CZ287604B6 - Non-catalytic recovery process of light valuable products that are contained in leavings originating from acrylic acid preparation process and from said acid ester preparation - Google Patents

Abstract

Recovery of noble light prods. (I) (i.e. acrylic acid monomer, acrylic ester monomer and 1-8C alcohol contained in distillation residues obtd. during the manufacture of acrylic acid or 1-8C acrylic acid ester (II), by thermal cracking of the residues. The process is characterised in that: (a) cracking is carried out, in the absence of a catalyst, on heavy distillation residues from the manufacture of acrylic acid on the one hand and on heavy distillation residues from the manufacture of acrylic acid ester on the other hand, (b) the light fraction from the dissociation reactions is continually vaporised during cracking, and (c) the light fraction is distilled so as to recover (I) after condensation.

Description

Process for the non-catalytic recovery of light valuable products contained in the distillation residues resulting from the acrylic acid production process and the esters of this acid

Technical field

The invention relates to a process for the non-catalytic recovery of light valuable products (or light products) contained in distillation residues resulting from the process of producing acrylic acid and the production of esters of such acrylic acid with alcohols containing 1 to 8 carbon atoms by thermal dissociation residues. By these light valuable products is meant acrylic acid monomer, acrylic acid ester monomer and the alcohols mentioned.

BACKGROUND OF THE INVENTION

The acrylic acid synthesis process, for example using catalytic oxidation of propylene, produces heavy by-products which are removed at the bottom of the terminal distillation column or distillation columns. These mixtures of heavy compounds mainly contain derivatives of the general formula

X - (CH ₂ CH _{2 -} C - O) _{n -} H

O in which n is greater than or equal to 1, which are formed by the condensation reactions occurring on the double bond of acrylic acid:

- with acrylic acid alone:

Xje

CH = CH ² C ² o

- with acetic acid:

Xje

O

- or with water:

Xje

HIM-.

Similarly, in the process for the synthesis of acrylic esters, the heavy products resulting from this process, which are removed from the bottom of the distillation column or columns, contain the corresponding esters of the compounds with the alcohol used in the process for producing said esters, as well as the condensation products of these alcohols (X is RO-, wherein R is an alkyl group containing 1 to 8 carbon atoms), and this condensation also occurs at the double bond of said compounds.

-1 CZ 287604 B6

In addition, a certain proportion of the polymerization inhibitors used in these polymerization processes are also present in these heavy product mixtures.

These heavy product mixtures can be vaporized to give a major proportion of the monomers (i.e., acrylic acid monomer and acrylic acid ester monomers) contained in the heavy products. If there is no suitable process for recovering these products, then the substances are lost because they have to be disposed of in some way and, since the proportion of these products is large, difficult to dispose of, and, in addition, monomers and alcohols are lost. .

The liquid phase regeneration process of these monomers by thermal dissociation of these derivatives as the products of the double bond acrylic acid is well described in the prior art publications.

The main problem associated with the thermal dissociation process of this type, which is applied to said mixture of heavy products obtained at the bottom of the terminal or end columns for the distillation of acrylic acid, is the high viscosity of the residual product, which viscosity is gradually so high This product can no longer be conveyed by pipeline. This excess viscosity is accompanied by the insolubility of tar deposits causing fouling of the crack reactor walls, and as a result of these deposits, the heat exchange efficiency passing through the walls of the reactor decreases and ultimately reduces the cracking yield. This phenomenon associated with the clogging of the walls makes it necessary to carry out cleaning operations at regular intervals, which means that the process in this way prevents the process from being carried out in a continuous manner and, furthermore, in this intermittent mode of operation the efficiency of the entire process is reduced.

The viscosity of these residual products obtained as a result of the cracking process increases with increasing retention time of this mixture of heavy products to be processed at high temperatures and with increasing amounts of light monomers separated by distillation. If the viscosity of the residual product, i.e. viscosity, which corresponds to the normal transport conditions for the liquid stream and in addition to reducing wall fouling, is to be achieved, these two parameters must necessarily be limited, which has the effect of reducing cracking yield.

These disadvantages can be reduced if the process described in French patent FR-B2 194 681 is applied to the process of recovering valuable products contained in heavy end products originating from the production of acrylic acid esters.

These processes, which are described in connection with the recovery of valuable products contained in heavy products derived from acrylic acid production, are essentially catalytic processes. The catalysts may be catalysts of various kinds, such as carboxylates, phosphates, borates (see French patent FR-A-2,261,252), acids such as sulfuric acid H2SO4 (see Japanese patent JP-05 025086), alumina or alumina or silica (see Japanese patent JP-75 69014), secondary and tertiary amines or phosphines (see French patent FR-1 572 316), solid acids such as zeolites (see Japanese patent JP-03 178 949), Friedel catalysts Crafts type (see U.S. Patent No. 2,806,878) and alkoxide titanates (see Japanese Patent JP-06 0655149).

In addition to the fact that the above processes do not solve the problem of limiting the recovery yield due to excessive viscosity of these residual products and the formation of undesirable

Other disadvantages of these processes are related to the use of catalysts, in particular the following disadvantages:

- cost of catalyst used,

- occurrence of corrosion,

- difficulties in disposing of the following substances contained in these heavy residual products, resulting in high costs for the disposal of waste products:

- inorganic waste materials which are difficult to burn,

- the presence of metal residues causing fouling of the furnaces,

- the removal of aqueous washings which cause an increase in the level of pollution when these washes are discharged into waste water,

problems related to the deactivation of solid catalysts due to fouling of the active catalyst pores in the form of partially polymerized compounds.

In an attempt to alleviate these disadvantages, U.S. Patent 3,086,046 describes a non-catalytic process for treating these residual products by evaporating a cracking mixture followed by thermal dissociation in a vapor phase at a very high temperature (at a temperature ranging from 350 [deg.] C. to 650 [deg.] C.) and at a pressure ranging from 670 Pa to 20 kPa. This process is suitable for processing mixtures that are very rich in low molecular weight products (such as acrylic acid and acrylic dimer), but cannot be used in the case of truly heavy bottoms resulting, for example, from the acrylic acid production process. of propylene and oxygen. The fraction of this mixture, which is evaporated in the first stage, is reduced in this case by a small amount of products with substantially lower boiling points, or increasing the proportion requires reaching the evaporation temperature, which is difficult and this problem again limits the process.

The process for extracting acrylic acid contained in a reaction mixture resulting from thermal dissociation using water is described in several patents, for example, in French patent FR-A2 415 092, Japanese patent JP-57 062 229, in which a basic aqueous solution is used, and Japanese Patent JP-56 147 745, which describes a process in which water is added to the mixture, followed by extraction with an organic solvent. The main disadvantage of these processes is that the regenerated monomer or regenerated monomers are not removed (or not removed) from this mixture immediately as they are formed during the thermal dissociation reaction process. As a result, immediate recombination (reverse reaction) due to the addition of polymerization derivatives cannot be avoided, starting with the dissociated products present in the mixture.

Another way to reduce the problem of excessive viscosity of heavy residual products obtained by thermal cracking of heavy end products from acrylic acid production is through the use of solvents. However, the disadvantage of this method is that in this case it is necessary to use expensive devices for recovering the solvents used.

SUMMARY OF THE INVENTION

According to the present invention, it has surprisingly been found that when thermal dissociation or cracking of heavy products (or heavy waste products) resulting from acrylic acid synthesis is carried out in the presence of heavy products obtained in the

At the same time, the recovery yield of these valuable products can be greatly improved, while at the same time reducing the fouling of the dissociation reactor and reducing the viscosity of the residual products obtained at the outlet of the acrylic esters. process of thermal dissociation.

The present invention relates to a process for the non-catalytic recovery of light valuable products contained in distillation residues resulting from the process of producing acrylic acid and the production of esters of such acrylic acid with alcohols containing 1 to 8 carbon atoms by thermal cracking of these residues. are acrylic acid monomer, acrylic acid ester monomers and alcohols, and the process is characterized in that the non-catalytic cracking is carried out with a mixture of heavy distillation residual products originating from both the acrylic acid production process and the esters of the above-mentioned esters. acid, the light fraction resulting from these dissociation reactions is continuously evaporated during the cracking operation and the light fraction is distilled and after condensation is recovered obtain the desired light valuable products.

In the mixture of residual products to be treated according to the process of the present invention, the weight ratio of the heavy residues (or heavy residuals) resulting from the acrylic acid production to the heavy residues resulting from the acrylic esters production process is preferably in the range 9: 1 to 1: 9.

The cracking process is preferably carried out at a temperature in the range of from 140 ° C to 260 ° C, preferably at a temperature in the range of from 180 ° C to 220 ° C, with a residence time in the range of 0 , 5 hours to 3 hours.

The distillation of the light fraction is preferably carried out under reduced pressure, i.e. at a pressure below atmospheric pressure, and also preferably in the presence of at least one polymerization inhibitor. the inhibitors to be introduced into the process simultaneously with feeding a portion of the feed stream to the rain column.

According to a preferred embodiment of the process according to the invention, the light valuable products obtained in this process are recycled back to the ester production unit from which the heavy residual products used are used together with the heavy residual products derived from the acrylic acid production.

According to a first embodiment of the process according to the invention carried out in a continuous manner, the process consists of the following steps:

- cracking the mixture of heavy residual products to be cracked, possibly pre-heated, in the reactor R1.

- injection of light cracking products into the distillation column C1,

- distillation to obtain the desired mixture of light valuable products at the top of the distillation column C1,

- recycling of the stream obtained at the bottom of the distillation column C1 to the reactor R1,

- recovering the heavy residual product in the reactor R1 and discharging the heavy residual product for separation treatment, optionally after diluting the fraction with a portion of the stream

The exhaust of this stream is recycled to the RL reactor.

According to a second embodiment of the process of the present invention, the mixture of used heavy products (or waste heavy products) is distilled at the same time as the light end portions (or light valuables) obtained at the end of the cracking stage. columns. This method of carrying out the process of the invention is particularly suitable for treating heavy terminal portions that are rich in free light products (such as acylic acid, ester monomers and alcohols). This variant of the process according to the invention is carried out in a continuous manner, comprising the following steps:

- introduction of a mixture of heavy residual products to be cracked into a distillation column C’l,

distillation to give a mixture of light valuable products at the top of the distillation column C'1.

introducing the stream obtained at the bottom of the distillation column C'l into the cracking reactor R '1. process to distillation column C'l,

recovering the heavy recovered product in the reactor R'1 and introducing this portion for subsequent separation treatment, optionally after diluting a portion of the stream obtained at the bottom of the distillation column C'1.

introducing the remainder of this stream into the cracking reactor R1.

DETAILED DESCRIPTION OF THE INVENTION

The process for recovering the light valuable products contained in the distillation residues resulting from the acrylic acid production process and from the production of esters of acrylic acid with C1-C8 alcohols according to the present invention will be described in more detail below using two embodiments illustrated in detail in the attached figures. 1 and 2, each of which shows a corresponding schematic diagram of a production apparatus for carrying out various process variants according to the invention.

It is evident from the schematic representation of the first process variant of the present invention in FIG. 1 that a mixture of heavy products derived from acrylic acid production (fed via line 1), a mixture of heavy products derived from acrylic ester production (fed via line 2) and part of the stream obtained at the bottom of the distillation column C1 (fed via line 3) is fed to the cracking reactor R1 and fed to the reactor via line 4. The mixture thus formed is optionally preheated before being fed to the cracking reactor R1. This mixture is heated here in the reactor, and the light products thus produced are discharged via line 5 as feedstock to a distillation column C1, which preferably operates under reduced pressure. The top of this column C1 is supplied with a polymerization inhibitor selected from the group of commonly used inhibitors or may be a mixture of these inhibitors (such as phenothiazine, hydroquinone, phenols, phenol ethers and the like). The stabilization of the operation at the top of the column can advantageously be achieved by feeding a portion of the stream injected into the top of the column. The mixture of the light products obtained, part of which is reflux, is condensed after condensation from the top of this distillation column C1. The distilled product, practically free of heavy products, consists essentially of acrylic acid, acrylic ester monomer, alcohol and water. This mixture of light valuable products can preferably be recycled (by piping potrubí)

-5GB 287604 B6 back to the acrylic ester production process from which heavy end products are fed to the reactor R1 via line 2.

Optionally, the residual fraction obtained at the bottom of the reactor R1 (and discharged via line 6) can be diluted with a portion of the stream discharged from the bottom of distillation column C1 (via line 8). The remainder of the stream obtained at the bottom of column C1 is discharged as feedstock to reactor R1 (via line 3). This waste heavy residual product is then sent to a subsequent separation treatment process (via line 9), which is carried out according to conventional techniques known in the art.

From the schematic representation of the second process variant of the present invention, which is shown in FIG. 2, it can be seen that a mixture of heavy products derived from acrylic acid production (supplied via line J '), a mixture of heavy products derived from acrylic ester production (supplied via and all or part of the 15 light end products obtained at the top of the cracking reactor R'1 (fed via line 3 ') is fed as feedstock to the distillation column C'1, the mixture being fed via line 4' ).

The distillation column C '1 is preferably operated at reduced pressure, and polymerization inhibitors are fed to the top of the column as already described in connection with the first embodiment of the process of the invention. This solution allows most of these heavy products to separate at the bottom of the distillation column. The distilled product consists mainly of acrylic acid, acrylic acid monomer, alcohol and water. This mixture of light valuable products may preferably be recycled (via line 5 ') back to the acrylic ester production process from which heavy end products are fed to the distillation column C1 via line 2'.

The stream discharged from the bottom of the distillation column C '1 is discharged to the cracking reactor R' 30 (via line 6 '). In this reactor R'1, the feedstock to be treated is heated and the vaporized light product mixture is discharged as feedstock to the distillation column C'1 via line 3 '. The waste heavy residual product stream generated in the cracking reactor R1. This portion may optionally be diluted with a portion of the stream discharged from the bottom of the distillation column C1 through line 8 '. This waste heavy product is then sent to a subsequent separation process (via line 9 '), which is carried out according to conventional techniques.

The process for recovering the light valuable products contained in the distillation residues resulting from the acrylic acid production process and the production of esters of acrylic acid 40 with C1-C8 alcohols according to the invention will be described in more detail below with reference to the following specific examples. In these examples, all percentages are by weight and the following abbreviations are used for each substance:

AA: acrylic acid,

AAH: heavy product fraction from AA production,

EA: ethyl acrylate,

EAH: heavy product fraction from EA production,

MA: methyl acrylate,

MAH: heavy product fraction from MA production,

AA dimer and trimer: compounds of formula

-6GB 287604 B6

CH, = CH — C — O — CH ₉ —CH ₉ —C — OR

II il

O O and formulas: CH _? = CH — C — O — CH _{O —} CH ₉ —C — CH ₉ —CH _? —C — OH 2 2 2.2 2. II II II O OO

resulting from the condensation of acrylic acid itself,

EAP: ethylakiyloyloxypropionate (AA dimer ethyl ester),

MAP: methylacryloyloxypropionate (AA dimer methyl ester),

EEP: ethyl 2-ethoxypropionate (formed by the addition of ethanol to the double bond of EA), MMP: methyl ester of 2-methoxypropionic acid (formed by the addition of methanol to the double bond of MA).

Cracking ratio: the ratio of the light fraction obtained during the cracking to the mixture of heavy end products fed to the reactor, expressed as a percentage by weight.

Regeneration ratio of AA and esters: ratio of AA monomers and ester formed by fractional distillation during the cracking process to a mixture of heavy end products fed to the reactor, 20 expressed as a percentage by weight.

Example 1

200 grams of AAH and EAH were introduced into a 0.5 L stirred reactor, heated in an oil bath, and equipped with a short column equipped with several Vigreux demister sites and equipped with a condenser and sink. The mixture was heated to boiling and the light products resulting from the reaction were distilled off.

The AAH mixture consisted of 2.8 wt% AA, 25.4 wt% AA dimer and 9.8 wt% hydroquinone, the remainder being substantially heavy AA condensation products.

The EAH mixture consisted essentially of 9.2 wt% AA monomer, 8.8 wt% AA dimer, 0.08 wt% EA, 0.08 wt% ethanol and 1.3 wt% hydroquinone, the remainder being mainly EAP, EEP and heavier condensation products AA or EA.

Tables 1 to 4 summarize the results of a series of tests performed at different AAH / EAH ratios for different cracking ratios. The temperatures reached during the tests were in the range of 190 ° C to 250 ° C.

The results of these procedures are expressed in the following values:

- Viscosity of residue obtained at the end of the cracking process. This viscosity is expressed in units of Pa.s as measured at 100 ° C (Table 1). The results clearly show the difference in viscosity of the residue obtained after cracking when AAH was used.

287604 B6 and EAH, as compared to the procedure where the cracking was carried out starting from the AAH fraction itself.

- Regeneration ratio AA and EA (Tables 2 and 3).

By extrapolating these results, the recovery ratio AA and EA can be calculated for the corresponding viscosity of the cracking residue. Table 4 shows the results of this calculation for a viscosity of 500 Pa.s at 100 ° C.

TABLE 1

Viscosity of heavy residues after cracking (in Pa.s at 100 ° C)

Crack ratio AAH / EAH ratio 100/0 60/40 50/50 40/60 0/100 30% 280 30 20 May 13 4 40% 1100 50% > 10,000 174 85 46 7 60% 3440 381 70% 180 21

TABLE 2

Regeneration ratio AA in g / 100 grams of heavy end products fed

Crack ratio AAH / EAH ratio 100/0 60/40 50/50 40/60 0/100 Initial AA (%) 2.8 5.4 6 6.6 9.2 30% 30.2 22.3 20.9 19.1 14 40% 39.2 50% 48.7 35 32.7 31.1 18.4 60% 40.7 37.1 70% 36.9 23.1

TABLE 3

EA regeneration ratio in g / 100 grams of heavy end products fed

Crack ratio AAH / EAH ratio 100/0 60/40 50/50 40/60 0/100 Initial AA (%) 0 0.1 0.1 0.1 0.1 30% 1.4 1,8 1.9 2.4 40% 50% 2.9 3.4 4.2 3.8 60% 4.8 4.6 70% 7.9 6

-8EN 287604 B6

TABLE 4

The regeneration ratio extrapolated to a residual viscosity of 500 Pa.s at 100 ° C

AAH / EAH ratio Crack ratio (500 Pa.s) (%) AA Regeneration ratio (%) EA Total 100/0 35 35 0 35 60/40 56 38 3.8 41.8 50/50 62 37.5 4.8 42.3 40/60 66 36 7 43 0/100 85 26 8.3 34.3

The results shown in Table 4 show an improvement in the monomer recovery ratio achieved with the cracking of the AAH and EAH fraction compared to either the AAH fraction or the EAH fraction.

Example 2

In this example, a continuous process is illustrated schematically in FIG. 1 using a device composed of the following parts:

(a) Reaction Section:

A 1 liter, 1 liter, heavy cracked product mix container equipped with a mechanical stirrer and an oil heated jacket at a temperature controlled to 90 ° C to continuously inject the mixture into the crack reactor.

A 0.5 liter cracking reactor R1, equipped with a mechanical stirrer, a jacket in which controlled temperature oil circulated, a thermally insulated outlet at the bottom of the reactor to remove the residue after the cracking reaction and a temperature probe. Above this reactor was a short thermally insulated column equipped with Vigreux sites to prevent entrainment of the liquid phase (demister) and a condenser downstream of the demister supplied with water at 20 ° C.

A thermally insulated container for collecting the heavy end products obtained at the bottom of the cracking reactor R1.

Container for collecting a mixture of light end products condensed in the reactor head R1.

(b) Distillation section:

- An adiabatic Vigreux column C1 with an efficiency of 6 theoretical plates, to which a mixture of light products condensed in the reactor head R1 was continuously fed as feedstock and equipped with:

-9EN 287604 B6

- a bottom-heat cooker with an outer wall heated by oil maintained at a controlled temperature,

- an upper condenser to which water at 20 ° C has been supplied,

- upper temperature probe,

- a draw-off system which allows the return of a portion of the condensed liquid phase, thereby ensuring reflux at the top of the column,

- a vacuum pumping system equipped with a control system to maintain the reduced pressure in this column,

- injection of phenothiazine at the top of this column in the form of a 1% strength by weight solution in acrylic acid,

a reservoir for collecting the current drawn from the bottom of the column C1.

- a container for collecting a mixture of light products distilled off from the top of the column C1.

The operating conditions and results obtained in this reaction in the reaction section are summarized in Table 5 for the following different mixtures of heavy products to be cracked:

- AAH / EAH 50/50 mixture having the following composition:

AA monomer: 3.8% by weight,

AA dimer: 15.6% by weight,

EA: 0.06% by weight, ethanol: 0.3% by weight, the remainder: consisting of substantially heavier AA or EA condensation products,

- AAH / MAH 50/50 mixture having the following composition:

AA monomer: 1.3% by weight,

AA dimer: 9.4 wt%, MA: 0.01 wt%, methanol: 0.09 wt%, the remainder: consisting of substantially heavier AA or MA condensation products,

- AAH itself having the following composition:

AA monomer: 1.8% by weight,

AA dimer: 22.5% by weight,

AA trimer: 4.1% by weight, hydroquinone: 9.8% by weight, the remainder: consisting of substantially heavier AA condensation products.

-10GB 287604 B6

TABLE 5

Viscosity and regeneration ratio for various mixtures of heavy end products - continuous reaction.

AAH / EAH ratio = 50/50 Temperature in R1 (° C) 206 221 Delay time in R1 (minutes) 54 54 Crack ratio (%) 41 61 Viscosity at 100 ° C 34 1055 Regeneration ratio: - AA (%) 25.5 34.8 - ester (%) 2.4 3.7 - alcohol (%) 0.5 0.7

TABLE 5 (continued)

Viscosity and regeneration ratio for various mixtures of heavy end products - continuous reaction.

AAH / EAH ratio = 50/50

Temperature in R1 (° C) 203 206 216 Delay time in R1 (minutes) 55 58 53 Crack ratio (%) 37 46 56 Viscosity at 100 ° C 69 277 1285 Regeneration ratio: - AA (%) 22.1 27.5 29.9 - ester (%) 2.8 4.4 4.3 - alcohol (%) 0.3 0.3 0.4

TABLE 5 (continued)

Viscosity and regeneration ratio for various mixtures of heavy end products - continuous reaction.

AAH used alone

Temperature in R1 (° C) 200 230 Delay time in R1 (minutes) 75 74 Crack ratio (%) 34 49 Viscosity at 100 ° C 4210 * > 10,000 * Regeneration ratio: - AA (%) 31.4 42.5 - ester (%) 0 0 - alcohol (%) 0 0

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Again, it can be observed that the viscosity of the heavy residual products obtained at the bottom of the R1 reactor has been significantly reduced, while the regeneration ratio for the corresponding viscosity value has been increased after thermal cracking of mixtures 5 containing AAH and EAH compared to thermal cracking processes. where the processing was carried out with the AAH fraction itself. In particular, viscosity values greater than 4000 Pa.s (measured at 100 ° C) achieved during the cracking of the AAH fraction itself are too high to allow a stable uninterrupted flow of the residual products thus obtained.

After this thermal cracking step, the light end products obtained at the top of the reactor R1 are distilled off continuously in a production plant as described above. The operating conditions used and the results obtained are summarized in Tables 6 and 7 below.

TABLE 6

Operating conditions and results obtained after distillation stage - AAH / EAH cracking

Injection Analysis Cl (%)

AA64.3

AA dimer0,7

EA9.7 ethanol1.7

EEP4,6

EAP5.7 water5.6

Operating conditions for distillation

Flow rate (g / h):

- injection250

current drawn from the top 180

Pressure (kPa) 6.7

Top temperature (° C) 57

Analysis of Cl distillate (%)

AA 81.7 EA 12 ethanol 1.9 EEP 0.2 water 4.2

-12GB 287604 B6

TABLE 7

Operating conditions and results obtained after the distillation stage - AAH / MAH cracking

Injection Analysis Cl (%)

AA 65.5 AA dimer 1.4 MA 7.7 methanol 1,2 MMP 1.5 MAP 10.9 water 5

Operating conditions for distillation

Flow rate (g / h): - injection 200 - current drawn from the top 120 Pressure (kPa) 6 Top temperature (° C) 51

Analysis of Cl distillate (%)

AA 87.6 MA 6.2 methanol 0.9 MMP 0.7 water 4,5

Example 3

In this example, a continuous process is illustrated schematically in Fig. 2 using a device composed of the following parts:

(a) Distillation section:

- A 1 liter production container to which a mixture of AAH and EAH to be cracked and the proportion of light end products obtained during the cracking reaction have been fed. This tank was equipped with a mechanical stirrer and an oil heated jacket at a temperature controlled to 90 ° C.

- An adiabatic Vigreux column C'1 with an efficiency of 12 theoretical plates, into which the mixture contained in said production container was continuously fed to the central part of the column as feedstock, and the column was equipped with:

- 13 GB 287604 B6

- a bottom-heat cooker with an outer wall heated by oil maintained at a controlled temperature,

- an upper condenser to which water at 20 ° C has been supplied,

- upper temperature probe,

- a draw-off system which allows the return of a portion of the condensed liquid phase, thereby ensuring reflux at the top of the column,

- a vacuum pumping system equipped with a control system to maintain the reduced pressure in this column,

- injection of phenothiazine at the top of this column in the form of a 1% strength by weight solution in acrylic acid,

- a container for collecting the current drawn from the bottom of the column C'1,

a container for collecting a mixture of light products distilled off from the top of the column C'1.

(b) Reaction Section:

A 0.5 liter cracking reactor R1 equipped with a mechanical stirrer, a jacket in which controlled temperature oil circulated, a thermally insulated outlet at the bottom of the reactor to remove the residue after the cracking reaction and a temperature probe. Above this reactor was a short thermally insulated column equipped with Vigreux sites to prevent entrainment of the liquid phase (demister) and a condenser downstream of the demister supplied with water at 20 ° C. The product obtained at the bottom of column C'1 was fed continuously into the reactor.

A thermally insulated container for collecting the residual product obtained at the bottom of the cracking reactor R * 1.

- Container for collecting a mixture of light end products condensed in the reactor head R’l.

The operating conditions and results obtained in carrying out the simulated distillation stage are summarized in Table 8 below.

TABLE 8

Operating conditions and results obtained during the distillation stage

Operating conditions

Injection flow rate in g / h 200 250 Distillation flow rate in g / h 122 175 Pressure (kPa) 3.7 19 Dec Top temperature Cl (° C) 59 70

- 14GB 287604 B6

TABLE 8 (continued)

Operating conditions and results obtained during the distillation stage

Operating conditions Composition in C * l:

- AAH (%) 41.6 26 - EAH 41.7 62 - Lightweight end products R'l (%) 16.7 12 Flow analysis C'l Injection Analysis: - AA (%) 47.2 47.3 - AA dimer (%) 13.2 5.1 - AA trimmer (%) 1,2 - EA (%) 3.8 10.8 - EEP (%) 4.6 6.3 - water (%) 2.2 2.6 - hydroquinone (%) 2.3 Analysis at the top of Cl: - AA (%) 87.1 74.6 - EA (%) 3.8 15 Dec - ethanol (%) 1.3 6.3 - EEP (%) 2 <0.1 - water (%) 2.8 4 Analysis at the bottom of C'l: - AA (%) 4 5.6 - AA dimer (%) 25.7 18.6 - AA trimmer (%) 2.9 2.4 - EA (%) < <0.2 <0.2 - hydroquinone (%) 4.8 3.4

TABLE 9

Operating conditions and results obtained during the cracking stage

Operating conditions

Temperature in R'l (° C) 218 218 Dwell time in R'l (minutes) 105 97 Crack ratio (%) 81 79 Flow analysis Analysis of injection into R'l: - AA (%) 4 5.6 - AA dimer (%) 25.7 18.6 - AA trimmer (%) 2.9 2.4 - EA (%) < <4.8 3.4

-15GB 287604 B6

TABLE 9 (continued)

Operating conditions and results obtained during the cracking stage

Operating conditions Analysis of distillate R'l: - AA (%) 54.7 44.6 - EA (%) 9.7 10.6 - ethanol (%) 1.4 1,2 -EEP (%) 12.7 21.7 - water (%) 3.1 2.6

Claims (9)

PATENT CLAIMS A method of non-catalytic recovery of light valuable products which are contained 20 in distillation residues resulting from the process of producing acrylic acid and from the production of esters of acrylic acid with C1-C8 alcohols by thermal cracking of these residues, the valuable products being acrylic acid monomer, acrylic acid ester monomers and said alcohols, characterized by: in that the non-catalytic cracking is carried out with a mixture of heavy distillation residual products originating on the one hand The light fraction resulting from these dissociation reactions is continuously evaporated during the cracking operation, and the light fraction is distilled to recover the desired light valuable products after condensation. 30 The process according to claim 1, wherein the weight ratio of the heavy residues derived from the acrylic acid production to the heavy residues derived from the acrylic ester production process is in the range from 9: 1 to 1: 9. A process according to claim 1 or 2 wherein said ester is methyl acrylate or ethyl acrylate. Method according to any one of claims 1 to 3, characterized in that the cracking process is carried out at a temperature ranging from 140 ° C to 260 ° C, with a residence time ranging from 0.5 hours to 3 hours. Process according to any one of claims 1 to 4, characterized in that the distillation of the evaporated light fraction is carried out at a pressure below atmospheric pressure. Process according to one of Claims 1 to 5, characterized in that the distillation is carried out 45 in the presence of at least one polymerization inhibitor, wherein the polymerization inhibitor or inhibitors can be introduced into the process simultaneously with feeding a portion of the feed stream to the distillation column. Method according to one of Claims 1 to 6, characterized in that it is lightly valuable The products obtained in this process are recycled back to the ester production unit from which used the heavy residual products used together with the heavy residual products derived from the acrylic acid production. - 16GB 287604 B6 Method according to any one of claims 1 to 7, characterized in that it is carried out in a continuous manner and comprises the following steps: - cracking of a mixture of heavy residual products to be cracked, possibly pre-heated, in the reactor (R1), - injection of light cracking products into the distillation column (C1), - distillation to give the desired mixture of light valuable products at the top of the distillation column (C1), - recycling of the stream obtained at the bottom of the distillation column (C1) to the reactor (R1), recovering the heavy residual product in the reactor (R1) and discharging the heavy residual product for separation treatment, optionally after diluting a portion of the stream removed from the bottom of the column (C1), the remainder of this stream being recycled to the reactor (R1). Method according to any one of claims 1 to 7, characterized in that it is carried out continuously and comprises the following steps: - introduction of a mixture of heavy residual products to be cracked into a distillation column (C'l), - distillation to give a mixture of light valuable products at the top of the distillation column (C'l), - introducing the stream obtained at the bottom of the distillation column (C'l) into the cracking reactor (R’i), - recycling of a mixture of light products from the cracking process to a distillation column (C'l), - recovering the heavy recovered product in the reactor (R'1) and introducing this portion for subsequent separation treatment, optionally after dilution of portions of the stream obtained at the bottom of the distillation column (C'1), introducing the remainder of this stream into the cracking reactor (R'1).