Process for the recovery of heavy by-products from acrylic acid and esters of said acid by thermal cracking with partial condensation

Abstract

The present invention relates to an improved method for the regeneration by thermal cracking of a mixture of heavy by-products (residues) from acrylic acid and acrylic ester production units, resulting in acrylic acid, acrylic esters and alcohols, for the purpose of recycling in acrylic ester production sites.

Description

[Technical field]

[0001] The present invention relates to an improved process for the regeneration by thermal cracking of a mixture of heavy by-products (residues) coming from a unit for the production of acrylic acid and a unit for the production of acrylic esters, aimed at recycling the by-products in a plant for the production of acrylic esters, resulting in obtaining acrylic acid (AA), acrylic esters (AE) and alcohols. [Background technology]

[0002] Under the influence of temperature during the distillation step, the production of acrylic acid and acrylic esters is accompanied by the formation of heavy compounds, which are derivatives of the addition of compounds with nucleophilicity to the double bonds of the unsaturated carbonyl-containing monomers by the Michael reaction. "Heavy" compounds are those which have a higher boiling point than the acrylic monomers produced.

[0003] The main factor limiting the efficiency of recovery of compounds derived from the Michael reaction contained in the heavy stream from the AA and acrylic ester plants is the increase in viscosity of the heavy residue obtained at the cracker bottoms, when the acrylic monomer and alcohol-rich fractions produced by cracking are evaporated.

[0004] Evaporation of light compounds during cracking results in a concentration of heavy products in the residue stream and an increase in the viscosity of this stream, but the residue must remain sufficiently fluid after cooling to be transported and then processed for destruction purposes.

[0005] In document EP717031 it was shown that if the cracking is carried out starting from a mixture of heavy products coming from the unit for the production of AA and from the unit for the production of acrylic esters, it is possible to improve the efficiency of the recovery of these upgradable inert products compared to the separate cracking of the heavy streams from these units. The effect of the addition of the heavy products coming from the ester unit to the heavy products coming from the AA unit is to reduce the viscosity of the final residue. The cracking reaction is carried out starting from a mixture having a ratio of AA heavy products / ester heavy products of 9 / 1 to 1 / 9, at a residence time of 0.5 to 3 hours, at atmospheric pressure and at a temperature of 180 to 220° C. In this method, the cracking and evaporation of the light compounds produced are carried out in a reactor, then the produced gas stream is sent into a distillation column and finally the bottom stream from the distillation column is recycled to the reactor. On the other hand, since the light fraction obtained by cracking consists mainly of acrylic monomers of AA and esters, which are particularly susceptible to polymerization, the distillation stage must necessarily be carried out under reduced pressure in order to reduce the temperature in order to prevent the formation of polymers in the column. Moreover, the rectification plates of the distillation column provide an efficient separation of the polymerization inhibitors entrained in the gas mixture, which flow back to the bottom of the column, and as a result, it is necessary to introduce new polymerization inhibitors at the top of the column in order to prevent the formation of polymers in the upper part of the column. For this reason, the reaction stage carried out under higher pressure and the distillation stage carried out under reduced pressure must be separated. The installation for carrying out the process must therefore be equipped with a reactor and a head condenser operated at the same pressure, as well as a distillation column operated at reduced pressure, fed with the condensed product, containing a boiler at the bottom and a condenser at the top, reflux equipment and an inhibitor feed. This arrangement is complex and expensive.

[0006] As a result of the presence of high concentrations of alcohols in the acrylic ester synthesis stream, the majority of the heavy product streams from these production units consist of derivatives of the addition of alcohols to AA and monomer ester double bonds. For example, in the case of ethyl acrylate, the derivatives are ethyl 3-ethoxypropionate and 3-ethoxypropionic acid. These alkoxy-propionic compounds contain COC bonds that are less easily broken than the CC bonds of the other derivatives. Under the temperature conditions usually used for the regeneration of acrylic heavy products, these compounds can only be dissociated in the presence of high concentrations of catalysts. For this reason, the amount of products that can be upgraded starting from the heavy products from the acrylic ester units is smaller than that from the heavy products from the acrylic acid units. The amount of compounds that can potentially be upgraded by thermal cracking is therefore approximately twice as much in the heavy products from the AA units. As a result, in a platform for the production of acrylic monomers, there is an advantage in upgrading the heavy products from the AA units as a first priority compared to the heavy products from the ester units.

[0007] However, when the AA heavy products / AE heavy products (AAHP / AEHP) ratio increases, the increase in viscosity of the residue from the cracking reaction becomes increasingly sensitive to parameters that allow improving the cracking yield, namely increasing the reaction temperature and / or increasing the reaction time. This effect is particularly important when the ratio of AA unit heavy products to the combined mixture of AA heavy products and ester heavy products exceeds 50%.

[0008] As a result, there is a need to improve the yield of recovery by thermal cracking of heavy compounds coming from AA and ester units containing more than 50% AA heavy products, while reducing the effect of the increase in viscosity of the residue during evaporation of the monomer-rich mixture during cracking.

[0009] As seen above, the efficiency of the regeneration essentially depends on two parameters: the temperature and the residence time of the reaction. An increase in these two parameters tends to improve the regeneration yield, but this occurs at the expense of an increase in the viscosity of the cracking residue.

[0010] A minimum temperature of approximately 140°C is required to crack efficiently the Michael derivatives contained in the mixture of AAHP and AEHP, but at this temperature, the reaction time must be very long if it is desired to obtain an acceptable yield. In the specific case of thermal dissociation of Michael derivatives starting from a mixture of AA and AE heavy products, an increase in residence time at this relatively low temperature level is not favorable for increasing the recovery yield, because there is a competition between the cracking reaction of Michael derivatives to obtain monomers and the cracking reaction to form Michael derivatives from monomers, the latter favoring intermediate temperatures (140-160°C) and long reaction times. It is therefore preferable to carry out the cracking at higher temperatures (above 160°C, preferably above 180°C) and at shorter residence times (less than 6 hours, preferably less than 4 hours).

[0011] In platforms for the production of AA and AE, it is quite common that there are large fluctuations in the flow rates of the production of AA and AE, and correspondingly in the flow rates of heavy by-products from these units, depending on market demand. As a result, when the cracking operation is carried out by the method in a continuous mode, severe fluctuations can be observed in the residence time in the cracking reactor, which depends on the feed flow rate and the proportion of heavy products generated from the AA and ester units.

[0012] As a result, it would be advantageous to have available a method of cracking heavy compounds from AA and AE units that makes it possible to obtain good upgrading yields whatever the variations in flow rate and ratio of AA to AE heavy products. Summary of the Invention

[0013] The present invention relates to a process for the regeneration of a mixture of heavy by-products resulting from a unit for the production of acrylic acid and from a unit for the production of acrylic esters of formula CH2=CH-C(=O)-OR, where R is a C1-C8 alkyl group, comprising the steps of: i. introducing said mixture into a reactor and subjecting it to thermal cracking to produce a gaseous overhead stream and a bottom stream (residue) concentrated in heavy products; ii. partial condensation of said overhead stream, resulting in an overhead stream containing acrylic acid, acrylic esters and alcohols R-OH, which are particularly intended to be recycled to an acrylic ester production plant, and a bottom stream, iii. recovering said residue for removal purposes. The present invention relates to a method comprising the steps of:

[0014] Advantageously, steps i) and ii) are carried out at the same absolute pressure, between 200 and 2000 hPa, preferably between 300 and 1500 hPa.

[0015] According to various implementations, the method includes the following characteristics, when appropriately combined:

[0016] According to one embodiment, the partial condensation operation is carried out in an exchanger (condenser) causing condensation of a portion of the vapors produced during thermal cracking, said vapors having not previously undergone fractionation in a distillation column comprising one or more rectification plates.

[0017] According to one embodiment, the temperature of the gas mixture leaving the partial condensation stage (top stream) is between 140°C and 180°C.

[0018] According to one embodiment, the cracking temperature is between 140°C and 260°C, preferably between 180°C and 210°C.

[0019] According to one embodiment, the residence time of the reaction mixture in the cracking reactor is between 0.5 and 10 hours, preferably between 2 and 7 hours.

[0020] According to one embodiment, the bottom stream (residue) from the reactor obtained at the end of the thermal cracking operation exhibits a dynamic viscosity of less than 1 Pa·s, measured at a temperature of 100° C., for example using a Brookfield “CAP1000+” viscometer of cone / plate type.

[0021] According to one embodiment, the bottom stream from the partial condenser is at least partially recycled to the reactor.

[0022] According to one embodiment, the liquid bottom stream from the partial condenser is recycled via a dip pipe in the reactor either directly to the liquid phase of the reactor or to a pipe for recycle of the reaction medium through an external exchanger, preferably upstream of this external exchanger.

[0023] According to one embodiment, the uncondensed gaseous top stream coming from the partial condenser, rich in AA, acrylic esters and alcohols, is recycled, preferably in liquid form, after condensation in a second condenser to the unit for the production of acrylic esters.

[0024] According to one embodiment, the weight ratio of the condensate stream to the gas stream entering the condenser is between 5% and 50%, preferably between 10% and 40%.

[0025] According to one embodiment, the weight ratio of AAHP / AEHP is between 3 / 7 and 9 / 1, preferably between 1 / 1 and 9 / 1.

[0026] According to one embodiment, the R group is a C1-C4 alkyl group.

[0027] According to one embodiment, the ester is ethyl acrylate and the alcohol is ethanol.

[0028] According to one embodiment, the regeneration method is carried out continuously.

[0029] According to one embodiment, polymerization inhibitors are introduced in the partial condenser and, if used, in the second condenser. These inhibitors are selected from polymerization inhibitors known to those skilled in the art, phenol derivatives such as hydroquinone and its derivatives, such as hydroquinone methyl ether, 2,6-di(tert-butyl)-4-methylphenol (BHT) and 2,4-dimethyl-6-(tert-butyl)phenol (Topanol A), phenothiazine and its derivatives, manganese salts such as manganese acetate, salts of thiocarbamic or dithiocarbamic acids, such as metal thiocarbamates and dithiocarbamates, such as copper di(n-butyl)dithiocarbamate, N-oxyl compounds such as 4-hydroxy-2,2,6,6-tetramethylpiperidineoxyl (4-OH-TEMPO), compounds with nitroso groups, such as N-nitrosophenylhydroxylamine and its ammonium salts, amine compounds such as para-phenylenediamine derivatives, or mixtures of these inhibitors.

[0030] According to one embodiment, the thermal cracking reaction occurs in the absence of a catalyst.

[0031] According to one embodiment, the thermal cracking reaction takes place in the presence of a catalyst, which may include Bronsted acids such as sulfuric acid, sulfonic acid, phosphoric acid, zeolites, alumina or silica and alumina based catalysts, Lewis acids such as titanates, bases, alkali metals or their salts, amines, phosphines, or combinations thereof.

[0032] The present invention makes it possible to overcome the disadvantages of the prior art. More particularly, it provides a simplified process for the thermal cracking of a mixture of heavy by-products resulting from a unit for the production of acrylic acid and from a unit for the production of acrylic esters, making it possible to efficiently recover monomers that can be upgraded in the manufacture of acrylic esters. This is achieved thanks to the combination of a stage of thermal cracking of said mixture and a stage of partial condensation of the top stream resulting from the cracking, the two stages being carried out at the same pressure.

[0033] Advantageously, the method of cracking heavy compounds from AA and AE units according to the invention makes it possible to obtain good upgrading yields whatever the variations in flow rate and in the ratio of AA heavy products to AE heavy products.

[0034] The main advantages of the method according to the invention are: Increase in the recovery yield of inert products from the heavy products derived from the Michael reaction present in the heavy product stream from the AA and ester plant by pushing the cracking reaction more thoroughly without limitations due to viscosity and by processing a mixture of AA heavy products and ester heavy products that are richer in AA heavy products; A process that is simple and relatively inexpensive in capital cost, since it requires essentially only one additional piece of equipment (the partial condenser), and is simple to carry out (the partial condensation step at the same pressure as the cracking reaction); A method that allows reducing emissions by reducing the amount of cracking residues; A method that allows optimizing the recovery yield despite variations in residence time and in the ratio of AA heavy products / ester heavy products. It is. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 shows an embodiment of an installation according to the invention. [Diagram 2] FIG. 4 shows another embodiment of the installation according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The invention will now be described in more detail, in a non-limiting manner, in the description that follows.

[0037] The term "heavy by-products resulting from a unit for the production of acrylic acid" means 3-Acryloyloxypropionic acid, a derivative of the addition of acrylic acid to the double bond of another acrylic acid molecule, also called "acrylic acid dimer" or "AA dimer", Derivatives of the addition of acrylic acid to a double bond on an AA dimer molecule to form an "AA trimer" and other oligomers formed by successive additions of acrylic acid to the double bond of a preceding AA oligomer; Derivatives of the addition of carboxylic acids (e.g. acetic acid) formed as by-products of acrylic acid or of water to the double bonds of AA or of the above mentioned oligomers Includes.

[0038] The term "heavy by-products from units for the production of acrylic esters (AE)" refers to the same compounds as mentioned above, as well as Alkyl esters of these compounds, where the alkyl group is the group of an AE ester; Michael reaction addition derivatives resulting from the addition of alcohols to the double bonds of acrylic acid, AA dimers or AA oligomers, and also their esters. Includes.

[0039] The term "partial condensation" refers to the operation during which the gas stream produced during the thermal cracking stage is partially condensed in the form of a liquid stream.

[0040] The term "partial condenser" refers to an equipment that allows the production of a liquid fraction (reflux) from a hot vapor stream by cooling on walls that are colder than the vapor. A partial condenser is generally a heat exchanger that is kept cooler than the vapor by the circulation of a coolant. The coolant can be, for example, a gaseous stream such as air, water, or any other liquid stream that originates from a make-up outside the process or is recycled from the process stream. The temperature of the vapor at the outlet of the exchanger is adjusted to the desired temperature to obtain more or less liquid flow by partial condensation by changing the temperature and flow rate of the coolant in contact with the walls in the partial condenser. Types of heat exchangers may include shell-and-tube exchangers, consisting of an internal shell and a bundle of tubes, in which the two fluids (vapor produced in the reactor and the coolant) circulate separately. Spiral or plate exchangers, or any other type of exchanger known to the skilled person that allows partial condensation of vapors, may also be mentioned. These exchangers may be horizontal or vertical equipment.

[0041] The term "total condensation" or "total condenser" refers to an operation or equipment that performs the condensation of condensable compounds contained in the uncondensed vapor at the outlet of the partial condenser, which is removed in the form of a liquid (distillate).

[0042] The present invention is based on a thermal cracking process with a partial condensation operation, the two stages being carried out at the same pressure. The process of the present invention is applicable to the regeneration of acrylic monomers from a mixture of heavy by-products from a unit for the production of acrylic acid and from a unit for the production of acrylic esters, making it possible to efficiently recover these monomers which can be upgraded in the manufacture of acrylic esters.

[0043] According to the embodiment of the process shown in FIG. 1, a mixture of streams originating from a plant for the production of acrylic acid (AAHP) and acrylic esters (AEHP) is continuously introduced in liquid form into a reactor R. This mixture (1) is rich in heavy compounds derived from the Michael addition, produced during the stages of synthesis and purification of the corresponding monomers (AA and AE), and also contains other heavy compounds, in particular polymerization inhibitors, accumulated during the synthesis and purification process. The mixture (1) is introduced into a reactor, where it is heated to the temperature necessary to carry out the cracking of the derivatives of the Michael addition to obtain lighter compounds, which are extracted in the form of a gaseous mixture (2) at the reactor head. This gaseous stream is sent to a partial condenser E1, for example consisting of a shell-and-tube exchanger. Said exchanger circulates water at a temperature and flow rate suitable for cooling the steam to the required temperature, measured in the uncondensed vapor stream (3) at the exchanger outlet, and for obtaining the desired condensation ratio. This uncondensed vapor stream, rich in upgradable compounds (AA, esters, alcohols) and containing less heavy compounds in low concentrations, is advantageously recycled to the process for the production of AE esters, either directly in vapor form or after total condensation in exchanger E2. In the latter case, it is the liquid stream (4) that is recycled to the AE esters production unit.

[0044] At the bottom of the partial condenser, a liquid stream (5) (also called reflux) is recovered, which is richer in heavy compounds whose boiling point is intermediate between that of the monomer and that of the heaviest compounds, in particular 3-alkoxypropione Michael derivatives, and which also contains small amounts of polymerization inhibitors. This stream (5) is returned to the reactor at least in part by introduction, preferably directly into the liquid phase of the reactor, via a separate dip pipe or via a dip pipe for feeding the AAHP and AEHP compounds to the reactor.

[0045] According to an embodiment not shown in FIG. 1, a portion of the liquid stream condensed in the partial condenser, which contains a low concentration of polymerization inhibitors, is pumped back to the outlet at the top of the partial condenser so as to protect the equipment from the risk of polymerization in the condenser.

[0046] The residue stream (6) recovered at the bottom of the reactor is cooled and then removed in the form of a liquid of moderate viscosity so that it can be transported without difficulty, for example by pump, to a storage tank or an incineration unit.

[0047] According to an embodiment not depicted in FIG. 1, the feed streams comprised of the AAHP and AEHP are preheated through a heat exchanger before being introduced into the reactor.

[0048] According to another embodiment, the thermal cracking reaction is carried out discontinuously.

[0049] According to one embodiment, the feed stream is introduced directly into the liquid phase of the reactor via a dip pipe.

[0050] The diagram of Figure 2 describes an embodiment of the process according to the same principle as the diagram of Figure 1, specifying a possible implementation when the reactor is heated by recirculation using a pump P of the reaction medium (7) contained in the reactor through a heat exchanger E3. In this embodiment, the liquid stream fraction (5) returned to the reactor will advantageously be recycled in a recirculation loop, preferentially upstream of the exchanger E3, for example upstream of the recirculation pump P. EXAMPLES

[0051] The following examples illustrate the invention without limiting it.

[0052] 1, in these examples the reaction temperature is the temperature measured on the liquid contained in the liquid phase of the reactor R, the "head temperature" is the temperature of the vapor (stream 3) measured at the outlet of the partial condenser E1, the "residence time" in the reactor is measured by the weight ratio of the working volume of the reactor (volume of the liquid phase in the reactor) to the feed flow rate of the heavy end (stream 1), the "topping ratio" is the weight ratio of the flow rate of the condensate stream (stream 4) at the outlet of the partial condenser E2 to the feed flow rate (stream 1), and the "effective recovery" is the weight ratio of the sum of the upgradable compounds (AA, AE and ethanol) collected in the distillate after partial condensation (stream 4) to the feed flow rate of the heavy end (stream 1). "Effective conversion" is the weight ratio of the sum of the upgradable compounds produced by cracking and recovered in the total contraction stream (stream 4) minus the sum of these compounds present in the feed (stream 1) to the feed flow rate of the reactor (stream 1) minus the upgradable compounds (AA, AE and ethanol) present in this stream. Finally, "Viscosity at 100°C" is the value of the viscosity in Pa·s of the residue obtained at the bottom of the reactor (stream 6) at a temperature of 100°C, measured using a Brookfield "CAP1000+" viscometer of the cone / plate type equipped with spindle No. 2 at a rotational speed of 750 revolutions per minute.

[0053] All tests were carried out at atmospheric pressure.

[0054] Example 1: Cracking with partial condensation and reflux of condensed liquid into the reactor gas headspace The assembly consists of a glass reactor with a total volume of 1 liter, heated by oil recirculation through a jacket, equipped with a side outlet for leaving the residue, providing a working volume of 240 ml of liquid contained in the reactor.

[0055] The reactor is equipped with an agitator, a temperature probe immersed in the liquid phase, a vertical pipe in the upper part for extracting the vapors, and a partial condenser. The partial condensation is achieved by cooling the reaction vapors on a thimble placed inside the vertical tube for the extraction of the vapors, in which oil circulates at a controlled temperature of 150 ° C. The temperature probe makes it possible to measure the temperature of the uncondensed vapors at the outlet of the partial condenser. These uncondensed vapors go to the total condenser, which consists of a jacketed cooler in which water circulates at 10 ° C. The liquid (distillate) is collected in a receiver and analyzed. The elements of the assembly in contact with the vapors from their production in the reactor until they enter the second condenser are covered to reduce heat exchange with the outside. In this assembly, the vapor fraction condensed in the partial condenser flows naturally back to the reactor.

[0056] A mixture consisting of 60% by weight of heavy compounds coming from a unit for the production of AA and 40% by weight of heavy compounds coming from a unit for the production of ethyl acrylate (EA) is fed continuously into the reactor at a flow rate of 70 g / h. Under these conditions, the residence time is 3.4 hours. The feed mixture consisted essentially of upgradeable compounds (AA 9% and <0.1% AE and <0.1% ethanol) with heavy compounds derived from the Michael reaction (AA dimer (AA2) 35.5%, AA trimer (AA3) 1.5%, 3-ethoxypropionic acid (EPA) 3.3%, 3-hydroxypropionic acid (HPA) 0.3%, ethyl 3-ethoxypropionate (EEP) 6.2%, ethyl 3-acryloyloxypropionate (EAP) 6.7%, ethyl 3-hydroxypropionate (EHP) 0.5%, and polymerization inhibitors (hydroquinone (HQ) 2.7%, phenothiazine (PTZ) 0.6%).

[0057] In Example 1, after more than 24 hours of operation under stable conditions, the reaction temperature is 195°C and the temperature of the vapors at the outlet of the partial condenser is 157°C.

[0058] The operating conditions and performance qualities of these tests are summarized in Table 1.

[0059] Examples 2 and 3 (comparison): (SF57-4 and SF58-4) Prior art cracking without condensation These two examples were carried out with the same assembly and under the same conditions as Example 1, apart from the fact that the inner thimble was empty, which suppressed the cooling effect of circulating coolant.

[0060] After more than 24 hours of operation under stable conditions, the results obtained are given in Table 1 below. TIFF0007620645000001.tif67170

[0061] These comparative examples show the advantage of reducing the temperature of the vapors at the reactor outlet, resulting in partial condensation of the vapors and reflux of the liquid into the reactor, resulting in improved recovery yields of inert compounds with reduced viscosity of the residue from the cracking reaction.

[0062] It is also observed that the reaction temperature in Test 3, which is carried out at a residence time of 6 hours, is much lower compared to Test 2, which is carried out at a residence time of 3.5 hours, while still obtaining a similar cracking residue. At higher temperatures, the viscosity of the residue increases significantly, making the liquid difficult to transport. The reduction in the temperature that can be used at longer residence times without an excessive increase in viscosity results in a significant reduction in cracking performance quality.

[0063] Example 4: Partial condensation of streams resulting from reactions for cracking AA heavy products and AE heavy products The liquid mixture resulting from the total condensation of the operation for cracking a mixture of AAHP (60%) and AEHP (40%) is evaporated and partially condensed in a shell-and-tube condenser at a temperature of 160° C. A condensed liquid stream is obtained, which represents 30% by weight of the feed stream of the condenser. This liquid condensate has a composition representative of the reflux stream (5) of FIG. 1, containing 35.4% AA, 0.3% AE, 4.4% AA2, 0.4% AA3, 11.5% EPA, 22% EEP, 6.2% EAP, 0.1% EHP, 0.3% HQ, 0.04% PTZ.

[0064] Examples 5 to 8: Cracking with partial condensation and recycling of the condensate into the liquid phase of the reactor These examples are intended to illustrate the operating conditions of the method according to the invention of Figure 1. The operating conditions and performance qualities of these various tests are summarized in Table 2.

[0065] In addition to the definitions given above, the "effective conversion" is the weight ratio of the sum of the upgradeable compounds produced by cracking and recovered in the total contraction stream (stream 4) minus the sum of these compounds present in the feed (stream 1) and in the recycled stream (stream 5) to the feed flow rate of the reactor (stream 1) minus the upgradeable compounds (AA, AE and ethanol) present in this stream (1).

[0066] The experimental assembly is the same as in Example 1, apart from the fact that the vapours produced during the cracking reaction are sent directly to the total condenser (E2) and the flow rate of the condensate stream obtained in Example 3 is introduced by a dip pipe into the reactor, in addition to the AAHP and AEHP feeds. This arrangement makes it possible to closely simulate the recycling of the condensed cracker stream at a temperature of 160° C., according to an expected recycling / feed rate of 22% AAHP to AEHP, corresponding to a condensation rate of 30% of the vapours.

[0067] In Examples 5, 6 and 7 (residence time 3 hours), the reactor is fed with the mixture of AAHP and AEHP described in Example 1 at a flow rate of 80 g / h, and the condensate stream (stream 5) of Example 3 is introduced into the reactor by a dip pipe into the liquid phase at a flow rate of 17.6 g / h. In Example 8 (residence time 6 hours), the feed flow rate of AAHP and AEHP (1) is 40 g / h and the recycled condensate flow rate (5) is 8.8 g / h.

[0068] After operating under stable conditions for more than 24 hours, samples of the stream coming from the total condenser E2 (stream 4) and the residue at the bottom of the reactor (stream 6) are drawn off and analyzed.

[0069] Examples 9 and 10 (comparison): Cracking without condensation according to the prior art The assembly and operating conditions used are the same as those described in Examples 5 to 8, apart from the fact that the recycle of the stream resulting from the partial condensation (stream 5) was excluded. As in Examples 5 to 7, the feed flow rates of the AAHP and AEHP in Example 9 (residence time 3 hours) are 80 g / h, and in Example 10 (residence time 3 hours) the feed flow rates are the same as in Example 8, i.e. 40 g / h.

[0070] The operating conditions and performance qualities of these tests are summarized in Table 2 below. TIFF0007620645000002.tif60170

[0071] These examples show that, in a very simple assembly using a condenser operated at the same pressure as the cracking reaction, it is possible, by carrying out the partial condensation of the cracking vapors and recycling the condensed portion to the reactor, to significantly improve the recovery yield of upgradable products while obtaining a lower viscosity of the cracking residue than in the prior art.

[0072] Tests 9 and 10 allow a comparison of the cracking performance quality at different residence times. With respect to the corresponding viscosity of the residue, a comparison of tests 7 and 8 shows that the cracking reaction temperature must be reduced if the residence time is longer, but the recovery performance quality nevertheless remains much better under these conditions of longer residence times (test 8) than test 9 carried out according to the prior art, despite the more favorable operating conditions of shorter residence times, and in addition, with a lower viscosity of the residue. This therefore shows that even when the flow rate of the heavy products being treated is lower due to fluctuations in the production rates of the AA and ester plants, which leads to an increase in the residence time, the method according to the invention makes it possible to continue to recover much more inert products from one and the same AAHP-AEHP mixture.

Claims

1. A heavy by-product from a unit for the production of acrylic acid, and R is C １ ~C ８ The alkyl group of formula CH ２ 1. A process for the regeneration of a mixture of heavy by-products resulting from a unit for the production of acrylic esters of =CH-C(=O)-OR, said process comprising the steps of: i. introducing said mixture into a reactor and subjecting it to thermal cracking to produce a gaseous overhead stream and a bottom stream (residue) concentrated in heavy products; ii. subjecting said overhead stream to partial condensation, resulting in an overhead stream containing acrylic acid, an acrylic acid ester and an alcohol R-OH, and obtaining a bottom stream; iii. Recovering said residue for removal purposes. The method includes:

2. 2. The method of claim 1, wherein steps i) and ii) are carried out at the same absolute pressure.

3. The method of claim 1, wherein steps i) and ii) are carried out at the same absolute pressure between 200 and 2000 hPa.

4. 4. The process according to any one of claims 1 to 3, wherein the cracking temperature is between 140°C and 260°C.

5. 5. The process according to any one of claims 1 to 4, wherein the residence time of the reaction mixture in the cracking reactor is between 0.5 and 10 hours.

6. 6. The process according to any one of claims 1 to 5, wherein the bottom stream (residue) from the reactor resulting from the thermal cracking operation exhibits a dynamic viscosity measured at 100°C of less than 1 Pa·s.

7. 7. The process according to any one of claims 1 to 6, wherein the bottom stream from the partial condenser is at least partially recycled to the reactor.

8. 8. The process according to claim 1, wherein the overhead stream containing acrylic acid, acrylic esters and alcohols R-OH obtained from the partial condenser is recycled to a unit for the production of acrylic esters.

9. 8. The process according to claim 1, wherein the overhead stream containing acrylic acid, acrylic ester and alcohol R-OH obtained from the partial condenser is recycled in liquid form, after condensation in a second condenser, to a unit for the production of acrylic ester.

10. 10. The method of claim 1, wherein the ester is ethyl acrylate and the alcohol is ethanol.

11. 11. The method of any one of claims 1 to 10, wherein the weight ratio of the condensate stream to the gas stream entering the condenser is between 5% and 50%.

12. A method according to any one of claims 1 to 10, wherein the weight ratio of the condensate flow to the gas flow entering the condenser is between 10% and 40%.

13. 13. The process according to any one of claims 1 to 12, wherein the weight ratio of AA heavy ends / AE heavy ends is between 3 / 7 and 9 / 1.

14. The method of claim 1, wherein the weight ratio of AA heavy products to AE heavy products is between 1 / 1 and 9 / 1.

15. 15. The process according to any one of claims 1 to 14, wherein at least one polymerization inhibitor is introduced in a partial condenser.

16. 16. The process according to any one of claims 1 to 15, wherein the thermal cracking reaction occurs in the absence of a catalyst.

17. 16. The process according to any one of claims 1 to 15, wherein the thermal cracking reaction occurs in the presence of a catalyst selected from sulfuric acid, sulfonic acid, phosphoric acid, zeolites, alumina, silica and alumina-based catalysts, titanates, bases, alkali metals, alkali metal salts, amines, phosphines, or combinations thereof.

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