METHOD FOR PURIFYING AN AQUEOUS-ALCOHOLIC FEEDSTOCK COMPRISING ETHANOL AND ACETALDEHYDE

Abstract

The invention concerns a method for purifying a hydroalcoholic feedstock, comprising: a) a step of counter-current liquid-liquid extraction, comprising an extraction section supplied at the top with said hydroalcoholic feedstock and at least one intermediate raffinate fraction from step b) and at the bottom with an extraction solvent, and producing at the top an extraction stream and at the bottom a raffinate, wherein the extraction section is operated at a mean temperature in the extractor of between 10 and 40° C.; b) a counter-current liquid-liquid back-extraction comprising a back-extraction section supplied at the top with an acidic aqueous solution, having a pH between 0.5 and 5.0, and at the bottom with the extraction stream from step a), and producing at the top an extract and at the bottom the intermediate raffinate, wherein the back-extraction section is operated at a mean temperature between 40 and 80° C.

Claims

1. A process for the purification of a hydroalcoholic feedstock (1) comprising at least water, ethanol, acetaldehyde and impurities, said process comprising: a) a step of countercurrentwise liquid-liquid extraction, comprising an extraction section comprising an extractor (2) that is fed at the top by said hydroalcoholic feedstock (1) and at least a fraction of an intermediate raffinate resulting from the back-extraction step b) and at the bottom by an extraction solvent (3), and that produces at the top an extraction stream (5) and at the bottom a raffinate (4) comprising water, ethanol and acetaldehyde, wherein said extraction section is operated at a mean temperature in the extractor of between 10 and 40° C.; b) a step of countercurrentwise liquid-liquid back-extraction comprising a back-extraction section comprising a back-extractor (6) that is distinct from the extractor of step a) and fed at the top by an acidic aqueous solution (7), having a pH of between 0.5 and 5.0, and at the bottom by the extraction stream (5) resulting from step a), and that produces at the top an extract (8) and at the bottom said intermediate raffinate, wherein said back-extraction section is operated at a mean temperature in the back-extractor that is distinct from the mean temperature in the extractor of step a) and of between 40 and 80° C.

2. The process as claimed in claim 1, wherein the mean temperature in the extraction column (2) of step a) is of between 15 and 30° C.

3. The process as claimed in claim 1, wherein the mean temperature in the back-extraction column (6) of step b) is of between 45 and 60° C.

4. The process as claimed in claim 1, wherein the back-extractor of step b) is an adiabatic column fed at the top by said acidic aqueous solution (7), at a temperature for entry of said acidic aqueous solution into said adiabatic column of between 50 and 90° C., preferably between 60 and 85° C.

5. The process as claimed in claim 1, wherein said acidic aqueous solution (7) which feeds the back-extraction column (6) of step b) exhibits a pH of between 2 and 4, preferably between 2.5 and 3.5.

6. The process as claimed in claim 1, wherein the hydroalcoholic feedstock (1) comprises between 30% and 70% by weight of ethanol, preferably between 40% and 60% by weight of ethanol, with respect to the total weight of the hydroalcoholic feedstock, between 1% and 30% by weight of acetaldehyde, preferably between 5% and 10% by weight of acetaldehyde, with respect to the total weight of the hydroalcoholic feedstock, and between 0.5% and 20% by weight of impurities, in particular between 1% and 20% by weight of impurities, with respect to the total weight of the hydroalcoholic feedstock.

7. The process as claimed in claim 1, wherein the hydroalcoholic feedstock (1) additionally comprises at least one acetal and/or hemiacetal, in particular diethyl acetal and/or ethyl hemiacetal.

8. The process as claimed in claim 1, wherein the hydroalcoholic feedstock (1) is an hydroalcoholic effluent resulting from a step of separation of the butadiene at the outlet of the conversion reactors in a Lebedev process.

9. The process as claimed in claim 1, wherein the extraction solvent (3) is an organic solvent, preferably a nonpolar organic solvent, in a preferred way a mixture of hydrocarbons having between 6 and 40 carbon atoms, preferably between 10 and 20 carbon atoms.

10. The process as claimed in claim 9, wherein the extraction solvent (4) is hexadecane.

11. The process as claimed in claim 1, wherein said acidic aqueous solution (7) which feeds the back-extraction column (6) of step b) comprises less than 2% by weight, preferably less than 1% by weight, of the ethanol and acetaldehyde combination, in a preferred way is free from ethanol and acetaldehyde.

Description

LIST OF THE FIGURES

[0072] FIG. 1 diagrammatically and nonlimitingly represents an arrangement of the process according to the invention. The hydroalcoholic feedstock comprising water, ethanol, acetaldehyde and impurities (1) feeds, at the top, a liquid-liquid extraction section (2) in which step a) is carried out. The liquid-liquid extraction section (2) is also fed at the top by an intermediate raffinate resulting from the back-extraction section (6) of step b) and at the bottom by an extraction solvent (3). An extraction stream (5), also called intermediate extract, is produced at the top of the extraction section (2) while a raffinate (4) is withdrawn at the bottom of the extraction section (2). The extraction stream (5) feeds, at the bottom, the back-extraction section (6) of step b). The back-extraction section (6) is fed, at the top, by an acidic aqueous solution (7). An extract (8) is withdrawn at the top of the back-extraction section (6) while at the bottom an intermediate raffinate is produced. Said intermediate raffinate feeds the liquid-liquid extraction section (2).

EXAMPLES

[0073] In the following examples, an hydroalcoholic feedstock comprising ethanol, acetaldehyde, water and impurities, in particular nonpolar impurities or impurities with low polarity, such as diethyl ether (regarded as an impurity), with a composition given in table 1 and with a flow rate by weight of 3.65 kg/hour, is treated.

TABLE-US-00001 Weight Content (% by weight with respect Compounds to the total weight of the feedstock) Acetaldehyde 3.91% Ethanol 62.95% Acetone 0.07% Ethyl vinyl ether 0.04% Diethyl ether 1.00% Butanal 0.03% Butanone 0.01% Ethyl acetate 1.37% Acetic acid 0.63% Butanol 0.41% Diethyl acetal 4.46% Styrene 0.10% Water 25.01%

[0074] In the following examples, the extraction and back-extraction sections are operated under the same following conditions; only the mean temperatures of the extraction and back-extraction sections and the weight content of acetic acid of the acidic aqueous solution used as back-extraction solvent differ.

[0075] The extraction and back-extraction columns are distinct columns, both of ECR Sulzer type with internals having plate openings of 40%, with an internal diameter of 32 mm and a working height of 1.8 m.

[0076] The extraction column is fed at the bottom with hexadecane at a flow rate of 1.28 kg/hour. The back-extraction column is fed at the top with water acidified by acetic acid, the flow rate of this back-extraction solvent being at 0.56 kg/hour.

[0077] The extraction column is operated in dispersed aqueous phase. The back-extraction column is operated in continuous aqueous phase.

[0078] The stirring speed is adjusted in both columns so that the fraction by volume of dispersed phase is approximately 15% by volume in the extraction column and 3% by volume in the back-extraction column.

[0079] The extraction column produces at the top an extraction stream which is injected at the bottom of the back-extraction column. The extraction column produces at the bottom a raffinate comprising ethanol and acetaldehyde. The back-extraction column produces at the top of the column an extract and at the bottom an intermediate raffinate, the latter being injected at the top of the extraction column.

[0080] In the various examples, the acetic acid concentration of the acidic aqueous solution (back-extraction solvent), thus the pH of this acidic aqueous solution, and also of the mean temperatures of the extraction and back-extraction sections vary. Table 2 below summarizes the variable operating conditions and the results obtained in terms of efficiency of extraction of the impurity diethyl ether and of efficiency of back-extraction of diethyl acetal.

[0081] The efficiency of extraction of diethyl ether (DEE) and the efficiency of back-extraction of diethyl acetal (DEA) are calculated, for each example, as presented above in the description, that is to say in the following way:

Efficiency of extraction of DEE=[(weight content of DEE of the extract)×(flow rate by weight of the extract)/(weight content of DEE of the hydroalcoholic feedstock)×(flow rate by weight of the hydroalcoholic feedstock)].

Efficiency of back-extraction DEA=1−[(weight content of DEA of the extract)×(flow rate by weight of the extract)/(weight content of DEA of the intermediate extract)×(flow rate by weight of the intermediate extract)].

[0082] The weight contents of DEE of the extract and of the hydroalcoholic feedstock and the weight contents of DEA of the extract and of the intermediate extract were determined by gas chromatography.

TABLE-US-00002 Acetic pH of Efficiency acid the Back- Efficiency of back- content acidic Extraction extraction of extraction extraction (% by aqueous temperature temperature of DEE (% of DEA (% Examples weight) solution (° C.) (° C.) by weight) by weight) 1 3% 2.5 20 20 81% 93% 2 1% 2.8 20 20 81% 74% 3 1% 2.8 40 40 72% 92% 4 1% 2.8 50 50 43% 98% 5 1% 2.8 20 50 81% 98%

[0083] Example 1 illustrates the reference case in accordance with the prior art. With an acetic acid content of the back-extraction solvent of 3% by weight and an operating temperature equal to 20° C. for the two columns, the efficiency of extraction of diethyl ether (DEE) and the efficiency of back-extraction of diethyl acetal (DEA) are satisfactory, since respectively greater than 80% by weight (81% efficiency of extraction of DEE) and greater than 90% by weight (93% efficiency of back-extraction of DEA).

[0084] Example 2 shows that, at the same operating temperature as above (20° C. in both columns), when the acetic acid content in the acidic aqueous solution used as back-extraction solvent decreases (1% by weight instead of 3% by weight), the efficiency of back-extraction of DEA decreases substantially and becomes less than 75% by weight.

[0085] According to examples 3 and 4, the joint increase in the temperature in both columns (extraction and back-extraction), to 40° C. for example 3 and 50° C. for example 4, makes it possible to recover a satisfactory efficiency of back-extraction (92% and 98% respectively) for low acetic acid contents in the aqueous back-extraction solvent (1%). However, the effect on the extraction of DEE is detrimental since the efficiency of extraction of DEE becomes less than 75%: more precisely, the efficiency of extraction of DEE is 72% by weight in example 3 and 43% by weight in example 4.

[0086] Example 5, in accordance with the invention, clearly demonstrates that, even for a low content of acetic acid in the acidic aqueous solution used as back-extraction solvent, imposing two distinct temperatures between the extraction and the back-extraction, and in particular a temperature of 20° C. in the extraction column and a mean temperature of 50° C. in the back-extraction column, makes it possible to obtain an optimized extraction of DEE, with an efficiency of extraction of DEE equal to 81% by weight, and a high back-extraction of DEA, with an efficiency of back-extraction of DEA equal to 98% by weight, an efficiency of back-extraction which is greater than that obtained in example 1 according to the prior art.

[0087] It thus clearly appears that the process according to the invention, for purifying a hydroalcoholic feedstock comprising water, ethanol, acetaldehyde and impurities, makes it possible to extract the nonpolar impurities or impurities with low polarity in an optimal manner and to improve the back-extraction of the condensed form of ethanol and acetaldehyde, with a substantially reduced consumption of acetic acid.