FR3060559A1 - PROCESS FOR TREATING AN AQUEOUS SOLUTION COMPRISING ETHANOL USING A COLUMN - Google Patents

Abstract

The invention relates to a method using a bulkhead column for separating a feedstock comprising ethanol, acetaldehyde, butadiene and water, particularly in the context of the Lebedev process.

Description

Holder (s): IFP ENERGIES NOUVELLES Public establishment, COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN Limited partnership with shares, MICHELIN RECHERCHE ET TECHNIQUE S.A. Société anonyme.

Agent (s): IFP ENERGIES NOUVELLES.

PROCESS FOR TREATING AN AQUEOUS SOLUTION COMPRISING ETHANOL USING A PARTITION COLUMN.

The invention relates to a process using a bulkhead column to separate a feed comprising ethanol, acetaldehyde, butadiene and water, in particular in the context of the Lebedev process.

FR 3 060 559 - A1

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for treating an aqueous solution comprising ethanol, acetic acid and brown oils using a bulkhead column.

PRIOR ART

The process for producing 1,3-butadiene from ethanol, generally known as the "Lebedev process", has a limited pass conversion rate. This process is described in numerous publications, including the book “Synthetic rubber”, chapter 4 (W.J. Toussaint and J. Lee Marah), or more recently the document FR 3 026 100.

In the rest of the text, the Lebedev process is therefore called a process for converting ethanol into 1,3-butadiene, comprising at least one reaction step, and one step for treating effluents.

The catalyst used to produce 1,3-butadiene generates numerous by-products in small quantities:

• hydrocarbons comprising from 1 to 16 carbon atoms, saturated or unsaturated, or even aromatic, • oxygenated products (such as alcohols, phenols, aldehydes, ketones, acids, esters, ethers, acetals, ...), saturated or unsaturated, even aromatic.

Some of these by-products are generated in significant quantities, in particular diethyl ether or ethyl acetate.

Furthermore, the reaction for converting ethanol or an ethanol / acetaldehyde mixture to 1,3butadiene produces water (approximately 2 moles of water per mole of 1,3-butadiene), which must be eliminated from the process.

The unconsumed reagent (s) must therefore pass several times in a sequence of unitary separation operations as well as in the reactor (s) before being converted into 1,3butadiene. Each loss in unit operations results in an overall loss within the process which quickly becomes unacceptable from an economic point of view.

It is not easy to remove the liquid byproducts of unconverted ethanol and acetaldehyde before recycling them to the catalytic reactor producing 1,3-butadiene. In particular, a large proportion (around 70% by weight) of liquid by-products have an intermediate volatility between that of ethanol and acetaldehyde. A fraction of these liquid by-products with intermediate volatility between that of ethanol and acetaldehyde can be eliminated by simple distillation, but with a loss in ethanol and acetaldehyde which makes the process unattractive from an economic point of view. .

Other byproducts are generated in minute quantities. These thousands of hydrocarbon and oxygenated compounds produced in the reaction sections are called "brown oils". These "brown oils" have the particularity of being soluble in ethanol, but insoluble in water. Although present in small quantities, they foul and clog equipment wherever they are not diluted in a large amount of ethanol.

Ethanol and acetaldehyde react together to form diethylacetal and water. The reaction for the formation of diethylacetal is balanced: the reaction towards diethylacetal is favored by a low temperature, and the reverse reaction by a high temperature. The kinetics are obviously favored by a high temperature, but also by the presence of acid, in particular acetic acid which is one of the impurities produced in the second reactor. The production of diethylacetal therefore occurs partly within unitary separation operations which are used to purify and recycle ethanol and acetaldehyde. According to the sequence of unit operations which is implemented, this diethylacetal can be eliminated with the by-products, which then represents an indirect loss in ethanol and acetaldehyde, reducing the economic advantage of the process.

It can therefore be seen that the recycling of ethanol and acetaldehyde is particularly important for the viability of the process. The process also consumes a lot of water for the different washing stages. For the reasons mentioned above, it is essential that the flows of recycled water, ethanol and acetaldehyde are as low as possible in acetic acid and brown oils.

In the CARBIDE process for the production of 1,3-butadiene in two stages, presented in the book "Synthetic rubber", chapter 4 (WJ Toussaint and J. Lee Marah), a liquid effluent containing ethanol and acetaldehyde not converted , the water produced by the reaction and introduced into the process to purify the gaseous effluents, as well as the numerous liquid by-products, is treated by a sequence of three columns to be distilled. Lateral racking, followed by partial washing and recycling were planned, and even under these conditions, the operation was often interrupted to wash the unit before restarting.

The water / ethanol distillation sections of the processes of the prior art make it possible to obtain an ethanol effluent capable of being recycled, but the water drawn off at the bottom of the section comprises all the acetic acid produced by the reaction, thus the traces of oils that may have escaped previous separations. These traces of brown oils are troublesome for the use of water in the different washing and / or separation units: they can cause fouling and possibly clogging. Acetic acid is present in significant quantities and can increase the production of diethylacetal from ethanol and acetaldehyde, which poses an increased risk of loss of ethanol and acetaldehyde in certain separations. The water drawn off at the bottom of the section could be treated before recycling, but the biological treatments, which are particularly suitable, are heavy and expensive.

The object of this patent is to overcome these drawbacks by treating an aqueous solution comprising ethanol, acetic acid and brown oils so as to produce an ethanol effluent and a water effluent capable of being recycled without generating the problems discussed above.

OBJECT AND INTEREST OF THE INVENTION

The invention relates to a process for treating an aqueous solution comprising ethanol, acetic acid and brown oils to produce at least one ethanol-rich effluent, a water-rich effluent and a dirty water effluent, comprising a step consisting in using a partition column supplied at least with said aqueous solution, said partition partitioning the lower two-thirds of the column into two compartments, the compartment in which the feeding is carried out being called inlet compartment, the second compartment being called lower compartment, the upper part of the column not comprising a partition being called head compartment, said inlet compartment comprising between 8 and 25 theoretical plates, said lower compartment comprising between 8 and 25 theoretical plates, said head compartment comprising from 3 to 10 theoretical platforms.

The invention also relates to a Lebedev method comprising a step of treating an aqueous solution comprising ethanol, acetic acid and brown oils to produce at least one effluent rich in ethanol, an effluent rich in water and a dirty water effluent, consisting in using a partition column supplied at least with said aqueous solution, said partition partitioning the lower two thirds of the column into two compartments, the compartment in which the supply is carried out being called inlet compartment, the second compartment being called lower compartment, the upper part of the column comprising no partition being called head compartment, said inlet compartment comprising between 8 and 25 theoretical plates, said lower compartment comprising between 8 and 25 theoretical plates, said compartment head comprising from 3 to 10 theoretical plates, said effluents rich in ethanol, and rich in water being recycled respectively to the reaction and washing stages of said Lebedev process, said effluent dirty water being removed from said process.

In the process according to the invention, the butanol and ethyl acetate supplied with said aqueous solution are drawn off in said effluent rich in ethanol. Thus, they are advantageously recycled with ethanol in the reaction stages of a Lebedev process where they can react again, limiting the overall losses of the process.

Another advantage of the invention is that said effluent rich in water can supply the various stages of the Lebedev process where water is necessary without causing the defects present in the prior art, because it contains very little acetic acid, which promotes the conversion reactions of ethanol and acetaldehyde to diethyl acetal, and includes such low contents of brown oils that they will not increase the problems of fouling.

Dividing wall columns are described in many patents such as US patent 5,914,012.

DETAILED DESCRIPTION OF THE INVENTION

Said partition column is supplied at least with, preferably only with an aqueous solution comprising ethanol, acetic acid and brown oils, and produces at least, preferably only, an effluent rich in ethanol, an effluent rich in water and an effluent dirty water.

Said effluents rich in water and dirty water are produced at the bottom of said column, and said effluent rich in ethanol is produced at the top.

Said aqueous solution supplying the partition column advantageously comprises from 25 to 40% of ethanol, from 0 to 1%, advantageously from 0.1 to 1% of acetic acid, from 0 to 0.4% of acetate. ethyl, from 0 to 0.5% butanol and from 0 to 0.1%, advantageously from 0.01 to 0.1% of brown oils. Said aqueous solution advantageously comprises from 0 to 0.5% of butanol, advantageously from 0.1 to 0.5%. All percentages are expressed as molar percentages.

Said water-rich effluent can supply the various stages of the Lebedev process where water is required without causing the faults present in the prior art. By implementing the process according to the invention, said effluent rich in water comprises more than 99.8 mol% of water, at most 0.2 mol% of acetic acid and at most 100 ppm of brown oils.

Said dirty water effluent comprises at least 95% of the brown oils and at least 90% of the acetic acid fed into said wall column.

Said partition column comprises a partition partitioning the lower two-thirds of the column into two compartments. The compartment in which the feeding of said column is carried out is called the inlet compartment, the second compartment being called the lower compartment. The top of the column with no bulkhead is called the head compartment.

A distributor plate, a device known to those skilled in the art, allows the liquid from the head compartment to be distributed between the inlet and lower compartments. Advantageously, between 25 and 60 mol% of the liquid coming from the head compartment is directed towards the inlet compartment, preferably between 35 and 55% and very preferably between 35 and 45%, the residual fraction feeding the lower compartment.

The entry compartment comprises between 8 and 25 theoretical plates, advantageously between 12 and 20. The lower compartment comprises between 8 and 25 theoretical plates, advantageously between 12 and 20.

Said aqueous solution is fed to a tray located in the upper half of said inlet compartment. Thus, if for example the entry compartment comprises 14 theoretical stages, said mixture is supplied between the trays 1 and 7, the trays being numbered in the direction of flow of the liquid.

Water and acetic acid, which are less volatile, go to the bottom of the column, while the azeotropes butanol / water and ethanol / water go to the head.

The entry and lower compartments each have their reboiler.

The inlet compartment reboiler completely eliminates ethanol at the bottom of the column. From the bottom of this compartment is extracted the dirty water effluent, loaded with acetic acid and "brown oils", said dirty water effluent being subsequently advantageously treated in a process for reprocessing waste water.

The head compartment comprises from 3 to 10 theoretical plates, advantageously from 4 to 6. This compartment receives the gas phases coming from the inlet and lower compartments, which are mixed and brought into contact with the liquid in the tray of the head compartment located immediately above the partition.

Only the liquid from the head compartment descends into the lower compartment, which is therefore freed from most of the acetic acid and "brown oils". The reboiler at the bottom of the lower compartment eliminates all traces of ethanol. Thus, the water-rich effluent produced at the bottom of the lower compartment contains little acetic acid (at most 0.2 mol%), and no other impurity other than in trace amounts, that is to say say present at less than 0.1% by weight, advantageously at less than 0.01% by weight.

Said partition column is advantageously operated at a pressure between 0.1 and 0.5 MPa, preferably between 0.1 and 0.3 MPa. The temperatures at the top and bottom of said column are determined by the vaporization temperatures of the fluids circulating in said column. The temperature at the bottom of said column is thus advantageously between 90 and 150 ° C., preferably between 100 and 130 ° C. The temperature at the top of said column is advantageously between 50 and 150 ° C., preferably between 60 and 110 ° C.

In a particular arrangement, said partition column comprises a heat pump comprising a round-trip operation of refrigerant between the condenser and the reboilers of said column.

Said refrigerant, advantageously a mixture of hydrocarbons, very advantageously a mixture of hydrocarbons comprising from 3 to 5 carbon atoms, and very preferably an equimolar mixture n-butane / isobutane, is compressed to a pressure between 2 and 3 MPa, advantageously between 2.3 and 2.8 MPa. The compressed fluid is separated into two fractions sent respectively to the reboilers of the inlet compartment and the lower compartment, these fractions then being completely condensed. These fractions, separately or as a mixture, then preheat the feed to said wall column and are then expanded to a pressure between 0.5 and 1.5 MPa, advantageously between 0.8 and 1.4 MPa. If this has not been done after exchange in the reboilers, the two fractions are then mixed, the mixture being completely vaporized by heat exchange with the vapor drawn off at the head of said wall column in the condenser of said column before be compressed again, thereby closing the refrigerant circulation loop.

The low acetic acid content in the water-rich effluent makes it possible to limit the formation of diethylacetal, favored by the presence of acetic acid, in the stages where this effluent is recycled. In addition, the method according to the invention makes it possible to rid the effluent rich in water of any residues of brown oils which have not been previously separated.

Said effluents rich in ethanol and rich in water can then be recycled, in particular to the stages of a Lebedev process.

DESCRIPTION OF THE FIGURES

Figure 1 shows a schematic view of the bulkhead column of the method according to the invention.

An aqueous solution (70) is supplied to the inlet compartment of the bulkhead column (710). The partition wall (711) goes to the bottom of the column, but not to the head.

The bottom of the inlet compartment is reboiled by the reboiler (720), which makes it possible to completely eliminate the ethanol at the bottom of the column. From this compartment is withdrawn, via the pump (722), the effluent dirty water (72), charged with acetic acid and "brown oils" escaped from washing.

In the head compartment of the column, above the partition (711), the vapors from the inlet and lower compartments are mixed and brought into contact with the liquid of the last tray of this section. The overhead vapor from this section (712) is completely condensed in the condenser (713), then this cooled effluent (714) is fed into the reflux tank (715). The condensed liquid (716) is partly sent to the pump (717) to serve as reflux (718), the ethanol-rich effluent (724) being recycled by the pump (719) to the rest of the process.

At the bottom of the lower compartment, reboiled by the exchanger (721), a water-rich effluent (725) is withdrawn via the pump (723) which is recycled to the rest of the process.

FIG. 2 represents a variant according to the invention of thermal integration around the partition column of the method according to the invention.

The numbering is identical to that of figure 1. Only the additional elements are described here. They constitute the heat pump used in this variant of the method according to the invention.

The refrigerant is compressed by the compressor 7100 to a pressure of 2.5 Mpa. The temperature at the outlet of the compressor is 123 ° C. The compressed fluid is separated into two fractions (7101) and (7102) sent respectively to the heat exchangers (720) and (721) making it possible to reboil the two compartments of the column, and is completely condensed in these exchangers at a temperature of 118 ° C. At the outlet of the exchanger (720), the fluid (7103) is sent to the heat exchanger (7104), which will preheat a fraction of the charge of the column and vaporize it to about 11% mol . The mixture cooled to 98 ° C is sent to the heat exchanger (7106), where it is cooled to 95.5 ° C, then sent to the valve (7108), or it is expanded to 1.1 MPa , by partially vaporizing and cooling to 75 ° C.

At the outlet of the exchanger (721), the fluid (7113) is sent to the heat exchanger (7114), which will preheat the residual fraction of the charge of the column and vaporize it to approximately 11% mol . The mixture cooled to 98 ° C will be sent to the heat exchanger (7116), where it is cooled to 95.5 ° C, then sent to the valve (7118), cu it is expanded to 1.1 MPa, by partially vaporizing and cooling to 75 ° C.

The output of the valves (7108) and (7118) is mixed and sent to the heat exchanger (713) which is the column head condenser. The vaporized and slightly overheated mixture (7120) is sent to the compressor (7100) at a temperature of 81 ° C.

EXAMPLES

The following examples are based on process simulations integrating thermodynamic data calibrated on experimental points (binary liquid-vapor equilibrium data and liquid-liquid partition coefficient).

A partition column, the inlet and bottom compartments of which both comprise 15 stages and the head compartment of which comprises 5 stages, is supplied to tray 6 of the inlet compartment with 5950 kmol / h of an aqueous solution of molar composition:

Ethanol 31.95% Water 67.25% Ethyl acetate 0.17% Butanol 0.25% Acetic acid 0.36% Brown oils 0.02%

The numbering of the plates is done in the direction of flow of the liquid.

This column produces an effluent rich in water, an effluent dirty water and an effluent rich in ethanol having the following compositions respectively:

Water effluent Dirty water effluent Ethanol effluent Ethanol 63.01% Water 99.84% 99.08% 36.12% Ethyl acetate 0.34% Butanol 0.49% Acetic acid 0.16% 0.87% 0.04% Brown oils 0.000001% 0.05% 0.00% Total (kmol / h) 733 2200 3017

The process using a partition column according to the invention makes it possible to obtain an effluent rich in water 20 containing only a few traces of brown oils and less than 0.2 mol% of acetic acid, which can be used in the various stages of a Lebedev process without risk of accentuating the problems of fouling, nor of favoring the reactions of production of diethylacetal.

Claims (7)

1. Process for treating an aqueous solution comprising ethanol, acetic acid and brown oils to produce at least one effluent rich in ethanol, an effluent rich in water 5 and a dirty water effluent, comprising a step consisting in using a partition column supplied at least with said aqueous solution, said partition partitioning the lower two-thirds of the column into two compartments, the compartment in which the supply is carried out being called entry compartment, the second compartment being called lower compartment, the upper part of the column not comprising a partition being 10 called the head compartment, said entry compartment comprising between 8 and 25 theoretical plates, said lower compartment comprising between 8 and 25 theoretical plates, said head compartment comprising from 3 to 10 theoretical plates. 2. Method according to claim 1 wherein said partition column is supplied only 15 by said aqueous solution. 3. Method according to one of the preceding claims wherein said partition column produces only an ethanol-rich effluent, a water-rich effluent and a dirty water effluent. 20 4. Method according to one of the preceding claims, in which said aqueous solution feeding the partition column comprises from 25 to 40% of ethanol, from 0 to 1% of acetic acid, from 0 to 0.4% of acetate ethyl, 0 to 0.5% butanol and 0 to 0.1% brown oils, all the percentages being expressed in molar percentages. 5. Method according to one of the preceding claims, in which between 25 and 60 mol% of the liquid from the head compartment is directed towards the inlet compartment. 6. Method according to one of the preceding claims wherein said inlet compartment comprises between 12 and 20 theoretical plates. 7. Method according to one of the preceding claims wherein said head compartment comprises between 4 and 6 theoretical plates. 8. Method according to one of the preceding claims, in which said partition column 35 comprises a heat pump comprising a round-trip of refrigerant between the condenser and the reboilers of said column. 9. Method according to the preceding claim wherein said refrigerant is a mixture of hydrocarbons. 10. Method according to the preceding claim wherein said refrigerant is a mixture 5 of hydrocarbons comprising from 3 to 5 carbon atoms. 11. Lebedev method comprising a step of treatment of an aqueous solution comprising ethanol, acetic acid and brown oils to produce at least one effluent rich in ethanol, an effluent rich in water and an effluent in dirty water, consisting of using a column to 10 partition supplied at least with said aqueous solution, said partition partitioning the lower two thirds of the column into two compartments, the compartment in which the feeding is carried out being called the inlet compartment, the second compartment being called the lower compartment, the part upper column without partition being called head compartment, said inlet compartment comprising between 8 and 25 trays 15 theoretical, said lower compartment comprising between 8 and 25 theoretical plates, said head compartment comprising from 3 to 10 theoretical plates, said effluents rich in ethanol and rich in water being recycled respectively to the reaction and washing stages of said Lebedev process, said dirty water effluent being eliminated from said process.