchased from Greagent, ZrO\u003csub\u003e2\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (30%) were purchased from Aladdin Chemical.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 General reaction procedures.\u003c/h2\u003e \u003cp\u003eThe conversion of chitin was generally carried out in a small steel tube reactor (inner volume was 5.7 mL). In a typical experiment, chitin and additives were added to the reactor, and then heated in a muffle furnace preset to the reaction temperature and quenched with cold water after the reaction time was reached. The solid product after the reaction was collected by filtration, washed with deionized water and dried, and the liquid sample was collected by filtration with a 0.22 um filter head. Liquid samples were measured using HPLC (Agilent 1260) with SB-AQ columns and UV detectors.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Calculation of organic acid yield.\u003c/h2\u003e \u003cp\u003eThe yields of all products were calculated on a carbon basis using the following formula.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\text{The yield of organic acid = }\\frac{\\text{moles of carbon in product }}{\\text{moles of carbon in initial reactant }}\\text{\u0026times;100\\%}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Catalyst screening\u003c/h2\u003e \u003cp\u003eIn previous studies, metal oxides as catalysts played an important role in the conversion of chitin to organic acids. In this experiment, we selected several metal oxides to test their catalytic performance for the transformation. Due to some precious metals often had good catalytic effects, thus precious metal catalysts were also chosen for performance testing.\u003c/p\u003e \u003cp\u003eThe experiments were carried out under the initial conditions, 30 mg of chitin as the substrate, 0.09 mmol metal oxide catalysts, 2.66 mL deionized water, 0.34 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 220 \u003csup\u003eo\u003c/sup\u003eC, 2 h. By observing the high performance liquid chromatography (HPLC) of the product in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e after the reaction, organic acids including formic acid, acetic acid, and lactic acid along with some unknown compounds were formed. The results of catalyst screening were shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFirst, the catalysts combined with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e for the reaction were investigated. Among the catalysts tested, it could be found that the selectivity of ZrO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts for the preparation of organic acid from chitin was higher than that of other metal oxides, and formic acid was the main product with 25.4% and 24.9% yield, respectively (entries 3 and 5). The use of other metal oxide catalysts gave the lactic acid as the main product (entries 1, 2 and 4). However, precious metal catalysts Ru/C and Pt/C were uneffective to give the low yield of lactic acid, and 6.6% and 1.5% were obtained, respectively (entries 6 and 7). This might be because metal oxides with the certain oxidation promoted the decomposition of chitin to organic acids. Next, when only H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was added, an interested result was obtained in the highest 38.7% yields of lactic acid and total organic acids of 58.0%, respectively (entry 8). The results were better than the use of metal oxides and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e together, indicating that metal oxides could promote not only the decomposition of chitin but also the decomposition of lactic acid to reduce the yield of lactic acid, it could be explained the role of CuO in mechanism study later. In addition, chitin could also be converted into organic acids to a certain extent when both catalyst and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e were not added, which might be due to the acidity and alkalinity of the hot water itself under hydrothermal conditions. Therefore, only H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was chosen for subsequent experiments.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of catalysts on the yield of organic Acids \u003csup\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEntry\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCatalyst loading (mg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOxidizing\u003c/p\u003e \u003cp\u003eagent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAA Yields (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLA Yields (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFA Yields (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTotal yields (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCuO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" 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\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e19.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e25.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e47.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e17.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e8.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e29.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e22.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e24.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e50.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003csup\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRu/C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e10.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003csup\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePt/C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e38.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e18.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e58.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e11.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e30.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003e \u003cem\u003ea\u003c/em\u003e \u003c/sup\u003e Reaction Conditions: chitin 30 mg, 0.09 mmol metal oxide catalysts, 2.66 mL water, 0.34 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 220 \u003csup\u003eo\u003c/sup\u003eC, 2 h. \u003csup\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sup\u003e Precious metal catalysts Ru/C and Pt/C were fixed 8 mg.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBy comparing the phenomena before and after the reaction of chitin in Fig S2, the color of the liquid did not change much. It could be seen that chitin could not dissolve in the liquid and still kept a solid precipitation state before the reaction (Sample a). But no solid was observed after the reaction, indicating that chitin should be completely converted into organic acids (Sample b).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 The effect of different parameters on the reaction\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Effect of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e amount\u003c/h2\u003e \u003cp\u003eAlthough H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e can produce oxygen in the reaction and cooperatively oxidize itself, considering its extremely corrosive and oxidizing properties, it might corrode the catalyst or decompose the target product, so the total liquid volume is always set at 3 mL, and the amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is optimized from 0.1 mL to 1 mL, and results were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. With the increase of the amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the yield of lactic acid gradually increases, and the yield of formic acid decreased slowly while that of acetic acid increased gradually. When the amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was 0.9 mL, the lactic acid yield reached the maximum of 42.8%. When exceeded 0.9 mL, the decrease of Lactic acid, acetic acid and formic acid yield might be due to the strong oxidation of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, resulting in decomposition of organic acids.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 Effect of temperature and time\u003c/h2\u003e \u003cp\u003eGenerally, reaction temperature would affect the conversion of chitin. 160 \u003csup\u003eo\u003c/sup\u003eC as the initial temperature was set for the transformation. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, yield of formic acid gradually decreased with the increase of temperature, which might be due to the instability of formic acid, while the increase of acetic acid and lactic acid yields indicated that the temperature could promote the conversion of chitin. At 230 \u003csup\u003eo\u003c/sup\u003eC, the lactic acid yield reached a maximum of 46.4%, and the subsequent yield began to reduce, which might be due to the decomposition of lactic acid caused by excessive temperature.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDuring the reaction, reaction time was also an influencing factor for the yield of the product. The initial time was set 1 h. In Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, with the increase of time, lactic acid first increases and then decreases, 1.5 h was the suitable to give a good yield of 58.2%. After 1.5 h, the yield of lactic acid decrease might be because lactic acid gradually decomposed during a long reaction time.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3 Effect of water filling\u003c/h2\u003e \u003cp\u003eIn a fixed reactor, water filling would change the pressure and had a certain influence on the reaction. The conversion of chitin was conducted under the conditions of 0.2 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at 230 \u003csup\u003eo\u003c/sup\u003eC for 1.5 h, the water filling was increased from 1.5 mL to 2.7 mL. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the yield of organic acids increased with the increase of water filling to reach the maximum value at 2.1 mL, and then gradually decrease, indicating that high pressure benefited chitin and lactic acid decomposition. Under the optimal conditions, the yields of lactic acid and total organic acid reached 58.2% and 84.0% were achieved, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Mechanism study\u003c/h2\u003e \u003cp\u003eBased on the results above and previous work\u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e, it was found that lactic acid might be an intermediate to decompose into acetic acid and formic acid under the optimal conditions, and also metal oxides such as CuO with the certain oxidation could promote the decomposition of lactic acid. To verify these possibility, the experiments were carried out under the optimal conditions.\u003c/p\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Investigation of lactic acid as an intermediate\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, lactic acid with 0.4 mol/L as raw material was conducted under the optimal conditions of 2.1 mL water, 0.9 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and 230 \u003csup\u003eo\u003c/sup\u003eC for 1.5 h. When the reaction time was from 0 to 10 min, the concentration of lactic acid was greatly reduced to be almost completely transformed at 10 min, and the concentration of formic acid and acetic acid was increased up to the maximum value, which proved that lactic acid was an intermediate and could be decomposed into formic acid and acetic acid. The specific oxidation mechanism of lactic acid could be referred to our previous study on the oxidation mechanism of levulinic acid \u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 Investigation of role of CuO\u003c/h2\u003e \u003cp\u003eIn general, the use of oxidant could promote the conversion of chitin to produce lactic acid and organic acids, but the obtained yields of lactic acid and total yields were lower when CuO was used in entry 1 than that of the use of only H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e in entry 8 of Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, it was speculated that the reason might be that CuO as an oxidant promoted the decomposition of the lactic acid as an intermediate. To investigate the effect of CuO for the reaction without H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the reaction of the organic acid mixture as substrate after the conversion of chitin was carried out with 1 mmol CuO at 220 \u003csup\u003eo\u003c/sup\u003eC for 2 h. As a result in Fig S3, the yield of lactic acid decreased from 58.2\u0026ndash;22.7%, the yield of acetic acid increased from 23.4\u0026ndash;36.4%, and the yield of formic acid increased from 2.4\u0026ndash;7.2%. The results indicated that CuO could also oxidize lactic acid to produce acetic acid and formic acid. SEM images of CuO showed no change before and after the reaction in Fig S4, which proved that CuO was very stable during the decomposition of lactic acid into acetic acid and formic acid.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Application of shrimp shell as actual material for organic acids\u003c/h2\u003e \u003cp\u003eIn order to explore the application of shrimp shell as actual material for organic acids. Firstly, shrimp shell was pretreated by immersing in 1 mol/L NaOH solution and stirred at 85 \u003csup\u003eo\u003c/sup\u003eC for 1 h to remove proteins, and then took out and added 1 mol/L hydrochloric acid solution to stir for 3 h to remove the salt. Finally, washed it with pure water, and then dried it to get chitin (Fig S5). Compared to commercial chitin, chitin prepared from shrimp shell could still achieve 48.7% yield of lactic acid and total organic acids of 68.0%, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This showed that the conversion of shrimp shell was effective in the actual substance and provided a new method for the transformation of actual shrimp and crab shells.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe acid-producing effects of different chitin resource \u003csup\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIngredients\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAA Yields\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLA Yields (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFA Yields\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTotal acid yields (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChitin\u003c/p\u003e \u003cp\u003e(shrimp shell preparation)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e48.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e18.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e68.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChitin\u003c/p\u003e \u003cp\u003e(Purchase TCI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e58.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e23.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e84.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003e \u003cem\u003ea\u003c/em\u003e \u003c/sup\u003e Reaction Conditions: chitin 30 mg, 2.1 mL water, 0.9 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 230 \u003csup\u003eo\u003c/sup\u003eC, 1.5 h.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eWe have developed a catalyst and alkali-free oxidation system of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e that can efficiently convert chitin biomass to lactic acid under relatively mild conditions. Under the optimal conditions, the maxmum yield of lactic acid reached 58.2% along with the total organic acids yield of 84.0%. In addition, in practical application, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e catalyzes the production of lactic acid and total organic acid from chitin prepared from shrimp shells with high yield. This research group is further studying the conversion of chitin biomass into organic acids, nitrogen-containing compounds and other useful products. This study provides an economic and environmental protection method for the resource utilization of chitin biomass.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eCRediT Author StatementXiao Du: Conceptualization, Methodology, Software, Investigation, Formal Analysis, Writing - Original Draft;Tengfei Li: Data Curation, Writing - Original Draft;Lumei Wang: Visualization, Investigation;Dezhang Ren: Resources, Supervision;Zhibao Huo: Conceptualization, Writing - Review \u0026amp; Editing, Supervision.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe author gratefully acknowledge the financial support from Shanghai Pujiang Program (20PJ1404800). We thank the all reviewers and editors for reviewing the manuscript and providing valuable comments.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLooney, B, Bp. 69, 66 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYolcan, O.O, Innovation and Green Development. 2, 100070 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl Knidri, H., Belaabed, R., Addaou, A., Laajeb, A., Lahsini, A.J.I.\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ej.o.b.m\u003c/span\u003e\u003cspan address=\"http://j.o.b.m\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e, Int. J. Biol. Macromol. 120, 1181\u0026ndash;1189 (2018)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHamed, I., \u0026Ouml;zogul, F., Regenstein, J.M, Trends Food Sci. Technol. 48, 40\u0026ndash;50(2016)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, X., Sun, Z., Di, Q., Liang, C, Ecol Inform. 80, 102478 (2024)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou, H, Mar Policy. 147, 105344 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMahlous, M., Tahtat, D., Benamer, S., Nacer Khodja, A, Nucl. Instrum. Methods Phys. Res., Sect. B. 265, 414\u0026ndash;417 (2007)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDrover, M.W., Omari, K.W., Murphy, J.N., Kerton, F.M.J.R.A, RSC Adv. 2, 4642\u0026ndash;4644 (2012)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, X., Yang, H., Yan, N.J.C.A.E.J, Chem. Eur. J. 22, 13402\u0026ndash;13421 (2016)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYan, N., Chen, X.J.N, Nature. 524, 155\u0026ndash;157 (2015)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbdel-Rahman, M.A., Tashiro, Y., Sonomoto, K, Biotechnol. Adv. 31, 877\u0026ndash;902 (2013)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMazzoli, R., Bosco, F., Mizrahi, I., Bayer, E.A., Pessione, E, Biotechnol. Adv. 32, 1216\u0026ndash;1236 (2014)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDatta, R., Henry, M.J.J.o.C.T, J. Chem. Technol. Biotechnol. 81, 1119\u0026ndash;1129(2006)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMaki-Arvela, P., Salmi, T., Holmbom, B., Willfor, S., Murzin, D.Y.J.C.r, Chem. Rev. 111, 5638\u0026ndash;5666 (2011)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArcanjo, M.R.A., Silva, I.J., Rodr\u0026iacute;guez-Castell\u0026oacute;n, E., Infantes-Molina, A., Vieira, R.S, Catal. Today. 279, 317\u0026ndash;326 (2017)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, L., Shen, F., Smith, R.L., Qi, X.J.G.c, Green Chem. 19, 76\u0026ndash;81 (2017)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePalacio, R., Torres, S., Lopez, D., Hernandez, D, Catal. Today. 302, 196\u0026ndash;202 (2018)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePurushothaman, R.K.P., van Haveren, J., van Es, D.S., Meli\u0026aacute;n-Cabrera, I., Meeldijk, J.D., Heeres, H.J, Appl. Catal., B. 147, 92\u0026ndash;100 (2014)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWattanapaphawong, P., Reubroycharoen, P., Yamaguchi, A, RSC Adv. 7, 18561\u0026ndash;18568 (2017)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang, G.-Y., Ke, Y.-H., Ren, H.-F., Liu, C.-L., Yang, R.-Z., Dong, W.-S, Chem. Eng. J. 283, 759\u0026ndash;767 (2016)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao, X., Chen, X., Zhang, J., Guo, W., Jin, F., Yan, N.J.A.S.C, ACS Sustain Chem Eng. 4, 3912\u0026ndash;3920 (2016)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSu, H., Wang, J., Yan, L.J.A.S.C, ACS Sustain Chem Eng. 7, 18476\u0026ndash;18482(2019)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQi, M., Chen, X., Zhong, H., Wu, J., Jin, F, Base-Free, ACS Sustain Chem Eng. 8, 18661\u0026ndash;18670 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKun-asa, K., Reubroycharoen, P., Yamazaki, K., Mimura, N., Sato, O., Yamaguchi, A.J.C, ChemistryOpen. 10, 308\u0026ndash;315 (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDu, Y., Zhang, C., Li, Y., Zhang, N., Ren, D., Huo, Z.J.K.\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003eJ.o.C.E\u003c/span\u003e\u003cspan address=\"http://J.o.C.E\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e, Korean J. Chem. Eng. 40, 1912\u0026ndash;1918 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRen, D., Jiang, X., Zhang, N., Duo, J., Norinaga, K., Huo, Z.J.B.C., Biorefinery, Biomass Convers Bior. 1\u0026ndash;7 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRen, D., Zhao, C., Zhang, N., Norinaga, K., Zeng, X., Huo, Z, J. Environ. 10, 107188 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, J., Ren, D., Zhang, N., Lang, J., Du, Y., He, W., Norinaga, K., Huo, Z, Renewable Energy. 202, 952\u0026ndash;960 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, M., Jiao, X., Ren, D., Huang, C., Li, Y., Chen, D., Huo, Z, Fuel. 363, 131006 (2024)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFang, Y., Zeng, X., Yan, P., Jing, Z., Jin, F.J.I., research, e.c, Ind. Eng. Chem. Res. 51, 4759\u0026ndash;4763 (2012)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme ","content":"\u003cp\u003eSchemes 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"chitin, catalyst and base-free, organic acids, H2O2, lactic acid","lastPublishedDoi":"10.21203/rs.3.rs-4495093/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4495093/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn recent years, the research on the conversion of chitin to high value-added chemicals has attracted more and more attention. At present, the method of preparing lactic acid from chitin mostly uses strong base or catalyst. These reaction systems have disadvantages such as corrosion of containers and harm to human body. Herein, a simple and effective method to convert chitin to organic acids in catalyst and base-free conditions is developed. The use of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e only can efficiently convert chitin to organic acids in the absence of bases and catalysts. Under the optimal conditions of 30 mg chitin, 2.1 mL water, 0.9 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at 230 \u003csup\u003eo\u003c/sup\u003eC for 1.5 h, the lactic acid yield of chitin can reach 58.2% and the total organic acid yield can reach 84.0%. This work provides an efficient method for the resource utilization of chitin biomass.\u003c/p\u003e","manuscriptTitle":"Catalyst and base-free, direct oxidation of chitin to lactic acid with hydrogen peroxide","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-11 19:24:00","doi":"10.21203/rs.3.rs-4495093/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"35acbaf8-ef21-41cf-8bb8-d3f19e884594","owner":[],"postedDate":"June 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-07-21T15:32:12+00:00","versionOfRecord":{"articleIdentity":"rs-4495093","link":"https://doi.org/10.1016/j.carres.2024.109218","journal":{"identity":"carbohydrate-research","isVorOnly":true,"title":"Carbohydrate Research"},"publishedOn":"2024-07-01 15:32:12","publishedOnDateReadable":"July 1st, 2024"},"versionCreatedAt":"2024-06-11 19:24:00","video":"","vorDoi":"10.1016/j.carres.2024.109218","vorDoiUrl":"https://doi.org/10.1016/j.carres.2024.109218","workflowStages":[]},"version":"v1","identity":"rs-4495093","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4495093","identity":"rs-4495093","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}