Methanol-Based Esterification of Palm Oil Sludge – Preparation of Palmitic and Oleic Fatty Acid Ethyl Esters via Ethyl Acetate Transesterification

Methanol-Based Esterification of Palm Oil Sludge – Preparation of Palmitic and Oleic Fatty Acid Ethyl Esters via Ethyl Acetate Transesterification | 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 Methanol-Based Esterification of Palm Oil Sludge – Preparation of Palmitic and Oleic Fatty Acid Ethyl Esters via Ethyl Acetate Transesterification Javier CHAPARRO-ACOSTA, Juan-Manuel URBINA-GONZÁLEZ This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-762804/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Acid-catalyzed Fischer esterification of fatty acids with methanol as a reagent and solvent is used to prepare long chain alkyl methyl esters. Transesterification of palm oil in basic media using methanol is a synthesis route to prepare monoalkyl methyl esters of fatty acids. In this work, we report performing Fischer esterification of a sample of local palm oil sludge (rich in fatty acids) in the presence of methanol and obtaining ethyl esters of oleic and palmitic acids from transesterification reactions during extractions with ethyl acetate. Energy Engineering High Energy and Particle Physics Environmental Engineering methanol Fischer esterification ethyl acetate transesterification fatty acids palm oil sludge Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Biodiesel, a mixture of monoalkyl esters of biodegradable long chain fatty acids, contains insignificant amounts of sulfur and is nontoxic and renewable [ 1 ]. Biomass conversion via the transesterification of palm oil sludge (POS) with methanol is a common route to synthesize fatty acid methyl esters (FAMEs) [ 1 ]. Currently under study for potential applications as renewable oils and biofuels [ 2 ], fatty acid ethyl esters (FAEEs) can provide less toxic means to manage ethanol [ 3 ]. Our interest is modifying locally produced POS to produce fatty acid esters, and we hope to encourage others to build upon previous research in this field and eventually prepare substances of added value, e.g., surfactants. 2. Materials And Methods POS used in this study was obtained from the third lagoon of the oxidation ponding system of Palmas del Cesar S. A. at the plantation located in La Loma (San Martín municipality, Cesar Department, Colombia). The collected POS was purified by Soxhlet extraction with petroleum ether (PE). Then, 5.0 g of POS was poured into a round bottom flask, and 10 mL of methanol and H 2 SO 4 (0.13 g) catalyst were added. The mixture was heated at 60°C at 300 rpm for 3 h according to Nata et al. [ 1 ] After cooling the reactor, the mixture was treated with 200 mL saturated Na 2 CO 3 solution to pH > 10 to neutralize the H 2 SO 4 catalyst and poured into a continuous liquid-liquid extractor using 150 mL ethyl acetate (EA) as solvent and heating under reflux for 24 h. The organic layer was roto-evaporated, and solvents (methanol and ethyl acetate) were removed at 40°C under vacuum until a constant weight was obtained (4.78 g, 96 % mass). The resulting oily residue was purified by column chromatography (CC) on SiO 2 using petroleum ether (PE):ethyl acetate (EA) (ratio 90:1) as the eluent. After purification, 1.65 g of a colorless oily sample was isolated (35 %), Rf = 0.33 (PE:EA, ratio 90:1). Compounds in the sample were identified by gas chromatography-mass spectrometry GC-MS (Agilent 5977B GC/MSD, Santa Clara, CA 95051, United States) using an HP-5MS column (30 m; 0.25 mm i.d.; 0.25 mm film thickness), analyzed over a mass per charge ( m/z ) range of 50–550 and identified by comparing the mass spectra with the NIST (National Institute of Standards and Technology) mass spectral library. NIST MS Search 2.3 was used for mass spectra comparison [ 4 ]. MS Interpreter version Beta 3.1a [ 5 ] (part of the NIST Mass Spectral Search program) was used to obtain the formula and RDBE (ring and double bond equivalent) for selected mass spectra. 3. Results And Discussion PE Soxhlet extraction separated the substances of interest from insoluble inorganic (sand) and organic material (wood and cellulose). The FT-IR spectrum shows that the sludge contains mainly free fatty acids. Figure 1 (top) shows the main absorption signal of C = O stretching at 1697.5 cm − 1 for carboxylic acids, where no ester band of glycerides is observed. Then, methanol-based esterification was performed according to Nata et al. [ 1 ] Due to the difficulty in performing a liquid-liquid extraction in a separatory funnel, a continuous liquid-liquid extractor with EA was used. Then, the ester interchange reaction was carried out with continuous heating for 24 h [ 6 ], as corroborated by MS spectra of the less polar fraction obtained after CC. The FT-IR spectrum in Fig. 1 (bottom) shows the typical C = O stretching band for esters at 1737.5 cm − 1 . GC-MS analysis of the isolated fraction (column chromatography, 35 % mass yield, Rf = 0.33 SiO 2 , PE/EA 90:1) was carried out to identify the main compounds in that sample. Analyte MS spectra comparison using a mass spectral library search [ 7 ] corroborates the formation of ethyl esters of fatty acids instead of the expected methyl esters. Figure 2 presents the resulting gas chromatogram; the two main compounds in the fraction (91.7 %) were identified as ethyl palmitate (C 18 H 36 O 2 , 53.6 %) and ethyl oleate (C 20 H 38 O 2 , 38.1 %) with a higher match factor correspondence for its ( E )-stereoisomer, in agreement with Nata et al. [ 1 ]. The match factor is the measured value of the direct match of peak m/z values and relative intensities, while the reverse match factor ignores all peaks that are in the sample spectrum but not in the library spectrum [ 8 ]. Clearly, a transesterification reaction occurred during the liquid-liquid extraction with EA and turned the methyl esters into their ethyl derivatives, as the MS spectra data comparison demonstrates. The MS comparison is shown in Fig. 3 (top) for ethyl palmitate and in Fig. 3 (bottom) for ethyl oleate. Table 1 Match factors from the comparison of the mass spectra for the main analytes obtained in the CG-MS spectrum of the ester mixture and compounds in the NIST library. Peak Name tR (min) Area (%) Scan No. Molecular ion mass (g/mol) Assigned formula RDBE* Assigned compound Match Factor 1 9.128 0.87 444 228.2 C 14 H 28 O 2 1.0 Ethyl laurate [Ethyl dodecanoate] 870 Methyl tridecanoate 584 2 11.874 1.09 924 256.2 C 16 H 32 O 2 1.0 Ethyl myristate [Ethyl tetradecanoate] 910 Methyl pentadecanoate 632 3 13.717 1.59 1246 270.3 C 17 H 34 O 2 1.0 Methyl palmitate [Methyl hexadecanoate] 947 Ethyl pentadecanoate 605 4 14.758 53.54 1428 284.2 C 18 H 36 O 2 1.0 Ethyl palmitate [Ethyl hexadecanoate] 903 Methyl heptadecanoate 625 5 16.171 0.93 1675 296.3 C 19 H 36 O 2 2.0 Methyl oleate [Methyl (9 Z )- Octadec-9-enoate] 926 Methyl (9 E )- Octadec-9-enoate 922 6 17.316 38.13 1868 310.3 C 20 H 38 O 2 2.0 Ethyl (9 E )-octadec-9-enoate 917 Ethyl oleate [Ethyl (9 Z )-octadec-9-enoate] 892 Methyl (10 Z )-nonadec-10-enoate 726 7 17.562 3.84 1918 312.3 C 20 H 40 O 2 1.0 Ethyl stearate [Octadecanoic acid ethyl ester] 782 Methyl nonadecanoate 671 * Ring and double bond equivalent NIST MS Search 2.3 was used to compare the mass spectra of methyl and ethyl ester derivatives with the same molecular ion mass (same molecular formula). Considering the absence of glycerides (as ester signals) in the sludge IR spectra (Fig. 1 , black spectrum), the POS contained predominantly carboxylic acids similar to compositions described in other reports [ 9 ], i.e., palmitic acid and oleic acid as the main components. Then, the POS sample underwent Fischer esterification (heating under reflux of the carboxylic acid mixture in methanol), and the resulting reaction mixture was heated in basic aqueous media with ethyl acetate; under these conditions, the only expected derivatives of our POS were methyl and ethyl ester carboxylates. Based on that assumption, the molecular formula and ring and double bond equivalent (RDBE) assignments of the main signals in the chromatogram were calculated with MS Interpreter version Beta 3.1a considering only C x H y O 2 formulas. NIST MS Search 2.3 was used for the mass spectra comparison, and the results for the match factors are summarized in Table 1 . As reported by Dubé et al. [ 10 ], for our similar biphase system, ester interchange should occur in the interphase, as shown in Fig. 4 . The use of a weak base solution allowed the removal of the FFAs into the aqueous layer [ 11 ] as carboxylates, avoiding any interference in the reaction. Then, alkaline transesterification occurred in a similar way to the normal alkaline-catalyzed transesterification of vegetable oils to produce FAME and glycerol [ 11 ], considering that a small concentration of methoxide anion formed in the basic media through deprotonation of the residual methanol (used in the previous Fischer esterification) (Fig. 4 , orange arrow). With that assumption, our hypothesis is that the methoxide anion initially transesterified the ethyl acetate used as extraction solvent, turning it into methyl acetate and liberating ethoxide anion into the interphase where conditions allowed the ester to interchange from FAME to FAEE. The contact of the warm solvent with the aqueous layer provided the energy needed to drive the reaction to form FAEE products, and the equilibrium was shifted by excess ethyl acetate and the extended duration of the process (24 h). Although very low amounts of ester derivatives of linoleic acid were expected, they were not observed. Work is in progress to increase the yield of the first separated fraction analyzed in this report. This research covered several aspects of green chemistry, and the main compounds obtained are expected to serve as surfactants in diverse oil/water systems. 4. Conclusions In this study, free fatty acids (palmitic and oleic acids) contained in palm oil sludge were unexpectedly converted into their ethyl esters (FAEEs) by a sequence of Fischer esterification and transesterification reactions. The transesterification process probably occurred during an extraction when warm ethyl acetate from the liquid-liquid extractor dropped continuously into the basic aqueous phase containing FAME. These were appropriate conditions to convert methyl esters into their corresponding ethyl ester derivatives, as demonstrated by mass spectra data comparison. Declarations Availability of data and materials The data set (GC-MS file in *.ms format) generated and analyzed during this study is available in the Zenodo repository [DOI 10.5281/zenodo.5142503 at https://doi.org/10.5281/zenodo.5142503] Competing interests The authors declare they have no competing interests. Funding This work was supported by internal grant UIS-VIE 1870. Authors' contributions J. Ch.-A. performed the laboratory experiments and reported the results from the FT-IR and GC-MS analyses. J.-M. U.-G. supervised the experiments, checked the data and wrote the final report. All authors read and approved the final manuscript. Acknowledgements The authors wish to thank the Vicerrectoría de Investigación (VIE) at the Universidad Industrial de Santander (UIS) and Chemical Analysis Laboratory (Lab-308) at the School of Chemistry-UIS for providing the FT-IR and GC-MS analyses. We especially acknowledge Palmas del Cesar S. A. for providing the palm oil sludge samples. Authors' information (optional) J. Ch.-A. is a professional chemist with 5 years of experience in the industrial preparation of commercial liquid soaps. As a student in his final year of a Chemical Engineering M.Sc. program, he is developing his research about the use of palm oil sludge as a raw material for the preparation of surfactants. J.-M. U.-G. is lecturer in organic chemistry at the Universidad Industrial de Santander, and he is the supervisor of J. Ch.-A. in his M.Sc. research project. References Abdullah, Rahmawati Sianipar RN, Ariyani D, Nata IF. Conversion of palm oil sludge to biodiesel using alum and KOH as catalysts. Sustain Environ Res 2017;27:291–5. https://doi.org/10.1016/j.serj.2017.07.002 . Nduwayezu JB, Ishimwe T, Niyibizi A, Munyentwali A. Biodiesel production from unrefined palm oil on pilot plant scale. Int J Sustain Green Energy 2015;4:11–21. https://doi.org/10.11648/j.ijrse.20150401.13 . Yusoff MFM, Xu X, Guo Z. Comparison of fatty acid methyl and ethyl esters as biodiesel base stock: a review on processing and production requirements. J Am Oil Chem Soc 2014;91:525–31. https://doi.org/10.1007/s11746-014-2443-0 . NIST/EPA/NIH Mass Spectral Library with Search Program - Data ver. 2.3. Gaithersburg, MD, USA: National Institute of Standards and Technology (NIST); 2017. Y. Mirokhin, D. Tchekhovskoy, A. Mayorov, S. Stein. MS Interpreter Version BETA 3.1a. Gaithersburg, MD, USA: National Institute of Standards and Technology (NIST); 2017. Dijkstra AJ. Revisiting the mechanisms of low-temperature, base-catalysed ester interchange reactions. Ol Corps Gras Lipides 2008;15:208–12. https://doi.org/10.1051/ocl.2008.0200 . Kind T, Fiehn O. Advances in structure elucidation of small molecules using mass spectrometry. Bioanal Rev 2010;2:23–60. https://doi.org/10.1007/s12566-010-0015-9 . Stein SE, Wallace W, Ji W, Little J, Markey S, Mallard WG, et al. Software user’s manual for NIST Standard Reference Database 1A - NIST/EPA/NIH Mass Spectral Library (NIST 17) & NIST Mass Spectral Search Program (Version 2.3) 2017. Aranda DAG, Santos RTP, Tapanes NCO, Ramos ALD, Antunes OAC. Acid-catalyzed homogeneous esterification reaction for biodiesel production from palm fatty acids. Catal Lett 2008;122:20–5. https://doi.org/10.1007/s10562-007-9318-z . Ataya F, Dubé MA, Ternan M. Single-phase and two-phase base-catalyzed transesterification of canola oil to fatty acid methyl esters at ambient conditions. Ind Eng Chem Res 2006;45:5411–7. https://doi.org/10.1021/ie060152o . Nitbani FO, Tjitda PJP, Nurohmah BA, Wogo HE. Preparation of fatty acid and monoglyceride from vegetable Oil. J Oleo Sci 2020;69:277–95. https://doi.org/10.5650/jos.ess19168 . Cite Share Download PDF Status: Posted 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-762804","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research","associatedPublications":[],"authors":[{"id":43014842,"identity":"4a0bee76-5d4c-42a7-84a8-eef4b8905cdb","order_by":0,"name":"Javier CHAPARRO-ACOSTA","email":"","orcid":"","institution":"Industrial University of Santander: Universidad Industrial de Santander","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Javier","middleName":"","lastName":"CHAPARRO-ACOSTA","suffix":""},{"id":43014843,"identity":"24d3b836-715f-4e2e-bc28-4868d9ba7584","order_by":1,"name":"Juan-Manuel URBINA-GONZÁLEZ","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYBACxgYGNoYEBgY5BmYQl40ELcbEa4EpS2xAsAkA5hm5zx483GGXvuE4+wOGD2WHGfjbGwg4bEa6uUHimeTcDYd5DBhnnDvMIHHmACEtaWwSiW3MIC0MzLxthxkMJBKI0lKfbnCY/QHzXxK0HE4wACpmZiRKS88zdoPEtuOGM4F+OdhzLp2HoF8M29PYHv5sq5bnO3/84YMfZdZyBEPMEFkeZDwPfvVAIE9QxSgYBaNgFIwCAGcVP+AE8AYeAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-9193-026X","institution":"Industrial University of Santander: Universidad Industrial de Santander","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Juan-Manuel","middleName":"","lastName":"URBINA-GONZÁLEZ","suffix":""}],"badges":[],"createdAt":"2021-07-29 07:36:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-762804/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-762804/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":12085588,"identity":"d628a34a-c68e-4ebb-9ae9-26169792cb96","added_by":"auto","created_at":"2021-08-03 21:29:27","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":27537,"visible":true,"origin":"","legend":"FT-IR spectra of the palm oil sludge after Soxhlet extraction (in blue) and the obtained ester mixture (in black). The C=O stretching signal appears at 1697.5 cm-1 for carboxylic acids (top) and 1737.5 cm-1 for the mixture of esters (bottom).","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-762804/v1/e66c6fd713d6ea0e1f8b6f33.png"},{"id":12085812,"identity":"3b0896d6-4895-46c0-b264-d4f4f3855cce","added_by":"auto","created_at":"2021-08-03 21:32:27","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":10011,"visible":true,"origin":"","legend":"TIC obtained for the CG-MS of the ester mixture. Approximately 53.5 % corresponds to ethyl palmitate (peak No. 4) and 38.1 % to ethyl oleate (peak No. 6). For identification of the other numbered peaks, see Table 1.","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-762804/v1/fcd6ba3ba56e2033e3ef52dd.png"},{"id":12085590,"identity":"b790793b-12e9-46e0-8b3d-313e89d3b9eb","added_by":"auto","created_at":"2021-08-03 21:29:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":39828,"visible":true,"origin":"","legend":"Results of the comparison of the mass spectra with the NIST library. The MS spectrum for peak No. 4 (m/z = 284.2 g/mol, in red) matches the library spectrum for ethyl palmitate (in blue, top), and the MS spectrum for peak No. 6 (m/z = 310.3 g/mol, in red) matches the library spectrum for isomeric ethyl oleate (in blue, bottom). The match factor (MF) and reverse match factor (RMF) for each comparison are also included.","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-762804/v1/132cf2577b00f00585e4adb7.png"},{"id":12085591,"identity":"6450acd8-a866-438e-8e3b-23b370e93886","added_by":"auto","created_at":"2021-08-03 21:29:27","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":241749,"visible":true,"origin":"","legend":"Schematic diagram of the liquid-liquid continuous extractor used in the experiment and steps in the hypothetical sequence of reactions to convert FAMEs into FAEEs.","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-762804/v1/a0b79cd5e3403a0d47ede62d.png"},{"id":13708191,"identity":"1879e005-14ce-48da-9e7e-29dcb9dea2fa","added_by":"auto","created_at":"2021-09-17 14:06:22","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":775668,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-762804/v1/069c1f50-f836-4c05-89d9-d2f2386cff07.pdf"}],"financialInterests":"","formattedTitle":"Methanol-Based Esterification of Palm Oil Sludge – Preparation of Palmitic and Oleic Fatty Acid Ethyl Esters via Ethyl Acetate Transesterification","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eBiodiesel, a mixture of monoalkyl esters of biodegradable long chain fatty acids, contains insignificant amounts of sulfur and is nontoxic and renewable [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Biomass conversion via the transesterification of palm oil sludge (POS) with methanol is a common route to synthesize fatty acid methyl esters (FAMEs) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Currently under study for potential applications as renewable oils and biofuels [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], fatty acid ethyl esters (FAEEs) can provide less toxic means to manage ethanol [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Our interest is modifying locally produced POS to produce fatty acid esters, and we hope to encourage others to build upon previous research in this field and eventually prepare substances of added value, e.g., surfactants.\u003c/p\u003e"},{"header":"2. Materials And Methods","content":"\u003cp\u003ePOS used in this study was obtained from the third lagoon of the oxidation ponding system of Palmas del Cesar S. A. at the plantation located in La Loma (San Mart\u0026iacute;n municipality, Cesar Department, Colombia). The collected POS was purified by Soxhlet extraction with petroleum ether (PE). Then, 5.0 g of POS was poured into a round bottom flask, and 10 mL of methanol and H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (0.13 g) catalyst were added. The mixture was heated at 60\u0026deg;C at 300 rpm for 3 h according to Nata et al. [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] After cooling the reactor, the mixture was treated with 200 mL saturated Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e solution to pH\u0026thinsp;\u0026gt;\u0026thinsp;10 to neutralize the H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e catalyst and poured into a continuous liquid-liquid extractor using 150 mL ethyl acetate (EA) as solvent and heating under reflux for 24 h. The organic layer was roto-evaporated, and solvents (methanol and ethyl acetate) were removed at 40\u0026deg;C under vacuum until a constant weight was obtained (4.78 g, 96 % mass). The resulting oily residue was purified by column chromatography (CC) on SiO\u003csub\u003e2\u003c/sub\u003e using petroleum ether (PE):ethyl acetate (EA) (ratio 90:1) as the eluent. After purification, 1.65 g of a colorless oily sample was isolated (35 %), Rf\u0026thinsp;=\u0026thinsp;0.33 (PE:EA, ratio 90:1). Compounds in the sample were identified by gas chromatography-mass spectrometry GC-MS (Agilent 5977B GC/MSD, Santa Clara, CA 95051, United States) using an HP-5MS column (30 m; 0.25 mm i.d.; 0.25 mm film thickness), analyzed over a mass per charge (\u003cem\u003em/z\u003c/em\u003e) range of 50\u0026ndash;550 and identified by comparing the mass spectra with the NIST (National Institute of Standards and Technology) mass spectral library. NIST MS Search 2.3 was used for mass spectra comparison [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. MS Interpreter version Beta 3.1a [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] (part of the NIST Mass Spectral Search program) was used to obtain the formula and RDBE (ring and double bond equivalent) for selected mass spectra.\u003c/p\u003e"},{"header":"3. Results And Discussion","content":"\u003cp\u003ePE Soxhlet extraction separated the substances of interest from insoluble inorganic (sand) and organic material (wood and cellulose). The FT-IR spectrum shows that the sludge contains mainly free fatty acids. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (top) shows the main absorption signal of C\u0026thinsp;=\u0026thinsp;O stretching at 1697.5 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for carboxylic acids, where no ester band of glycerides is observed. Then, methanol-based esterification was performed according to Nata et al. [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] Due to the difficulty in performing a liquid-liquid extraction in a separatory funnel, a continuous liquid-liquid extractor with EA was used. Then, the ester interchange reaction was carried out with continuous heating for 24 h [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], as corroborated by MS spectra of the less polar fraction obtained after CC. The FT-IR spectrum in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (bottom) shows the typical C\u0026thinsp;=\u0026thinsp;O stretching band for esters at 1737.5 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGC-MS analysis of the isolated fraction (column chromatography, 35 % mass yield, Rf\u0026thinsp;=\u0026thinsp;0.33 SiO\u003csub\u003e2\u003c/sub\u003e, PE/EA 90:1) was carried out to identify the main compounds in that sample. Analyte MS spectra comparison using a mass spectral library search [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] corroborates the formation of ethyl esters of fatty acids instead of the expected methyl esters. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the resulting gas chromatogram; the two main compounds in the fraction (91.7 %) were identified as ethyl palmitate (C\u003csub\u003e18\u003c/sub\u003eH\u003csub\u003e36\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 53.6 %) and ethyl oleate (C\u003csub\u003e20\u003c/sub\u003eH\u003csub\u003e38\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 38.1 %) with a higher match factor correspondence for its (\u003cem\u003eE\u003c/em\u003e)-stereoisomer, in agreement with Nata et al. [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The match factor is the measured value of the direct match of peak \u003cem\u003em/z\u003c/em\u003e values and relative intensities, while the reverse match factor ignores all peaks that are in the sample spectrum but not in the library spectrum [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Clearly, a transesterification reaction occurred during the liquid-liquid extraction with EA and turned the methyl esters into their ethyl derivatives, as the MS spectra data comparison demonstrates. The MS comparison is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (top) for ethyl palmitate and in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (bottom) for ethyl oleate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \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\u003eMatch factors from the comparison of the mass spectra for the main analytes obtained in the CG-MS spectrum of the ester mixture and compounds in the NIST library.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePeak\u003c/p\u003e \u003cp\u003eName\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003etR\u003c/p\u003e \u003cp\u003e(min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eArea\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eScan\u003c/p\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMolecular\u003c/p\u003e \u003cp\u003eion mass\u003c/p\u003e \u003cp\u003e(g/mol)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAssigned\u003c/p\u003e \u003cp\u003eformula\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRDBE*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAssigned\u003c/p\u003e \u003cp\u003ecompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMatch Factor\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e9.128\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e0.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e444\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e228.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eC\u003csub\u003e14\u003c/sub\u003eH\u003csub\u003e28\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEthyl laurate\u003c/p\u003e \u003cp\u003e[Ethyl dodecanoate]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e870\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl tridecanoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e584\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e11.874\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e924\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e256.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eC\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e32\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEthyl myristate\u003c/p\u003e \u003cp\u003e[Ethyl tetradecanoate]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e910\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl pentadecanoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e632\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e13.717\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1246\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e270.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eC\u003csub\u003e17\u003c/sub\u003eH\u003csub\u003e34\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl palmitate\u003c/p\u003e \u003cp\u003e[Methyl hexadecanoate]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e947\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEthyl pentadecanoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e605\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e14.758\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e53.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1428\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e284.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eC\u003csub\u003e18\u003c/sub\u003eH\u003csub\u003e36\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEthyl palmitate\u003c/p\u003e \u003cp\u003e[Ethyl hexadecanoate]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e903\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl heptadecanoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e625\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e16.171\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e0.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1675\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e296.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eC\u003csub\u003e19\u003c/sub\u003eH\u003csub\u003e36\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl oleate\u003c/p\u003e \u003cp\u003e[Methyl (9\u003cem\u003eZ\u003c/em\u003e)- Octadec-9-enoate]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e926\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl (9\u003cem\u003eE\u003c/em\u003e)- Octadec-9-enoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e922\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e17.316\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e38.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e1868\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e310.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eC\u003csub\u003e20\u003c/sub\u003eH\u003csub\u003e38\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEthyl (9\u003cem\u003eE\u003c/em\u003e)-octadec-9-enoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e917\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEthyl oleate\u003c/p\u003e \u003cp\u003e[Ethyl (9\u003cem\u003eZ\u003c/em\u003e)-octadec-9-enoate]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e892\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl (10\u003cem\u003eZ\u003c/em\u003e)-nonadec-10-enoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e726\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e17.562\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e3.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1918\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e312.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eC\u003csub\u003e20\u003c/sub\u003eH\u003csub\u003e40\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEthyl stearate\u003c/p\u003e \u003cp\u003e[Octadecanoic acid ethyl ester]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e782\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMethyl nonadecanoate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e671\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003e* Ring and double bond equivalent\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eNIST MS Search 2.3 was used to compare the mass spectra of methyl and ethyl ester derivatives with the same molecular ion mass (same molecular formula). Considering the absence of glycerides (as ester signals) in the sludge IR spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, black spectrum), the POS contained predominantly carboxylic acids similar to compositions described in other reports [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], i.e., palmitic acid and oleic acid as the main components. Then, the POS sample underwent Fischer esterification (heating under reflux of the carboxylic acid mixture in methanol), and the resulting reaction mixture was heated in basic aqueous media with ethyl acetate; under these conditions, the only expected derivatives of our POS were methyl and ethyl ester carboxylates. Based on that assumption, the molecular formula and ring and double bond equivalent (RDBE) assignments of the main signals in the chromatogram were calculated with MS Interpreter version Beta 3.1a considering only C\u003csub\u003ex\u003c/sub\u003eH\u003csub\u003ey\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e formulas. NIST MS Search 2.3 was used for the mass spectra comparison, and the results for the match factors are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAs reported by Dub\u0026eacute; et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], for our similar biphase system, ester interchange should occur in the interphase, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The use of a weak base solution allowed the removal of the FFAs into the aqueous layer [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] as carboxylates, avoiding any interference in the reaction. Then, alkaline transesterification occurred in a similar way to the normal alkaline-catalyzed transesterification of vegetable oils to produce FAME and glycerol [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], considering that a small concentration of methoxide anion formed in the basic media through deprotonation of the residual methanol (used in the previous Fischer esterification) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, orange arrow). With that assumption, our hypothesis is that the methoxide anion initially transesterified the ethyl acetate used as extraction solvent, turning it into methyl acetate and liberating ethoxide anion into the interphase where conditions allowed the ester to interchange from FAME to FAEE. The contact of the warm solvent with the aqueous layer provided the energy needed to drive the reaction to form FAEE products, and the equilibrium was shifted by excess ethyl acetate and the extended duration of the process (24 h).\u003c/p\u003e \u003cp\u003eAlthough very low amounts of ester derivatives of linoleic acid were expected, they were not observed. Work is in progress to increase the yield of the first separated fraction analyzed in this report. This research covered several aspects of green chemistry, and the main compounds obtained are expected to serve as surfactants in diverse oil/water systems.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this study, free fatty acids (palmitic and oleic acids) contained in palm oil sludge were unexpectedly converted into their ethyl esters (FAEEs) by a sequence of Fischer esterification and transesterification reactions. The transesterification process probably occurred during an extraction when warm ethyl acetate from the liquid-liquid extractor dropped continuously into the basic aqueous phase containing FAME. These were appropriate conditions to convert methyl esters into their corresponding ethyl ester derivatives, as demonstrated by mass spectra data comparison.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data set (GC-MS file in *.ms format) generated and analyzed during this study is available in the Zenodo repository [DOI 10.5281/zenodo.5142503 at https://doi.org/10.5281/zenodo.5142503]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by internal grant UIS-VIE 1870.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ. Ch.-A. performed the laboratory experiments and reported the results from the FT-IR and GC-MS analyses. J.-M. U.-G. supervised the experiments,\u0026nbsp;checked\u0026nbsp;the data and wrote the final report. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors wish to thank the Vicerrector\u0026iacute;a de Investigaci\u0026oacute;n (VIE) at the Universidad Industrial de Santander (UIS) and Chemical Analysis Laboratory (Lab-308) at the School of Chemistry-UIS for providing the FT-IR and GC-MS analyses. We especially acknowledge Palmas del Cesar S. A. for providing the palm oil sludge samples.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; information (optional)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ. Ch.-A. is a professional chemist with 5 years of experience in the industrial preparation of commercial liquid soaps. As a student in his final year of a Chemical Engineering M.Sc. program, he is developing his research about the use of palm oil sludge as a raw material for the preparation of surfactants. J.-M. U.-G. is lecturer in organic chemistry at the Universidad Industrial de Santander, and he is the supervisor of J. Ch.-A. in his M.Sc. research project.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbdullah, Rahmawati Sianipar RN, Ariyani D, Nata IF. Conversion of palm oil sludge to biodiesel using alum and KOH as catalysts. Sustain Environ Res 2017;27:291\u0026ndash;5. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.serj.2017.07.002\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNduwayezu JB, Ishimwe T, Niyibizi A, Munyentwali A. Biodiesel production from unrefined palm oil on pilot plant scale. Int J Sustain Green Energy 2015;4:11\u0026ndash;21. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.11648/j.ijrse.20150401.13\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYusoff MFM, Xu X, Guo Z. Comparison of fatty acid methyl and ethyl esters as biodiesel base stock: a review on processing and production requirements. J Am Oil Chem Soc 2014;91:525\u0026ndash;31. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11746-014-2443-0\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNIST/EPA/NIH Mass Spectral Library with Search Program - Data ver. 2.3. Gaithersburg, MD, USA: National Institute of Standards and Technology (NIST); 2017.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eY. Mirokhin, D. Tchekhovskoy, A. Mayorov, S. Stein. MS Interpreter Version BETA 3.1a. Gaithersburg, MD, USA: National Institute of Standards and Technology (NIST); 2017.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDijkstra AJ. Revisiting the mechanisms of low-temperature, base-catalysed ester interchange reactions. Ol Corps Gras Lipides 2008;15:208\u0026ndash;12. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1051/ocl.2008.0200\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKind T, Fiehn O. Advances in structure elucidation of small molecules using mass spectrometry. Bioanal Rev 2010;2:23\u0026ndash;60. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12566-010-0015-9\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStein SE, Wallace W, Ji W, Little J, Markey S, Mallard WG, et al. Software user\u0026rsquo;s manual for NIST Standard Reference Database 1A - NIST/EPA/NIH Mass Spectral Library (NIST 17) \u0026amp; NIST Mass Spectral Search Program (Version 2.3) 2017.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAranda DAG, Santos RTP, Tapanes NCO, Ramos ALD, Antunes OAC. Acid-catalyzed homogeneous esterification reaction for biodiesel production from palm fatty acids. Catal Lett 2008;122:20\u0026ndash;5. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10562-007-9318-z\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAtaya F, Dub\u0026eacute; MA, Ternan M. Single-phase and two-phase base-catalyzed transesterification of canola oil to fatty acid methyl esters at ambient conditions. Ind Eng Chem Res 2006;45:5411\u0026ndash;7. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/ie060152o\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNitbani FO, Tjitda PJP, Nurohmah BA, Wogo HE. Preparation of fatty acid and monoglyceride from vegetable Oil. J Oleo Sci 2020;69:277\u0026ndash;95. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5650/jos.ess19168\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"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":"methanol Fischer esterification, ethyl acetate transesterification, fatty acids, palm oil sludge","lastPublishedDoi":"10.21203/rs.3.rs-762804/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-762804/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAcid-catalyzed Fischer esterification of fatty acids with methanol as a reagent and solvent is used to prepare long chain alkyl methyl esters. Transesterification of palm oil in basic media using methanol is a synthesis route to prepare monoalkyl methyl esters of fatty acids. In this work, we report performing Fischer esterification of a sample of local palm oil sludge (rich in fatty acids) in the presence of methanol and obtaining ethyl esters of oleic and palmitic acids from transesterification reactions during extractions with ethyl acetate.\u003c/p\u003e","manuscriptTitle":"Methanol-Based Esterification of Palm Oil Sludge – Preparation of Palmitic and Oleic Fatty Acid Ethyl Esters via Ethyl Acetate Transesterification","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-08-03 21:29:25","doi":"10.21203/rs.3.rs-762804/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":"990ff7ab-178f-447a-b551-1b365343449a","owner":[],"postedDate":"August 3rd, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":6172754,"name":"Energy Engineering"},{"id":6172755,"name":"High Energy and Particle Physics"},{"id":6172756,"name":"Environmental Engineering"}],"tags":[],"updatedAt":"2021-08-03T21:29:27+00:00","versionOfRecord":[],"versionCreatedAt":"2021-08-03 21:29:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-762804","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-762804","identity":"rs-762804","version":["v1"]},"buildId":"ehx78VzkSd0WSzXnipQa-","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}