MXPA97009836A - Method for purifying an inert gas while they prepare alternative sters inferio - Google Patents

Abstract

The present invention relates to a process for purifying an inert gas stream from a transesterification reaction, wherein a lower alkyl alcohol is released during the reaction. A second use of the process is to make a lower alkyl, for example, methyl, esters of the fatty acid, through a transesterification reaction using gaseous alcohols such as a source of the lower alkyl alcohols. The alcohol is diluted with nitrogen or another carrier of inert gas and is reacted with a fatty acid ester, preferably triglyceride, to form the methyl ester or lower alkyl fatty acid corresponding to

Description

METHOD FOR PURIFYING AN INERT GAS WHILE LOWER ALOUILIC ESTERS ARE PREPARED.

TECHNICAL FIELD This is a process for purifying a stream of inert gas from a transesterification reaction, wherein the lower alkyl alcohol is released during the reaction. A second use of the process is to make a lower alkyl, for example, methyl, fatty acid esters through a transesterification reaction using gaseous alcohols as a source of the lower alkyl alcohols. The alcohol is diluted with nitrogen or other inert gas carrier and reacted with a fatty acid ester, preferably triglyceride to form the lower alkyl or methyl fatty acid ester.

BACKGROUND OF THE INVENTION Transesterification reactions are commonly used to make new ester compounds; usually a new group of alcohol is added to the acid. Methyl esters are a less expensive carboxylic acid source than acid chlorides and anhydrides and are sufficiently reactive to provide a good source of fatty acids for complex esterification reactions. The economy of the reactions is such that the relatively small cost of methyl esters is important in the aggregate processing costs. Mainly used in the preparation of polyol polyesters and other fats, synthetics, waxes, diesel fuels and emulsifiers. The lower alkyl alcohol group is chosen because the alcohol can be easily removed in the subsequent transesterification reaction by vacuum distillation or by reducing the partial pressure of the alcohol using a nitrogen or inert gas spray, activating the transesterification reaction at the end. Typically, methyl esters of fatty acids are prepared from sources of naturally occurring fatty acids, usually triglycerides from vegetable or animal sources. Methyl alcohol replaces glycerin. The resulting mixture of methyl esters is easily divided, providing a purified source of fatty acids. This development is a method for making lower alkyl esters of fatty acids, mainly, by transesterification of a triglyceride with a lower alkyl alcohol using gaseous alcohol in an inert gas vehicle. Preferably, the reaction is carried out in a reactive absorption column, but it can be carried out in an intermittent process. The gaseous alcohol mixture is preferably an inert gas spray recovered from a transesterification process used to make more complex esters, i.e., a polyester polyol synthesis, or emulsifying synthesis reaction. More than 90% and up to 99.7% of the methanol is recovered in methyl esters, and the triglyceride is converted to glycerin and mono and diglycerides. The free alcohol or reduced alcohol nitrogen (inert gas) can then be continuously recirculated. This capacity of nitrogen recirculation improves the economy of the reactions. Reactive absorption columns have been used for the catalytic esterification of carboxylic acids and for making triglycerides of C6"C22 fatty acids using alkyl esters.The use of these columns for transesterification with a lower alkyl alcohol in an inert gas carrier is believed. under conditions claimed herein, it is new.A key economic activator for this procedure is the clear activation or coupling of methyl ester synthesis and transesterification reactions, which utilize these esters as sources of fatty acid or carboxylic acid. methanol can be recovered from the inert gas stream through condensation, absorption, to organic solvents (eg, triethylene glycol) or adsorption to activated carbon.This reaction, when coupled with the synthesis of polyester polyol, eliminates a methanol system separately, eliminates methanol handling and partially reduces methanol discharge into the environment. It is an object of this invention to provide a method for purifying the inert gas stream from a transesterification reaction using lower alkyl esters of fatty acids as the source of fatty acid. It is a further object of this invention to provide a method for making methyl esters for fatty acids through a transesterification reaction, using gaseous methanol in a reactive adsorption column.

BRIEF DESCRIPTION OF THE INVENTION A method is claimed to prepare lower alkyl esters to react triglyceride or other fatty acid ester with a gaseous mixture of an inert gas and lower alkyl alcohol at a temperature between about 20 ° C to about 100 ° C, at a pressure of approximately 0.9842 kg / cm2 (14 psia) (kilograms per absolute square centimeter) to 10.54 kg / cm2 (150 psia) in the presence of a catalyst. In the reaction process, a purified stream of inert gas is recovered. Alkyl esters are separated from glycerin through centrifugation or other separation technique and from mono and diglycerides through fractionation, as conventionally practiced in the art. The molar ratio of methanol to triglyceride is in the range of about 0.1: 1 to about 15: 1.

The exact molar ratio will depend on which reaction object is, ie, maximum removal of the nitrogen alcohol or maximum conversion of the triglyceride to the alkyl ester.

DESCRIPTION OF THE DRAWINGS Figure 1 shows a typical reactive adsorption column and the flow of materials to the reactor. A variety of column internals can be used. The illustrated column uses interstage deflectors (11) with an agitator (15) to control the triglyceride flow, and agitation to produce intimate contact of the gas and liquid phases. All percentages are by weight unless otherwise specified.

DETAILED DESCRIPTION OF THE INVENTION The process is described in detail with reference to methyl esters and methyl alcohol, since methyl is the most commonly used lower alkyl group. However, it should be readily understood that any lower alkyl alcohol can be used. By "lower alkyl" is meant the C- ^-CQ alkyl groups, including all their isomers. Monoalcohols are used. The process is illustrated with triglycerides as the source of fatty acid, but any natural or synthetic source of fatty acid esters can be used in place of the triglyceride. For example, diglycerides, glycol esters, waxes and other sources of fatty acids can be used. The triglyceride is the preferred source of fatty acid, since it is readily available, it is a renewable resource, and relatively inexpensive. Marine and fish oils are good sources of polyunsaturated fatty acids; Vegetable oils and animal oils and oils are resources of saturated and unsaturated fatty acids. These fats and oils can be separated and selectively hydrogenated to produce the desired acids for the formation of the methyl or alkyl esters. Preferred vegetable oils include corn oil, canola oil, olive oil, cottonseed oil, soybean oil, sunflower seed oil, rapeseed oil with a high content of erucic acid, soybean oil partially or totally hydrogenated, canola oil, partially or totally hydrogenated, sunflower seed oil, partially or totally hydrogenated, rapeseed oil with a high content of partially or fully hydrogenated erucic acid and partially or completely hydrogenated cottonseed oil. As used herein, the term "gaseous stream" or "gas stream" means that it encompasses the mixture of alcohol or inert gas that is used in the reaction. Nitrogen, carbon dioxide, helium or other inert gas can be used. Nitrogen is preferred due to its easy availability and cost. Steam and water is not acceptable, since the steam will neutralize the catalyst and can hydrolyze both the triglycerides and the methyl esters that are formed. The triglyceride is converted to the methyl ester or lower alkyl ester by the following procedure: The triglyceride is contacted in a gaseous stream of nitrogen or other inert gas and lower alkyl alcohol in an intermittent reactor or preferably in a continuous reactive absorption column. . Methanol comprises from 1 to 10% gaseous current. The partial pressure of the alcohol in 1 gaseous current affects the solubility of the alcohol and activates the reaction. Thus, the concentration of the alcohol in the inert gas, as well as the temperature and pressure of the gas / alcohol stream that enters are important. The gas / methanol stream enters the column in (1) and disperses through the spray ring (13). The flow velocity of the gas stream, i.e., the nitrogen alcohol mixture, as the column enters is from about 0.5: 1 to about 7: 5.1 (basis by weight) relative to the triglyceride flow. The exact shape and structure of the spray device 13 is not critical to the reaction and its configuration is easily determined by some aspect in the art. What is important is that the inert gas / alcohol stream is dispersed in the triglyceride in a form that contacts the triglyceride effectively allowing the alcohol to be absorbed by, and react with, the triglyceride and thereby convert the acids fatty to esters of alcohol. For a maximum conversion of the triglyceride to the alkyl ester, a molar excess of alcohol is used; in the range of 3 moles of alcohol to 1 mole of triglyceride up to a ratio of 15: 1. This represents a ratio of 1 to 5 times of the alcohol to the fatty acid group. For a maximum removal of methanol from the nitrogen stream, an excess of triglyceride is used. In this case, the ratio of alcohol to triglyceride is from 0.1: 1 to approximately 3: 1. Under preferred conditions, both a high methyl ester conversion and a high alcohol removal are achieved. The triglyceride and another source of fatty acid are mixed with an esterification catalyst and added to the reactor. In a countercurrent column reactor, the liquid enters (5) and flows down the column. The column contains material that disperses nitrogen or inert gas and methanol in the triglyceride. Packed or stirred stages are preferred. Other columns can be used, such as tray columns, perforated disk columns and bubble columns. The exact type of column that is used is not critical and depends on a number of factors that are easily apparent to some people. Nitrogen and methyl alcohol are passed through the triglyceride in a countercurrent fashion and the gas exits in (7). The liquid comes out in (3). Counter current or intermittent processing can also be used. The preferred catalyst is a basic catalyst, for example, an alkali metal or alkaline earth metal hydroxide, alkoxide or carbonate. Preferably, the reaction is catalyzed by potassium or sodium alkoxide, corresponding to the lower alkyl alcohol. When methanol is lower alkyl alcohol, sodium or potassium methoxide is used. Alkali metal alkoxides are readily available in commercial form or can be prepared through the reaction of potassium or sodium with an excess of alcohol. The most preferred catalysts are sodium or potassium methoxide or potassium carbonate. Acid catalysts such as p-toluenesulfonic acid, phosphonic acid, sodium potassium mono or diphosphate, hydrochloric acid or sulfuric acid may also be used. The catalyst is typically used at a level of from about 0.1% to about 1.0% of the triglyceride (base in weight). As the mono and diglycerides are formed, they facilitate the reaction and create a foam. The reaction time may vary from 5 minutes to 5 hours, preferably from 1/2 hour to 2 hours. The exact time depends on the size of the reaction vessel, as well as the material flow velocity, temperatures and pressure. In a reaction column, refined and refined and bleached vegetable oil is added to the reaction vessel together with the catalyst. The nitrogen and lower alkyl alcohol are intimately mixed to be added to the container. This can be done either by bubbling the nitrogen stream through the alcohol by vaporizing the alcohol in the inert gas or by using a stream of nitrogen, which is recovered from a transesterification reaction, where the lower alkyl alcohol is generated during the transesterification. A preferred source of this gaseous stream is the transesterification synthesis reaction of polyol polyester using methyl esters as the source of fatty acid. The gas stream is mixed with triglyceride in a ratio of about 15 moles of alcohol per mole of triglyceride to about 3 moles of alcohol to lower alkyl alcohol per mole of triglyceride. This causes the reaction to proceed so that most of the triglyceride (from 80% to 95%) is converted to methyl esters. When this reaction is used to clean the inert gas stream, the molar ratio of alcohol to triglyceride is from 0.1: 1 to about 3: 1. The reaction temperature is between about 20 ° C and about 100 ° C. The pressure of preference is atmospheric or above atmospheric. Usually, the reaction is carried out between 0.9482 kg / cm2a approximately 10.54 kg / cm2. The preferred pressure level for introducing methanol is in the range of 1053 kg / cm2 to 8.7875 kg / cm2 and more preferably 2.4605 kg / cm2 to 7.03 kg / cm2. The glycerin esters and any monoglyceride and diglyceride are recovered from the bottom of the column as a mixture with any unreacted triglyceride. In the countercurrent column reactor, these salts are through 3. The mixture is first separated by sedimentation or centrifugation, wherein the glycerin is also separated from the mixture. Optionally, additional methanol or alcohol can be added to activate the reaction that comes to term. In this case, a separation step of glycerin is referred to. The remaining catalyst and glycerin are removed by washing with water of the crude reaction mixture. The catalyst and glycerin dissolve in the water and the esters are removed by sedimentation or centrifugation. Cleaning of the crude reaction mixture is achieved through conventional processing. The methyl esters are then separated or purified by distillation or other conventional means. The methyl esters can be further purified through fractionation, including molecular distillation, if desired. The inert gas used in this reaction is preferably that recovered in a transesterification reaction. In the present process, the inert gas not only dilutes the methanol stream, but also provides an inert atmosphere and thus prevents oxidation of the reactants.

The nitrogen leaving this reaction is typically less than 2000 ppm methanol or alcohol and can be as low as 50 ppm alcohol. The lower levels of methanol or residual alcohol in the nitrogen are reacted with excess triglycerides. The following examples illustrate this invention, but are not intended to limit the same. Examples 1 to 3 are intended to show what lower levels of residual alcohol can be achieved in nitrogen (50 ppm at 520 ppm) at a broader range of pressures (1.0545 to 5.9755 kg / cm2) (15 psig or 85 psig) with a stoichiometric excess of triglyceride. The conversion of methyl esters was low in each case (approximately 20%).

Example 1 INGREDIENTS AMOUNT soybean oil stoichiometric excess (23.61 kg / h) sodium methoxide 0.05 mol / mol nitrogen oil 14.5 kg / h mmeettaannooll 4.0 g / min (16% N2) In a continuous multistage stirred column was fed triglyceride (refined, decolorized and deodorized soybean oil) containing sodium methoxide, continuously in the upper part of the reactor. The reactor has a diameter of 15.24 cm (6 inches) and a height of 121.9 cm (48 inches) and has 10 agitated stages. The agitator was operated at approximately 1500 rpm. The column was configured as in Figure 1. The triglyceride was passed countercurrent to a methanol / nitrogen stream fed from the bottom of the reactor. The reactor was maintained at 38 ° C and 4.54 kg / cm2 (64.7 psia) to (3.51 kg / cm2m) (50 psig). The nitrogen / methanol flow is 14.5 kg / h (32 lb / h). The nitrogen stream of the product conta40 ppm of methanol. This nitrogen stream was used in the polyester polyol synthesis described in Example 6.

EXAMPLE 2 In a reaction similar to Example 1, the stream of nitrogen gas containing 1.6% methanol was passed through the column at 23.6 kg / hour (52 pounds / hour). The triglyceride containing 0.05 moles of solid sodium methoxide per mole of triglyceride was fed to the top of the column at 23.6 kg / hour (52 pounds / hour). The temperature is 43 ° C and the pressure is 7,008 kg / cm2a (99.7 psia). The nitrogen outlet has 80 ppm of methanol therein.

EXAMPLE 3 Reactive absorption was performed in a multi-stage countercurrent stirred column. The triglyceride was continuously fed to the top of the reactor and the product was expelled to the bottom. The nitrogen / methanol was fed to the bottom of the reactor and discharged at the top. A stoichiometric excess of triglyceride was used.

Conditions: Liquid feed - 23.6 kg / hour (52 lb / h) catalyzed triglyceride (0.05 moles of solid NaOCH3 per mole of triglyceride) Gas feed - 14.5 kg / hour (32 lb / h) nitrogen, 4.0 grams / minute, methanol (16% MeOH) Temperature 37 ° C (98 ° F) Pressure - 1.0545 kg / cm2a (15 psig) Results: 520 ppm (0.52%) of methanol in nitrogen output.

EXAMPLE 4 Reactive absorption was carried out in a multistage, countercurrent stirred column, as in the previous example. The triglyceride was continuously fed to the top of the reactor and the product was expelled to the bottom. The nitrogen / methanol was fed to the bottom of the reactor and discharged at the top. Approximately a stoichiometric amount of triglyceride and methanol was used.

Conditions: Liquid feed - 36.28 kg / h (80 lb / h) of catalyzed triglyceride (0.15 mol of solid NaOCH3 per mole of triglyceride) Gas feed - 90.71 kg / h (200 lb / h) of nitrogen, 3.538 kg / h (7.8 lbs / h) of methanol Temperature 54 ° C (130 ° F) Pressure - 4.569 kg / cm2 (65 psig) Results: 2000 ppm (0.20%) of methanol in nitrogen output 81% conversion of triglyceride to esters methyl.

EXAMPLE 5 Reactive absorption conversion of triglyceride to methyl esters was analyzed in an intermittent stirred reactor of 1.5 liters. A stoichiometric excess of methanol was bubbled through catalyzed triglyceride.

Conditions: Liquid - 883 grams of triglyceride, 3.05 of sodium methoxide catalyst Gas - 1.6 liters / minute, nitrogen, 2.1 grams / minute, methanol Temperature -90 ° C (194 ° F) Pressure - atmospheric (14.7 psia) Results: 55% conversion of triglyceride to metesters in 30 minutes. 80% conversion to metesters in 75 minutes. The reaction mixture at 80% conversion was allowed to settle giving as a result of two phases. The heavier phase (mainly glycerin) was removed. The remaining mixture was further reacted under conditions similar to those described above for 75 minutes, leading to 96% metesters in the final product.

Claims (20)

1. A continuous process for purifying a stream of inert gas containing a lower alkyl alcohol, characterized in that it comprises: (i) intimately mixing an inert gas containing a lower alkyl alcohol with a source of fat at a temperature between about 20 ° C to about 100 ° C ° C, at a pressure of about 0.9842 to about 10.54 kg / cm2 (14 to about 150 psia) in the presence of a catalyst; and (ii) recover the methyl esters and the stream of purified inert gas.

2. The process according to claim 1, characterized in that the reaction is conducted at a pressure of between about 2.4605 to about 7.03 kg / cm2 (35 to about 100 psia).

3. The process according to claim 2, characterized in that the catalyst is selected from the group consisting of sodium methoxide, sodium or potassium alkoxide, sodium or potassium carbonate, and mixtures thereof.

4. The process according to claim 1, characterized in that the inert gas is nitrogen.

5. The process according to claim 1, characterized in that the lower alkyl alcohol is methanol and the inert gas is nitrogen.

6. The method according to claim 1, characterized in that the source of fatty acid is a triglyceride selected from the group consisting of vegetable oils, hydrogenated vegetable oils, marine oils and animal oils and fats.

7. The process according to claim 6, characterized in that the triglyceride is selected from the group consisting of canola oil, olive oil, cottonseed oil, soybean oil, sunflower seed oil, rapeseed oil with a high erucic acid content, partially or fully hydrogenated soybean oil, partial or totally hydrogenated canola oil, partially or fully hydrogenated sunflower seed oil, rapeseed oil with a high content of partially or fully hydrogenated erucic acid, seed oil cotton, partially or totally hydrogenated, and their mixtures.

8. The process according to claim 6, characterized in that the molar ratio of the lower alkyl alcohol to the triglyceride is from about 0.1: 1 to about 15: 1.

9. The process according to claim 8, characterized in that the reaction is conducted in a reaction column and the molar ratio of alkyl alcohol to triglyceride is from about 0.1: 1 to about 3: 1.

10. The method according to claim 1, characterized in that the column is selected from the group consisting of packed columns, tray columns, perforated disk columns, bubble columns and agitated columns.

11. The continuous process for preparing methyl esters, characterized in that it comprises: (i) reacting a source of fatty acid with an intimate mixture of an inert gas and a lower alkyl alcohol at a temperature of between about 14 to about 20 ° C to about 100 ° C, at a pressure of about 0.9842 to about 10.54 kg / cm2 (14 to about 150 psia) in the presence of a catalyst; and (ii) recover the methyl esters.

12. The process according to claim 11, characterized in that the reaction is conducted at a pressure of between about 2.4605 to about 7.03 kg / cm2 (35 to about 100 psia).

13. The process according to claim 12, characterized in that the catalyst is selected from the group consisting of sodium methoxide, sodium or potassium alkoxide, sodium or potassium carbonate, and mixtures thereof.

14. The process according to claim 11, characterized in that the inert gas is nitrogen.

15. The process according to claim 11, characterized in that the lower alkyl alcohol is methanol and the inert gas is nitrogen.

16. The method according to claim 1, characterized in that the source of fatty acid is a triglyceride selected from the group consisting of vegetable oils, hydrogenated vegetable oils, marine oils and animal oils and fats.

17. The process according to claim 16, characterized in that the triglyceride is selected from the group consisting of canola oil, olive oil, cottonseed oil, soybean oil, sunflower seed oil, rapeseed oil with a high erucic acid content, partially or fully hydrogenated soybean oil, partially or fully hydrogenated canola oil, partially or fully hydrogenated sunflower seed oil, rapeseed oil with a high content of partially or fully hydrogenated erucic acid, partially or totally hydrogenated , and its mixtures.

18. The process according to claim 16, characterized in that the molar ratio of the lower alkyl alcohol to the triglyceride is from about 0.1: 1 to about 15: 1.

19. The process according to claim 18, characterized in that the reaction is conducted in a reaction column.

20. The method according to claim 19, characterized in that the column is selected from the group consisting of packed columns, tray columns, perforated disk columns, bubble columns and agitated columns.