CONVERSION OF BUTANEDIOL INTO BUTADIENE, WITH SCRUBBING USING DIESTERS

Abstract

The invention pertains to a method for converting butanediol into butadiene that is fed with a butanediol feedstock, where said method comprises at least an esterification step, a pyrolysis step, and a step for separation of the pyrolysis effluent comprising at least one section for cooling said pyrolysis effluent and producing a liquid pyrolysis effluent and a steam pyrolysis effluent and a gas-liquid washing section that is fed at the top with a fraction of the butanediol diester effluent obtained from the esterification step and at the bottom with the steam pyrolysis effluent, where said section produces a butadiene effluent at the top and a washing effluent at the bottom.

Claims

1. Method for converting butanediol into butadiene that is fed with a butanediol feedstock, where said method comprises at least: a) an esterification step that comprises: a reaction section that is fed with a butanediol feedstock, with at least a fraction of the liquid pyrolysis effluent obtained from step c), and with the carboxylic acid effluent obtained from the separation section of step a), where said reaction section is implemented in the presence of an acidic catalyst at a pressure of between 0.01 and 1.0 MPa and an MMH in the reaction section of between 0.05 and 25 h.sup.1, where MMH is equal to the molar flow rate of diol that feeds said section over the mole number of the catalyst in said section, a separation section that separates the effluent obtained from the reaction section into at least a diester effluent of butanediol, a water effluent, and a carboxylic acid effluent; b) a pyrolysis step that comprises a pyrolysis reactor that is fed with at least a fraction of the diester effluent of butanediol obtained from esterification step a) and with a fraction of the washing effluent obtained from step c), where said reactor is operated at a temperature of between 500 and 650 C. and said step produces a pyrolysis effluent, c) a step for separation of said pyrolysis effluent obtained from step b) such as to produce at least a liquid pyrolysis effluent, a butadiene effluent, and a washing effluent and comprising at least: a section for cooling said pyrolysis effluent to a temperature of less than 150 C. and for producing a liquid pyrolysis effluent and a steam pyrolysis effluent; a gas-liquid washing section that is fed at the top with a fraction of the diester effluent of butanediol obtained from step a) and at the bottom with the steam pyrolysis effluent and that produces a butadiene effluent at the top and a washing effluent at the bottom.

2. Method in accordance with claim 1 in which said reaction section of said step a) is also fed with a make-up of carboxylic acid.

3. Method in accordance with claim 1 in which said reaction section of said step a) is implemented in a reactive distillation column in which the butanediol feedstock is introduced into the top part of the column and the carboxylic acid is introduced into the bottom part of the column, with the ratio of the molar flow rates of butanediol and carboxylic acid being between 2 and 6.

4. Method in accordance with claim 1 in which the carboxylic acid used is selected from among formic acid, acetic acid, propanoic acid, butanoic acid, or benzoic acid.

5. Method in accordance with claim 1 in which the carboxylic acid used is acetic acid.

6. Method in accordance with claim 5 in which said separation section of said step a) is implemented by heterogeneous azeotropic distillation using a carrier.

7. Method according to claim 1 in which the partial pressure of butanediol diester in pyrolysis step b) is adjusted by adding an inert diluent such as nitrogen, carbon dioxide, methane, or acetic acid.

8. Method in accordance with claim 1 in which the pyrolysis effluent is cooled to a temperature of less than 50 C. in the cooling section of step c).

9. Method in accordance with claim 1 in which the cooling section of step c) is implemented by quenching.

10. Method in accordance with claim 9 in which said quenching is carried out inside a quenching tower in which the effluent obtained from said pyrolysis reactor is introduced at the bottom and is brought into counter-current contact with a quenching liquid that is sprayed at the top of said quenching tower.

11. Method in accordance with claim 10 in which said quenching liquid is a fraction of said liquid pyrolysis effluent produced by said quenching tower that is pre-cooled before being reintroduced into the quenching tower.

12. Method in accordance with claim 11 in which said fraction of said liquid pyrolysis effluent is cooled to below 40 C.

13. Method in accordance with claim 1 in which said liquid pyrolysis effluent is sent back to esterification step a) without intermediate purification.

14. Method in accordance with claim 1 in which said liquid pyrolysis effluent is purified before being recycled to esterification step a).

15. Method in accordance with claim 1 in which said steam pyrolysis effluent is compressed and/or cooled before being introduced into said gas-liquid washing section.

Description

DESCRIPTION OF THE FIGURES

[0046] FIG. 1 depicts a schematic view of an arrangement of the method according to the invention.

[0047] Unit a), which corresponds to step a), comprises a reaction section and a separation section, not shown in the figure. The butanediol feedstock (1), a make-up of carboxylic acid (2), and the liquid pyrolysis effluent (8) feed the reaction section of esterification step a). The separation section produces a water effluent (3), an impurity effluent (3a), a butanediol diester effluent (4) and (5), and a carboxylic acid effluent (2a). The carboxylic acid effluent (2a) obtained from the separation section feeds the reaction section of step a).

[0048] One fraction of the butanediol diester effluent (5) feeds a pyrolysis step b) that produces a pyrolysis effluent (6) that feeds a separation step c).

[0049] The separation step c) is fed with the other fraction of the butanediol diester effluent (4) that is produced by step a) and with the pyrolysis effluent (6) obtained from step b). The separation step c) produces a liquid pyrolysis effluent (8) that is recycled to the esterification step a), a butadiene effluent (7), and a washing effluent (9) that is sent back to pyrolysis step b).

[0050] FIG. 2 depicts an arrangement of step c) according to the invention. The numeric references are identical for FIGS. 1 and 2.

[0051] A pyrolysis effluent (6) is introduced at the bottom of a quenching tower (C1). This quenching tower is fed at its top with a quenching liquid (64). This quenching tower produces, on the one hand, a steam pyrolysis effluent (61) that feeds a gas-liquid washing column (C2) and, on the other hand, a liquid pyrolysis effluent (62) that may optionally be purified in a purification section (X). One fraction of the liquid pyrolysis effluent (63) is cooled before being recycled (64) to the cooling tower (C1). The other fraction of the liquid pyrolysis effluent (8) is recycled to step a) of the method.

[0052] The steam pyrolysis effluent (61) is introduced at the bottom of the gas-liquid washing column (C2), which is fed at its top with a fraction of the butanediol diester effluent (4) that is produced at step a) of the method. Said gas-liquid washing column (C2) produces at its top a butadiene effluent (7) and at its bottom a washing effluent (9) that is sent back to pyrolysis step b).

EXAMPLE

[0053] A 2,3-butanediol feedstock is esterified in the presence of acetic acid. The effluent from the esterification step is separated into a butanediol diester effluent and an acetic acid effluent. A fraction of the diester effluent of 2,3-butanediol is pyrolyzed in a pyrolysis reactor, producing a pyrolysis effluent. The pyrolysis effluent is cooled to a temperature of 75 C. and is separated into a liquid pyrolysis effluent and a steam pyrolysis effluent.

[0054] The steam pyrolysis effluent feeds a gas-liquid washing column at its bottom at a temperature of 75 C.

[0055] In Example 1 (for comparison), this column is fed at the top with the acetic acid effluent at a temperature of 45 C.

[0056] In Example 2 (according to the invention), this column is fed at its top with the diester acid effluent of 2,3-butanediol at a temperature of 45 C.

[0057] The gas-liquid washing column is operated at a pressure of 0.1 MPa and comprises three theoretical steps. The ratio of the mass flow rate of solvent (acetic acid effluent, or 2,3-butanediol diester effluent) relative to the mass flow rate of gas is 3.

[0058] The molar fraction compositions of the flows are presented in the following table:

TABLE-US-00001 Example 1 Example 2 Steam Acetic 2,3-butanediol Pyrolysis Acid Washing butadiene Diester Washing Butadiene Molar Fraction Effluent Effluent Effluent Effluent Effluent Effluent Effluent 1,3-butadiene 85.2% 0.0% 1.5% 83.2% 0.0% 6.0% 93.4% Acetic Acid 5.7% 96.6% 94.8% 8.6% 0.1% 4.2% 1.5% Incondensibles (CO, CH.sub.4, 5.2% 0.0% 0.1% 5.1% 0.0% 3.4% 1.8% CO.sub.2, H.sub.2) Intermediate Pyrolysis 0.2% 0.0% 0.1% 0.0% 0.6% 0.7% 0.0% Products C.sub.4 Hydrocarbons 1.9% 0.0% 0.1% 1.6% 0.0% 0.1% 2.1% C.sub.4+ Hydrocarbons 1.5% 0.0% 0.4% 0.5% 0.0% 0.9% 0.6% Polar Impurities 0.1% 0.0% 0.0% 0.0% 0.5% 0.5% 0.1% (MEK, acetaldehyde) Water 0.3% 3.3% 3.0% 0.9% 0.0% 0.2% 0.1% Acetic Anhydride 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 2,3-butanediol Diacetate 0.0% 0.1% 0.1% 0.0% 98.8% 84.0% 0.5%

[0059] As is evident here, the washing of the steam pyrolysis effluent with the 2,3-butanediol diester effluent makes it possible to obtain a gas that is richer in 1,3-butadiene (93.4 mol %) compared to washing with the acetic acid effluent (83.2 mol %). This is due in particular to the fact that acetic acid is a relatively volatile compound that is thus found in large amounts in the purified gas (8.6 mol %) when acetic acid is used as a washing solvent.

[0060] In order to avoid losing this acetic acid, the washing effluent in accordance with Example 1 thus has then to be washed with water, adding a unit operation. Moreover, the acetic acid that is thus recovered has to be separated from the water. This is accomplished by heterogeneous azeotropic distillation and is thus relatively expensive.

[0061] By using the 2,3-butanediol diester effluent in accordance with the invention, a butadiene effluent is thus obtained that is of higher purity and that is produced at lower cost.

[0062] In addition, compared to Example 1, it is evident that the amount of 1,3-butadiene solubilized in the washing effluent is approximately 5 times greater in Example 2, as presented.

[0063] According to the invention, the washing effluent is sent back to the pyrolysis step. Thus, the 1,3-butadiene that is solubilized in the washing effluent is not lost: it turns around between the pyrolysis step and the gas-liquid washing column.

[0064] By contrast, in the case of Example 1, where the acetic acid effluent is used to wash the steam pyrolysis effluent, the washing effluent containing the acetic acid is sent back to the esterification step. This requires a recovery device that is adapted for solubilized 1,3-butadiene because, when the esterification step is carried out in reactive distillation, which is usually the case, the latter comes out in the distillate with the water and the acetic acid and thus goes on to heterogeneous azeotropic distillation, which is designed to separate the water from the acetic acid. The method according to the invention renders such an additional operation unnecessary and thus greatly streamlines the conventional system.