Process for production of bio-acrylic acid

Abstract

A process for converting a liquid feed based on hydroxypropanoic acid into bio-acrylic acid, comprising at least the following steps: a step of vaporization (a) of a liquid feed based on hydroxypropanoic acid (3), a step (b) of catalytic dehydration of the hydroxypropanoic acid-based gaseous stream (3) to form acrylic acid, and a specific recovery and purification sequence (steps c) to g)) for the bio-acrylic acid produced, to obtain a bio-acrylic acid purified in terms of propionic acid, said specific purification sequence being based in particular on a first step of azeotropic distillation of the aqueous acrylic acid effluent, making it possible to remove the propionic acid upstream of the transfer of the acrylic acid into the organic phase.

Description

[0001] PROCESS FOR PRODUCTION OF BIO-ACRYLIC ACID

[0002] Technical field

[0003] The present invention is applicable in the field of the production of bio-acrylic acid and its derivatives by a heterogeneous catalytic gas phase reaction of hydroxypropanoic acid, hydroxypropanoic acid derivatives, or mixtures thereof, followed by a recovery and purification section to obtain the bio-acrylic acid purified in terms of propionic acid. In the case of the biobased acrylic acid production process, certain impurities are produced in greater quantities than in the conventional propene oxidation process, notably propionic acid.

[0004] State of the art

[0005] Acrylic acid and its derivatives, or a mixture thereof, are a very important intermediate involved in the synthesis of many polymers, paints, absorbents, detergents, adhesives, coatings, etc. One very important outlet for glacial grade acrylic acid (also referred to here as AAg), representing about 35% of total acrylic acid production, is the manufacture of super adsorbent polymers.

[0006] The main industrial process for production of acrylic acid is based on the oxidation of propene. At a time of energy transition, and in the context of an inexorable depletion of fossil resources, the production of a large number of intermediaries must be reconsidered. The main alternative is the use of biomass, a chemically complex resource that requires rethinking all the reactions involved and developing the associated industrial processes.

[0007] Numerous attempts have been made over the past 50 years to manufacture acrylic acid and its biobased derivatives, such as lactic acid (known as 2-hydroxypropanoic acid), glycerol, carbon monoxide, carbon dioxide.

[0008] Among these different biobased sources, only lactic acid, which is produced today with a high yield and a high degree of purity from sugars, would make it possible to produce acrylic acid at a competitive cost compared to acrylic acid produced from petroleum source. This production is carried out by dehydration of lactic acid in the gas phase. However, due to parallel and secondary reactions, it is difficult to obtain high yields of acrylic acid. For this reason, the catalyst plays an important role in the orientation of selectivity. Patent application WO 17 / 040383 discloses several generations of catalysts, all composed of a mixture of alkali metal phosphates, some of which have the formula MxPOy(M = K or Cs). To produce bio-acrylic acid and its derivatives from liquid hydroxypropanoic acid, and its derivatives, two steps are required:

[0009] - a vaporization step in which the liquid solution of hydroxypropanoic acid and its derivatives is vaporized and brought to the reaction temperature;

[0010] - a catalytic reaction step in which hydroxypropanoic acid in gas form is converted into acrylic acid in contact with a solid catalyst.

[0011] Unfortunately, in aqueous solutions of hydroxypropanoic acid and its derivatives, many chemical species are also present, capable of reacting upstream, inside and downstream of the reactor.

[0012] Indeed, hydroxypropanoic acid and its derivatives degrade in the liquid phase by polymerization to form oligomers, the degradation increases with temperature. Therefore, during its vaporization, the residence time of hydroxypropanoic acid in the liquid phase at high temperature must be minimized so as not to degrade the reagent. On the other hand, hydroxypropanoic acid also degrades in the gas phase by thermal cracking to form byproducts, such as, but not limited to, acetaldehyde, carbon monoxide and carbon dioxide. The kinetics of degradation in the gas phase are dependent on the temperature. The processes described in the literature have yields of acrylic acid and derivatives of less than 70%, low selectivity with significant yields of secondary products, long residence times in the catalytic bed, and a fairly rapid deactivation of the catalyst, linked to deposits of by-products thereon. Owing to the formation of by-products and to variable conversion, yields of acrylic acid and derivatives are not optimal. Patent US 9 758 463 proposes controlling the degradation of hydroxypropanoic acid by using partial vaporization and by recycling the remaining liquid phase. By controlling the residence time and temperature below 350°C, the decomposition of hydroxypropanoic acid (reactions producing species such as acetaldehyde, propionic acid, 2,3-pentanedione, carbon oxides, etc.) is limited and the oligomers formed are stabilized for a long period of time.

[0013] Patent US 9 452 967 proposes a process for the conversion by catalytic dehydration of hydroxypropanoic acid and its derivatives into acrylic acid with a short residence time and a low yield of secondary products. This patent mentions the introduction of the liquid feed of lactic acid and water into the reactor through an atomization nozzle generating mean drop diameters of less than 500 pm. A large majority of atomization technologies are cited. Once vaporized, the gaseous mixture is transferred to the catalytic dehydration bed. The dehydration catalyst used comprises monohydrogen phosphate and dihydrogen phosphate anions described by the formulae [HPO4]2' and [H2PO4]' and at most two cations, such that the [HPO4]2[H2PO4]- molar ratio is between 0.1 and 10. Whether by the conventional route of acrylic acid production, i.e. by partial oxidation of propene over a heterogeneous catalyst, or from biobased resources, the acrylic acid obtained is rich in by-products and impurities such as water, acetic acid, formic acid, formaldehyde, acetaldehyde, maleic acid, propionic acid or furfural.

[0014] The quality of the acrylic acid, that is, its content of various impurities, plays a very large role in the subsequent polymerization processes. This has led manufacturers to use a whole series of purification steps to obtain different grades of acrylic acid representing different levels of purity. There are two grades of acrylic acid:

[0015] - The technical grade or "crude acrylic acid" as it is known, the purity of acrylic acid for this grade being approximately 94%. The impurities present (6% remaining) are mainly maleic anhydride, propionic acid, acetic acid, furfural. This grade is used for commodity products and, in particular, acrylate esters.

[0016] - The glacial or polymer grade (also called here AAg). This grade does not meet universally recognized specifications but means for each manufacturer the level of purity to be achieved in order to be able to successfully carry out subsequent transformations. By way of example, for an acrylic acid ex-propene, the effluent from the reactor outlet is subjected to a combination of steps which may differ in their sequence according to the process. In general, the glacial grade imposes minimum acrylic acid contents often of 99% by weight, or even of 99.7% by weight, relative to the total weight of the feed. In fact, the impurity contents are very low. For example, the total aldehyde content must be less than 10 ppm, the total saturated acid content must be less than 1600 ppm, the acetic acid content must be between 500-1500 ppm and the propionic acid content must be between 100-500 ppm.

[0017] Generally, the effluent produced from the reaction section is collected in the form of an acrylic solution by quenching the hot gas stream with an absorption solvent (mainly water or a hydrophobic solvent). The solvent, impurities and acrylic acid are then selectively separated, mainly through several distillation columns (conventional, heteroazeotropic or others). The combination of water quenching and liquid-liquid separations in an extraction column has commercial applications.

[0018] When water is used as an absorption solvent, two main methods can be used to purify acrylic acid: heteroazeotropic distillation or liquid / liquid extraction. The chosen solution depends on the concentration of acrylic acid in the aqueous stream, which can vary considerably from one plant to another, from about 30% by weight to 70% by weight. A hybrid solution involving the two types of unit operations in the purification process is disclosed in patent EP 3 406 587 and patent US 11 033 834. In the case of heteroazeotropic distillation, a solvent is used to form with water an azeotrope having a boiling point lower than that of acrylic acid. This implementation is well described in patents EP 1 382 592 A1 , US 6 084 127, EP 2 326 615 and EP 0 69. However, such heteroazeotropic distillation becomes very energy-intensive when the acrylic acid is too diluted in water, as described in patent EP 1 716 095.

[0019] In the case of liquid-liquid extraction, most purification processes focus on the separation of acrylic acid with water and acetic acid as the main impurity. Indeed, depending on the catalyst and the operating conditions, the oxidation of propene produces several impurities and acetic acid may be one of the most substantial. Liquid / liquid extraction is carried out to avoid polymerization associated with the acid in the acrylic acid / acetic acid separation column. Too high a percentage by mass of acetic acid in a stream rich in acrylic acid will cause fouling of the equipment and shutdown of the plant. Such processes were described at the beginning of the 1970s in patents US 3 798 264 and FR 2162486, and then developed in more complex form in patents US 6 737 546, US 10 029 976 and EP 3 404 015 B1 . After condensing of the gas formed during the oxidation of propene, the aqueous medium is introduced into a liquidliquid extraction column where it is brought into countercurrent contact with a hydrophobic solvent comprising one or more hydrophobic organic solvents having a boiling point lower than that of acrylic acid. The extracted organic phase is rich in solvent and contains, among other components, acrylic acid and acetic acid, which is then sent to different distillations to purify the acrylic acid. Additional purification is carried out by crystallization or specific distillation to achieve the glacial grade (AAg).

[0020] In the case of the biobased acrylic acid production process, certain impurities are produced in larger quantities than in the conventional propene oxidation process, for example propionic acid and hydroxyacetone. However, it is difficult to separate acrylic acid from propionic acid by conventional distillation because of their close boiling points (the boiling point of acrylic acid is 142.0°C, and that of propionic acid is 140.9°C). The removal of propionic acid is therefore a challenge.

[0021] Patents US 2020 / 0115312 and US 2020 / 0385329 propose the use of the water-propionic acid azeotrope to purify concentrated acrylic acid by adding water as an entrainer to carry out the azeotropic distillation.

[0022] Consequently, there is a need apparent for the placing on the market of a bio-acrylic acid based on a natural non-fossil carbon source, and meeting quality standards allowing its exploitation in the manufacture of a wide range of technical polymers, but without requiring an extremely thorough and therefore costly purification. The Applicant has developed a process for converting hydroxypropanoic acid and its derivatives into purified bio-acrylic acid, propionic acid and hydroxyacetone, with a high recovery rate and low energy consumption. The invention combines a reaction section to reduce the formation of by-products, in particular by implementing a rapid vaporization step followed by a catalytic dehydration step of the feed, to a specific acrylic acid recovery and purification sequence to produce propionic acid-purified bio-acrylic acid that is compatible with conventional glacial acrylic acid purification chains (ex-propene) while limiting energy consumption. This specific purification sequence includes in particular a first step of azeotropic distillation of the aqueous acrylic acid effluent to remove propionic acid upstream of the transfer of acrylic acid into the organic phase by liquid / liquid extraction and subsequent steps of purification by distillation. The formation of the propionic acid / water azeotrope allows propionic acid to be removed at a lower boiling point than that of the pure entities. Hydroxyacetone is removed during the liquid / liquid solvent extraction step, where acrylic acid is transferred from the aqueous phase to the organic phase, unlike hydroxyacetone, which has a greater affinity with water.

[0023] Subjects of the invention

[0024] The present invention concerns a process for converting a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof into bio-acrylic acid purified in terms of propionic acid, comprising at least the following steps: a) a step of vaporization by contacting a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof with an inert hot gas to obtain a gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof; b) a step of catalytic dehydration of the gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof obtained at the end of step a) to obtain a gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof; c) a step of separation of the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof obtained at the end of step b) to obtain a gaseous stream comprising at least carbon monoxide and carbon dioxide, and an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof; d) a step of azeotropic distillation in a first distillation column of the aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof, obtained at the end of step c) to obtain at the top of said distillation column an aqueous effluent rich in propionic acid and at the bottom of said distillation column an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid; e) a step of liquid / liquid extraction by contacting said aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid obtained at the end of step d) with an organic extractant in a liquid / liquid extraction column to obtain a first aqueous stream containing dissolved organic extractant at the bottom of said liquid / liquid extraction column, and an organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof at the top of said liquid / liquid extraction column; f) a step of heteroazeotropic distillation in a second distillation column of the organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof obtained at the end of step e) to recover at the top of said distillation column a first liquid stream comprising the organic extractant and a second aqueous stream containing the dissolved organic extractant, and at the bottom of said distillation column a stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof; g) a step of separation in a third distillation column of the stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof obtained at the end of step f) to obtain at the top of the column a stream of bio-acrylic acid purified in terms of propionic acid, and at the bottom of the column a stream comprising impurities.

[0025] According to one or more embodiments according to the invention, step d) is carried out under at least one of the following operating conditions:

[0026] - an absolute pressure of greater than 0.015 MPa, preferably greater than 0.05 MPa and even more preferably greater than 0.1 MPa;

[0027] - a column bottom temperature of less than 180°C, preferably less than 150°C and more preferably less than 130°C,

[0028] - a number of theoretical plates of the distillation column of greater than 20, preferably greater than 35, and more preferably greater than 50.

[0029] According to one or more embodiments according to the invention, during step d) at the top of the first distillation column, a gaseous stream is recovered which undergoes the following energy recovery sequence:

[0030] - passage of said gaseous stream through a compressor to obtain a compressed gaseous stream,

[0031] - passage of said compressed gaseous stream through a heat exchanger allowing the bottom of the distillation column to be reboiled to obtain a condensed gaseous stream. According to one or more embodiments according to the invention, the organic extractant used in step e) comprises at least one organic solvent or organic solvent mixture selected from aromatics, naphthenes, alkanes, esters, ketones, ethers, preferably ethers, and preferably methyl t-butyl ether (MTBE), and ethyl tert-butyl ether (ETBE).

[0032] According to one or more embodiments according to the invention, the gas stream comprising at least carbon monoxide and carbon dioxide obtained at the end of step c) is converted into inert gas in a step h) before being recycled to step a) in a reaction unit selected from reverse water gas shift reaction, thermal oxidation or CO boiler units.

[0033] According to one or more embodiments according to the invention, the gaseous stream comprising at least carbon monoxide and carbon dioxide obtained at the end of step c) is recycled to step a) in the following energy recovery sequence:

[0034] - mixing of the inert gas with a dilution water stream to form a gas / liquid mixture such that the molar concentration of water at the entry of catalytic dehydration step b) is between 1 mol % and 40 mol %, preferably between 2 mol % and 35 mol %, and even more preferably between 3 mol % and 30 mol %;

[0035] - vaporization of said gas / liquid mixture in contact with the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof obtained at the exit of step b) through an exchanger to obtain an inert gaseous stream;

[0036] - heating of the inert gas stream in a heating device to obtain said inert gas.

[0037] According to one or more embodiments according to the invention, the liquid stream comprising the organic extractant obtained at the end of step f) after condensation in the condenser is recycled upstream of the liquid / liquid extraction step e).

[0038] According to one or more embodiments according to the invention, the first aqueous stream containing the dissolved organic extractant obtained at the end of step e) is purified in a stripping column during a step i) to recover an aqueous effluent depleted in organic solvent at the bottom of said stripping column and a gaseous effluent enriched in organic solvent at the top of said stripping column.

[0039] According to one or more embodiments according to the invention, the second aqueous stream containing the dissolved organic extractant obtained at the end of step f) after condensation in the condenser is recycled upstream of step i) to recover an aqueous effluent depleted in organic solvent at the bottom of said stripping column and a gaseous effluent enriched in organic solvent at the top of said stripping column. According to one or more embodiments according to the invention, the aqueous effluent rich in propionic acid, obtained at the top of said distillation column of step d), is sent during a step j) into a distillation column at a temperature greater than 130°C in order to form acrylic acid oligomers within said distillation column and to recover at the top of said distillation column an aqueous effluent rich in by-products comprising propionic acid and at the bottom of the column oligomers of acrylic acids.

[0040] According to one or more embodiments according to the invention, the stream comprising impurities at the bottom of said distillation column from step g) is sent during a step k) of recovery of acrylic acid by thermal or catalytic cracking for an acrylic acid stream and a heavier compounds stream.

[0041] According to one or more embodiments according to the invention, the vaporization step a) is carried out by atomization.

[0042] According to one or more embodiments according to the invention, step b) of catalytic dehydration of the gaseous effluent based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof obtained at the end of step a) is carried out by contacting said gaseous stream with a fixed bed dehydration catalyst at a temperature of between 180°C and 450°C, at a pressure of between 0.1 MPa and 12 MPa and a feed mass flow rate to catalyst mass ratio of between 0.01 IT1and 100 IT1to obtain a gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof.

[0043] According to one or more embodiments according to the invention, the catalyst used in step b) comprises an active phase based on salts of sulfates, phosphates or a mixture of these salts and a support comprising at least one refractory oxide.

[0044] Another subject according to the invention concerns a bio-acrylic acid derived from a carbon source of natural origin and purified in terms of propionic acid, said acid comprising:

[0045] - an acrylic acid purity of greater than 99.0% by weight, preferably greater than 99.7% by weight,

[0046] - a water content of less than 2.5%,

[0047] - a propionic acid content of less than 500 ppm by weight, preferably less than 300 ppm,

[0048] - a hydroxyacetone content of less than 250 ppm. Description of the figures

[0049] Figure 1 shows a diagram of a process for converting a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof into bio-acrylic acid purified in terms of propionic acid according to a particular embodiment.

[0050] Figure 2 shows a detailed diagram of the reaction section, also referred to here as the hot section, of the conversion process described in Figure 1 according to a particular embodiment. Figure 3 shows a diagram of the azeotropic distillation column d) of the process diagram for the conversion of a liquid feed based on hydroxypropanoic acid, derivatives of hydroxypropanoic acid according to a particular embodiment.

[0051] Figure 4 shows a diagram of the acrylic acid recovery section j) after the first azeotropic distillation according to a particular embodiment.

[0052] Detailed description

[0053] Definitions

[0054] Bio-acrylic acid is understood to mean acrylic acid originating from a carbon source of natural origin.

[0055] Bio-acrylic acid purified in terms of propionic acid is understood to mean acrylic acid originating from a carbon source of natural origin with a propionic acid concentration of less than 500 ppm, preferably less than 300 ppm, and even more preferably less than 200 ppm.

[0056] The weight hourly space velocity (WHSV) is defined as follows:

[0057] [Math 1]

[0058] In this text, the yield of acrylic acid (AA) as the amount of hydroxypropanoic acid (and its derivatives) converted during the reaction according to the following equation:

[0059] [Math 2]

[0060] Rendement A A (%) = 100

[0061] Concentration of compound i in stream A containing compound i in % by weight: [Math 3] 100

[0062] Mass ratio of compound i to acrylic acid in stream A:

[0063] [Math 4]

[0064] In the remainder of the text, the mean diameter of the liquid droplets of the process according to the invention is measured by the laser particle size technique.

[0065] Description

[0066] A subject of the present invention is a process for converting a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof into bio-acrylic acid purified in terms of propionic acid, comprising at least the following steps: a) a step of vaporization by contacting a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (1) with an inert hot gas (2) to obtain a gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (3); b) a step of catalytic dehydration of the gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (3) obtained at the end of step a) to obtain a gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4); c) a step of separation of the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4) obtained at the end of step b) to obtain a gaseous stream comprising at least carbon monoxide and carbon dioxide (5), and an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6); d) a step of azeotropic distillation in a first distillation column (D) of the aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6) obtained at the end of step c) to obtain at the top of said distillation column an aqueous effluent rich in propionic acid (7) and at the bottom of said distillation column an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid (8); e) a step of liquid / liquid extraction by contacting said aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid (8) obtained at the end of step d) with an organic extractant (9) in a liquid / liquid extraction column (E) to obtain a first aqueous stream containing dissolved organic extractant (10) at the bottom of said liquid / liquid extraction column, and an organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof (11) at the top of said liquid / liquid extraction column; f) a step of heteroazeotropic distillation in a second distillation column (F) of the organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof (11) obtained at the end of step e) to recover at the top of said distillation column a first liquid stream comprising the organic extractant (12) and a second aqueous stream containing the dissolved organic extractant (13), and at the bottom of said distillation column a stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof (14); g) a step of separation in a third distillation column (G) of the stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof (14) obtained at the end of step f) to obtain at the top of the column a stream of bio-acrylic acid purified in terms of propionic acid (15), and at the bottom of the column a stream comprising impurities (16).

[0067] Steps a) and b) can be carried out within the same reactor.

[0068] Steps a) to g) are described in detail below. Moreover, other optional additional steps (h), i), j), k)) are described below.

[0069] The feed

[0070] According to the invention, the feed supplying the process for converting hydroxypropanoic acid and its derivatives into acrylic acid advantageously comprises at least one compound included in the list of hydroxypropanoic acid and its derivatives. Said feed advantageously comprises a hydroxypropanoic acid selected from 2-hydroxypropanoic acid and 3- hydroxypropanoic acid. Preferably, said feed comprises 2-hydroxypropanoic acid. Said feed comprises between 1 % and 99.9% by weight, preferably between 10 and 99.5% by weight, very preferably between 50 and 99% by weight and even more preferably between 55 and 85% by weight of hydroxypropanoic acid and its derivatives relative to the total weight of the feed. Preferably, said liquid feed is based on lactic acid.

[0071] Said feed may also comprise impurities linked, in particular, to the processes for obtaining hydroxypropanoic acid and its derivatives, such as fermentation. The content of impurities is preferably less than 10% by weight of said feed. The hydroxypropanoic acid or acids and derivatives thereof included in said feed can be of any origin, chemical, petrochemical or biobased.

[0072] Said feed comprises advantageously between 0.1% and 99% by weight, preferably between 0.05% and 90% by weight, very preferably between 1 % and 50% by weight and even more preferably between 2% and 40% by weight of water relative to the total weight of the feed.

[0073] The sum of the contents of hydroxypropanoic acid and its derivatives, of water, and of any impurities represents 100% by weight of the feed.

[0074] The vaporization step a) is carried out by bringing a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (1) into contact with an inert hot gas (2) to obtain a gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (3). The hot gas injected in step a) is selected from inert gases such as nitrogen, helium, argon, air, carbon monoxide, carbon dioxide, or water vapour; preferably, said hot gas is a mixture of water vapour and one or more inert gases. Optionally, a portion of this gas comes from recycling of the gases produced.

[0075] Preferably, the hot gas is injected in step a) at a temperature of between 350°C and 550°C, preferably between 380°C and 500°C, and even more preferably between 400°C and 480°C.

[0076] The total duration of step a) is advantageously less than 180 milliseconds, preferably less than 150 milliseconds, and even more preferably less than or equal to 100 milliseconds in order to minimize the contact time in the liquid and gas phase.

[0077] Preferably, the liquid feed of hydroxypropanoic acid is dispersed in the form of droplets with a mean diameter of less than 1 mm so as to offer a large exchange surface area between the droplet and the hot gas in order to obtain high vaporization rates and consequently a rapid vaporization. Preferably, the mean diameter of the droplets is less than 500 pm, and even more preferably less than 100 pm. These droplets are obtained by any dispersion means known to those skilled in the art (injector, pressure tube, atomization nozzle, etc.). Without this being limiting, mention may be made of pressurized nozzles, two-fluid nozzles, rotating nozzles and vortex nozzles. Preferably, the dispersion and vaporization take place in multitubular equipment (A) so as to promote the piston flow and control the residence time distribution of the liquid phase and the gas phase in each tube. According to the invention, a step b) of catalytic dehydration of the gaseous mixture from step a) is carried out by bringing said gas mixture into contact with a fixed-bed dehydration catalyst at a temperature of between 180°C and 450°C, at a pressure of between 0.1 MPa and 12 MPa and a feed mass flow rate to catalyst mass ratio (WHSV) of between 0.01 IT1and 100 IT1.

[0078] The concentration of hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof, at the entry of step b), is advantageously between 1 mol % and 10 mol %, preferably between 1 % and 5%, and even more preferably between 0.5 mol % and 5 mol %.

[0079] In this step, the weight hourly space velocity of the gaseous mixture in step b) is preferably between 0.05 h-1and 10 h-1, more preferably between 0.1 h-1and 0.3 h-1.

[0080] The temperature is advantageously between 180°C and 450°C, preferably between 250°C and 400°C, and even more preferably between 350°C and 390°C.

[0081] The catalytic dehydration pressure of step b) is advantageously between 0.1 MPa and 12 MPa, preferably between 0.2 MPa and 6 MPa, and even more preferably between 0.5 MPa and 5 MPa.

[0082] The catalytic dehydration water pressure of step b) is preferably between 0.1 MPa and 5 MPa, preferably between 0.2 MPa and 3 MPa, and even more preferably between 0.4 MPa and 2 MPa in order to maintain optimum catalytic activity of the catalyst.

[0083] The water content at the entry of the catalytic dehydration of step b) is preferably between 1 mol % and 40 mol %, preferably between 2 mol % and 35 mol %, and even more preferably between 3 mol % and 30 mol % in order to maintain optimum energy consumption (over the reaction section).

[0084] Optionally, the temperature of the catalytic dehydration zone is regulated by means of hot heat transfer fluid in order to compensate for the endothermicity of the catalytic reaction. This fluid may be either liquid or gaseous according to the embodiment.

[0085] The catalyst used in step b) preferably comprises an active phase based on salts of sulfates, phosphates or a mixture of these salts and a support comprising at least one refractory oxide. Preferably, the catalyst consists of a macroporous material based on at least one potassium phosphate salt and / or at least one caesium phosphate salt and silica.

[0086] The catalytic dehydration step is advantageously carried out in equipment (B) comprising at least one co-current downflow fixed bed reactor, or at least one multitubular reactor. Advantageously, the walls of the tubes, and catalytic reactors will be selected from, but not limited to, quartz, titanium, tantalum, stainless steel, inconel, given the corrosive nature of this type of feed but also the reactivity of certain surfaces.

[0087] This catalytic dehydration step b) produces a gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof. The conversion of the feed of hydroxypropanoic acid and its derivatives in step b) is greater than 90%, preferably greater than 95% and more preferably greater than 99%. Without limitation, the by-products of the reaction are carbon monoxide, carbon dioxide, oxygen, nitric oxide, nitrogen dioxide, acetaldehydes, propionic acid, acetic acid, pyruvic acid, 1 ,2-pentanedione, hydroxyacetones, acrylic acid derivatives of oligomer type. Thus, the gas mixture (4) resulting from step b) comprises light compounds which are non-condensable under the temperature and pressure conditions usually employed (for example nitrogen, oxygen, carbon monoxide, and carbon dioxide, water), light condensable compounds, in particular water, acrylic acid, light aldehydes, acetic acid, propionic acid, and heavy dimer compounds.

[0088] (c) Step of separation of the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof

[0089] The purpose of this separation step is to remove non-condensables, in particular carbon monoxide and carbon dioxide.

[0090] A first step of separation of the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4) obtained at the end of step b) is carried out in a separation device (C) to obtain a gaseous stream comprising at least carbon monoxide and carbon dioxide (5) and an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6). This separation takes place by cooling said gaseous effluent (4) in order to recover the acrylic acid and derivatives in the liquid phase. Such an exchange can be carried out by a simple cooling water exchanger, by an air cooler or preferably by a feed / effluent exchanger in order to recover the heat of the process as much as possible.

[0091] Preferably, the gaseous stream comprising at least carbon monoxide and carbon dioxide (5) is recycled to step a). In this case, the gaseous stream comprising at least carbon monoxide and carbon dioxide (5) is sent to a compressor. Advantageously, the gaseous stream comprising at least carbon monoxide and carbon dioxide (5) obtained at the end of step c) is converted into inert gas in a step h) before being recycled to step a) in a reaction unit selected from reverse water gas shift reaction, thermal oxidation (thermal oxidizer) or CO boiler units to obtain an inert gaseous stream (5a). The aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6) is sent to a separation / purification section d).

[0092] Given the high thermal levels of the reaction section, energy optimization of said reaction section of the process consisting of steps a), b) and c) (called hot section) is advantageously carried out. Reference is made to Figure 2 for more details on the recovery of energy from the hot section. Advantageously, the gaseous effluent comprising at least carbon monoxide and carbon dioxide (5) obtained after separation step c) is optionally converted into inert gas during a step h) to obtain a gaseous effluent, of which one part is purged by (5b) and the other (5a) is mixed into a dilution water stream (2a) to form a gas / liquid mixture (2b). Said gas / liquid mixture (2b) is then vaporized in flow in a feed / product heat exchanger (A1) in contact with the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4) obtained at the exit from step b) in order to obtain an inert gas stream (2c). The inert gas stream (2c) is then superheated in a heating device (A2), such as an oven, to obtain the inert gaseous stream (2) at a temperature sufficient to vaporize the liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (1) in step a) and to cause the resulting gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (3) to reach the temperature necessary for the dehydration reaction implemented in step b).

[0093] This implementation makes it possible to optimize energy recovery in the reaction section.

[0094] The purpose of this step is to remove propionic acid contained in a significant quantity in the aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof. At the entry to the azeotropic distillation step, the quantity of propionic acid relative to the quantity of acrylic acid, i.e. the mass ratio between propionic acid and acrylic acid, is between 0.001 and 0.075 (cf. [Math 4]).

[0095] The water-propionic acid mixture exhibits a positive azeotrope when the pressure is greater than 130 mbar (0.0130 MPa), i.e. when the composition of the azeotrope is present, the mixture has a lower boiling point than that of the pure entities. It is this feature that allows the separation of propionic acid from acrylic acid in aqueous solution. Below this pressure, the azeotrope does not exist, as described by James D. Olson, Richard E. Morrison, and Loren C. Wilson, Thermodynamics of Hydrogen-Bonding Mixtures. 5. GE, HE, and TSE and Zeotropy of Water + Acrylic Acid. Thus, according to the invention, the aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6) obtained at the end of step c) is sent to a first distillation column (D) to obtain at the top of said distillation column an aqueous effluent rich in propionic acid (7) and at the bottom of said distillation column an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid (8).

[0096] Advantageously, the number of theoretical plates of the distillation column (D) is greater than 20, preferably greater than 35, and more preferably greater than 50.

[0097] The absolute pressure of the distillation column is advantageously greater than 0.015 MPa, preferably greater than 0.05 MPa, and even more preferably greater than 0.1 MPa.

[0098] The column bottom temperature is advantageously less than 180°C, preferably less than 150°C and more preferably less than 140°C.

[0099] The implementation of this azeotropic distillation in order to remove propionic acid may prove, depending on the operating conditions, to be relatively energy-intensive. Referring to Figure 3, and in order to reduce the energy consumption of the azeotropic distillation column, the heat of the gaseous stream (6a) leaving at the top of the azeotropic distillation column (D) is advantageously recovered by recompression of said gaseous stream (6a) in a compressor (D1) to obtain a compressed gaseous stream (6b). Said compressed gaseous stream (6b) is then condensed in a heat exchanger (D2) allowing the bottom of the column (D) to be reboiled to obtain a partially condensed stream (6c). If necessary, a supplement to reboil the column bottom can be supplied by external energy to the process. The partially condensed stream (6c) is then sent to a gas-liquid separator (D3), of which part of the liquid phase returns to the distillation column as reflux (7a), the other part constitutes the aqueous, propionic acid rich effluent (7) which can optionally be sent to a step j) described below. The gas phase (7b) is evacuated to be reprocessed. This implementation significantly reduces the use of external energy.

[0100] The azeotropic distillation of step d) produces an aqueous effluent rich in propionic acid (7) which may, depending on the conditions under which the step is implemented, contain a non- negligible quantity of acrylic acid. In order to maximize its recovery rate, the aqueous effluent rich in propionic acid (7) is optionally introduced into a step j) for recovering the acrylic acid. Referring to Figure 4, the aqueous effluent rich in propionic acid (7) is sent to a distillation column (J) advantageously operating at a temperature greater than 130°C, preferably greater than 150°C and even more preferably greater than 180°C in order to produce oligomers of acrylic acids. Indeed, the oligomers formed have the advantage of having a boiling temperature markedly higher than that of water, propionic acid and other impurities included in the aqueous effluent rich in propionic acid (7). Thus, their separation is made easy. The water and propionic acid leave at the top (19) of the distillation column (J) while the acrylic acid oligomers (20a) leave at the bottom of the distillation column (J). The column bottom stream bearing the acrylic acid oligomers (20a) is then sent to a thermal or catalytic cracking section (J2) to recover a liquid acrylic acid stream (20) and a gaseous stream (20b). The liquid stream of acrylic acid (20) recovered can be reinjected into the process at various locations but preferably upstream of the liquid / liquid extraction column (E) of step e) described below.

[0101] The gaseous stream (20b) is evacuated to be reprocessed and optionally used as fuel gas for the energy requirements of the process.

[0102] The technologies for recovering the acrylic acid present in the oligomers may correspond to a thermal cracking implemented, for example and in a non-limiting manner, in various technologies such as scraped film evaporators or by catalytic cracking or any other means known to those skilled in the art, as described, for example, in patents US 4 317 926, US 5 734 075, US 9 758 463, US 20050245763 and US 2007280866. e) Liquid / liquid extraction step

[0103] This step makes it possible on the one hand to extract acrylic acid from the aqueous phase to transfer it to the organic phase and thus allow the subsequent purification steps, and on the other hand, by virtue of the properties of the solvent, to limit the transfer of impurity to the organic phase such as hydroxyacetone, or possibly residual hydroxypropanoic acid.

[0104] The aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid (8) obtained from step d) is contacted with at least one water- immiscible organic extractant (9) in a liquid / liquid extraction column (E) to obtain at the bottom of said liquid / liquid extraction column a first aqueous stream containing dissolved organic extractant and impurities including hydroxyacetone (10), and at the top of said liquid / liquid extraction column an organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof (11). Advantageously, the first aqueous stream containing the dissolved organic extractant (10) obtained at the end of step e) is purified in a stripping column (I) during optional step i) to recover an aqueous effluent depleted in organic solvent (17) at the bottom of said stripping column and a gaseous effluent enriched in organic solvent at the top of said stripping column (18).

[0105] The extractant (9) is selected so as to form a heterogeneous water / solvent azeotrope which will be separated in the subsequent distillation step f). Preferably, this extractant comprises at least one organic solvent or an organic solvent mixture selected from aromatic compounds, naphthenic compounds, alkanes, esters, ketones, ethers, preferably ethers, and preferably methyl t-butyl ether (MTBE), and ethyl tert-butyl ether (ETBE). Advantageously, the extractant (9) is mixed with a recycle stream comprising the organic extractant (12) obtained at the end of step f).

[0106] Advantageously, the number of theoretical plates of the extraction column is between 5 and 15.

[0107] Preferably, the extractant (9) and said aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (8) circulate in countercurrent.

[0108] The absolute pressure in the extraction column is advantageously less than 1 MPa, preferably less than 0.5 MPa and even more preferably less than 0.2 MPa.

[0109] The temperature of the column is advantageously less than 70°C, preferably less than 50°C and more preferably less than 40°C.

[0110] Preferably, the extraction column operates continuously.

[0111] The ratio of aqueous phase / organic phase volume flow depends on the degree of dilution of the acrylic acid. A person skilled in the art will adjust this ratio so as to sufficiently extract the acrylic acid. f) Heteroazeotropic distillation step

[0112] The heteroazeotropic distillation step separates the acrylic acid from the solvent and recovers the solubilized water.

[0113] Indeed, the organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof (11) contains mainly solvent, acrylic acid and water. Under the conditions for carrying out the distillation, the water dissolved in the organic phase forms a positive azeotrope with the water when the mixture is brought to boiling. The boiling point of the azeotropic water-solvent mixture is in this case lower than that of the pure entities, whether water, solvent or acrylic acid, and the gas phase generated has the composition of the azeotrope. This lowering of the temperature facilitates the separation between acrylic acid on the one hand and water and solvent on the other.

[0114] Unlike a homogeneous azeotrope, two immiscible liquid phases are formed when the gas phase is condensed. The interest here is on the one hand to be able to carry out distillation at a lower head temperature (positive azeotrope) and on the other hand to be able to separate the water from the solvent by simple decantation (resulting heterogeneous phases).

[0115] The organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof (11) obtained at the end of step e) is therefore sent to heteroazeotropic distillation step f) in a second distillation column (F) to recover at the top of said column two liquid streams after condensation in a condenser (C1) located at the top of said distillation column (F), one comprising the organic extractant (12), the other comprising a second aqueous stream containing dissolved organic extractant (13), and at the bottom of said distillation column a stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof (14). Advantageously, the liquid stream comprising the organic extractant (12) obtained at the end of step f) after condensation in the condenser (C1) is recycled upstream of step e) of liquid / liquid extraction.

[0116] The number of theoretical plates of said distillation column is advantageously greater than 6, preferably greater than 10.

[0117] The absolute pressure is advantageously less than 0.1 MPa, preferably less than 0.05 MPa and even more preferably less than 0.02 MPa.

[0118] The column bottom temperature is advantageously less than 110°C, preferably less than 100°C and more preferably less than 90°C.

[0119] The technologies of the internals of the distillation column used are conventional technologies such as trays or bulk packing or structured packing and preferably packed columns.

[0120] The column can be evacuated by any means known to those skilled in the art, such as, for example, the use of a steam ejector or a liquid ring pump.

[0121] The aqueous streams (10) and (13) obtained at the end of step e) and f), containing dissolved solvent, may optionally be sent to a distillation column (I) called a steam stripping column in order to recover therefrom the dissolved solvent by steam stripping by formation of a heteroazeotrope between water and said solvent during a step i). In this optional step, the top stream (18) of the column is condensed. After condensation, the resulting upper liquid phase is recycled to liquid / liquid extraction step e), and the lower liquid phase is refluxed into column (I). Depending on the purity of the column bottom stream (17), it is sent to a water retreatment unit.

[0122] The number of theoretical plates of said distillation column (I) is advantageously greater than 6, preferably greater than 10.

[0123] The absolute pressure is advantageously less than 1 MPa, preferably less than 0.5 MPa and even more preferably less than 0.2 MPa. q) Separation step in a third distillation column

[0124] This so-called rectification stage makes it possible to separate acrylic acid from a mixture containing acrylic acid, heavy compounds, in particular acrylic acid dimers, and other impurities with a high boiling point, such as a small part of the unconverted feed (hydroxypropanoic acid and its derivatives). Indeed, the passage of acrylic acid through the different steps of the separation process leads to the formation of dimers or oligomers. The stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof (14) obtained at the end of step f) is sent to a third distillation column (G) to obtain at the column top bioacrylic acid purified in terms of propionic acid (15), and at the column bottom a stream comprising impurities (16).

[0125] The number of theoretical plates of said distillation column (G) is advantageously greater than 6, preferably greater than 10.

[0126] Given the sensitivity of acrylic acid to temperature, the distillation column is advantageously used under high vacuum so as not to exceed a bottom temperature of 130°C, preferably less than 110°C and more preferably less than 100°C, limiting the degradation of the acrylic acid. The absolute pressure is consequently advantageously less than 0.1 MPa, preferably less than 0.05 MPa and even more preferably less than 0.02 MPa.

[0127] The column can be evacuated by any means, such as by the use of a steam ejector, a liquid ring pump or any other means known to those skilled in the art.

[0128] In order to maximize the yields of acrylic acid, an optional step k) aimed at converting the oligomerization products of acrylic acid that are present in the stream comprising impurities (16) into acrylic acid is advantageously implemented. This solution for recovering acrylic acid contained in the heavy impurities can correspond either to a thermal cracking carried out, for example and in a non-limiting manner, in various technologies, such as scraped film evaporators, either with catalytic cracking or any other means known to those skilled in the art, as described for example in patents US 4 317 926, US 5 734 075, US 9 758 463, US 2005 / 0245763, or else US 2007 / 280866. The optional step k) makes it possible to recover a stream of acrylic acid (16b) which can be returned to the third distillation column (G) of step g) and a stream of residual heavy compounds (16a).

[0129] The products

[0130] The main product obtained at the end of the steps of the process according to the invention is a bio-acrylic acid, obtained from a carbon source of natural origin, purified in terms of propionic acid with an acrylic acid purity of greater than 99.0% by weight, preferably greater than 99.7% by weight, a water content of less than 2.5%, a propionic acid content of less than 500 ppm by weight, preferably less than 300 ppm, a hydroxyacetone content of less than 250 ppm and a total content of other impurities of less than 300 ppm by weight. A conventional polymerization inhibitor known in this application was also added in-line, to total at least 200 ppm in the final product. The bio-acrylic acid purified in terms of propionic acid produced according to at least steps a) to g) of the invention can then be subjected to an additional crystallization process to obtain the high purity acrylic acid known as glacial grade (AAg).

[0131] Examples

[0132] In Examples 1 and 2, only the reaction steps (referred to as hot section steps a), b) and c)) are described. Examples 1 and 2 make it possible to visualize the impact of the water content at the entry to step b) on the energy consumption of the reaction section.

[0133] In Examples 3 and 4, steps a), b), c) are identical. Two purification sequences, steps d) to g), will be compared on the propionic acid content.

[0134] The composition of the gas phase is analysed by gas chromatography. The liquid phase is analysed by high-performance liquid chromatography (HPLC) and by measuring the total organic carbon (TOC).

[0135] The catalyst used is realized in the following way: use is made of a source of colloidal silica sol (12.4%) and a source of potassium dihydrogen phosphate powder (KH2PO4; Aldrich) (15.2%) ground and sieved to 100 pm are introduced and mixed in the vessel of a centrifugal planetary mixer. The suspension obtained, a Methocel™ powder (K15M) (3%) and a precipitated silica powder (Nyasil20; Nyacol) (72.4%) are introduced and premixed in a mixer. Water is added dropwise until a paste is obtained. The paste obtained is then extruded using a cylindrical die with a diameter of 1.6 mm. The extrudates are dried at 120°C. Finally, the extrudates are subjected to a calcination temperature of 800°C for 4 hours.

[0136] Then 2.8 grams of potassium hydrogen phosphate (K2HPO4, M = 174 g / mol) and 2.1 g of ammonium hydrogen phosphate ((NH^zHPC , M = 132 g / mol) are first dissolved in 4.2 ml of distilled water at ambient temperature. After dissolution is complete, the mixture is added dropwise to 20 grams of material precursor C2. The solid is matured at ambient temperature for 40 minutes and then dried under air at 120°C for 10 hours. It is then calcined under air at 450°C for 4 hours in order to prepare the catalyst used.

[0137] The compositional analysis of the above material by X-ray fluorescence (XRF) gives a weight content of K of 8.7% by weight and of P of 7.5% by weight relative to the total weight of the catalyst. The equivalent average weight content of KPO3 after calcination is 27% by weight relative to the total weight of the catalyst. Example 1 : Steps a), b) and c) with a water content at the entry to step b) of 22.2 mol % A liquid feed of 24.435 tonnes / hour containing 70% by weight of hydroxypropanoic acid and 30% by weight of water is converted into acrylic acid in contact with the solid catalyst described above. The catalytic dehydration reaction (step b) takes place in the gas phase, at 1.82 MPa absolute and at a temperature of 365°C. The concentration of hydroxypropanoic acid at the catalyst entry is 2.5 mol %.

[0138] Part of the recycled gaseous effluent (5a) is mixed with a dilution water stream (2a) to obtain a gas / liquid mixture (2b). The flow rates of each of these streams were adjusted so as to obtain a hydroxypropanoic acid content of 2.5 mol % and a water content of 22.2 mol % at the catalyst entry. The composition of the feed and the flow rates are given in Table 1.

[0139] Table 1 : Flow rate and composition of streams entering step a)

[0140] Step a): Vaporization of the liquid feed Said gas / liquid mixture (2b) is vaporized in a feed / product exchanger (A1) in contact with the effluent from the catalytic dehydration reactor (4) resulting from step b) in a gaseous stream (2c) whose temperature is 328°C. The gaseous stream (2c) is superheated in an oven (A2) to 512°C, which is a sufficient temperature for the hydroxypropanoic acid stream (1) injected in the form of droplets through several single-fluid atomization nozzles to be vaporized in step (a) and for the resulting mixture (3) to reach 365°C before being contacted with the catalyst.

[0141] The energy required for the operation of the recycling loop (compressor and oven (A2)) is given in Table 2. The aim is to vaporize 201.8 tonnes / hour of the liquid feed (1) and to bring the temperature of the resulting gaseous stream (3) to 512°C using the heat supplied via the stream (2a) of water vapour and part of the recompressed recycle gas (5a) from step c) and the external energy provided by the oven (A2).

[0142] The ratio between the power of the oven and the energy required to vaporize and bring the hydroxypropanoic acid feed under the temperature and pressure conditions of the dehydration reaction is defined. In Example 3, the ratio is 1.16, which means that the external energy supplied to the oven is almost compensated by the energy recovered at the exchanger (A1). The energy recovery is optimal.

[0143] This implementation consequently makes it possible to optimize energy recovery in the reaction section comprising steps a), b) and c). Steps b) and c) are described below.

[0144] Table 2: Energies external to the process for steps a), b), c) (so-called hot reaction section)

[0145] Step b) Catalytic dehydration

[0146] The vaporized stream (3) then enters a multitubular catalytic dehydration reactor. Based on a WHSV of 0.2 IT1, the mass of catalyst required for the reaction is 85.5 tonnes (distributed in the various tubes). Under these conditions, the final production of acrylic acid is 11.35 tonnes / hour. A yield of acrylic acid of 83% is obtained.

[0147] The composition at the exit from the catalytic dehydration reactor is given in Table 3. Table 3: Temperature, pressure, flow rate and composition at the entry and exit of the catalytic dehydration reactor (step b) Step c) Gas / liquid separation

[0148] This step makes it possible to recover the acrylic acid-based dehydration effluent in liquid form and to remove / recycle the non-condensables.

[0149] The effluent from the catalytic dehydration reactor (4) is cooled by passing through the effluent feed exchanger (A1) and then through other exchangers to 40°C in order to obtain a gas / liquid effluent (4) which will be separated in a separating drum (C) making it possible to recover the gas (5) which is recycled to the vaporization section (a) via a compressor as described in a) and an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6). The temperatures, pressures, compositions and flow rates of the streams leaving step c) are given in Table 4. Table 4: Temperature, pressure, flow rates and composition after gas / liquid separation step c)

[0150] Example 2: Steps a), b) and c) with a water content at the entry to step b) of 45.2 mol % In Example 2, the implementation is identical to Example 1 , where a liquid feed of 24.435 tonnes / hour containing 70% by weight of hydroxypropanoic acid and 30% by weight of water is converted into acrylic acid in contact with the solid catalyst described above. The catalytic dehydration reaction (step b) takes place in the gas phase, at 0.88 MPa absolute and at a temperature of 365°C. The concentration of hydroxypropanoic acid at the catalyst entry was 2.5 mol % and the water flow rate was adjusted so as to reach 45.2 mol % at the catalyst entry.

[0151] The total pressure makes it possible to reach a partial pressure of water of 0.4 MPa.

[0152] The composition of the feed is given in Table 5. Table 5: Flow rate and composition of streams entering step a)

[0153] Step a): Vaporization of the liquid feed

[0154] A portion of the recompressed recycled gaseous effluent (5a) is mixed with a dilution water stream (2a) to form a liquid gas mixture (2b). The flow rates of each of these streams were adjusted so as to obtain a hydroxypropanoic acid content of 2.5 mol % and a water content of 45.2 mol % at the catalyst entry of reaction section b).

[0155] Said stream (2b) is partially vaporized in the feed / product exchanger (A1) by contact with the stream (4) leaving the dehydration reactor of step b) into a gas stream (2c) whose temperature is 148°C. The gas stream (2c) is superheated in the oven (A2) to obtain an inert gas stream

[0156] (2) at 516°C, i.e. a temperature sufficient for the hydroxypropanoic acid stream (1) injected in the form of droplets through several single-fluid atomization nozzles to be vaporized in step a) and for the resulting mixture to reach 365°C before being contacted with the dehydration catalyst of step b). The external energy supplied by the oven and compressor running the recycling loop is given in Table 6. Under these conditions, where the water concentration at the entry to step b) is greater than 40%, the external energy consumption of the reaction section comprising steps a), b) and c) is very high. Compared to Example 1 , the energy to be supplied to the compressor to recycle the gas stream is almost twice as high, as is the energy to be supplied to the oven for the same amount of hydroxypropanoic acid to be vaporized and converted.

[0157] The ratio between the power of the oven and the energy required to vaporize and bring the hydroxypropanoic acid feed under the temperature and pressure conditions of the dehydration reaction is 2.19. Energy recovery is degraded.

[0158] Table 6: Energies external to the process for steps a), b), c) (so-called hot reaction section)

[0159] For Examples 3 and 4, reaction steps a), b) and c) are identical to those of Example 1. Examples 3 and 4 compare different purification sections.

[0160] Example 3: Purification according to steps d') to g) with step d') using a conventional distillation (comparative)

[0161] The aqueous effluent (6) obtained at the end of step c) is sent to a recovery / purification sequence consisting of steps d’) to g). However, step d1) is operated so as not to carry out the separation of propionic acid by azeotropic distillation, but simply to separate the light compounds from the heavy products containing in particular water, acrylic acid and some impurities by simple distillation.

[0162] Stage d’) First distillation

[0163] In this example, the main purpose of this step is to remove light compounds from the aqueous acrylic acid effluent. The liquid phase (6) at the exit from separation step c) enters a first distillation column in order to recover the light acrylic acid compounds at the top of the column. The first distillation column is equipped with trays for a total of 10 theoretical plates and operates at 0.22 MPa at the top to reach 129°C at the bottom.

[0164] The effluent from the liquid phase reactor recovered at the column top (7) mainly comprises acetaldehyde, water, and light compounds of the CO2 type. This effluent is cooled to 40°C by passing through several exchangers. The column bottom consists mainly of acrylic acid (8).

[0165] In this example, 99.9% by weight of acrylic acid is recovered at the bottom of said column and then sent to a liquid-liquid extraction column E.

[0166] Step e) Liquid / liquid extraction

[0167] This step makes it possible to extract the acrylic acid from the aqueous phase to transfer it to the organic phase and thus allow the subsequent purification steps.

[0168] The acrylic acid recovered at the bottom of the first distillation column after step d) is brought into contact in a liquid / liquid extraction column with the extraction solvent MTBE (9). The extraction column comprises 6 theoretical plates. The ratio of the mass flow rate between the acrylic acid and the solvent was adjusted to 0.78 so as to recover 99% acrylic acid in the extract corresponding to the stream (11).

[0169] The acrylic acid is extracted from the aqueous medium by transfer into the solvent phase in the stream extracted at the top of the column (11). The aqueous phase at the bottom of the column corresponds to the raffinate (10). The use of MTBE as a solvent makes it possible to greatly reduce impurities in the extraction phase such as hydroxyacetone, the remaining acetaldehyde, unconverted hydroxypropanoic acid, which passes into the aqueous phase (10).

[0170] Step f) A second heteroazeotropic distillation step

[0171] This step separates the acrylic acid from the solvent and recycles said solvent.

[0172] The organic stream containing the extracted acrylic acid (11) is sent to a second vacuum distillation column (F) where the extraction solvent is recovered at the top of the column and the stream rich in acrylic acid at the bottom of the column (14). The distillation column (F) is composed of a packing corresponding to 10 theoretical plates. The upper pressure is controlled at 0.018 MPa in order to reach 96°C at the bottom of the column and avoid thermal degradation of the acrylic acid. The recovery rate of acrylic acid is 99.7%.

[0173] After condensation of the upper stream from the vacuum distillation column in the condenser (C1) located at the top of said distillation column, allowing recovery of the solvent (12) to be recycled to the liquid / liquid extraction column (E) on the one hand and the aqueous phase containing the dissolved organic extractant (13) to be sent to the water stripping column (I) to recover the dissolved solvent on the other hand. Rectification step g)

[0174] This step separates the acrylic acid from the acrylic acid-rich stream (14) also containing heavy compounds, especially acrylic acid dimers produced during the passage of the acrylic acid through the various steps of the separation process and other impurities with a high boiling point such as a small part of the unconverted feed (hydroxypropanoic acid and its derivatives).

[0175] The distillation column (G) is composed of a packing corresponding to 10 theoretical plates.

[0176] The upper pressure is controlled at 0.018 MPa in order to reach 91°C at the bottom of the column and limit the thermal degradation of the acrylic acid. The recovery rate of acrylic acid is 99.7%. The compositions of the different streams obtained after each step are given in Table 7.

[0177] The purity of the acrylic acid in the final organic stream (15) is 97.7%, a water concentration of 0.1 % and a propionic acid concentration of greater than 2% by weight. Owing to the use of the MTBE solvent, hydroxyacetone is present only at a level of 240 ppm. This product is not compatible with conventional glacial acrylic acid (ex-propene) purification chains. Table 7: Temperature and composition of the streams along the different steps d’) to g) of the separation / purification section (Example 3) Example 4: Purification according to steps d) to g) with step d) using azeotropic distillation (according to the invention)

[0178] Reaction steps a), b) and c) are identical to those of Example 1. This time, the effluent (6) passes through an azeotropic distillation column D in order to separate the propionic acid from the acrylic acid and to bring the propionic acid concentration on the final product (15) to 500 ppm.

[0179] Step d) First azeotropic distillation

[0180] The liquid phase (6) at the exit from separation step c) enters an azeotropic distillation column in order to recover the propionic acid from the acrylic acid at the top of the column.

[0181] This distillation column is equipped with a packing for a total of 50 theoretical plates and operates at 0.22 MPa at the top for a temperature of 134°C at the bottom.

[0182] The effluent from the liquid phase reactor recovered at the top of the column (7) mainly comprises water, propionic acid and a minority of acrylic acid as described in Table 9. This effluent is cooled to 40°C by passing through several exchangers. The column bottom consists mainly of acrylic acid (8).

[0183] The azeotropic distillation column is operated with a reboiler heated with superheated steam. The condenser is cooled with an air cooler system. The energy consumption of these two elements is presented in Table 8. The energy consumption of the reboiler and the condenser of this azeotropic distillation column for carrying out the separation is very high.

[0184] Table 8: Energy to be supplied to the azeotropic distillation column (step d)

[0185] If a compressor is used on the overhead gas, it is then possible to reduce the energy consumption of the column (D), as illustrated in Figure 3. Indeed, the top flow of this column (6a) is compressed from 0.22 MPa to 0.49 MPa in the compressor (D1), its temperature increasing to 226°C. Said compressed stream (6b) is condensed in exchanger (D2), bringing said compressed effluent (6b) into contact with the bottom of said column (D) at the bottom reboiler, the temperature of which is 134°C. The heat exchange at the exchanger (D2) is 46.0 MW, which exactly compensates for the energy consumption of the reboiler (cf. Table 8). The external energy to be supplied to the compressor is 4.0 MW electric.

[0186] Steps e) and g) are carried out in the same manner as in Example 3. The compositions of the different flows are presented in Table 9.

[0187] The purity of the acrylic acid in the final organic stream (15) is 99.8%, a water concentration of 0.1 %, a propionic acid concentration of less than 500 ppm and a hydroxyacetone concentration of 248 ppm.

[0188] This product is compatible with conventional glacial acrylic acid (ex-propene) purification chains.

[0189] Table 9: Temperature and composition of the streams along the various steps d) to g) of the separation / purification section (Example 4)

Claims

CLAIMS1. Process for converting a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof into bio-acrylic acid purified in terms of propionic acid, comprising at least the following steps: a) a step of vaporization by contacting a liquid feed based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (1) with an inert hot gas (2) to obtain a gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (3); b) a step of catalytic dehydration of the gaseous stream based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (3) obtained at the end of step a) to obtain a gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4); c) a step of separation of the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4) obtained at the end of step b) to obtain a gaseous stream comprising at least carbon monoxide and carbon dioxide (5), and an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6); d) a step of azeotropic distillation in a first distillation column (D) of the aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (6) obtained at the end of step c) to obtain at the top of said distillation column an aqueous effluent rich in propionic acid (7) and at the bottom of said distillation column an aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid (8); e) a step of liquid / liquid extraction by contacting said aqueous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof and depleted in propionic acid (8) obtained at the end of step d) with an organic extractant (9) in a liquid / liquid extraction column (E) to obtain a first aqueous stream containing dissolved organic extractant (10) at the bottom of said liquid / liquid extraction column, and an organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof (11) at the top of said liquid / liquid extraction column; f) a step of heteroazeotropic distillation in a second distillation column (F) of the organic stream based on acrylic acid, acrylic acid derivatives or mixtures thereof (11) obtained at the end of step e) to recover at the top of said distillation column a first liquid stream comprising the organic extractant (12) and a second aqueous stream containing the dissolved organic extractant (13), and at the bottom of said distillation column a stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof (14);g) a step of separation in a third distillation column (G) of the stream enriched in acrylic acid, acrylic acid derivatives or mixtures thereof (14) obtained at the end of step f) to obtain at the top of the column a stream of bio-acrylic acid purified in terms of propionic acid (15), and at the bottom of the column a stream comprising impurities (16).2) Process according to Claim 1 , wherein step d) is carried out under at least one of the following operating conditions:- an absolute pressure of greater than 0.015 MPa, preferably greater than 0.05 MPa and even more preferably greater than 0.1 MPa;- a column bottom temperature of less than 180°C, preferably less than 150°C and more preferably less than 130°C,- a number of theoretical plates of the distillation column of greater than 20, preferably greater than 35, and more preferably greater than 50.3) Process according to one of Claims 1 or 2, wherein during step d) a gaseous stream (6a) undergoing the following energy recovery sequence is recovered at the top of the first distillation column (D):- passage of said gaseous stream (6a) through a compressor (D1) to obtain a compressed gaseous stream (6b),- passage of said compressed gaseous stream (6b) through a heat exchanger (D2) allowing the bottom of the distillation column (D) to be reboiled to obtain a condensed gaseous stream (6c).4) Process according to any one of the preceding claims, wherein the organic extractant (9) used in step e) comprises at least one organic solvent or organic solvent mixture selected from aromatics, naphthenes, alkanes, esters, ketones, ethers, preferably ethers, and preferably methyl t-butyl ether (MTBE), and ethyl tert-butyl ether (ETBE).5) Process according to any one of the preceding claims, wherein the gaseous stream comprising at least carbon monoxide and carbon dioxide (5) obtained at the end of step c) is converted into inert gas (5a) in a step h) before being recycled to step a) in a reaction unit selected from reverse water gas shift reaction, thermal oxidation (thermal oxidizer) or CO boiler units.6) Process according to Claim 5, wherein the gaseous stream comprising at least carbon monoxide and carbon dioxide (5) obtained at the end of step c) is recycled to step a) in the following energy recovery sequence:- mixing of the inert gas (5a) with a dilution water stream (2a) to form a gas / liquid mixture (2b) such that the molar concentration of water at the entry of catalytic dehydration step b) is between 1 mol % and 40 mol %, preferably between 2 mol % and 35 mol %, and even more preferably between 3 mol % and 30 mol %;- vaporization of said gas / liquid mixture (2b) in contact with the gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4) obtained at the exit of step b) through an exchanger (A1) to obtain an inert gaseous stream (2c);- heating of the inert gaseous stream (2c) in a heating device (A2) to obtain said inert gas (2).7) Process according to any one of the preceding claims, wherein the liquid stream comprising the organic extractant (12) obtained at the end of step f) after condensation in the condenser (C1) is recycled upstream of the liquid / liquid extraction step e).8) Process according to any one of the preceding claims, wherein the first aqueous stream containing the dissolved organic extractant (10) obtained at the end of step e) is purified in a stripping column (I) during a step i) to recover an aqueous effluent depleted in organic solvent (17) at the bottom of said stripping column and a gaseous effluent (18) enriched in organic solvent at the top of said stripping column.9) Process according to any one of the preceding claims, wherein the second aqueous stream containing the dissolved organic extractant (13) obtained at the end of step f) after condensation in the condenser (C1) is recycled upstream of step i) to recover an aqueous effluent depleted in organic solvent (17) at the bottom of said stripping column and a gaseous effluent (18) enriched in organic solvent at the top of said stripping column.10) Process according to any one of the preceding claims, wherein the aqueous effluent rich in propionic acid (7), obtained at the top of said distillation column (D) of step d), is sent during a step j) into a distillation column (J) at a temperature greater than 130°C in order to form acrylic acid oligomers within said distillation column and to recover at the top of said distillation column an aqueous effluent rich in by-products comprising propionic acid (19) and at the bottom of the column oligomers of acrylic acids (20).11) Process according to any one of the preceding claims, wherein the stream comprising impurities (16) at the bottom of said distillation column (G) from step g) is sent during a step k) of recovery of acrylic acid by thermal or catalytic cracking for an acrylic acid stream (16b) and a heavier compounds stream (16a).12) Process according to any one of the preceding claims, wherein the vaporization step a) is carried out by atomization.13) Process according to any one of the preceding claims, wherein step b) of catalytic dehydration of the gaseous effluent based on hydroxypropanoic acid, hydroxypropanoic acid derivatives or mixtures thereof (3) obtained at the end of step a) is carried out by contacting said gaseous stream with a fixed bed dehydration catalyst at a temperature of between 180°C and 450°C, at a pressure of between 0.1 MPa and 12 MPa and a feed mass flow rate to catalyst mass ratio of between 0.01 IT1and 100 IT1to obtain a gaseous effluent based on acrylic acid, acrylic acid derivatives or mixtures thereof (4).14) Process according to Claim 13, wherein the catalyst used in step b) comprises an active phase based on salts of sulfates, phosphates or a mixture of these salts and a support comprising at least one refractory oxide.15) Bio-acrylic acid derived from a carbon source of natural origin and purified in terms of propionic acid, said acid comprising:- an acrylic acid purity of greater than 99.0% by weight, preferably greater than 99.7% by weight,- a water content of less than 2.5%,- a propionic acid content of less than 500 ppm by weight, preferably less than 300 ppm,- a hydroxyacetone content of less than 250 ppm.

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