HK1103069B - Method of making alkyl esters using glycerin - Google Patents

Description

Method for preparing alkyl ester using glycerin

Background

Alkyl esters or particularly methyl esters such as biodiesel are a clean burning alternative to traditional petroleum-based diesel. Biodiesel can be produced from natural, renewable resources such as new or used vegetable oils or animal fats. Biodiesel is a fatty acid alkyl ester (typically C)₁₆To C₁₈) And are typically burned in combustion ignition engines as direct replacements for petroleum-based diesel. The advantages of biodiesel, in addition to being available from renewable resources, provide the additional advantage that it burns less than petroleum-based diesel.

Alkyl esters, in particular biodiesel, can be obtained from soybean oil or rapeseed oil. Crude vegetable oil from these sources is filtered, refined and subjected to several processing steps before the oil is used as biodiesel. In addition, the biodiesel may be from different grades of vegetable oil. These grades include straight run oils, yellow grease, used oils from food processing, or by-products from edible oil refining processes such as soapstock. Each of the sources mentioned above has different amounts of free fatty acids and/or glycerides, i.e. mono-, di-or triglycerides, which can be processed into biodiesel.

Among the above sources of vegetable oils, soapstock is generally considered to be the most economical source. Soapstock is derived from crude oil extracted from soybean or rapeseed. The crude oil of these seeds can be separated into two components: refined oils (which may be subsequently further processed and converted into edible oils) and soapstock. The soapstock may then be acidified with sulfuric acid to provide a composition containing about 70% free fatty acids, which may be further processed into biodiesel.

One contemplated method of processing free fatty acids from the different grades of vegetable oils described above is to directly transesterify the free fatty acids in the presence of a base to obtain fatty acid alkyl esters for use as biodiesel. However, this process precipitates free fatty acids in the form of soaps, creating an additional recovery step in the contemplated process.

To avoid the precipitation problem, a two-step process for processing free fatty acids is proposed. This process can be found in EP07708813 and WO02/28811 and generally consists of the following steps: (1) acid catalyzed esterification of the free fatty acids with methanol in the presence of sulfuric acid, and (2) neutralization of the acid catalyst followed by conventional base catalyzed transesterification. These steps can be described by the following reaction scheme.Wherein each R may be the same or different and is a fatty chain commonly found in vegetable or animal oil sources, typically C₈To C₂₂。

Even if the transesterification reaction is catalyzed by both acid and base, the acid catalyst must be neutralized because acid catalyzed transesterification reactions generally exhibit slower kinetics than base catalyzed transesterification reactions under comparable conditions. The two-step process disclosed in EP07708813 and WO02/28811 has the disadvantages that neutralization generates additional salt waste, long periods and inconvenient recovery of residual free fatty acids and that separation of methanol from water is required for recovery and/or disposal of the waste.

Summary of The Invention

It is therefore an object of the present invention to provide a process for processing free fatty acids from vegetable or animal oil sources into alkyl esters, wherein salt and aqueous waste is reduced or avoided.

It is a further object of the present invention to provide a process for processing free fatty acids from vegetable or animal oil sources into alkyl esters wherein the necessity of separating the alkyl alcohol (e.g., methanol) from the reaction water is reduced or eliminated.

It is a further object of the present invention to provide a process for processing free fatty acids from vegetable or animal oil sources into alkyl esters, particularly biodiesel, wherein the recovery scheme of residual free fatty acids can be conveniently carried out or the need for such recovery is eliminated.

These and other advantages are achieved by the following process: contacting a vegetable or animal oil source with a glycerol source first converts the free fatty acid component of the oil source to glycerides and in a second step converts the newly formed glycerides and the originally present glycerides to fatty acid alkyl esters for use as biodiesel. The two-step process of the present invention does not include a neutralization step or separation of methanol and water, thus simplifying the prior art process. The process of the present invention will generally be described as follows, wherein the glycerides originally present in the oil source are represented by triglycerides, however it will be appreciated that the glycerides originally present in the oil source may be mono-, di-and/or triglycerides.Wherein each R may be the same or different and is a fatty chain commonly found in vegetable or animal oil sources, typically C₈To C₂₂. Accordingly, the present invention provides: (1) a method of preparing an alkyl ester comprising the steps of: providing an oil source comprising free fatty acids and/or glycerides; providing at least 0.3 equivalents of a source of glycerol; contacting the glycerol source with the oil source for a time sufficient to effect conversion of free fatty acids and glycerides to a mixture of mono-, di-, and triglycerides; providing methanol in an excess of about 1.0 equivalent to about 3 equivalents; reacting the mixture of glycerides with methanol effective to convert the glycerides to fatty acid alkyl esters; recovering the fatty acid alkyl ester. (2) The process according to item (1) above, wherein the step of contacting the glycerol source with the oil source is carried out in the presence of a catalyst. (3) The process according to item (2) above, wherein the catalyst is selected from the group consisting of an organotin compound, an organotitanium compound, an alkali metal acetate, an alkaline earth metal acetate, a Lewis acid, an alkali metal carbonate, an alkaline earth metal carbonate and a combination thereof. (4) The above-mentioned first(3) The process of clause, wherein the catalyst is dibutyltin oxide. (5) The process of the above item (3), wherein the catalyst is tetrabutyl titanate. (6) The method of item (1) above, wherein the glycerol source is United States Pharmacopeia (USP) grade glycerol or purified glycerol. (7) The process according to item (1) above, wherein the glycerin source is crude glycerin recovered from fat cracking or methanolysis of a vegetable oil. (8) The method of the above item (1), further comprising the steps of: recovering glycerol produced from the reaction of the glyceride with methanol; and wherein the glycerol source comprises at least a portion of the recovered glycerol without further purification. (9) The process of item (1) above, wherein said step of contacting the glycerol source with the oil source is carried out at a temperature of about 140 ℃ to 245 ℃. (10) The process according to item (9) above, wherein the temperature is about 160 ℃ to 200 ℃. (11) The method of the above (10), wherein the temperature is about 180 ℃. (12) The process of item (1) above, wherein said step of contacting the glycerol source with the oil source is carried out under reduced pressure of about 760 mm Hg to 1 mm Hg. (13) The process according to the above (1), wherein the step of contacting the glycerin source with the oil source is carried out under reduced pressure and under a constant nitrogen flow. (14) The process according to item (1) above, wherein the step of contacting the glycerol source with the oil source is carried out under a constant nitrogen flow. (15) The process according to item (1) above, wherein the process is carried out in a batch manner. (16) The process according to item (1) above, wherein the process is carried out in a continuous manner. (17) The process according to the above item (1), wherein the step of contacting the glycerin source with the oil source is carried out until the residual acid value is less than 5 (mgKOH/g). (18) The process according to item (1) above, wherein said step of contacting the glycerin source with the oil source is carried out until the residual acid value is from about 0.1 to about 1 (mgKOH/g).

Brief Description of Drawings

FIG. 1 shows a reaction apparatus which can be used for carrying out the process of the invention.

Figure 2 shows the acid number as a function of time for three examples of the invention.

Detailed Description

As noted above, the method of processing a vegetable or animal oil source of the present invention can be represented by the following reaction scheme wherein the glycerides originally present in the oil source are represented by triglycerides, however it is understood that the glycerides originally present in the oil source can be mono-, di-and/or triglycerides.Wherein each R may be the same or different and is a fatty chain commonly found in vegetable or animal oil sources, typically C₈To C₂₂. The reaction may be generally carried out in a small scale batch system as shown in figure 1 or more generally in a scaled-up version of the system shown in figure 1 for commercial use. The system 8 of FIG. 1 includes a 1L resin reactor 10. Reactor 10 was equipped with a teflon turbine agitator 12, thermocouple 14 with associated temperature controller 16 and heating mantle 17, nitrogen sparge tube 18 with associated nitrogen source 20, and packed reflux column 22(30 cm high and 2.5 cm diameter) connected to dean stark trap 24 with condenser 26. A vacuum line 28 is connected to the top of the condenser 26, and the condenser 26 is connected to a vacuum pump 30 through an in-line ice trap 32. The vacuum is controlled by a solenoid 34. A bubbler 36 may also be used. One skilled in the art would also foresee that the process of the present invention can be carried out in a continuous mode using standard equipment commonly used in chemical processes.

The first step of the reaction to convert the free fatty acids to glycerides may be carried out at a temperature of between about 140 ℃ to about 245 ℃, more preferably between about 160 ℃ to about 200 ℃, and most preferably at about 180 ℃. The first step may further be conducted under reduced pressure of about 760 mm hg to about 1 mm hg, under a constant nitrogen flow, or under reduced pressure and a constant nitrogen flow simultaneously.

The invention has been found to be particularly effective when using crude glycerol obtained from methanolysis of vegetable oils or other fats (or recovered from fat cracking processes). The crude glycerol obtained from the methanolysis process contains about 80-85% glycerol, 13-18% methanol, about 1-2% water, small amounts of mono-and diglycerides, and residual alkali. However, the method of the present invention is applicable to both United States Pharmacopeia (USP) grade glycerol or purified glycerol. The glycerol source may be used at a concentration of at least 0.3 equivalents.

The use of crude glycerol provides the opportunity to use process by-products without further purification and increases the acid conversion in the acidified soapstock over the use of purified glycerol. This was unexpected because the crude glycerol contained a large amount of basic catalyst. Thus, mixtures containing acidified soapstock and crude glycerin may be nearly neutralized at a pH of about 5.5, while mixtures of purified glycerin and soapstock exhibit a pH of about 2.5-3.5. The esterification reaction is acid catalyzed as described in "Advanced Organic Chemistry" 4 th edition, 395 p, John Wiley & Sons, n.y., 1992; thus, the conversion rate cannot be expected to increase at higher pH.

The reaction between the purified glycerol (e.g., USP grade) and the soapstock (without additional catalyst) ended (as determined by an acid number of 0.5 or less) at 220-. Esterification was complete after about 14 hours at a temperature of 180 c using USP grade glycerol without addition of catalyst (see example 1 below). A shorter reaction time to complete the reaction between about 9 hours and about 10 hours was achieved by using crude glycerol (see examples 2 and 3 below and figure 2).

The resulting glyceride mixture is then subjected to base-catalysed methanolysis to form methyl esters and glycerol as a by-product. The glycerol produced in the second step of the process may be recovered and used in the first step to form glycerides with the free fatty acids contained in the acidified soapstock or other oil source. In the latter case, further purification of the recovered glycerol is not necessary.

The reaction scheme, particularly the first step of the reaction scheme, may be carried out with a catalyst. Contemplated catalysts include, but are not limited to, organotin compounds (e.g., dibutyltin oxide), organotitanium compounds (tetrabutyltitanate), alkali metal acetates, alkaline earth metal acetates, lewis acids, alkali metal carbonates, alkaline earth metal carbonates, and combinations thereof.

The advantages of the method of the invention can be summarized as follows: 1) using the unchanged glycerol fraction obtained by alcoholysis of fats and oils; 2) the unchanged glycerol fraction of the residual base obtained by using a mixture comprising methanol, water and alcoholysis of fats and oils is improved over the purified glycerol conversion; 3) the glycerol part of the method can be recycled; 4) the use of the unaltered glycerol fraction obtained from methanolysis of fats and oils lowers the processing temperature; 5) the formation of salt is reduced; and 6) eliminating the need for a means to separate excess alcohol (e.g., methanol) from water.

To illustrate the effectiveness of the above-described reaction scheme of the present invention, an acidified soapstock sample was applied to the reaction scheme and the acid number of the reaction product was determined as a function of time. The reduction in acid number indicates that the reaction scheme provides a satisfactory method for converting the free fatty acids of the acidified soapstock into glycerides. The first step of the reaction scheme is preferably carried out until the residual acid value is less than 5mgKOH/g and more preferably the residual acid value is from about 0.1 to about 1 mgKOH/g.

Example 1

549 grams of acidified soapstock and 108 grams of USP grade glycerin were charged to a 1 liter resin kettle 10 (figure 1). The reaction apparatus 8 of FIG. 1 was used. The resin kettle 10 was heated to a reaction temperature of 180 ℃ over 60 minutes at atmospheric pressure. After about 65 minutes from the time of heat input, vacuum was applied in stages to aid in the removal of the water of reaction as indicated in table 1. After a reaction time of 340 minutes (calculated from the beginning of the heat input), a nitrogen flow was applied in addition to the vacuum. Samples were taken intermittently to monitor the progress of the reaction. After about 880 minutes, the reaction was complete (AV ═ 0.5). The collected fraction was weighed out to 26.11 grams, which included a thin layer on top of the reaction water, consisting of light (C6-C8) fatty acids. The total recovered mass of the glyceride mixture was 622.67 grams.

Table 1 lists the reaction parameters and measured acid numbers for example 1, showing the progress of converting the free fatty acids of the soapstock sample to glycerides. TABLE 1 reaction parameters for example 1

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Milliliter of 0.1NNaOH	AV[meq/g]	Nitrogen purging
							0	22.0	760			96.60	Is free of
10	61.0	760				Is free of
							25	121.3	760				Is free of
50	169.7	760				Is free of
							60	180.0	760				Is free of
65	179.5	350				Is free of
							95	179.5	350				Is free of
105	179.4	350	1.1951	11.152	52.35	Is free of
							125	180.1	350				Is free of
130	180.9	250				Is free of
							145	180.6	250	1.5196	11.084	40.92	Is free of
175	179.6	250	1.3568	7.850	32.46	Is free of
							220	179.5	250	1.4444	6.050	23.50	Is free of
280	179.8	250	1.6529	4.584	15.56	Is free of
							290	180.0	180				Is free of
295	180.6	100				Is free of
							325	179.8	100				Is free of
340	179.9	100	2.0267	4.056	11.23	30 ml/h
							400	180.1	100	1.6630	2.328	7.85	30 ml/h
410	180.1	90				30 ml/h
							420	180.1	50				30 ml/h

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Milliliter of 0.1NNaOH	AV[meq/g]	Nitrogen purging
							460	180.1	60	2.5286	2.138	4.74	30 ml/h

640	180.0	50	2.5232	0.435	0.97	30 ml/h
							760	180.0	50	2.6908	0.250	0.52	30 ml/h
820	180.0	50	3.0017	0.248	0.46	30 ml/h
							880	180.0	50	2.5690	0.194	0.42	30 ml/h

Example 2

583.9 grams of acidified soapstock and 135.97 grams of crude glycerol from methanolysis of soybean oil (containing 86% glycerol and equilibrium as water, methanol and residual base catalyst) were charged to a 1 liter resin kettle 10 (fig. 1). The reaction apparatus 8 of FIG. 1 was used. The pH of the mixed material was measured to be 5.34 and was a 10% suspension in a mixture of isopropanol and water at 50/50 volumes. The mixture was heated to a reaction temperature of 180 ℃ and a vacuum and nitrogen flow was applied to aid in the removal of the water of reaction, as shown in table 2. The total amount of the weighed fractions was 58.58 g, which included methanol and reaction water, and about 3.5 ml of low molecular weight fatty acids. The recovered mass of glycerides was 654.68 grams (90.9% based on total mass input). In summary, this example shows that by using raw glycerol, the duration of the vacuum application combined with nitrogen sparging can be significantly shortened, and the total reaction time to reach an equivalent acid number (880 minutes versus 615 minutes) is significantly shortened, when compared to example 1.

Table 2 lists the reaction parameters and measured acid numbers for example 2, showing the progress of converting the free fatty acids of the soapstock sample to glycerides. TABLE 2 reaction parameters for example 2

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							0	20.4	760			94.10	Is free of
15	62.0	760				Is free of
							30	106.4	760				Is free of
45	131.2	760				Is free of
							60	157.1	760				Is free of
75	177.0	760				Is free of
							80	180.4	760				Is free of

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							90	181.0	760				Is free of
105	180.3	760				Is free of
							120	180.5	760	1.3349	12.848	53.99	Is free of
135	180.7	760				Is free of
							140	180.3	350				Is free of

150	180.4	350	1.8577	13.610	41.10	Is free of
							170	180.1	350				Is free of
190	180.0	350	1.6703	9.378	31.50	Is free of
							195	179.7	250				Is free of
235	179.5	250	2.3303	8.814	21.22	Is free of
							240	180.8	170				Is free of
245	181.7	100				Is free of
							305	180.0	100	1.8723	4.284	12.84	Is free of
365	180.5	100	2.3596	3.495	8.31	Is free of
							370	178.7	40				30 ml/h
435	180.0	40				30 ml/h
							465	179.9	40	2.2633	1.040	2.58	30 ml/h
615	180.1	40	2.8797	0.182	0.35	30 ml/h

Example 3

Example 3 shows that the earlier in the process the use of vacuum and nitrogen purge together can reduce the cycle time even more without adversely affecting the final product, such as by removing raw materials from the reactor resulting in reduced yields. 528.5 grams of the acidified soapstock was mixed with 124.4 grams of crude glycerin and reacted as described in examples 1-2. Immediately after mixing the starting materials, the pH of the reaction mixture was measured to be 5.04. The total weight of the fractions was found to be 54.77 g and the individual yield of glycerides was 589.68 g (90.3% based on total mass input).

Table 3 lists the reaction parameters and measured acid numbers for example 3, showing the progress of converting the free fatty acids of the soapstock sample to glycerides. TABLE 3 reaction parameters for example 3

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							0	20.4	760			104.20	Is free of
15	71.4	760				Is free of
							30	111.2	760				Is free of
35	121.0	760				Is free of
							45	140.5	760				Is free of
60	166.0	760				Is free of
							75	180.4	760	1.6758	24.830	83.12	Is free of
90	179.8	760				Is free of
							105	179.4	760	1.5155	17.476	64.69	Is free of

135	180.3	760	1.1391	10.158	50.03	Is free of
							145	181.4	350				Is free of
165	180.0	350	1.8234	12.272	37.76	Is free of
							195	180.2	350				Is free of
200	179.5	250				Is free of
							225	179.7	250	2.0317	8.580	23.69	Is free of
230	179.9	160				Is free of
							235	180.1	100				Is free of
255	179.1	100				Is free of
							285	180.5	100	2.3684	5.854	13.87	30 ml/h

135	180.3	760	1.1391	10.158	50.03	Is free of
							290	179.9	40				30 ml/h
345	179.8	40	2.0354	2.452	6.76	30 ml/h
							405	180.1	40	2.1778	0.802	2.07	30 ml/h
465	179.9	40	2.3043	0.190	0.46	30 ml/h
							525	180.0	40	1.9636	0.138	0.39	30 ml/h

Figure 2 compares the conversion of free fatty acids of the soapstock of examples 1, 2 and 3 and shows that the conditions of example 3 provide the most improved conversion.

Example 4

Example 4 shows the effect of reducing the amount of glycerol. 520.2 grams of acidified soapstock and 91.8 grams of raw glycerin (15 wt% available glycerin) were charged to a 1 liter resin kettle 10 (FIG. 1) and treated as in the above example. To maintain a similar pH as in examples 1 and 2, adjustment was performed with 7.35 g of 25% sodium methoxide in methanol. The total amount of the recovered fraction was 53.5 g and the yield of glycerides was 548.71 g.

Table 4 lists the reaction parameters and measured acid numbers for example 4, showing the progress of converting the free fatty acids of the soapstock sample to glycerides. TABLE 4 reaction parameters for example 4

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							0	20.4	76			104.20	Is free of
15	72.8	76				Is free of
							25	101.5	76				Is free of
30	112.5	76				Is free of
							35	123.2	76				Is free of
40	133.1	76				Is free of
							50	151.5	76				Is free of

65	173.2	76				Is free of
							75	181.2	76				Is free of
90	180.8	76	1.2199	15.8780	73.02	Is free of

65	173.2	76				Is free of
							100	179.9	76				Is free of
105	180.2	76				Is free of
							110	181.0	76				Is free of
120	179.5	76	1.3880	13.4200	54.24	Is free of
							130	179.2	76				Is free of
135	179.7	55				Is free of
							140	181.3	35				Is free of
160	178.8	35				Is free of
							165	178.4	25				Is free of
180	180.6	25	1.3293	8.2000	34.61	Is free of
							215	179.4	25				Is free of
240	180.4	25	1.3045	4.9940	21.48	Is free of
							245	181.6	10				Is free of
300	179.7	10	1.2125	2.7960	12.94	Is free of
							310	180.2	4				Is free of
360	179.9	4	1.4515	2.1060	8.14	Is free of
							370	179.7	4				30 ml/h
420	180.1	4	1.3065	0.5260	2.26	30 ml/h
							570	180	4	2.0472	0.1440	0.39	30 ml/h

Example 5

Example 5 is similar to example 4 except that the pH is not adjusted. The pH of the combined glycerin and soapstock was 5.03. The nitrogen purge for the last 1 hour was increased from 30 ml/h to 60 ml/h. The final amount of the collected fraction was 55.25 g and 552.73 g of glycerides were recovered.

Table 5 lists the reaction parameters and measured acid numbers of example 5, showing the progress of converting the free fatty acids of the soapstock sample to glycerides. TABLE 5 reaction parameters for example 5

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							0	24.8	760			104.20	Is free of
15	82.5	760				Is free of
							40	139.6	760				Is free of
60	173.2	760				Is free of
							70	180.1	760				Is free of

75	180.1	760	1.0755	17.1360	89.38	Is free of
							90	179.2	760				Is free of
105	180.2	760				Is free of
							120	180.1	760	0.8893	9.4660	59.71	Is free of
130	180.6	760				Is free of
							135	179.5	350				Is free of
165	178.6	350	0.9661	7.4100	43.03	Is free of
							205	182.7	350	1.5781	8.9740	31.90	Is free of
210	180.0	100				Is free of
							300	181.3	100	1.3542	4.4440	18.41	Is free of
310	180.2	40				30 ml/h
							420	180.0	40	1.8068	2.2180	6.89	30 ml/h
600	180.1	4	1.8589	0.3300	1.00	30 ml/h
							610	180.1	5				60 ml/h
660	180.0	5	1.8270	0.1280	0.39	60 ml/h

Example 6

Example 6 is a comparative reaction highlighting the fact that: glycerolysis can be carried out using a variety of raw material sources such as yellow grease and acidified glycerol (recovered glycerol from methanolysis of soybean oil but without alkali or methanol) and conventional esterification catalysis can be carried out. 498.1 g of yellow grease and 50.0 g of acidified glycerol were charged together with 1.0 g of dibutyltin oxide in a 1l resin kettle 10 (FIG. 1) and heated to a reaction temperature of 200 ℃. When the reaction temperature reached 200 ℃, a vacuum of 250 mm hg was applied. After about 6 hours, an acid number of 0.5AV was measured and about 5.5 ml of liquid was collected in a dean stark trap. The reaction mixture was cooled to the appropriate temperature to safely add 116 grams of methanol and 7.5 grams of 25% sodium methoxide in methanol. The reactor was then heated to 77 ℃ for 2 hours while stirring. The heating was stopped and the mixture was allowed to settle. The phase containing a total amount of 147.43 grams of glycerol was removed from the bottom of the mixture. The residual material was stripped at 60 ℃ to remove excess methanol. The residual crude ester phase was washed with 110 ml of water, stirred for 5 minutes and allowed to settle for about 30 minutes before the aqueous layer was drained from the bottom. This procedure was repeated two more times with the same amount of water. The combined aqueous phases (408.2 g) were collected and weighed. The washed ester was then vacuum stripped to dryness (final water content 430ppm) at about 60 ℃. The yield of biodiesel ester was 366.3 g.

Example 7

684 grams of acidified soapstock and 163 grams of crude glycerin were charged into a 1 liter resin kettle 10 (FIG. 1) along with 3.5 grams of potassium acetate (pH of mixture 5.48). As shown in table 6, the reaction mixture was heated to temperature and vacuum and nitrogen were applied as in the previous examples. The final acid number was 0.21 with 72.56 grams of collected fractions and a yield of about 758.76 grams of glycerides (taking into account sampling during the reaction).

After the reaction was cooled, 120 g of methanol and 5.7 g of sodium methoxide solution (25% in methanol) were added and the reactor was heated to 65-68 ℃ for 1.25 hours, after which the reaction mixture was allowed to precipitate for 1.25 hours. The glycerol portion (198.33 g) was then removed from the bottom of the reactor, followed by removal of excess methanol (17.66 g) in vacuo. Then 22 g of distilled water was added to the reactor and stirred for 10 minutes. After 3 hours of precipitation, 52.57 grams of the aqueous phase was removed (an additional 10.57 grams of ester was recovered from the initial aqueous phase overnight). 254.95 g of the ester prepared in this manner were distilled under vacuum (10-20 mm Hg) to give 224.61 g of an almost colorless methyl ester product.

Table 6 lists the reaction parameters and measured acid numbers for example 7, showing the progress of converting the free fatty acids of the soapstock sample to glycerides. TABLE 6 reaction parameters for example 7

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							0	16.4	760			112.00
30	81.6	760
							65	136.7	760
95	169.9	760
							100	172.2	760
110	177.4	760
							115	180.2	760

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							130	182.0	760	1.7476	17.350	55.70
155	180.6	760
							160	180.1	400
165	180.0	350
							170	182.2	250
190	180.3	250	2.0585	12.072	32.90
							200	179.9	250				30 ml/h
230	180.4	250				30 ml/h
							230	178.8	40				30 ml/h
250	181.0	40				30 ml/h

255	180.0	40	2.3054	6.766	16.46	30 ml/h
							300	180.1	40				30 ml/h
370	179.6	40	3.2247	2.268	3.95	30 ml/h
							435	179.6	40	4.0911	0.301	0.41	30 ml/h
480	179.6	40	2.7252	0.100	0.21	30 ml/h

Example 8

541.29 grams of acidified soapstock was charged with 108.5 grams of USP glycerol in a 1 liter resin kettle 10 (FIG. 1) and heated to a reaction temperature of 180 ℃. When the reaction temperature reached 180 ℃, a gradual vacuum was applied. Using a syringe to inject tetrabutyl titanate twice at a position lower than the liquid level of the reactorTBT), once at 270 minutes and the second at 405 minutes of reaction time. After about 12 hours, the acid number was measured to be 0.94AV, and about 24.15 grams of distillate was collected in an ansamik trap.

Table 7 lists the reaction parameters and measured acid numbers for example 8. TABLE 7 reaction parameters for example 8

Time [ min ]]	Reactor [ deg.C]	Pressure [ holder ]]	Sample [ g ]]	Ml of 0.1N NaOH	AV[meq/g]	Nitrogen purging
							0	33	760			96.60	Is free of
15	77.6	760				Is free of
							30	128.6	760				Is free of
45	160.6	760				Is free of
							60	177.5	760	1.7029	25.616	84.39	Is free of
65	180.3	500				Is free of
							70	181.7	450				Is free of
90	180.5	450	1.1478	13.330	65.15	Is free of
							120	180.0	450	1.4322	12.616	49.42	Is free of
150	180.1	450				Is free of
							165	180.3	450				Is free of
180	179.5	450	1.5293	8.768	32.16	Is free of
							185	180.5	370				Is free of
188	181.1	350				Is free of
							270	180.1	350	1.7471	5.120	16.44	Is free of
285	180.0	350				Is free of
							300	180.5	350				Is free of

302	180.5	290				Is free of
							305	181.1	250				Is free of
330	180.5	250	1.5455	3.466	12.58	Is free of
							345	178.8	150				30 ml/h

302	180.5	290				Is free of
							360	180.7	100				30 ml/h
390	180.1	100	1.9501	3.036	8.73	30 ml/h
							405	180.1	60				Is free of
420	180.1	60				Is free of
							450	179.4	60	2.1709	2.274	5.88	Is free of
510	179.7	50	1.4046	0.944	3.77	Is free of
							690	180.1	40	2.6843	0.885	1.85	Is free of
710	179.6	15				30 ml/h
							740	179.9	15	2.4716	0.416	0.94	30 ml/h

Example 9

250.7 g of yellow fat (AV 29.5mg KOH/g) and 14.7 g of acidified glycerol were added together and heated to a reaction temperature of 230 ℃. After entering the reaction for 45 minutes, vacuum was applied at 23 inches to aid in the removal of water. After a reaction time of 8 hours, the acid number was 0.37.

Example 10

515.0 g of acidified soapstock (acid value 126mgKOH/g) and 133.1 g of acidified glycerol were added together and heated to 230 ℃. After 45 minutes, a vacuum was applied at 20 inches at 230 ℃ to help remove the water of reaction. After a total reaction time of 7.5 hours, the acid number was 0.34.

Table 8 summarizes the reaction parameters and AV results for examples 1 to 10.

Table 8-summary of the results of examples 1-10.

Examples	Wt% Glycerol	Final AV	Reaction time [ min ]]	Rxn temperature [. degree.C]	Added catalyst
						1	20(P)	0.42	880	180	Is free of
2	20(C)	0.35	615	180	Is free of
						3	20(C)	0.39	525	180	Is free of
4	15(C)	0.39	570	180	Is free of
						5	15(C)	0.39	660	180	Is free of

Examples	Wt% Glycerol	Final AV	Reaction time [ min ]]	Rxn temperature [. degree.C]	Added catalyst
						6*	10(R)	0.50	360	200	0.5wt％DBTO
7	20(C)	0.41	435	180	0.5wt％KAc
						8	20(P)	0.94	740	180	0.2wt％TBT

9*	5.75(R)	0.37	480	230	Is free of
						10	25(R)	0.34	450	230	Is free of

n.d. ═ indeterminate ═ glycerol recovered as comparison DBTO ═ dibutyltin oxide TBT ═ tetrabutyl titanate crude glycerol of approximately 86% purity (C) USP glycerol > 99.9% purity (P) approximately 98% purity (R)

Example 11

Example 11 shows the effectiveness of the process of the invention on a large scale. To 1,670 pounds of acidified soapstock was added 304 pounds of glycerin with force. The mixture was stirred and heated to a reaction temperature of 180 ℃ while removing residual methanol and reaction water formed in the formation of glycerides from the recovered glycerol. Vacuum (40 mm hg maximum) and nitrogen purge were used to aid in the removal of the water of reaction. After about 16 hours (including about 2 hours of warm-up time), an acid number of 1.0 was reached. The reaction was cooled to < 60 ℃ and methanol (732 lbs) and 45 lbs of sodium methoxide (21% in methanol) were added. The reactor was heated to 68 ℃ and held at this temperature for 1 hour. The stirring was then stopped and the glycerol phase was allowed to settle at the bottom of the reactor for about 1 hour. After draining the glycerin phase, the residual methanol was removed in vacuo and 20 lbs of wash water was added and the mixture was stirred for 15 minutes and then allowed to precipitate. The aqueous phase was removed from the bottom of the reactor. The reactor was then vented to remove residual water produced in the crude methyl ester product. The crude methyl ester product was then vacuum distilled to yield about 1,429 lbs of near colorless distilled ester.

Example 12

Example 12 shows the effectiveness of the process of the invention on a large scale. To 1,521 lbs of acidified soapstock was added 380 lbs of glycerin consisting of 304 lbs of crude glycerin obtained by methanolysis of soybean oil and 76 lbs of glycerin portion recovered from the original large scale recycle of example 10. The mixture was stirred and heated to a reaction temperature of 180 ℃ while removing residual methanol and reaction water formed in the formation of glycerides from the recovered glycerol. Removal of the water of reaction is aided by the use of vacuum (40 mm hg maximum) and nitrogen purge. After about 12 hours (including about 2 hours of warm-up time), an acid number of 0.5 was reached. The reaction was cooled to < 60 ℃ and methanol (434 lbs) and 41 lbs of sodium methoxide (21% in methanol) were added. The reactor was heated to 68 ℃ and held at this temperature for 1 hour. The stirring was then stopped and the glycerol phase was allowed to settle at the bottom of the reactor for about 1 hour. After draining the glycerin phase, the residual methanol was removed in vacuo and 20 lbs of wash water was added and the mixture was stirred for 15 minutes and then allowed to precipitate. The aqueous phase was removed from the bottom of the reactor. The reactor was then vented to remove residual water produced in the crude methyl ester product. The crude methyl ester product was then vacuum distilled to yield about 1,370 lbs of near colorless distilled ester.

While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. Accordingly, it is to be understood that the above-described embodiments are intended to be illustrative only and not to limit the spirit and scope of the invention, which is to be determined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.

Claims (18)

1. A method of preparing an alkyl ester comprising the steps of:

providing an oil source which is free fatty acids and/or glycerides;

providing at least 0.3 equivalents of a source of glycerol;

contacting the glycerol source with the oil source for a time sufficient to effect conversion of free fatty acids and/or glycerides to a mixture of mono-, di-, and tri-glycerides;

providing methanol in an excess of 1.0 to 3 equivalents;

reacting the mixture of glycerides with methanol effective to convert the glycerides to fatty acid alkyl esters;

recovering the fatty acid alkyl ester.

2. The process of claim 1, wherein said step of contacting the glycerol source with the oil source is carried out in the presence of a catalyst.

3. The process of claim 2 wherein the catalyst is selected from the group consisting of organotin compounds, organotitanium compounds, alkali metal acetates, alkaline earth metal acetates, lewis acids, alkali metal carbonates, alkaline earth metal carbonates, and combinations thereof.

4. A process according to claim 3 wherein the catalyst is dibutyltin oxide.

5. The process of claim 3, wherein the catalyst is tetrabutyl titanate.

6. The method of claim 1, wherein the glycerol source is usp grade glycerol or purified glycerol.

7. The process of claim 1, wherein the glycerol source is crude glycerol recovered from fat cracking or methanolysis of vegetable oils.

8. The method of claim 1, further comprising the steps of:

recovering glycerol produced from the reaction of the glyceride with methanol;

and wherein the glycerol source comprises at least a portion of the recovered glycerol without further purification.

9. The process of claim 1, wherein said step of contacting the glycerol source with the oil source is carried out at a temperature of from 140 ℃ to 245 ℃.

10. The method of claim 9, wherein the temperature is from 160 ℃ to 200 ℃.

11. The method of claim 10, wherein the temperature is 180 ℃.

12. The process of claim 1, wherein said step of contacting the glycerol source with the oil source is carried out at a reduced pressure of from 760 mm hg to 1 mm hg.

13. The process of claim 1, wherein the step of contacting the glycerol source with the oil source is conducted under reduced pressure and under a constant nitrogen flow.

14. The process of claim 1, wherein said step of contacting the glycerol source with the oil source is conducted under a constant flow of nitrogen.

15. The process of claim 1, wherein the process is conducted in a batch mode.

16. The process of claim 1, wherein the process is conducted in a continuous manner.

17. A process according to claim 1, wherein said step of contacting the glycerol source with the oil source is carried out to a residual acid value of less than 5 mgKOH/g.

18. A process according to claim 17, wherein said step of contacting the glycerol source with the oil source is carried out to a residual acid value of from 0.1 to 1 mgKOH/g.