WO2018114695A1

WO2018114695A1 - Method for treating an aqueous solution comprising ethanol using a dividing wall column

Info

Publication number: WO2018114695A1
Application number: PCT/EP2017/083071
Authority: WO
Inventors: Beatrice Fischer; Rejane Dastillung
Original assignee: IFP Energies Nouvelles; Compagnie Generale Des Etablissements Michelin
Priority date: 2016-12-21
Filing date: 2017-12-15
Publication date: 2018-06-28
Also published as: FR3060559A1

Abstract

The invention relates to a method using a dividing wall column in order to separate a feed comprising ethanol, acetaldehyde, butadiene and water, in particular in the context of the Lebedev method.

Description

PROCESS FOR TREATING AN AQUEOUS SOLUTION COMPRISING ETHANOL

USING A CLOSURE COLUMN

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 referred to as the Lebedev process, has a limited pass conversion rate. This process is described in numerous publications, among which mention may be made of 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, Lebedev process is therefore called a process for converting ethanol to 1,3-butadiene, comprising at least one reaction step, and an effluent treatment step.

The catalyst making it possible to produce 1,3-butadiene generates very numerous by-products in small quantities:

Hydrocarbons comprising 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, or even aromatic. Some of these by-products are generated in significant amounts, such as diethyl ether or ethyl acetate.

Moreover, the conversion reaction of ethanol or of an ethanol / acetaldehyde mixture to 1,3-butadiene produces water (approximately 2 moles of water per mole of 1,3-butadiene), which must be eliminated from the process. The reagent (s) not consumed (s) must therefore pass several times in a sequence of unit separation operation and in the reactor (s) before being converted into 1,3-butadiene. Each loss in unit operations results in an overall loss within the process that quickly becomes unacceptable from an economic point of view. It is not easy to remove liquid byproducts from unconverted ethanol and acetaldehyde before recycling them to the catalytic reactor producing 1,3-butadiene. In particular, a significant portion (about 70% by weight) of liquid by-products have an intermediate volatility between that of ethanol and acetaldehyde. A fraction of these liquid by-products of intermediate volatility between that of ethanol and acetaldehyde can be removed by simple distillation, but with a loss of ethanol and acetaldehyde which makes the process unattractive from an economic point of view. .

Other by-products are generated in minute quantities. These thousands of hydrocarbon and oxygen compounds produced in the reaction sections are called "brown oils". These "brown oils" have the distinction of being soluble in ethanol, but insoluble in water. Although present in small quantities, they foul and clog the equipment wherever it is not diluted in a large quantity of ethanol.

Ethanol and acetaldehyde react together to form diethyl acetal and water. The diethyl acetal formation reaction is balanced: the reaction to the diethyl acetal is favored by a low temperature, and the reverse reaction by a high temperature. The kinetics is 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 diethyl acetal therefore occurs partly within the unitary separation operations that are implemented to purify and recycle ethanol and acetaldehyde. Depending on the sequence of unit operations that is implemented, this diethyl acetal can be removed with the by-products, which then represents an indirect loss of ethanol and acetaldehyde, decreasing the economic interest of the process.

It can be seen that the recycling of ethanol and acetaldehyde is particularly important for the viability of the process. The process is also a major consumer of water for the different washing steps. For the reasons mentioned above, it is essential that recycled water, ethanol and acetaldehyde streams be as poor 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 unconverted ethanol and acetaldehyde , the water produced by the reaction and introduced into the process for purifying the gaseous effluents, as well as the numerous liquid by-products, is treated by a series of three distillation columns. Lateral racking followed by washing and partial recycling were provided, 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 that can be 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 brown oils that may have escaped the previous separations. These traces of brown oils are troublesome for the use of water in the different washing units and / or separation: it can cause fouling and possibly clogging. Acetic acid is present in a significant amount and can increase the production of diethyl acetal from ethanol and acetaldehyde, which causes an increased risk of loss of ethanol and acetaldehyde in some separations. The water withdrawn at the bottom of the section could be treated before recycling, but the biological treatments, particularly adapted, 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 that can be recycled without generating the problems mentioned above.

OBJECT AND INTEREST OF THE INVENTION

The invention relates to a method 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 of using a partition column fed at least by said aqueous solution, said partition partitioning the bottom two-thirds of the column into two compartments, the compartment in which the supply is made being called input compartment, the second compartment being called the lower compartment, the upper part of the column comprising no partition being called the head compartment, said input 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. The invention also relates to a Lebedev process comprising a step of treating an aqueous solution comprising ethanol, acetic acid and brown oils to produce at least one effluent rich in ethanol, a water-rich effluent and a effluent dirty water, consisting of using a partition column fed at least by said aqueous solution, said partition partitioning the lower two-thirds of the column into two compartments, the compartment in which the supply is made being called input compartment, the second compartment being called the lower compartment, the upper part of the column comprising no partition being called the head compartment, said input 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 trays, said effluents rich in ethanol, and rich in water being respectively recycled to the reaction and washing steps of said Lebedev process, said dirty water effluent being removed from said process.

In the process according to the invention, butanol and ethyl acetate fed 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 conversion reactions of ethanol and acetaldehyde to diethyl acetal, and includes such low levels of brown oils that they will not increase the fouling problems.

The partition walls (dividing wall column according to the English name) are described in many patents such as US Patent 5,914,012.

DETAILED DESCRIPTION OF THE INVENTION Said bulkhead is fed at least with, preferentially only with an aqueous solution comprising ethanol, acetic acid and brown oils, and produces at least, preferably only, an effluent rich in water. 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 feeding 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, 0 to 0.5% butanol and 0 to 0.1%, preferably 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 effluent rich in water can supply the different stages of the Lebedev process where water is necessary without causing the defects present in the prior art. By implementing the process according to the invention, said water-rich effluent 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 walled column. Said bulkhead comprises a partition dividing the two lower thirds of the column into two compartments. The compartment in which the supply of said column is made is called the entrance compartment, the second compartment being called the lower compartment. The upper part of the column does not include a partition is called head compartment. A dispenser tray, a device known to those skilled in the art, distributes the liquid from the head compartment between the inlet and bottom compartments. Advantageously, between 25 and 60 mol% of the liquid from the head compartment is directed to the inlet compartment, preferably between 35 and 55% and very preferably between 35 and 45%, the residual fraction feeding the lower compartment. The input 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 input compartment comprises 14 theoretical stages, said mixture is fed between the plates 1 and 7, the trays being numbered in the direction of flow of the liquid.

Water and acetic acid, less volatile, move towards the bottom of the column, while azeotrope butanol / water and ethanol / water head towards the head.

The inlet and bottom compartments each have their reboiler. The reboiler of the inlet compartment makes it possible to totally eliminate the 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 effluent dirty water being subsequently advantageously treated in a wastewater reprocessing process.

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

Only the liquid coming from the head compartment, which is thus rid of most of the acetic acid and "brown oils", is lowered into the lower compartment. The reboiler of the bottom of the lower compartment makes it possible to eliminate all traces of ethanol. Thus, the effluent rich in water produced at the bottom of the lower compartment contains little acetic acid (at most 0.2 mol%), and no other impurity other than in the form of traces, that is to say less than 0.1% by weight, advantageously less than 0.01% by weight.

Said partition column is advantageously operated at a pressure of 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-turn 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 respectively sent to the reboilers of the inlet compartment and the lower compartment, these fractions then being condensed completely. These fractions, separately or in a mixture, then preheat the feed of said walled column and are then expanded to a pressure of 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 totally vaporized by heat exchange with the steam withdrawn at the top of said wall column in the condenser of said column before to be compressed again, thus closing the circulation loop of the refrigerant.

The low acetic acid content in the effluent rich in water makes it possible to limit the formation of diethyl acetal, favored by the presence of acetic acid, in the stages where this effluent is recycled. In addition, the process according to the invention makes it possible to rid the water-rich effluent of any brown oil residues that have not been separated beforehand.

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

DESCRIPTION OF THE FIGURES FIG. 1 shows a schematic view of the partition column of the method according to the invention.

An aqueous solution (70) is fed into the inlet compartment of the bulkhead column (710). The partition (71 1) 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 allows to completely eliminate the ethanol at the bottom of the column. From this compartment is drawn off, via the pump (722), the effluent dirty water (72), loaded with acetic acid and "brown oils" escaped washing.

In the head compartment of the column, above the partition (71 1), the vapors from the inlet and bottom compartments are mixed and brought into contact with the liquid of the last plate of this section. The overhead vapor of this section (712) is condensed completely in the condenser (713), and then this cooled effluent (714) is fed into the reflux tank (715). The condensed liquid (716) is sent partially 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), is withdrawn via the pump (723) a water-rich effluent (725) which is recycled to the rest of the process.

FIG. 2 represents a variant according to the invention of the 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 implemented 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 outlet temperature of the compressor is 123 ° C. The compressed fluid is separated into two fractions (7101) and (7102) respectively sent to the heat exchangers (720) and (721) for reboiling the two compartments of the column, and is completely condensed in these exchangers at a temperature of 1 18 ° 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 1 1% mole . 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 , partially vaporizing and cooling to 75 ° C. At the outlet of the exchanger (721), the fluid (71 13) is sent to the heat exchanger (71 14), which will preheat the residual fraction of the charge of the column and vaporize it to about 1 1% mole. The mixture cooled to 98 ° C will be sent to the heat exchanger (71 16), where it is cooled to 95.5 ° C, then sent to the valve (71 18), or it is expanded to 1, 1 MPa, partially vaporizing and cooling to 75 ° C. The output of the valves (7108) and (71 18) is mixed and sent to the heat exchanger (713) which is the overhead 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 incorporating thermodynamic data calibrated on experimental points (binary liquid-vapor equilibrium data and liquid-liquid partition coefficient). Example 1 (compliant)

A partition column whose inlet and bottom compartments both comprise 15 stages and the head compartment comprises 5 stages is fed tray 6 of the inlet compartment by 5950 kmol / h of an aqueous solution of molar composition:

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

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

The method using a bulkhead column according to the invention makes it possible to obtain a water-rich effluent containing only a few traces of brown oils and less than 0.2 mol% of acetic acid, which could be used in the various stages. of a Lebedev process without the risk of aggravating fouling problems, nor of promoting diethylacetal production reactions. Example 2 (comparative)

A distillation column comprising 35 theoretical plates is fed to the theoretical plate 11 (the numbering of the trays of the head towards the bottom of the column) with an aqueous solution having the same composition as that of Example 1 (see Table 1). ) and at the same flow rate (5950 kmol / h). This column produces a water-rich effluent, of brown color, and an effluent rich in ethanol, respectively having the following compositions:

The process using a conventional distillation column produces only two effluents: a water-rich effluent, of brown color, and an effluent rich in ethanol. It does not make it possible to obtain an effluent rich in "clean" water. If the water-rich effluent produced is recycled in the different stages of a Lebedev process, there is a high risk of fouling.

Claims

A method of 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 of using a partition column fed at least by said aqueous solution, said partition partitioning the bottom two-thirds of the column into two compartments, the compartment in which the supply is made being called the inlet compartment, the second compartment being called lower compartment , the upper part of the column comprising no partition being called the head compartment, said input 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 plateaus. The method of claim 1 wherein said bulkhead is fed solely by said aqueous solution. The process according to one of the preceding claims wherein said bulkhead column produces only an ethanol rich effluent, a water rich effluent and a dirty water effluent. Process according to one of the preceding claims, in which the said aqueous solution feeding the partition column comprises 25 to 40% of ethanol, 0 to 1% of acetic acid, 0 to 0.4% of acetate of ethyl, from 0 to 0.5% butanol and from 0 to 0.1% of brown oils, all percentages being expressed as molar percentages. A process as claimed in any one of the preceding claims wherein between 25 and 60 mol% of the liquid from the head compartment is directed to the inlet compartment. Method according to one of the preceding claims wherein said input compartment comprises between 12 and 20 theoretical plates. Method according to one of the preceding claims wherein said head compartment comprises between 4 and 6 theoretical plates. Method according to one of the preceding claims wherein said partition column comprises a heat pump comprising a round-turn of refrigerant between the condenser and the reboilers of said column. Process according to the preceding claim wherein said refrigerant is a mixture of hydrocarbons. 0. Process according to the preceding claim wherein said refrigerant is a mixture of hydrocarbons comprising from 3 to 5 carbon atoms.

1. A Lebedev process comprising a step of 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, using a partition column fed at least by said aqueous solution, said partition partitioning the bottom two-thirds of the column into two compartments, the compartment in which the supply is made being called the inlet compartment, the second compartment being called lower compartment , the upper part of the column comprising no partition being called the head compartment, said input 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, said effluents rich in ethanol, and rich in water being respectively recycled to the reaction and washing steps of said Lebedev process, said dirty water effluent being removed from said process.