Pretreatment process for vegetable oils by heterogeneous catalysis of fatty acid esterification

Abstract

Continuous process for pretreating a batch of oil containing a maximum of 20 wt% free fatty acids by countercurrent esterification of the free fatty acids, in which a vertical liquid / liquid contact apparatus containing a solid-form esterification catalyst, supplied by an alcohol batch containing at least 40 wt% alcohol and up to 50 wt% water, as well as impurities whose content is a maximum of 1 wt% of the alcohol batch, and heteroelements with a content of less than 500 ppm, wherein the alcohol is methanol or ethanol, and the oil batch contains, the contact device is operated at a temperature between 25 and 120 °C and a pressure between 1 and 20 bar, wherein the contact apparatus performs the contact in liquid / liquid countercurrent between a heavy phase and a light phase, wherein the heavy phase is either an oil-rich phase or an alcohol-rich phase.

Description

AREA OF INVENTION

[0001] The present invention relates to a pretreatment process for vegetable oil in which the existing fatty acids are esterified by heterogeneous catalysis in a countercurrent liquid-liquid contact apparatus. STATE OF THE ART

[0002] In an international context characterized by the rapid increase in the demand for fuels, especially diesel and kerosene bases in the European Community, the exploration of new renewable energy sources presents a major challenge.

[0003] Among batches derived from renewable resources, the use of vegetable or animal oils, which may be semi-refined, is often recommended.

[0004] These oils, which are poorly suited for direct use in modern diesel engines of passenger cars and consist essentially of triglycerides, must be converted, for example, by transesterification or subjected to a hydrotreatment step in order to obtain high-quality fuel bases that meet specific requirements, either directly or after mixing with other fractions from the refining of crude oil.

[0005] The increase in the prices of raw materials of biological origin and the recent controversy surrounding first-generation biofuels necessitate both the diversification of triglyceride sources (for example, Jatropha curcas) and the use of less refined raw materials to improve the overall yield of the industry, or the use of lower-value by-products from the food-producing industry, such as fats from the slaughter of poultry, sheep, and cattle, as well as used frying oils.

[0006] Crude oil is obtained by pressing and washing oilseeds with water: The oilseeds are heated and then pressed to extract the pressed oil. The remaining solid, which still has a very high fat content, undergoes a solvent extraction step, usually with hexane, and the oil obtained after the hexane evaporates is called extraction oil.

[0007] The extracted oil is now mixed with water. Water and oil are only sparingly soluble compounds. This addition of water is accompanied by the appearance of an aqueous phase in which the existing water-soluble compounds (phospholipids, plant mucilage) dissolve. This two-phase mixture is then separated by centrifugation, and the fatty phase is called crude oil. The steps described above may vary depending on the oilseed being treated; however, to those skilled in the art, crude oil is understood to be an oil that, as a further treatment, has undergone only washing with water and then centrifugation to remove a large proportion of the water-soluble compounds.

[0008] These oils consist primarily of triglycerides, comprising 80 to 98% by weight. The minor compounds, present at 2 to 20% by weight, include (but are not limited to) free fatty acids, mono- and diglycerides, glyceride oxide compounds from oil degradation, polymers, waxes (natural hydrocarbons present in the oil), proteins containing sulfur and / or nitrogen, phospholipids, tocopherols, sterols, natural pigments, and more or less volatile fragrance compounds. Other minor compounds include elements containing heteroelements such as phosphorus, magnesium, calcium, iron, and zinc, with concentrations of these elements reaching 2500 ppm. In the case of phosphorus, magnesium, and calcium, these elements are primarily present as phospholipids and / or sterols. Magnesium, in particular, is present as pigments.In the case of iron and / or zinc, these substances can be present in the form of sterols and / or soaps (Oils and Fats Manual: A Comprehensive Treatise, Volume 1, page 90, Karleskind A. et al.).

[0009] Semi-refined oil is defined as crude oil as defined above that has undergone a pre-refining step aimed at eliminating minority compounds, and in particular at least some of the phospholipids and at least some of the free fatty acids. The pre-refining of crude oil generally includes: - a degumming step consisting of eliminating at least some of the phospholipids or plant mucilage by separation in the presence of acidified water, - a neutralizing paste formed in this step is generally separated by centrifugation and carries away some of the impurities contained in the oil and - a washing step with water to eliminate traces of sodium salts, - and a drying step under vacuum.

[0010] The semi-refined oil that has undergone these steps is also called "DNS" oil (Demucilaginee, Neutralisee et Séchée - demucalized, neutralized, and dried). This semi-refined oil may still contain up to 20 ppm of phosphorus, calcium, magnesium, iron, and / or zinc in the form of phospholipids (Oils and Fats Manual: A Comprehensive Treatise, Volume 1, page 90, Karleskind A. et al.), as well as free fatty acids.

[0011] However, free fatty acids negatively impact existing technologies for converting oils—used oils from the food production and catering industries, and oils of animal origin (tallow, fat from poultry, sheep, and cattle)—into fuel. In particular, the present fatty acids can have a corrosive effect on preheating lines (in the case of hydrotreating vegetable oils), lead to yield losses (in the case of homogeneous transesterification processes), or shorten the catalyst's lifespan and reduce performance (in the case of heterogeneous transesterification processes). They can be extracted upstream of the vegetable oil-to-fuel conversion units using conventional treatments, such as neutralization, as explained above.The main disadvantage of this technique stems from the fact that the extracted fatty acids are byproducts that cannot be used as fuel, resulting in a significant loss of material yield and therefore considerably impacting the profitability of production plants that manufacture biofuels from vegetable oils. This effect is all the more pronounced when the fatty acid content of the original oil is high. Another solution is to esterify the fatty acids into fatty acid esters according to the following reaction: . Fatty acid + alcohol ⇌ water + fatty acid ester C n H 2n+1 COOH + R-OH ⇌ H2O + C n H 2n+1 COOR

[0012] Esterification allows the yield of oil-to-fuel conversion to be improved by 1 to 20% compared to treatments that aim to extract the fatty acid, which becomes an unusable by-product for the fuel fraction, by converting the fatty acid into usable esters in the fuel fraction.

[0013] Esterification is a well-known reaction documented in the literature and recent patents. It is a balanced reaction; therefore, a reaction product must be removed to accelerate the conversion. Evaporating water, for example, is a common method for achieving this shift in equilibrium. Since methanol is more volatile than water, it must first be evaporated, a process generally carried out under vacuum (typically on the order of one hundred millibars to avoid temperatures that could lead to product losses through thermal degradation), which increases the energy costs of this type of process.

[0014] The conventional reaction therefore consists of two reaction steps, separated by complete evaporation of the water and the methanol that has not reacted.

[0015] Commercially available solutions have been developed to carry out the esterification of free fatty acids on ion exchange resins. However, implementation on an industrial scale has not yet been carried out due to its high economic cost.

[0016] In its brochure "BayFAME® Continuous Free Fatty Acid Esterification," Bayer Technology Service describes a process that allows all acidic oil batches containing up to 100% free fatty acids—that is, oils containing exclusively fatty acids—to be treated by esterification of the free fatty acids. The reaction is catalyzed by an acidic resin. The process consists of a sequence of reaction steps, each followed by a separation step of the water + methanol fraction and a separation step of the methanol / water fraction. The number of steps ranges from one to three, depending on the initial fatty acid content of the batch.

[0017] Patent applications WO 2009 / 056 230 A1 and WO 2009 / 056 231 A1 teach essentially the same principle: the fatty acid is esterified by heterogeneous catalysis on an acidic resin. This reaction step is followed by a separation step of the water and methanol from the oil fraction, and then a separation of the water / methanol mixture.

[0018] Cairncross R, Melick C, “Novel Reactor Design for the Production of Biodiesel from Free Fatty Acids,” AICHE 2008 Meeting, describes the use of a bubble column in which methanol vapor forms bubbles in a liquid phase containing the fatty acids and oil. These bubbles must then diffuse through the liquid to carry out the esterification reaction. A high excess of methanol is necessary both to allow the methanol bubbles to pass through the column and thus ensure a sufficient amount of methanol is transferred into the oil phase, and to carry along the water produced during the reaction. Furthermore, in the case of a gas-to-liquid conversion (methanol gas stream), temperature and pressure conditions are required that allow the reaction to proceed above the methanol bubble point.The methanol must transition into a liquid phase for the reaction to occur, but oleic acid is only very slightly volatile under the reaction conditions. The reaction volume is therefore limited to the volume of the liquid phase. The present invention eliminates these disadvantages by proposing a liquid-to-liquid reaction between the methanol and the oil contaminated with fatty acids. Through diffusion, both phases contain oleic acid and alcohol and are therefore the site of the esterification reaction. This results in a more compact equipment design.

[0019] US 2010 / 0249442A1 describes the esterification of fatty acids in the presence of an acidic and macroporous polymer resin containing free sulfone groups. The esterification takes place in a fixed bed in the presence of alcohol, whereby the fatty acids are first separated from the oil to be treated and then fed countercurrently into the fixed bed in a mixture with the alcohol.

[0020] DE 101 55 241 C1 discloses an esterification process of free fatty acids in vegetable or animal fats using polyalcohols in a reactor in the presence of a solid neutral catalyst at a temperature between 150 and 220°C, carried out using a vacuum for a reaction time of 6 hours in the form of a gas-liquid contact.

[0021] An object of the present invention is to propose a pretreatment process for a crude oil or semi-refined oil which makes it possible to convert the free fatty acids contained in the oil by esterification in such a way that the fatty acid content in the oil pretreated by the process according to the invention is less than 1 wt.% of the pretreated oil. SUMMARY AND BENEFITS OF THE INVENTION

[0022] The process according to the invention makes it possible to eliminate the constraint of water release at reaction equilibrium during the esterification reaction of fatty acids. It therefore allows very high conversion levels of the fatty acids to be achieved in a single reaction apparatus and eliminates the need for intermediate drying of the oil to remove this water, which adversely affects the reaction equilibrium. This process also makes it possible to react the most stable oil, i.e., the oil with the lowest free fatty acid content, with the alcohol with the lowest water content. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention relates to a continuous process for pretreating a batch of oil containing a maximum of 20 wt% free fatty acids by esterification of the free fatty acids, in which a vertical liquid / liquid contact apparatus containing a solid-form esterification catalyst is supplied countercurrently by a batch of alcohol containing at least 40 wt% of an alcohol and the batch of oil, wherein the contact apparatus is operated at a temperature between 25 and 120 °C, wherein the contact apparatus performs the contact in a liquid / liquid countercurrent between a heavy phase and a light phase, wherein the heavy phase can be either an oil-rich phase or an alcohol-rich phase.

[0024] Pretreatment is defined as the fact that the inventive process is placed upstream of a treatment process for the vegetable and / or animal oils. In a preferred embodiment, the inventive pretreatment process is placed upstream of a hydrotreatment process for the oils. In another preferred embodiment, the inventive pretreatment process is placed upstream of a transesterification process for the oils.

[0025] The pretreatment method according to the present invention therefore allows the use of either a vegetable or animal crude oil that has not undergone any pretreatment, or a semi-refined vegetable or animal oil, to produce distillate bases (kerosene and diesel oil).

[0026] The oil batch consists of all sources containing triglycerides and free fatty acids. Preferably, the oil batch is a crude or semi-refined oil batch derived from renewable vegetable terrestrial, aquatic, or animal oil sources, as well as from mixtures of such oils.

[0027] The vegetable oils of terrestrial or aquatic origin are advantageously selected from palm oil, soybean oil, palm kernel oil, copra oil, rapeseed oil, sunflower oil, corn oil, cottonseed oil, peanut oils, jatropha oil (Jatropha curcas), castor oil, linseed oil and crambe oil and all oils that, for example, are derived from sunflowers or rapeseed by genetic modification or hybridization or also from algae or aquatic organisms, or from partially modified oils, for example by polymerization or oligomerization, such as the "stand oils" from linseed, sunflower, the vegetable oils, the oils from used frying oils, the by-products of the refining of the oils: PFAD (Palet Fatty Acid Distillates) or broken pastes.

[0028] The animal oils are advantageously selected from animal fats and preferably from bacon and fats composed of residues from the food-producing industry or from the gastronomic industry, tallow, lard, residues from the slaughter of poultry, pigs, sheep and cattle.

[0029] The densities of these oils at 15°C are advantageously between 850 and 940 kg / m3, and their kinematic viscosities at 40°C are between 20 and 400 mm² / s and preferably between 30 and 50 mm² / s.

[0030] The oil batch generally also contains various impurities, particularly heteroatoms such as nitrogen and / or sulfur. The nitrogen and sulfur content in batches from renewable sources is generally between 1 ppm and 100 ppm by weight, and, depending on their composition, preferably lower than 100 ppm. It can reach up to 1% by weight in certain oils. The free fatty acid content in the oil batch is a maximum of 20% by weight.

[0031] The alcohol batch comprises an alcohol selected from ethanol and methanol. The alcohol batch contains at least 40% by weight of alcohol. The alcohol batch also contains up to 50% by weight of water, as well as impurities such as aldehydes, ketones, and acids, the content of which is a maximum of 1% by weight of the alcohol batch, and heteroelements such as Na, K, Al, and Fe in ionic form with a content of less than 500 ppm, preferably less than 100 ppm, wherein these heteroelements negatively affect the service life of the ion exchange resins that are advantageously used in the process according to the invention.

[0032] The ternary diagram (either methanol or ethanol) / water / ester shows that there are temperature, pressure, and composition conditions under which these three substances form a single liquid phase, and others under which they form two phases: an alcohol-rich phase and an oil-rich phase. "Rich" is defined as a phase where the composition exceeds 50 wt% of the phase. These are called phase separation conditions when the temperature, pressure, and composition conditions are such that two liquid phases coexist.

[0033] Therefore, by implementing a sophisticated set of operating conditions and selecting an appropriate alcohol concentration, conditions are created under which separation occurs and is maintained at all points in the liquid-liquid contact apparatus. The coexistence of the two liquid phases allows for the implementation of a liquid-liquid countercurrent.

[0034] The density of the alcohol batch varies depending on the respective alcohol and water contents. For lower water contents, the alcohol batch therefore has a lower density than the oil batch. For high water contents, the alcohol batch has a higher density than the oil batch. In a preferred arrangement, the water content of the alcohol batch is adjusted such that the alcohol batch has a higher density than the oil batch. In another preferred arrangement, the water content of the alcohol batch is adjusted such that the alcohol batch has a lower density than the oil batch.

[0035] The liquid phase with the lowest density is called the light phase, and the liquid phase with the highest density is called the heavy phase. Depending on the water content of the alcohol batch, it can therefore form either the light or the heavy phase.

[0036] A liquid / liquid countercurrent is a system in which two liquid phases circulate in countercurrent to each other.

[0037] The contact apparatus of the method according to the invention is arranged vertically. It has at least two feed points and at least one extraction point. A feed point is a point through which a liquid phase enters the contact apparatus. An extraction point is a point through which a liquid phase is extracted from the contact apparatus.

[0038] A heavy phase is fed into the contact apparatus at at least one injection point located above the feed point of a light phase. A light phase is drawn off from the contact apparatus at at least one extraction point located above at least one feed point of a heavy phase. A heavy phase is drawn off from the contact apparatus at at least one extraction point located below at least one feed point of a light phase.

[0039] The extracted, oil-rich phase, which is called the light phase or the heavy phase depending on the water content of the alcohol batch, forms the pretreated oil drain.

[0040] Due to the density difference, the lighter phase circulates from bottom to top in the contact apparatus, while the heavier phase circulates from top to bottom. The lighter and heavier phases are therefore brought into contact with each other in countercurrent flow.

[0041] The contact apparatus features a solid-state esterification catalyst.

[0042] The catalyst is held in place within the contact apparatus by any means known to a person skilled in the art. For example, it can be placed, but is not limited to, in perforated baskets, in small stacked bags, or encapsulated in a structured filling.

[0043] The catalyst is an acidic solid, preferably selected from silicon dioxide-aluminum dioxides, acidic clays, sulfated zircons and acidic resins, which may be taken alone or in mixture and are preferably selected from the acidic resins.

[0044] Preferably, the catalyst has an acid capacity, which represents the number of active sites of the catalyst, dosed by potentiometry during neutralization by a KOH solution (equivalent of method ASTM D2187) to 0.2 to 6 mmol H+ equivalent per gram, preferably 0.2 to 4.5, preferably 0.2 to 4.2 and particularly preferably 1.2 to 4.2 mmol H+ equivalent per gram.

[0045] Acidic solids commonly available commercially are the clays that have been treated with acids to make them acidic (such as montmorillonite).

[0046] An acidic resin, which can advantageously be used as a catalyst in the process according to the invention, comprises sulfone groups grafted onto an organic support consisting of aromatic and / or haloaliphatic compounds. It advantageously has between one and two terminal sulfone groups per aromatic and / or haloaliphatic group. The acidic resin is prepared by polymerization or copolymerization of an aromatic vinyl group followed by sulfonation, wherein the aromatic vinyl groups are selected from styrene, vinyltoluene, vinylnaphthalene, vinylethylbenzene, methyl-5-styrene, vinylchlorobenzene, and vinylxylene, the resin having a crosslinking ratio between 20 and 40%, preferably between 25 and 35%, and preferably between 30 and 35%. The resin particle size is between 0.15 and 1.5 mm. Resin particle size refers to the diameter of the smallest sphere enclosing the resin particles.Resin size classes are measured by sieving over seven, which are adjusted according to a technique known to the expert.

[0047] A preferred resin is one composed of aromatic monovinyl and aromatic polyvinyl copolymers, and particularly preferably of divinylbenzene and polystyrene copolymers. The resin is, for example, resin TA801, sold by Axens.

[0048] The catalyst can occupy the entire cross-section of the contact apparatus. It is therefore in contact with both the light and the heavy phases.

[0049] In a preferred arrangement, the heavy phase is rich in oil and the light phase is rich in alcohol, meaning that the density of the alcohol batch is lower than the density of the oil batch.

[0050] The esterification reaction takes place within the contact apparatus primarily in the oil-rich phase. This reaction produces water, which diffuses into the alcohol-rich phase due to its affinity with the alcohol. The diffusion of this water increases the density of the alcohol-rich phase (light phase). Therefore, the density of the alcohol batch, which constitutes the light phase in this preferred arrangement, must be sufficiently low to ensure that its density never exceeds that of the oil-rich phase, which constitutes the heavy phase. Such a reversal of the density ratio would cause a reversal of the phase circulation direction and consequently halt the operation of the liquid-liquid contact apparatus.

[0051] In this preferred arrangement, the contact apparatus advantageously comprises at least one collecting zone for the light phase, one collecting zone for the heavy phase, one zone for establishing contact between the heavy phase and the catalyst, and one redistribution zone for the light and heavy phases. The collecting zone can be designed according to the principle of column plates for gas / liquid distillation with a liquid barrier height.

[0052] Upon contact with the catalyst, the esterification reaction takes place between the free fatty acids and the alcohol contained in the light and heavy phases. This reaction produces esters and water. Just as the alcohol transfers from the alcohol-rich phase to the oil-rich phase, the water produced transfers from the oil-rich phase to the alcohol-rich phase. The water therefore separates from the oil and the esters formed by the reaction.

[0053] The oil-rich phase therefore gradually becomes poorer in free fatty acids and richer in esters. Since the circulation is countercurrent, the oil-rich phase is in contact with an alcohol-rich phase that becomes increasingly richer, meaning it contains less and less water.

[0054] This liquid-liquid countercurrent reaction therefore allows the oil, which is lower in free fatty acids and thus more difficult to treat, to come into contact with the purer alcohol. Conversely, the oil richer in free fatty acids is brought into contact with the alcohol, which is more heavily water-charged.

[0055] It is therefore no longer possible to be subject to the constraint of water release on the reaction equilibrium. This allows for very high conversion levels of the fatty acids to be achieved in a single reaction apparatus, eliminating the need for intermediate drying of the oil to remove this water, which negatively affects the reaction equilibrium.

[0056] The alcohol batch advantageously consists of the alcohol-rich phase that is drawn off from the contact apparatus and returned to the contact apparatus mixed with an alcohol additive. The alcohol phase drawn off from the contact apparatus is advantageously treated before being returned so that the water content in the alcohol batch is maintained at the desired value.

[0057] The alcohol-rich phase also gradually becomes enriched with free fatty acids. Since this phase is advantageously returned to the contact apparatus after any distillation, the free fatty acids are also returned and therefore not lost.

[0058] The contact apparatus also features a system that allows the dispersion of the light phase to be maintained, for example, and not restrictively, in the form of plates or fillings, which may or may not be structured.

[0059] According to the invention, the liquid-liquid contact apparatus is operated at a temperature between 25 and 120 °C, preferably between 25 and 100 °C. Since the process is carried out in the liquid phase, the pressure is of little importance. The liquid-liquid contact apparatus is operated at a pressure sufficient to keep the phases in the liquid state, preferably between 1 and 20 bar absolute.

[0060] The alcohol mass ratio contained in the alcohol batch to the oil batch is preferably between 15:85 and 85:15, more preferably between 20:80 and 80:20 and more preferably between 40:60 and 60:40.

[0061] The contact time between the light phase and the heavy phase within the liquid / liquid contact apparatus is at least 30 minutes and is preferably shorter than 1 hour 30 minutes.

[0062] The conversion of the free fatty acids contained in the oil batch into esters by the pretreatment process according to the invention is higher than 98%. EXAMPLES Example 1 according to the state of the art

[0063] An oil batch containing a mixture of vegetable corn oil with 10% w / w free fatty acids is used to supply a fatty acid esterification system. The alcohol batch consists of dry methanol (water content < 500 ppm).

[0064] A 1000 kg / h oil batch and a 225 kg / h alcohol batch are supplied, resulting in a molar ratio of 20:1 methanol / oil at the inlet of the editorial section.

[0065] The catalyst is a sulfone resin, Amberlyst BD20, marketed by Rohm & Haas. The acid capacity of this solid is 1.2 mm H+ eq / g. The first reactor contains 1 m³ of resin (Liquid Hourly Space Velocity, LHSV = 1.2 h⁻¹). The reaction takes place at 80 °C and a pressure of 20 bar. An 85% conversion of the fatty acids is observed, which is insufficient to make the treated oil compatible with use in oil treatment processes such as hydrogenation or transesterification.

[0066] Since the reaction at the reactor outlet has progressed close to thermodynamic equilibrium, it is necessary to remove one of the reaction products to achieve a more complete conversion of the fatty acids. Evaporation under vacuum (230 mbar) is carried out to volatilize the unreacted methanol and the water produced during the reaction. The vacuum is achieved using a liquid ring pump operating at a vacuum pressure of 13 mbar. A second reaction stage, identical to the first, is then carried out after adding 200 kg / h of methanol to complete the reaction. The measured conversion of the fatty acids after the second reaction step is 99%.

[0067] A final drying process takes place in the case where the water is rehibitive for the downstream usable phases of the product (for example, for its storage, where the water causes degradation reactions of the oil that has not reacted into fatty acid). Example 2: Countercurrent esterification with dry methanol (according to the invention)

[0068] An oil batch identical to that of Example 1 is introduced into a vertical liquid-liquid contact apparatus containing a sulfonic acid TA 801 type catalyst, marketed by Axens, with an acid capacity of 4.1 mmol H+ eq / g. The oil batch is introduced at the top of the contact apparatus and forms the heavy phase.

[0069] The density of the oil phase is 0.917.

[0070] The methanol charge, containing methanol and 1 wt% water, is introduced at the bottom of the contact apparatus. A throughput of 1000 kg / h of the alcohol charge is used, ensuring that the mixture is in the liquid-liquid equilibrium lens of the methanol / water / ester mixture. The alcohol charge forms the light phase.

[0071] The resin is arranged in two stages, each 2 m high, within a bag-type device made of polymer fabric, which allows for an empty space ratio of approximately 60% per section of the contact apparatus. The two zones are separated by conventional internal partitions (perforated grids).

[0072] The contact apparatus is operated at a temperature of 50 °C and a pressure of 10 bar. The two countercurrent separation stages achieve a total conversion rate of 99.7% for the fatty acids. The water produced is recovered in the upper phase of the contact apparatus from the light phase, which is rich in alcohol. Fatty acids are also present in the light phase and are returned to the contact apparatus along with the alcohol batch. A portion of the alcohol batch is distilled to maintain the water content at 1% by weight.

[0073] The pre-treated oil is recovered in the heavy phase, which is drawn off at the bottom of the contact apparatus. This oil contains no water, but it does contain 5% by weight methanol, which is harmless for the downstream oil treatment processes (hydrotreatment or transesterification). Example 3: Countercurrent esterification with moist ethanol - not according to the invention

[0074] An oil batch identical to that of Example 1 is introduced into a contact apparatus of the same type as that of Example 2, which contains the same catalyst as in Example 2.

[0075] The oil charge is introduced at the bottom of the contact apparatus and forms the light phase.

[0076] The alcohol batch, containing 40% by weight ethanol and 60% by weight water, is introduced into the head of the contact apparatus. The density of the alcohol batch is 0.935.

[0077] In an initial experiment, the contact apparatus was operated at a temperature of 60 °C, an absolute pressure of 10 bar, and an oil / ethanol mass ratio of 1. The conversion of free fatty acids was 99%.

[0078] In a second experiment, the contact apparatus is operated at a temperature of 50 °C, an absolute pressure of 10 bar, and an oil / ethanol mass ratio of 0.5. The conversion of free fatty acids is 98.4%.

[0079] The oil-rich phase that is tapped from the contact apparatus, i.e. the pretreated oil, contains approximately 7 wt% ethanol and 0.6 wt% water.

[0080] The process allows the esterification reaction to be carried out almost completely without intermediate drying using moist ethanol, while the water acts as an inhibitor of the reaction (resulting in a balanced reaction). Example 4: Countercurrent esterification with dry ethanol

[0081] An oil batch identical to that of Example 1 is introduced into a contact apparatus identical to that of Example 2 at the top of the contact apparatus. An alcohol batch containing ethanol and 1% water by weight is introduced at the bottom of the contact apparatus.

[0082] In this case, the contact apparatus must be operated at a low temperature with a low oil / ethanol ratio in such a way that segregation is maintained throughout the entire contact apparatus.

[0083] The contact apparatus is operated at a temperature of 50 °C with an oil / ethanol mass ratio of 1:5 and an absolute pressure of 10 bar. The conversion of free fatty acids is 99.7%.

[0084] Due to the high ethanol content, the pretreated oil contains approximately 20% by weight ethanol. However, the resulting pretreated oil is very dry, with a water content of 10 ppm.

[0085] The withdrawn, alcohol-rich phase contains a small amount of entrained ester and acid (approximately 0.1 wt% compared to the alcohol). The water produced by the reaction is also almost completely recovered in this stream.

Claims

[1] Continuous process for pretreating a batch of oil containing a maximum of 20 wt% free fatty acids by countercurrent esterification of the free fatty acids, in which a vertical liquid / liquid contact apparatus containing a solid-form esterification catalyst, supplied by an alcohol batch containing at least 40 wt% alcohol and up to 50 wt% water, as well as impurities whose content is a maximum of 1 wt% of the alcohol batch, and heteroelements with a content of less than 500 ppm, wherein the alcohol is methanol or ethanol, and the oil batch contains, the contact device is operated at a temperature between 25 and 120 °C and a pressure between 1 and 20 bar, wherein the contact apparatus performs the contact in liquid / liquid countercurrent between a heavy phase and a light phase, wherein the heavy phase is either an oil-rich phase or an alcohol-rich phase. [2] Method according to claim 1, wherein the water content of the alcohol batch is adjusted such that the alcohol batch has a density that is higher than that of the oil batch. [3] Method according to claim 1, wherein the water content of the alcohol batch is adjusted such that the alcohol batch has a density that is lower than that of the oil batch. [4] Method according to claim 3, wherein the contact apparatus advantageously comprises at least one collecting zone of the light phase, one collecting zone of the heavy phase, one zone for establishing contact between the heavy phase and the catalyst, and one redistribution zone of the light phase and the heavy phase. [5] Method according to any one of claims 1 to 4, wherein the esterification catalyst is selected from silicon dioxide aluminum dioxides, acidic clays, sulfated zircons and acidic resins, which are taken alone or in mixture. [6] The method of claim 5, wherein the esterification catalyst is an acidic resin having a crosslinking rate between 20 and 40% and an acid capacity between 0.2 and 6 mmol H+ equivalent per g. [7] Method according to any one of claims 1 to 6, wherein the alcohol mass ratio contained in the alcohol batch to the oil batch is between 15:85 and 85:

15. [8] Method according to any one of claims 1 to 7, wherein the alcohol batch consists of the alcohol-rich batch which is drawn off from the contact apparatus and returned to the contact apparatus mixed with an alcohol additive. [9] Method according to claim 8, wherein the alcohol phase drawn from the contact apparatus is advantageously treated before being returned, so that the water content in the alcohol batch is maintained at the desired value.