Use of a Lewis donor solvent to purify a feedstock that contains ethanol, acetaldehyde, and impurities

Abstract

The invention pertains to the use of a solvent that comprises a Lewis donor compound that is selected from the group made up of unsaturated fatty acids that have between 12 and 18 carbon atoms, phosphate esters that have between 12 and 30 carbon atoms, and mixtures thereof to separate the impurities from a feedstock that contains ethanol, acetaldehyde, and impurities.

Claims

1. A method for purifying a feedstock that contains ethanol, acetaldehyde, and impurities using a solvent, referred to as a Lewis donor solvent, that comprises a Lewis donor compound that is selected from the group made up of unsaturated fatty acids that have between 12 and 18 carbon atoms, phosphate esters that have between 12 and 30 carbon atoms, and mixtures thereof, where said method comprises: a counter-current liquid-liquid extraction step A) that is fed at the top with said feedstock in a mixture with the raffinate obtained from re-extraction step B), wherein said mixture constitutes the feed for said step A), and at the bottom is fed with the Lewis donor solvent-rich effluent obtained from regeneration step C), a Lewis donor solvent make-up that may optionally be mixed with said Lewis donor solvent-rich effluent, where said step produces at the top an extract and at the bottom a purified feedstock and operates at a temperature of between 10 and 70 C. and at a pressure of between 0.1 and 0.5 MPa with a continuous-phase mass flow rate/dispersed-phase mass flow rate ratio of less than 70; a counter-current liquid-liquid re-extraction step B) that is fed at the top with an auxiliary solvent and at the bottom with the extract obtained from step A) and that produces at the top an extract and at the bottom a raffinate, where said raffinate feeds said step A), with this step operating at a temperature of between 10 and 70 C. and at a pressure of between 0.1 and 0.5 MPa with a continuous-phase mass flow rate/dispersed-phase mass flow rate ratio of less than 70; a regeneration step C) in which the extract obtained from step B) is separated by a first distillation into a distillate that is rich in light impurities and a residue that undergoes a second distillation, where the latter produces at the top an effluent that is rich in Lewis donor solvent and a residue that is rich in heavy impurities; where said Lewis donor solvent comprises a Lewis donor selected from the group made up of unsaturated fatty acids that have between 12 and 18 carbon atoms, phosphate esters that have between 12 and 30 carbon atoms, and mixtures thereof.

2. The method in accordance with claim 1 in which said Lewis donor compound is selected from the group made up of oleic acid, linoleic acid, tributyl phosphate, and mixtures thereof.

3. The method in accordance with claim 1, in which said Lewis donor solvent also comprises at least one hydrocarbon that contains at least 12 carbon atoms, with the proportion (Lewis donor compound)/hydrocarbon+Lewis donor compound) falling into a range of from 1 to less than 100% by weight.

4. The method in accordance with claim 1 in which said ratio falls into a range of from 15 to less than 100% by weight.

5. The method in accordance with claim 1 in which said auxiliary solvent solution is water.

6. A process for separating impurities from a feedstock containing ethanol, acetaldehyde, and impurities, comprising subjecting the feedstock to a solvent that comprises a Lewis donor compound that is selected from the group made up of unsaturated fatty acids that have between 12 and 18 carbon atoms, phosphate esters that have between 12 and 30 carbon atoms, and mixtures thereof.

7. The process according to claim 6 in which said Lewis donor compound is selected from the group made up of oleic acid, linoleic acid, tributyl phosphate, and mixtures thereof.

8. The process according to claim 7 in which said Lewis donor compound is oleic acid.

9. The process according to claim 6 in which said solvent that comprises a Lewis donor compound also comprises at least one hydrocarbon containing at least 12 carbon atoms, with the proportion (Lewis donor compound)/hydrocarbon+Lewis donor compound) falling into a range of from 1% to less than 100% by weight.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 depicts in schematic form a general arrangement of the method according to the invention.

(2) A counter-current liquid-liquid extraction step A) is fed with a feedstock (1) in a mixture with the raffinate (23) obtained from re-extraction step B), where this mixture constitutes the feed (21) for said step A), and at the bottom is fed with the Lewis donor solvent-rich effluent (10) obtained from regeneration step C) and produces an extract (22) and a purified feedstock (3).

(3) A counter-current liquid-liquid re-extraction step B) is fed with an auxiliary solvent (2) and at the bottom with the extract (22) obtained from step A) and produces at the top an extract (4) and at the bottom a raffinate (23), where said raffinate feeds said step A).

(4) A regeneration step C) is fed with the extract (4) obtained from step B) and separates a distillate that is rich in light impurities (5), an effluent that is rich in Lewis donor solvent (10), and a residue that is rich in heavy impurities (9).

(5) FIG. 2 depicts in schematic and non-limiting form an arrangement of the method according to the invention. The notation of the streams in FIG. 2 is identical to that in FIG. 1.

(6) In the arrangement depicted in FIG. 2, steps A) and B) are carried out in a single device ELL 1.

(7) The feedstock containing ethanol and acetaldehyde (1) feeds a liquid-liquid extraction column ELL1. The latter is fed at the top with an auxiliary solvent (2) and at the bottom with the Lewis donor solvent-rich effluent obtained from step C) (10). The extract (4) from step B) is drawn off at the top of the column ELL1, while the purified feedstock (3) from step A) is drawn off at the bottom of the column ELL1.

(8) In the arrangement depicted in FIG. 2, step C) is carried out in two distillation columns D1 and D2.

(9) The extract (4) obtained from step B) feeds a distillation column D1. A distillate rich in light impurities (5) is separated at the top, and a residue is drawn off at the bottom. When the proportion of heavy impurities in this residue is small, only a fraction (7) of said residue feeds a second distillation column D2, with the residual fraction (6) being recycled to step A) in column ELL1 in a mixture with the flow (8) as a Lewis donor solvent-rich effluent (10).

(10) An optional Lewis donor solvent make-up (not shown) can be provided in a mixture with the Lewis donor solvent-rich effluent (10) to make up for the losses of Lewis donor or during the start-up of the process.

(11) At the top the second distillation column D2 separates a Lewis donor solvent-rich effluent (8), which is recycled to step A) in column ELL1 in a mixture with the residual fraction (6), and at the bottom separates a residue that is rich in heavy impurities (9), which residue is eliminated from the process.

EXAMPLES

Example 1

(12) In this example, the performance levels achieved with a solvent according to the invention are compared to the performance levels achieved with the solvents described in the prior art for a given solvent/feedstock mass ratio.

(13) An analysis is made of the performance levels obtained for purifying the key impurities in a feedstock whose composition is similar to that of industrial effluent from a process of the Lebedev type (ethanol=50% by weight; acetaldehyde=9% by weight; water=27% by weight; impurities=14% by weight). The mass ratio of solvent to feedstock is 1.

(14) The partition coefficient K is measured for ethyl acetate and diethyl ether between a hydroalcoholic phase and different solvents that were tested. The term key impurities is defined here to mean that the capacity for separating these impurities is representative of the capacity for separating the complex mixture of impurities in an actual flow.

(15) We write K.sub.i=[1].sub.S1/[1].sub.S2, where [1].sub.S1 is the concentration of type 1 in mol/kg in the extraction solvent, denoted S1, and [1].sub.S2 is a concentration of type 1 in mol/kg in the hydroalcoholic phase, denoted S2.

(16) Selectivity for absorption of impurities i is also defined with respect to ethanol S.sub.1/ethanol=K.sub.1/K.sub.ethanol.

(17) Various non-compliant extraction solvents were tested: a hydrocarbon having fewer than 12 carbon atoms: hexane a fatty acid having fewer than 12 carbon atoms: nonanoic acid a phosphate ester having fewer than 12 carbon atoms: triethyl phosphate a hydrocarbon having at least 12 carbon atoms: hexadecane.

(18) These solvents are compared against the following compliant solvent: a mixture of a hydrocarbon and a Lewis donor compound having more than 12 carbon atoms: a mixture of oleic acid and hexadecane.

(19) The partition coefficients of the two key impurities (ethyl acetate and diethyl ether), their ethanol selectivity values, and the presence or absence of a deposit are presented in the table below and for different solvents, according to the invention and according to the prior art:

(20) TABLE-US-00001 30% Oleic Acid Nonanoic Triethyl (C.sub.18) + Extraction Hexane Acid Phosphate Hexadecane 70% Solvent (C.sub.6) (C.sub.9) (C.sub.6) (C.sub.16) Hexadecane Formation Yes Yes Monophasic Yes No of a Deposit K.sub.ethyl acetate 4.7 4.2 0.6 1.1 K.sub.diethyl ether 2.3 4.4 1.4 2.2 S.sub.ethyl acetate 47.8 4.3 28 7.6 S.sub.diethyl ether 22.8 4.5 69 15.3

(21) In the case of triethyl phosphate, separation is not possible because the mixture is monophasic. Hexane is an excellent extraction solvent, but the mixture with the feedstock is diphasic only under narrow conditions of concentration, making it tricky to use in liquid-liquid extraction.

(22) It should be noted that the use in accordance with the invention of a hexadecane-oleic acid mixture leads to better extraction than with hexadecane by itself. Moreover, despite the fact that selectivity is a bit lower, the mixture does not form deposits in the equipment.

Example 2

(23) In this example, the performance levels achieved with a solvent that is compliant with the invention are compared with solvents that have different chemical functions for a given solvent/feedstock mass ratio.

(24) An analysis is made of the performance levels obtained in separating the impurities and brown oils of a feedstock that is close in composition to an industrial composition (ethanol=50% by weight; acetaldehyde=9% by weight; water=27% by weight; impurities=14% by weight). The solvent/feedstock mass ratio is 1.

(25) Various non-compliant extraction solvents were tested: a fatty-acid methyl ester composed of 18 carbon atoms: sunflower methyl ester; an alcohol composed of 18 carbon atoms: oleic acid;
as well as the compliant solvents as follows: a fatty acid composed of 18 carbon atoms and a double bond: oleic acid; a fatty acid composed of 18 carbon atoms and two double bonds: linoleic acid; an organophosphorus compound: tributyl phosphate, composed of 12 carbon atoms.

(26) The partition coefficients of two key impurities (ethyl acetate, diethyl ether), their levels of selectivity with respect to ethanol, and the presence or absence of a deposit are given in the table below and for different solvents, according to the invention and according to the prior art:

(27) TABLE-US-00002 Sunflower Extraction Methyl Oleic Oleic Linoleic Tributyl Solvent Ester Alcohol Acid Acid Phosphate Formation Yes Yes No No No of a Deposit K.sub.ethyl acetate 1.8 2.0 2.1 2.5 1.7 K.sub.diethyl ether 2.5 2.4 2.6 3.1 1.8 S.sub.ethyl acetate 4.0 3.6 2.8 3.6 1.8 S.sub.diethyl ether 17.2 4.4 3.6 4.6 2.0

(28) This comparative example clearly illustrates the benefit of using a Lewis donor compound as prescribed for the purposes of the invention, where said compound makes it possible to avoid the formation of a deposit.