JP5112899B2 - Method for esterifying free fatty acids in triglycerides - Google Patents

Description

  The present invention generally relates to a process for esterifying free fatty acids in triglycerides with alcohols to produce fatty acid alkyl esters.

High fuel prices and environmental concerns are driving the development of alternative fuels, especially those derived from renewable resources. Some such fuels, commonly known as “biodiesel” fuels, contain methyl esters of fatty acids and are burned in diesel engines. Biodiesel fuel is produced by transesterification of triglycerides such as vegetable oils with alcohols, typically methanol. However, the small amount of free fatty acids present in the triglycerides causes problems including foaming of the reaction mixture in the transesterification process. Prior art discloses methods for esterifying these free fatty acids, for example in WO 2006/064643. However, the prior art teaches that high crosslinker level resins are required to catalyze the esterification of free fatty acids in triglycerides.
International Publication WO2006 / 064643 Pamphlet

  The problem addressed by the present invention is to find an improved method of esterifying free fatty acids in triglycerides.

The present invention relates to a method for esterifying free fatty acids in triglycerides with C ₁ -C ₈ aliphatic alcohols or diols, the method comprising (a) a gel type having a cross-linking agent of 0.25% to 2.75%. Providing a catalyst comprising an acidic ion exchange resin; and (b) under conditions suitable for esterification, said catalyst is (i) a triglyceride having at least 1% free fatty acid, and (ii) C ₁ -C _8. Contacting with a reaction mixture comprising an aliphatic alcohol or diol.

  Unless otherwise indicated, all percentages are by weight and all temperatures are in degrees Celsius. The weight percent of ion exchange resin is based on dry resin. An “alkyl” group is a saturated hydrocarbyl group having from 1 to 20 carbon atoms in a linear, branched, or cyclic configuration. In one preferred embodiment, the alkyl group is acyclic. The “triglyceride” used in the present invention is a fat or oil containing a glycerin triester of a fatty acid. Preferably, the triglycerides are in the form of vegetable oils, but animal fats can also be used as starting materials. Fatty acids are acyclic aliphatic carboxylic acids containing 8 to 20 carbon atoms, typically they contain 12 to 18 carbon atoms. With respect to carbon-carbon bonds, these fatty acids may be saturated, monounsaturated, or polyunsaturated (typically 2 or 3 carbon-carbon double bonds). Natural fats may also contain small amounts of other esterified or free fatty acids, as well as small amounts (1-4%) of phospholipids such as lecithin, and very small amounts (<1%) of other compounds such as tocopherols. Good.

  In one embodiment of the invention, the reaction mixture is heated at a temperature in the range of 40 ° C. to 150 ° C. for at least 15 minutes in contact with the catalyst. Alternatively, the temperature is at least 50 ° C, alternatively at least 55 ° C, alternatively at least 60 ° C. Alternatively, the temperature is 110 ° C or lower, alternatively 90 ° C or lower, alternatively 85 ° C or lower, alternatively 80 ° C or lower, alternatively 75 ° C or lower. When the reaction is carried out in a batch reactor, preferably the reaction time is at least 0.5 hours, alternatively at least 1 hour, alternatively at least 2 hours, alternatively at least 3 hours, alternatively at least 6 hours. Alternatively, the reaction time is 24 hours or less, alternatively 16 hours or less, alternatively 10 hours or less, alternatively 6 hours or less. In one embodiment where the temperature is 55-75 ° C, the reaction time is 0.5-6 hours. The catalyst is removed from the reaction mixture by filtration, centrifugation, or any other standard method for separating solids and liquids. When the reaction is carried out in a continuous reactor, preferably the contact time is at least 30 minutes, alternatively at least 45 minutes. Preferably, the contact time is 6 hours or less, alternatively 4 hours or less, alternatively 2 hours or less.

  In one embodiment of the invention, the triglycerides are free from 1% to 99%, alternatively up to 80%, alternatively up to 50%, alternatively up to 40%, alternatively up to 30%, alternatively up to 20%, alternatively up to 10%. Contains esterified fatty acids. In one embodiment, the triglycerides contain at least 1%, alternatively at least 2%, alternatively at least 3%, alternatively at least 5% free fatty acids. In one embodiment of the invention, the triglycerides contain 2% to 40% free fatty acids.

In one embodiment of the present _invention, C 1 -C ₈ aliphatic alcohol or diol _is either C 1 -C ₄ alcohol, or methanol, ethanol, or a n- butanol, or methanol or ethanol, Most preferred is methanol. In one embodiment of the present _invention, C 1 -C ₈ aliphatic alcohol or _diol, C 1 -C ₈ diol or _C 1 -C ₄ diol, for example ethylene glycol. In one embodiment of the present invention, the alcohol is present in an amount of at least 1.1 equivalents, alternatively at least 2 equivalents, alternatively at least 5 equivalents, alternatively at least 10 equivalents, alternatively at least 15 equivalents, based on the free fatty acids. In one embodiment of the invention, the alcohol is present in an amount of 25 equivalents or less.

The ion exchange resin used in the present invention is a gel type resin and not a macroreticular resin. The macroreticular resin is a resin having a surface area of 25 m ² / g to 200 m ² / g and an average pore diameter of 50 to 500 あ る い は, or a surface area of 30 m ² / g to 80 m ² / g and an average pore diameter of 100 to 300 Å. Suitable gel type resins include, for example, acrylic resins, styrene resins, and combinations thereof. The resin contains polymerized units of a multiethylenically unsaturated monomer (crosslinking agent). Preferably, the level of crosslinker in the resin is 2.5% or less, alternatively 2.25% or less, alternatively 2% or less, alternatively 1.75% or less. In one embodiment, the level of crosslinker is at least 0.5%, alternatively at least 0.75%, alternatively at least 1%. Preferably, the average particle size of the gel resin is 100 μm to 2000 μm, more preferably 200 μm to 800 μm. In one embodiment of the invention, the ion exchange resin comprises styrene and a crosslinker, such as a divinyl aromatic compound; di-, tri-, and tetra- (meth) acrylate or (meth) acrylamide; di-, tri-, and Tetra-allyl ethers and esters; including polymerized units of glycols and polyols polyallyl and polyvinyl ether. In one embodiment of the invention, the crosslinker is diethylenic unsaturation, such as divinylbenzene (DVB). In one embodiment of the present invention, the acid functional group of the ion exchange resin comprises a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, or a mixture thereof. Typical acidic ion exchange resins have an acid functionality of 0.4 to 8 meq / kg, alternatively at least 2 meq / kg, alternatively at least 4 meq / kg on a dry basis. Preferably, the acid functional group is in the form of a sulfonic acid group. In one embodiment of the invention, when the reaction is carried out in a batch reactor, the resin is from 0.1% to 20% (based on the dry weight of the resin), alternatively from 1% to 15%, alternatively from 2%. Present in an amount of 8%. The reaction can also be carried out in a continuous reactor where the catalyst is confined to the reactor (eg in the catalyst bed).

  The esterification reaction data is based on the percent conversion of free fatty acids (FFA) to methyl esters. The FFA used in these examples is reagent grade stearic acid, mixed in vegetable oil (food grade canola oil with <0.1% total acid), 2 in methanol with a certain amount of solid phase catalyst, Refluxed for 4 or 6 hours. Standard conditions are stearic acid 8.2% (22.5 g), oil 73.6% (202.5 g), methanol 18.2% (50 g), and dry resin 5% (13.75 g). . Specific reaction conditions are detailed in Example 1. The procedure outlined in Example 1 remained constant throughout this esterification test. All modifications of catalyst type, catalyst amount, and FFA amount were performed under the same experimental conditions as outlined in Example 1. All subsequent reactions using commercially available oils such as European chicken oil and Malaysian palm oil were conducted under the same conditions as in Example 1. Esterification of FFA separated from waste glycerol was performed under the same conditions as shown in Example 1.

Example 1: Esterification of stearic acid in vegetable oil Ion exchange resin washed with methanol into a 1 L 4-neck RB flask equipped with a Soxhlet condenser containing 50 g of activated molecular sieve 3A, thermometer and mechanical stirrer Catalyst beads (13.75 g, 5% by weight of reaction mixture) were added. Canola oil (202.5 g, 0.23 mol triglyceride) was charged to the flask and mechanical stirring was started at 185 rpm. Stearic acid (22.5 g, 0.079 mol, 8.2% of oil) was then added and the flask was heated with an external infrared lamp until it reached 60 ° C. over 20 minutes. At 60 ° C., methanol (50 g, 1.56 mol or 20 equivalents based on FFA) was charged to the flask. The mixture was allowed to reach reflux temperature (˜65-67 ° C.) with effective stirring (235 rpm). The reflux was condensed with a water condenser and returned to the flask through a molecular sieve.

  The reaction was carried out at 65 ° C. to 67 ° C. (reflux temperature) and atmospheric pressure for 6 hours. Samples were taken at 30 minute intervals using a long stem polyethylene pipette with a small diameter to avoid removal of the catalyst beads. The sample was filtered through a 0.45 um MILLIPORE PTFE filter and placed in a tared 1 oz glass vial. The weight of the sample was recorded. The sample was separated into two phases: an upper methanol phase containing a mixture of methyl esters of fatty acids and a lower phase mainly of unreacted stearic acid and canola oil. After 6 hours, the mixture was cooled to ambient temperature. The catalyst was recovered from the organic phase by filtration. A final sample of the liquid phase was taken for analysis and the remaining oil, methanol, stearic acid mixture was discarded.

  Examples 2 to 36 are the same as Example 1 except that the type and amount of catalyst, the type of oil, and the type and amount of FFA change as described in the table.

GC method To analyze methyl stearate, a GC / MS analysis of the reaction mixture was performed. This analysis showed 100% conversion in 120 minutes for a gel resin with a DVB content of 2%.

  The reaction mixture sample was diluted to 1% with THF. This diluted sample was injected into an HP5890 Series II GC equipped with an HP5972MS detector. The GC column was SUPELCO EQUITY1, 30 m × 0.25 mm, and the film thickness was 0.25 μm. The injector was 1 μl, split 22: 1, and the injection temperature was 250 ° C. The carrier gas was helium and the linear velocity was 32 cm / sec @ 210 ° C. in constant flow mode. The oven temperature was held at 210 ° C. for 8 minutes, and the temperature was raised to 320 ° C. at 15 ° C./min, and at 320 ° C. for 5 minutes.

  To analyze the ester, GC / MS analysis of the starting canola oil and reaction mixture was performed. The analysis showed the presence of a mixture of methyl esters of fatty acids {typical biodiesel mixtures (methyl esters such as palmitic acid, stearic acid, linoleic acid, and linolenic acid)} and the presence of stearic acid. This analysis also revealed the presence of glycerol.

  These tables show the percent yield of methyl stearate, with the exception of Table 2 which shows the percent of initial stearic acid remaining.

The catalyst had the following characteristics: All were styrene resins having sulfonic acid groups. The harmonic mean particle size (HMS), weight capacity (wt cap), and volume capacity (vol cap) of the resin beads are shown in Table 1.

  The results of these experiments show that the gel phase, low DVB (less than 3%) strong sulfonic acid resin is very easy to catalyze the reaction of FFA to methyl ester in a quantitative and selective manner, and all requirements ( Fast speed, total conversion, and resin recycling). Lightly (2%) cross-linked gel cation resin had fast reaction rate (converted in less than 1 hour), complete conversion (100%), and good resin recycling (no loss of activity even after 10 cycles). It was. Testing with commercial oils also looks promising for both fast speed and complete reaction.

  Good selectivity of esterification was demonstrated by analysis on undetected dimethyl ether by-products as well as by a mass balance accounting for essentially all stearic acid.

Claims (7)

A method of transesterifying triglycerides with an aliphatic alcohol or diol, comprising:
(A) A catalyst comprising a gel type acidic ion exchange resin having 0.5 to 2.5% by weight of a crosslinking agent , wherein the gel type acidic ion exchange resin is a styrene resin having a sulfonic acid functional group providing a catalyst; under conditions suitable for and (b) esterification, the catalyst (i) a triglyceride having at least 1 wt% of free fatty acids, and _(ii) C 1 ~C ₈ aliphatic alcohol or diol Contacting with a reaction mixture comprising: C ₁ -C ₈ aliphatic alcohol or diol The method of claim 1, wherein methanol or ethanol. Triglycerides The method of claim 2, wherein with 1 wt% to 80 wt% of free fatty acids. The method of claim 3 , wherein the resin has an average particle size of 100 µm to 2000 µm. The process of claim 4 , wherein the reaction mixture is heated in a batch reactor at a temperature range of 40 ° C to 100 ° C for at least 0.5 hours. The process of claim 4 , wherein the reaction mixture is contacted with the catalyst in a continuous reactor at a temperature range of 40 ° C to 100 ° C for at least 15 minutes. C ₁ -C ₈ aliphatic alcohol or diol The _method of claim 1 wherein the C 1 -C ₄ diol.