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US-12616917-B2 - Method for purifying an aqueous-alcoholic feedstock comprising ethanol and acetaldehyde

US12616917B2US 12616917 B2US12616917 B2US 12616917B2US-12616917-B2

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.

Inventors

  • Frederic Augier
  • Pierre Olivier DREGER

Assignees

  • IFP Energies Nouvelles
  • COMPAGNIE GÉNÉRALE DES ETABLISSEMENTS MICHELIN

Dates

Publication Date
20260505
Application Date
20200406
Priority Date
20190425

Claims (14)

  1. 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 a countercurrentwise liquid-liquid 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 15 and 30° C.; and b) the 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 ), 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) of between 4° and 80° C., wherein said acidic aqueous solution ( 7 ) comprises a content of acetic acid of less than or equal to 1.5% by weight of acetic acid with respect to the total weight of said acidic aqueous solution.
  2. 2 . The process as claimed in claim 1 , wherein the mean temperature in the extraction column ( 2 ) of step a) is 20° C.
  3. 3 . The process as claimed in claim 1 , wherein the mean temperature in the back-extraction column ( 6 ) of step b) is between 45 and 60° C.
  4. 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 5° and 90° C.
  5. 5 . The process as claimed in claim 1 , wherein the hydroalcoholic feedstock ( 1 ) comprises between 30% and 70% by weight of ethanol with respect to the total weight of the hydroalcoholic feedstock, between 1% and 30% by weight of acetaldehyde with respect to the total weight of the hydroalcoholic feedstock, and between 0.5% and 20% by weight of impurities with respect to the total weight of the hydroalcoholic feedstock.
  6. 6 . The process as claimed in claim 1 , wherein the hydroalcoholic feedstock ( 1 ) additionally comprises at least one acetal and/or hemiacetal.
  7. 7 . The process as claimed in claim 1 , wherein the hydroalcoholic feedstock ( 1 ) is an hydroalcoholic effluent resulting from a step of separation of butadiene at an outlet of a conversion reactor in a Lebedev process.
  8. 8 . The process as claimed in claim 1 , wherein the extraction solvent ( 3 ) is a nonpolar organic solvent.
  9. 9 . The process as claimed in claim 8 , wherein the extraction solvent ( 4 ) is hexadecane.
  10. 10 . 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 of the ethanol and acetaldehyde combination.
  11. 11 . The process as claimed in claim 1 , wherein said acidic aqueous solution comprises a content of acetic acid of less than 1.5% by weight of acetic acid with respect to the total weight of said acidic aqueous solution.
  12. 12 . The process as claimed in claim 8 , wherein the extraction solvent ( 3 ) is a mixture of hydrocarbons having between 6 and 40 carbon atoms.
  13. 13 . The process as claimed in claim 8 , wherein the extraction solvent ( 3 ) is a mixture of hydrocarbons having between 10 and 20 carbon atoms.
  14. 14 . The process as claimed in claim 1 , wherein the mean temperature in the extraction column ( 2 ) of step a) is 20° C. and the mean temperature in the back-extraction column ( 6 ) of step b) is between 50 to 80° C.

Description

TECHNICAL FIELD The present invention relates to a process for the treatment of a feedstock comprising at least water, ethanol and acetaldehyde, by liquid-liquid extraction and back-extraction, making it possible to maximize the removal of impurities, in particular nonpolar impurities or impurities with low polarity, while optimizing the recovery of the ethanol and the acetaldehyde. The process according to the invention can advantageously be integrated in a more general process for the conversion of ethanol into butadiene, also called the Lebedev process. It then makes it possible to purify the liquid effluent resulting from the conversion reactors while improving the recovery of the ethanol and of the acetaldehyde not converted into butadiene. PRIOR ART The process for producing butadiene from ethanol was developed in particular by American teams during the Second World War starting from the studies of Ostromilenski. In this process, the conversion per pass is less than 50%, which implies significant recyclings of the ethanol and acetaldehyde. Furthermore, a great variety of impurities of different natures (saturated, unsaturated or aromatic hydrocarbons, oxygen-based products, such as alcohols, ketones, aldehydes, phenols, acids, esters or ethers) and having very different molar masses is produced (between 50 and 10 000 g/mol). It is thus necessary to put in place a line of unit operations with the aim of removing as many impurities as possible while losing as little ethanol and acetaldehyde as possible. From an economic viewpoint, it is essential to reduce the production cost of butadiene, which requires: a) losing as little ethanol and acetaldehyde as possible,b) not recycling impurities in the reactors, which impurities would result in a fall in selectivity for butadiene or would accumulate at unacceptable levels, requiring a purge and thus losses of ethanol and acetaldehyde. At the outlet of the catalytic reactors, the produced effluent, that comprises butadiene, ethanol, water, acetaldehyde and impurities, undergoes several unit operations in order to separate the undesired gaseous and liquid byproducts from the butadiene formed and from the compounds ethanol, water or acetaldehyde, called “noble” compounds, wherein liquid and gaseous are understood at ambient temperature and pressure. Among the byproducts which are gaseous at ambient temperature and pressure, hydrogen, carbon monoxide, carbon dioxide and C1-C4 olefins and alkanes may be mentioned. It is essential to remove these byproducts from the effluent rich in butadiene in order to obtain a butadiene product with the required specifications. Among the byproducts which are liquid at ambient temperature and pressure, acetone, diethyl ether, butanal, butanol, butanone, ethyl acetate, crotonaldehyde and acetic acid may be mentioned. Other byproducts can be generated in a smaller amount in the reaction zone. In the continuation of the document, the term “impurities” will denote this combination of thousands of hydrocarbon or oxygen-based compounds. In the first process schemes of the American teams, ethanol, acetaldehyde, water and the liquid byproducts are separated by a line of three distillation columns (U.S. Pat. No. 2,403,742). The effluent rich in ethanol, acetaldehyde, water and liquid byproducts feeds a first distillation column in which an effluent rich in acetaldehyde is separated from the remainder of the effluent. A second distillation column makes it possible to separate the liquid byproducts from an effluent rich in ethanol and water. The final distillation column makes it possible to separate the ethanol from the water. Most of the process patents filed in the period 1940-1960 by Carbide & Carbon or Koppers (U.S. Pat. Nos. 2,403,743, 2,393,381, 2,395,057 and 2,439,587) aim to improve this part of the scheme. One of the problems of the process, observed in the years 1945, is a significant formation of diethyl acetal and/or ethyl hemiacetal resulting in particular from the reaction of ethanol with acetaldehyde, which results in a not insignificant loss of reactants (ethanol, acetaldehyde) and thus a fall in the butadiene yield. Toussaint et al., Industrial and Engineering Chemistry, 1947, Vol. 39, No. 2, pp. 120-125, indicate in particular that 20 kg of diethyl acetal are produced per tonne of butadiene formed. In the patents FR 3 026 100 and FR 3 026 101, the liquid impurities are removed, at least in part, by liquid-liquid extraction. The liquid effluent at the outlet of the reactors, that comprises ethanol, acetaldehyde, water and impurities, feeds a liquid-liquid extraction column. The latter is fed at the bottom with a scrubbing solvent, the aim of which is to scrub the feedstock countercurrentwise. At the outlet of this scrubbing section, the extract is composed predominantly of the scrubbing solvent and of the extracted byproducts (such as diethyl ether) and comprises small amounts of ethanol and acetaldehyde. This extract is su