Method for refining of soapstock by acidulation and solvent extraction

Abstract

The invention refers to the vegetable oil processing and energy sector, in particular the obtaining of raw material for the production of biodiesel from the oil refining process waste, called soapstock (SS), that is formed after the washing of the crude oil with an aqueous alkali solution. The invention is to be used for the industrial production of advanced biodiesel from the SS, which is generally considered a waste to be deposited and which cannot be used for the production of food. A high-yield high-quality acid oil, that can be used to produce modern biodiesel, is obtained via the developed two-stage process that includes the acidulation of the SS to pH 2-3 with subsequent high-temperature treatment in an ultrasound environment and the extraction of raw materials for the synthesis of advanced biodiesel from the resulting mixture using an ultrasound environment without prior separation of the aqueous phase.

Description

FIELD OF THE INVENTION

[0001] The invention relates to the vegetable oil refining and energy sector, in particular to the production of a raw material for the industrial manufacturing of advanced biodiesel from the residue of vegetable oil refining process, called a soapstock (SS), which is obtained after washing the crude oil with aqueous alkaline solution.BACKGROUND OF THE INVENTION

[0002] Fossil fuels in the form of LPG, petrol, diesel, and jet fuels continue to dominate the transportation sector, exerting catastrophic effect on the environment and facilitate the climate change. The replacement of fossil fuels in the transport sector is particularly relevant. As a waste material containing free fatty acids (FFA) and mono-, di- and triglycerides (MDTG) acid oil (AO) leads to a high interest in the production of all commodities containing fatty acid moiety, including biodiesel. As the production of biofuels from food materials (conventional biofuels) is planned to be limited to 7%, ensuring the prognosticate increase in the total share of biofuels becomes a rather difficult challenge. Significance of low-quality feedstock, including AO, increases [2].

[0003] AO is obtained by acidulation of soapstock (SS) by adding an acid and lowering the pH of the mixture to around 2-3 so as to fully convert the soap into FFA [4]. SS is generated at almost 6% of the volume of the crude oil production amounts, and is classified as both a waste and a low quality by-product which costs significantly less than vegetable oil, therefore it can be considered as a raw material for synthesis of advanced biodiesel.

[0004] SS contains a high amount of water, which is emulsified with lipid components, such as acylglycerols, FFA, salts (soap), and other components (phosphoacylglycerols, tocopherols, sterols, and pigments) from crude oil. It is known that the acidulation of SS is always carried out simultaneously with at least of partial hydrolysis of glycerides in the presence of phosphoric, hydrochloric, or sulfuric acid [4, 5]. The reaction temperature usually does not exceed 90 °C and the reaction time is about 1 h [4].

[0005] Wang et al describes recovery technology of acid oil (AO) from SS with only sulfuric acid solution addition under the ambient temperature (25±2 °C) [6]. After drying, AO contained 50.0% FFA, 15.5% TG, 6.9% DG, 3.1% MG, 0.8% water, and other inert materials. The recovery yield of AO was about 97% (w / w) based on the total fatty acids of the SS. But Shao et al describes a process for preparing AO from SS by means of adjusting the acidity of a SS to a pH of 2-3 at 90 °C [7]. After washing and drying, AO was separated in FFA rich fraction and MDTG rich fraction by wiped-film molecular distillation.

[0006] Systematic studies of acidulation at room temperature, as well as the results of literature [8], showed that acidulation alone does not provide a quality feedstock for biodiesel synthesis and requires an additional purification process. This process can be extraction with organic solvent. Acidulation and extraction with organic solvent can be performed in one step [9, 10].

[0007] The disadvantage of this method is the low yield of the required products. More often, however, acidulation and extraction are carried out as two separate processes. The method makes it possible to dry the substrate before the extraction, which significantly increase the extraction yield

[11] . Usually such fat well-dissolving solvent as hexane

[11] is used, but for isolation of fatty components also isopropyl alcohol, toluene, fusel oil, and a mixture of common salt and non-ionic surfactants

[12] were used. The extraction temperature is around 60 °C

[11] and the extraction time is 2 to 12 h. Ultrasound environment increases the extraction yield from dry substrate

[11] .

[0008] Pure extracts can be prepared by consecutive extraction method using few organic solvents

[13] , but it substantially lowers the yield of products and is not acceptable for industrial purpose. Soxhlet extraction with hexane taking more than 6 h is often successfully performed [14, 15] and can be considered as a standard extraction method. Its main disadvantage is longevity of the process and energy consumption

[16] .

[0009] Other processes are offered in patent application US3965085A, patent application CN 113717796 A and patent EP 1809755 B1. According to the US3965085A, the extraction is carried out with water-immiscible solvents (hexane, heptane, benzene and light petroleum) from a previously prepared mixture obtained by adding a low-molecule ketone (acetone) to the raw material and then carrying out the extraction. The result is a water-acetone phase containing fatty acids and fatty acid-containing saponifiable products and an organic phase. The disadvantage of the method is the use of at least 2 solvents (acetone and a water-immiscible solvent) that need to be recovered and the long duration of the process. The production of raw materials suitable for the synthesis of biofuels does not take place directly, but by trying to remove the impurities with the help of acetone-water solution. Acetone recovery is problematic and the yield is not high.

[0010] EP 1809755 B1 applies to a compact and more environmentally friendly fatty acid esterification production process to make alkyl and mainly methyl and ethyl esters starting directly from SS waste. The benefit of this process is the use of enzymes as esterification catalysts able to convert the FFA into esters in the presence of water, salts, soaps, and many other impurities. As the process should be carried out from a contaminated environment, the enzymatic process is expensive and inefficient.

[0011] CN 113717796 A is a process which employs ultrasound in the treatment of soapstock, although there is no mention of also using cyclohexane.SUMMARY OF THE INVENTION

[0012] SS is an emulsion of complex organic and inorganic substances in water, a mixture of monoglycerides (MG), diglycerides (DG), triglycerides (TG) and free fatty acids (FFA). Feedstock for biodiesel called acid oil (AO), must first be obtained from SS. MDTG and FFA are the raw material for obtaining advanced biodiesel and AO can be used for its synthesis. In this invention, a new and efficient method for obtaining AO from SS with good yield and high quality is proposed. The proposed method is based on acidulation and extraction of SS in ultrasound environment in a fast and energy consuming process.

[0013] The objective of the invention is to change the acidification of soapstock (SS) and extraction of acid oil (AO) in such a way that it takes place within a maximum of 2-3 h, excluding the dehydration and drying of the intermediate and ensuring a high yield and quality of AO.

[0014] The goal is achieved by the invented method, which comprises following steps: a) providing soapstock of vegetable oil refining process; b) acidulation of the soapstock of step (a) with phosphoric acid in amount which provides reduction of the pH of said soapstock to pH 2-3, obtaining a mixture (i); c) heating the mixture (i) from step (b) in an ultrasonic environment at a temperature 95-97 °C for 15-45 min, obtaining mixture (ii); d) cooling of the mixture of step (c) to room temperature; e) extraction of mixture of step (d) at room temperature in an ultrasonic environment for 25-45 min by adding a quantity of cyclohexane in ml that is equal or exceeds 1.5-fold the mass in g of the mixture (ii), obtaining mixture (iii); f) centrifugation of the mixture (iii) of step (e), obtaining a liquid mixture (iv); g) obtaining of an oil layer and a water layer by settling of the mixture (iv) of step (f) h) separating the oil layer of step (g); i) obtaining an acid oil by distilling cyclohexane from the oil layer of step (h). Substances suitable for the synthesis of biodiesel from various complex formations, such as phospholipids, are separated at a temperature of 95-97 °C for 15-45 min using ultrasound. Due to the short duration of the process, the hydrolysis of glycerides during acidulation is negligible and the resulting AO contains a high content (more than 30%) of triglycerides, which allows obtaining advanced biodiesel with a high yield.

[0015] Significant simplification has been made in the extraction process with cyclohexane. The extraction process takes place in an ultrasonic environment, without prior separation of the water layer. Such extraction without ultrasound would lead to a significant (30-50%) reduction in the yield of AO, but in the ultrasonic environment the opposite effect is observed, therefore it is possible to simplify the extraction process. The extraction with cyclohexane in an ultrasonic medium takes place at the same time as rinsing the raw material with the water contained in the SS. As a result, the AO's output increases and its quality improves.

[0016] Another aspect of the disclosure is an acid oil, obtained by the method according to the invention and use of this acid oil in advanced biodiesel synthesis.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 shows production of advanced biodiesel, comparing the invention and industrial methods, which shows both the formation of SS in the oil refining process and its use in the production of advanced biodiesel.DETAILED DESCRIPTION OF THE INVENTION

[0018] The invention is described but not limited by the following examples, and is defined in scope by the appended claims.

[0019] According to the preffered embodiment obtaining an acid oil comprises following steps: a) providing 40 g soapstock of vegetable oil refining process; b) acidulation of the soapstock of step (a) with phosphoric acid in amount which provides reduction of the pH of said soapstock to pH 2-3, obtaining a mixture (i); c) heating the mixture (i) from step (b) in an ultrasonic environment at a temperature 95 °C for 30 min, obtaining mixture (ii); d) cooling of the mixture of step (c) to room temperature; e) extraction of mixture of step (d) at room temperature in an ultrasonic environment for 30 min by adding 60 ml of cyclohexane without water removing, obtaining mixture (iii); f) centrifugation of the mixture (iii) of step (e), obtaining a liquid mixture (iv); g) obtaining of an oil layer and a water layer by settling of the mixture (iv) of step (f) and h) separating the oil layer of step (g); i) obtaining an acid oil by distilling cyclohexane from the oil layer of step (h).

[0020] The second embodiment obtaining an acid oil comprises following steps: a) providing 40 g soapstock of vegetable oil refining process; b) acidulation of the soapstock of step (a) with phosphoric acid in amount which provides reduction of the pH of said soapstock to pH 2-3, obtaining a mixture (i); c) heating the mixture (i) from step (b) in an ultrasonic environment at a temperature 95 °C for 15 min, obtaining mixture (ii); d) cooling of the mixture of step (c) to room temperature; e) extraction of mixture of step (d) at room temperature in an ultrasonic environment for 25 min by adding 40 ml of cyclohexane without water removing, obtaining mixture (iii); f) centrifugation of the mixture (iii) of step (e), obtaining a liquid mixture (iv); g) obtaining of an oil layer and a water layer by settling of the mixture (iv) of step (f) and h) separating the oil layer of step (g); i) obtaining an acid oil by distilling cyclohexane from the oil layer of step (h).

[0021] The third embodiment obtaining an acid oil comprises following steps: a) providing 40 g soapstock of vegetable oil refining process; b) acidulation of the soapstock of step (a) with phosphoric acid in amount which provides reduction of the pH of said soapstock to pH 2-3, obtaining a mixture (i); c) heating the mixture (i) from step (b) in an ultrasonic environment at a temperature 97 °C for 30 min, obtaining mixture (ii); d) cooling of the mixture of step (c) to room temperature; e) extraction of mixture of step (d) at room temperature in an ultrasonic environment for 30 min by adding 40 ml of cyclohexane without water removing, obtaining mixture (iii); f) centrifugation of the mixture (iii) of step (e), obtaining a liquid mixture (iv); g) obtaining of an oil layer and a water layer by settling of the mixture (iv) of step (f) and h) separating the oil layer of step (g); i) obtaining an acid oil by distilling cyclohexane from the oil layer of step (h).

[0022] The fourth embodiment obtaining an acid oil comprises following steps: a) providing 40 g soapstock of vegetable oil refining process; b) acidulation of the soapstock of step (a) with phosphoric acid in amount which provides reduction of the pH of said soapstock to pH 2-3, obtaining a mixture (i); c) heating the mixture (i) from step (b) in an ultrasonic environment at a temperature 95 °C for 45 min, obtaining mixture (ii); d) cooling of the mixture of step (c) to room temperature; e) extraction of mixture of step (d) at room temperature in an ultrasonic environment for 30 min by adding 40 ml of cyclohexane without water removing, obtaining mixture (iii); f) centrifugation of the mixture (iii) of step (e), obtaining a liquid mixture (iv); g) obtaining of an oil layer and a water layer by settling of the mixture (iv) of step (f) and h) separating the oil layer of step (g); i) obtaining an acid oil by distilling cyclohexane from the oil layer of step (h).

[0023] The fifth embodiment obtaining an acid oil comprises following steps: a) providing 40 g soapstock of vegetable oil refining process; b) acidulation of the soapstock of step (a) with phosphoric acid in amount which provides reduction of the pH of said soapstock to pH 2-3, obtaining a mixture (i); c) heating the mixture (i) from step (b) in an ultrasonic environment at a temperature 95 °C for 30 min, obtaining mixture (ii); d) cooling of the mixture of step (c) to room temperature; e) extraction of mixture of step (d) at room temperature in an ultrasonic environment for 45 min by adding 40 ml of cyclohexane without water removing, obtaining mixture (iii); f) centrifugation of the mixture (iii) of step (e), obtaining a liquid mixture (iv); g) obtaining of an oil layer and a water layer by settling of the mixture (iv) of step (f) and h) separating the oil layer of step (g); i) obtaining an acid oil by distilling cyclohexane from the oil layer of step (h).

[0024] The production of AO by the invented acidification-extraction method provides a significantly higher yield of AO from SS than the previously known methods and is feasible in a shorter time with lower energy consumption.

[0025] The invention is applicable to the industrial production of advanced biodiesel from SS, which is generally considered as waste and cannot be used for food production. As a result of the use of the method, SS is transformed from waste into a feedstock for the production of the advanced biodiesel. The use of SS will expand the feedstock base for advanced biodiesel production and promote the production of fuel from non-food feedstocks.REFERENCES CITED IN THE DESCRIPTION Non-patent literature cited in the description

[0026] [1] Eurostat Statistics Explained - Europa EU, 2020. https: / / ec.europa.eu / eurostat / statistics-explained / index. php [2] Directive (EU) 2018 / 2001, PE / 48 / 2018 / REV / 1 [3] EU Biofuels Annual 2020,https: / / www.fas.usda.gov / data / 9eaction-union-biofuels-annual-0 [4] Michael J. Haas, Improving the economics of biodiesel production through the use of low value lipids as feedstocks: vegetable oil soapstock. Fuel Processing Technology, 86(2005), 1087-1096. 10.1016 / j.fuproc.2004.11.004 [5] M. M. Ostafin et al. Recovering of the long-chain fatty acids from soapstock, PRZEMYSL CHEMICZNY. 2018-3. DOI:10.15199 / 62.2018.3.9 [6] Z.M.Wang, J.S. Lee, J.Y. Park, Z.H.Yuan. Novel biodiesel production from soybean soapstock. Korean J. Chem. Eng. 24(2007), 1027-1030. https: / / doi.org / 10.1007 / s11814-007-0115-6 [7] P. Shao, J. He, P. Sun, S. Jiang. Process optimisation for the production of biodiesel from rapeseed soapstock by a novel method of short path distillation. Biosyst. Eng. 102 (2009), 285-290, https: / / doi.org / 10.1016 / J.BIOSYSTEMSENG.2008.11.014 [8] C. Echim, R.Verhé, W. De Grey, C. Stevens. Production of biodiesel from sidestream refining products. Energy Environ. Sci., 2(2009), 1131-1141. https: / / doi.org / 10.1039 / B905925C [9] US20010049452A1 - Method for soapstock acidulation.

[10] C. Nakyung, J.S. Lee, J. Kwak, J. Lee, I.H. Kim. Production of Biodiesel from Acid Oil via a Two-Step Enzymatic Transesterification, J. Oleo Sci. 65 (2016), 913-921. doi : 10.5650 / jos.ess16092

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[12] Y.I. Prokof'ev, T. N. Poyarkova, A. R. Bykov, A. S. Shestakov, V. A. Kuznetsov, O.G. Androsova. Influence of the isolation method of the soapstock fatty component on its characteristics. Res. Agr. Eng., 61 (2015), 111-115. doi: 10.17221 / 20 / 2014-RAE

[13] H. Nawaz, M. A. Shad, N. Rehman, H. Andaleeb, N. Ullah. Effect of solvent polarity on extraction yield and antioxidant properties of phytochemicals from bean (Phaseolus vulgaris) seeds. Braz. J. Pharm. Sci., 56 (2020) ISSN 2175-9790 https: / / doi.org / 10.1590 / s2175-97902019000417129

[14] M. Cruz, E. Costa, M. F. Almeida, M. da Conceicao Alvim-Ferraz, J. M. Dias. Recovery of by-products from the olive oil production and the vegetable oil refining for biodiesel production. Detritus, 4 (2018), DOI:10.31025 / 2611-413512018.13728

[15] I. Efthymiopoulos, P. Hellier, N. Ladommatos, A. Kay, B. Mills-Lamptey. Integrated strategies for water removal and lipid extraction from coffee industry residues. Sustainable Energy Technologies and Assessments 29 (2018) 26-35 https: / / doi.org / 10.1016 / j.seta.2018.06.016

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[0027] US3965085 A EP 1809755 B1 CN113717796 A

Claims

1. A method of obtaining an acid oil wherein the method comprises following steps: a) providing soapstock of vegetable oil refining process; b) acidulation of the soapstock of step (a) with phosphoric acid in amount which provides reduction of the pH of said soapstock to pH 2-3, obtaining a mixture (i); c) heating the mixture (i) from step (b) in an ultrasonic environment at a temperature 95-97 °C for 15-45 min, obtaining mixture (ii); d) cooling of the mixture of step (c) to room temperature; e) extraction of mixture of step (d) at room temperature in an ultrasonic environment for 25-45 min by adding a quantity of cyclohexane in ml that is equal or exceeds 1.5-fold the mass in g of the mixture (ii), obtaining mixture (iii); f) centrifugation of the mixture (iii) of step (e), obtaining a liquid mixture (iv); g) obtaining of an oil layer and a water layer by settling of the mixture (iv) of step (f) h) separating the oil layer of step (g); i) obtaining an acid oil by distilling cyclohexane from the oil layer of step (h).

2. The method according to claim 1, wherein the mixture (i) from step (b) is heated in an ultrasonic environment at a 95 °C for 30 min.

3. The method according to claim 1 or 2, wherein the extraction of step (e) is carried out for 30 min.

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