MX2008010086A - Acrylic acid preparation method - Google Patents

Abstract

The invention relates to a method for preparing acrylic acid from propylene, consisting of a first step comprising theoxidation of propylene to acrolein and a second step comprising the oxidation of acrolein to acrylic acid, including a glycerol dehydration step performed in the presence of a gas containing proplyene and, more specifically, in the presence of the reaction gas originating from the propylene to acrolein oxidation step. The inventive method enables the use, in part, of a renewable raw material, while increasing acrylic acid production.

Description

METHOD OF PREPARATION OF ACRYLIC ACID FIELD OF THE INVENTION The present invention concerns a process for the preparation of acrylic acid from propylene comprising a first step of oxidation of propylene to give acrolein and a second step of oxidation of acrolein to acrylic acid, which is it makes use of a glycerol dehydration step in the presence of a gas comprising propylene and more particularly in the presence of the reaction gas resulting from the oxidation step of propylene to give acrolein.

BACKGROUND OF THE INVENTION The conventional process for the synthesis of acrylic acid uses a catalytic propylene reaction using a mixture comprising oxygen. This reaction is generally carried out in the vapor phase and more often in two stages: the first stage carries out the substantially quantitative oxidation of the propylene to give a mixture rich in acrolein, in which the acrylic acid is a minor component, the second step carries out the selective oxidation of acrolein to give acrylic acid. The reaction conditions of these two steps, carried out in two reactors in series, are different and require catalysts suitable for the reaction. It is not necessary to isolate acrolein during this process in two stages. The reaction can also be carried out in a single reactor but, in this case, it is necessary to separate and recycle large amounts of acrolein in the oxidation step. In many cases, it may be advantageous to be able to increase the production capacities of acrylic acid of existing units. The production of acrylic acid is very dependent on the initial propylene material. Propylene, obtained by steam fractionation or catalytic fractionation of petroleum fractions, has the disadvantage of contributing to increase the greenhouse effect due to its fossil origin. In addition, propylene resources can become limited. Accordingly, it appears particularly advantageous to be able to increase the productive yield of acrylic acid while reducing dependence on a fossil resource. It has been known for a long time that glycerol can result in the production of acrolein. Glycerol results from methane lysis of vegetable oils, at the same time as methyl esters, which are themselves employed as fuels in diesel oil and heating oil. This is a natural product that enjoys a "green" aura, is available in large quantities and can be stored and transported without difficulty. Numerous studies were dedicated to give an economic value to glycerol according to its degree of purity and the dehydration of glycerol to give acrolein is one of the origins contemplated. The reaction involved in producing acrolein from glycerol is: CH2OH-CHOH-CH2OH < »CH2 = CH-CHO + 2H20 Generally, the hydration reaction is promoted at low temperatures and the dehydration reaction is promoted at high temperatures. In order to obtain acrolein, it is therefore necessary to employ a satisfactory temperature and / or a partial vacuum in order to displace the reaction. The reaction can be carried out in the liquid phase or in the gas phase. This type of reaction is known to be catalyzed by acids. Various processes for the synthesis of acrolein from glycerol in the prior art are described; Particular mention may be made of documents FR 695 931, US 2 558 520, WO 99/05085 and US 5 387 720. WO 2005/073160 describes a process for the preparation of acrylic acid from glycerol in two stages, the first stage consisting in subjecting the glycerol to a dehydration reaction in the gas phase and the second stage consisting of subjecting the gas reaction product thus obtained to a gas phase oxidation reaction. It has now been found that the dehydration reaction of glycerol to acrolein can be carried out in the presence of a gas comprising propylene and more particularly in the presence of the reaction gas resulting from the oxidation step of propylene to give acrolein. Therefore, it is advantageous to introduce glycerol in the conventional catalytic oxidation process in propylene gas phase in two stages in order to prepare acrylic acid, which makes it possible to use a renewable initial material, while increasing the production of acrylic acid. Such a process then corresponds to the criterion associated with the new concept of "green chemistry" in a more general context of sustainable development.

SUMMARY OF THE INVENTION The subject matter of the present invention is therefore a process for the preparation of acrylic acid from propylene comprising a first step of oxidation of propylene to give acrolein and a second step of oxidation of acrolein to give acrylic acid , characterized in that it comprises a step of dehydrating glycerol in the presence of a gas comprising propylene. Preferably, the gas comprising propylene is the reaction gas resulting from the oxidation step of propylene to give acrolein. Without the Applicant company which is bound to any explanation, it is believed that the glycerol dehydration step makes it possible to cool the reaction gases resulting from the first stage of oxidation of propylene to acrolein, before carrying out the second stage of oxidation of acrolein to give acrylic acid. This is because, in the reaction for the oxidation of propylene to acrolein, the reaction gases leave the reaction region at a high temperature, the reaction for the oxidation of propylene is exothermic. In a two-step process for the preparation of acrylic acid from propylene, it is necessary to cool the reaction gases resulting from the first stage of oxidation of propylene to give acrolein before entering the second stage of oxidation of acrolein for give acrylic acid when the reaction for the oxidation of acrolein to acrylic acid is carried out at a lower temperature than the reaction for the oxidation of propylene to give acrolein. In addition, acrolein can self-calcify at high temperatures resulting in loss of performance. This cooling is generally obtained by virtue of a heat exchanger placed current below the catalytic region of the first stage. The same effect may, in whole or in part, be obtained by virtue of the use of an endothermic reaction, such as the dehydration of glycerol. In the present invention, the glycerol dehydration reaction exhibits the advantage of resulting in the same main reaction product (acrolein) as the reaction for the oxidation of propylene. Accordingly, this results in an increase in the productive yield of acrolein, while efficiently recovering heat from the oxidation reaction, and consequently an increase in the productive yield of acrylic acid.

Other features and advantages of the invention will emerge more clearly upon reading the following description, with reference to the appended figures, in which: BRIEF DESCRIPTION OF THE DRAWINGS - Figures 1, 2 and 3 diagrammatically represent conventional configurations for the oxidation of propylene to give acrylic acid in two stages. - Figures 4 and 5 diagrammatically represent different configurations corresponding to embodiments of the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION In the process of the invention, the dehydration stage of glycerol is carried out in the gas phase in the presence of a catalyst at a temperature ranging from 150 ° C to 500 ° C, preferably between 250 ° C and 350 ° C, and a pressure between 1 and 5 bar. The glycerol dehydration step is carried out at the beginning of the reaction for the catalytic oxidation of propylene to give acrolein in the presence of the feed gas comprising propylene, or at the end of the reaction for the catalytic oxidation of propylene to give acrolein in the presence of the gas mixture resulting from this reaction. It can be incorporated directly into the oxidation reactor or it can be carried out in a reactor placed immediately towards the inlet or towards the outlet of the reactor for the oxidation of propylene to give acrolein. As the dehydration reaction is slightly endothermic, it is not necessary to have a multi-tubular bed for this reaction. The conventional fixed bed and a configuration like modules (sheets or trays) may be adequate. The modules exhibit the advantage of being able to be easily loaded and unloaded when the catalyst is deactivated. Catalysts that are suitable are homogeneous or multi-phase materials that are insoluble in the reaction medium and have an acidity of Hammett, registered as H0, of less than +2. As indicated in patent US 5 387 720, which refers to the article by K. Tanabe et al in "Studies in Surface Science and Catalysis", Vol. 51, 1989, Chapters 1 and 2, Hammett acidity is determined by means of titration of amine using indicators or by adsorption of a base in the gas phase. The catalysts corresponding to the criterion of acidity H0 of less than +2 can be selected from silicic materials (natural or synthetic) or acid zeolites; inorganic supports, such as oxides, covered with inorganic mono-, di-, tri- or polyacid acids; mixed oxides or oxides or also heteropolyacids. Advantageously, the catalysts are selected from zeolites, Nafion® compounds (based on sulfonic acid of fluoropolymers), chlorinated aluminas, phosphotungstic and / or silicotungstic acids and salts of acids, and various solids of the type comprising metal oxides, such as tantalum Ta205, niobium oxide Nb205, alumina A1203, titanium oxide Ti02, zirconia (Zn02, tin oxide Sn02, silica Si02 or silica alumum Si02 / Al203, impregnated with acid functional groups, such as functional groups borate B03, sulfate S04, tungstate W03, P04 phosphate, Si02 silicate or Mo03 molybdate, according to literature data, these catalysts all have an acidity of Hammett H0 of less than + 2. The preferred catalysts are sulphated zirconia, phosphatized zirconia, tungsten zirconia, zirconia silica, sulfated titanium or tin oxides, or aluminas or phosphated silicas, these catalysts all have an acidity mmett H0 of less than +2, the acidity H0 can then vary greatly, going down to values that are at least -20 on the reference scale with Hammett indicators. The table given on page 71 of the acid / base catalysis publication (C. Marcilly), Vol. 1, in Editions Technip (ISBN No. 2-7108-0841-2), the examples illustrate solid catalysts in this range of acidity. The glycerol is used pure or in the form of a dilute or concentrated aqueous solution. Advantageously, use is made of pure glycerol or an aqueous glycerol solution with a concentration ranging from 10% to 100% by weight, preferably ranging from 50% to 100% by weight, when used at the beginning of the oxidation of the propylene; the vapor present in the reaction gas resulting from the step of oxidation of propylene to acrolein makes it possible to dilute the glycerol solution and thus prevent side reactions, such as the formation of glycerol ethers or reactions between acrolein produced and glycerol . In the embodiment of the invention where the glycerol dehydration step is carried out towards the beginning of the reaction for the catalytic oxidation of propylene, use may be made of an aqueous glycerol solution, preferably at a concentration ranging from 10 to 50. % by weight, more particularly from 15% to 30% by weight. Glycerol can be injected in the liquid form or in the gas form. The injection in the liquid form makes it possible to benefit from the latent heat of vaporization of glycerol, therefore it is possible to cool the gases resulting from the previous stage of oxidation of propylene. In this case, the dehydration catalyst can be preceded by a bed of inert materials on which the vaporization of the glycerol is carried out. It can be injected in the gas form at a lower temperature than that of the gases leaving the oxidation region, which makes it possible to further intensify the cooling effect of these gases. In addition, the glycerol can be injected under pressure so that the reduction in gas pressure makes possible an additional heat sorption. The gas mixture feeding the reactor for the first step of oxidation of propylene to acrolein is generally composed of propylene, steam, an inert gas, which may be nitrogen or argon, and molecular oxygen or a gas comprising molecular oxygen. The reaction gas resulting from the step of oxidation of propylene to acrolein is generally composed of a mixture of unreacted gases (unconverted propylene, propane initially present in propylene, inert gas, steam, oxygen, CO, C02). acrolein produced and various by-products, such as acrylic acid, acetic acid and other minor compounds.

The reaction for the dehydration of glycerol in the process according to the invention consequently takes place in the presence of molecular oxygen, which occurs either in the mixture of gases that feed the reactor for the first stage of oxidation of propylene to give acrolein or in the gas mixture resulting from the oxidation step of propylene to give acrolein. Molecular oxygen may be present in the form of air or in the form of a gas mixture comprising molecular oxygen. In accordance with one embodiment of the invention, it is possible to add an additional quantity of molecular oxygen or a gas comprising molecular oxygen for the dehydration step of the glycerol. The amount of oxygen is selected so that it is outside the range of flammability and all points of the plant. The presence of oxygen makes it possible to limit the deactivation of the dehydration catalyst by coking. In addition, the addition of oxygen improves the performance of the reaction by numerous catalyst systems. The reaction for the catalytic oxidation of propylene to acrylic acid in two steps in the process according to the invention is carried out in accordance with the conditions known to the person skilled in the art by passing a gas mixture, which may comprise propylene, steam, an inert gas, which may be nitrogen or argon, and molecular oxygen or a gas comprising molecular oxygen, on a catalyst for the oxidation of propylene in order to obtain a gas mixture rich in acrolein. Then, the reaction for the selective oxidation of acrolein to give acrylic acid is carried out on a catalyst suitable for the oxidation of acrolein. The process can be carried out in a reactor or in two reactors placed in series. The reactors are generally multi-tubular fixed-bed reactors. It is also possible to use a bale exchanger with a modular arrangement of the catalyst, such as described in EP 995 491, EP 1 147 807 or US 2005/0020851. In the case where the catalytic oxidation of propylene is carried out in the presence of a thermal regulator, as described, for example, in EP 293 224 Al, which makes possible the use of a propylene expense more high, the gas mixture resulting from the reaction has a higher specific Cp heat. The process according to the invention is particularly advantageous in this case to discharge the excess heat transported by the reaction gases. A preferred embodiment of the invention is to use propane as an inert gas as a total or partial replacement for the nitrogen in the air. Propane, by virtue of its higher specific heat, carries more heat to the reactor, which makes it possible to more easily carry out the reaction for the dehydration of glycerol. The gas resulting from the dehydration step then comprises, as main constituents, steam, propane, acrolein and residual oxygen. This gas then directly feeds the oxidation step of the acrolein to give acrylic acid. In this case, the propane is to move away the heat of the oxidation reaction, which is very exothermic. After absorption of the acrylic acid, the propane-rich gases can be recycled to the dehydration stage. Preferably, the gas is subjected to purification treatments in order to remove impurities which may be detrimental to the dehydration and oxidation reactions, such as CO and / or CO2, and in order to limit the concentration of gases of these impurities in the circuit of recycling. In this case, it is particularly advantageous to control the concentration of argon in the gas circuit by its very low specific heat. It can be mentioned, as separation techniques that can be used alone or in combination, of the selective oxidation of CO to give C02, washing techniques with amines, washing with potassium hydroxide, adsorption, pro membrane separation or cryogenic separation. With reference to Figures 1 and 2, in a conventional process for the oxidation of propylene to acrylic acid in two stages in a single reactor, a mixture of gases 1 comprising propylene, steam, nitrogen and molecular oxygen is passed in a multi reactor -tubular from the bottom up on a catalyst 2 for the oxidation of propylene. The resulting mixture of this reaction, comprising unreacted gases, the produced acrolein and by-products, subsequently passes over a catalyst 4 for the oxidation of acrolein to give acrylic acid. A mixture 10 is obtained which comprises the produced acrylic acid, residual acrolein, unreacted gases, water and by-products. Liquid coolers circulate in 6 and 7 to maintain a reaction temperature that can be between 300 ° C and 380 ° C for the reaction for the oxidation of propylene to give acrolein and a temperature that can be between 260 ° C and 320 ° C for the oxidation of acrolein to give acrylic acid. A heat exchanger 8 which makes it possible to cool the reaction gases, as in Figure 1, is placed towards the outlet of the two oxidation stages.; preferably, the heat exchanger 8 of Figure 1 is towards the outlet of the reactor and not in the reactor, which facilitates the loading and unloading of the reactor. A second heat exchanger 8 can be placed between the two catalytic beds, as shown in Figure 2, making it possible to cool the intermediate gas mixture. With reference to Figure 3, in a conventional process for the oxidation of propylene to give acrylic acid in two stages in two consecutive reactors, a mixture of gases 1 comprising propylene, steam, nitrogen and molecular oxygen is passed in a first multi reactor -tubular from the top down on a catalyst 2 for the oxidation of propylene. The mixture 3 resulting from this reaction, comprising the unreacted gases, the produced acrolein and by-products, feeds a second reactor comprising a catalyst 4 for the oxidation of acrolein to acrylic acid. The second reactor is optionally fed in 9 with oxygen or air. A mixture 10 is obtained which comprises the acrylic acid produced, residual acrolein, unreacted gases, water and by-products. Liquid coolers circulate in 6 and 7, to maintain a reaction temperature that can be between 300 ° C and 380 ° C for a reaction for the oxidation of propylene to give acrolein and a temperature between 260 ° C and 320 ° C for the oxidation of acrolein to give acrylic acid. A heat exchanger 8 which makes it possible to cool the reaction gases resulting from the first stage is placed at the bottom of the first reactor. A second heat exchanger 8 is placed at the outlet of the two oxidation stages. The exchanger 8 can be outside the reactors.

According to a first embodiment of the process according to the invention, illustrated diagrammatically in Figure 4, the heat exchanger 8 in the conventional configuration of Figure 2, which is placed between the two catalytic beds and which makes it possible to cool the Gas mixture resulting from the reaction for the oxidation of propylene to give acrolein is replaced with a dehydration step of glycerol. This step consists of passing a mixture 11, composed of glycerol in the form of a vaporized aqueous solution and optionally of oxygen, at the same time as the gas mixture leaving the oxidation region comprising catalyst 2 for the oxidation of propylene to give acrolein, on a catalyst 5 for the dehydration of glycerol. A mixture of acrolein, resulting both from the reaction for the oxidation of propylene and from the reaction for the dehydration of glycerol, and also the by-products resulting from these two reactions, is obtained at the outlet of the region comprising the catalyst 5. . This mixture subsequently passes over the catalyst 4, on which the acrolein is oxidized to give acrylic acid. A mixture 10 is obtained comprising the produced acrylic acid, residual acrolein, unreacted gases, water and by-products. According to a second embodiment of the process of the invention, illustrated diagrammatically in Figure 5, the heat exchanger 8 placed at the outlet of the first reactor in a conventional process for the oxidation of propylene to give acrylic acid in two stages in two reactors consecutive, as depicted in Figure 3, is replaced with a glycerol dehydration step. This step consists of passing a mixture 11, composed of glycerol in the form of a vaporized aqueous solution and optionally of oxygen, at the same time as the gas mixture leaving the oxidation region comprising catalyst 2 for the oxidation of propylene to give acrolein, on a catalyst 5 for the dehydration of glycerol. It is obtained at the outlet of the region comprising the catalyst 5, a mixture 3 of acrolein, resulting both from the reaction for the oxidation of propylene and from the reaction for the dehydration of glycerol, and also the by-products resulting from these two reactions. This mixture 3 feeds the second reactor comprising the catalyst 4 on which the acrolein is oxidized to give acrylic acid. A mixture 10 is obtained comprising the produced acrylic acid, residual acrolein, unreacted gases, water and by-products.

In accordance with the process of the invention, it is possible to obtain an increase in the productive yield of acrylic acid in the order of 50 to 200% compared to conventional processes. It is possible to contemplate using another endothermic reaction than that of glycerol dehydration in order to efficiently recover the heat of reaction for the oxidation of propylene to give acrolein. In particular, the oxydehydration reaction of propane-1, 3-diol or the dehydration of propan-1-ol or propan-2-ol are also advantageous from some angles, more particularly if the bed of dehydration catalyst is placed at the reactor inlet for the oxidation of propylene to give acrolein. This is because the dehydration of propan-1,3-diol can result in allyl alcohol, which, in turn, can be oxidized on the catalyst for the oxidation of propylene to give acrolein. Propan-1-ol or propan-2-ol can be dehydrated to propylene and subsequently can be oxidized to give acrolein on the oxidation catalyst. The following examples illustrate the present invention, however, without limiting the scope thereof. In the examples, the formed products, acrolein and acrylic acid, are analyzed by chromatography on a capillary column EC-1000 adapted to a chromatograph HP6980 equipped with an FID detector. The quantitative analysis was carried out with an external standard. Example 1: Use is made of a reactor configuration in which the glycerol is covered by the gas mixture comprising the propylene from the top downwards and which comprises three beds of catalyst. The Pyrex reactor is equipped with a sintered glass in order to retain the catalyst. A weight of 5 g of catalyst for the oxidation of acrolein to give acrylic acid with the reference ACS4 (from Nippon Shokubai), reduced to a powder in a particle size of 100 to 160 microns and diluted with 5 ml of silicon carbide with a particle size of 0.125 mm, everything is first charged. Subsequently, 9 ml of silicon carbide with a particle size of 0.5 mm are charged. Subsequently, 6,498 g of catalyst for the oxidation of propylene to acrolein were loaded with the reference ACF4 (from Nippon Shokubai), diluted with 7 ml of silicon carbide with a particle size of 0.125 mm. Subsequently, different beds of silicon carbide were loaded, in order to separate the catalyst for the oxidation of propylene from the dehydration catalyst and independently control its temperature: 2 ml with a particle size of 0.125 mm, then 7 ml with a size of particle of 0.5 mm and again 2 ml with a particle size of 0.125 mm, and finally 1 ml with a particle size of 0.062 mm. Subsequently, 1,537 g of dehydration catalyst was loaded with the reference Z1C44 (zirconia tungstado from Dailchi KK), diluted with 4 ml of silicon carbide with a particle size of 0.062 mm. Finally, the reactor is calibrated with silicon carbide with a particle size of 0.125 mm (2 ml) and 0.5 mm, then 1.19 mm. The reactor is subsequently connected to the test parts. The temperatures of the three layers of the catalyst are regulated independently at 305 ° C for the two upper layers for the dehydration of glycerol and the oxidation of propylene and at 280 ° C for the lower layer for the oxidation of acrolein to give acrylic acid.

The reactor is fed with a mixture of propylene / oxygen / helium-krypton / water-glycerol gases with hourly molar costs (expressed as micromoles per hour) of 30 089/55 584/288 393 / water; 53 489- glycerol: 4509. The helio-krypton gas mixture comprises 4.92% krypton, which acts as an internal standard. The glycerol water mixture comprises 30% by weight of glycerol. These conditions represent a total molar charge of C3 compounds (propylene + glycerol) of 34 598 micromoles / h). The effluents were collected at the outlet of the reactor via a cold trap comprising ice and the acrolein and the acrylic acid produced are quantitatively determined by means of chromatographic analysis. The effluents are accumulated in the trap for a time of 80 minutes. The non-condensable gases are analyzed during the duration of the evaluation. The amount of acrolein produced is 503 micromoles / h and the amount of acrylic acid is 26 103 micromoles / hour. Example 2 (Comparative): Example 1 was repeated but the aqueous glycerol solution was replaced with pure water. The molar cost of the reactants is then: propylene / oxygen / helium-krypton / water-glycerol: 30 089/55 584/288 393 / water: 76 666 - glycerol: 0 micromoles / h.

The effluents accumulated in the trap for a time of 78 minutes. The non-condensable gases are analyzed during the duration of the evaluation. The amount of acrolein produced is 457 micromoles / h and the amount of acrylic acid is 23 257 microns, Example 3 (Comparative); Example 2 was repeated but while the dehydration catalyst was replaced with silicon carbide. The same feeding conditions were used. Effluents were collected in the trap for a period of 75 minutes. The incondensable gases are analyzed during the duration of the evaluation. The amount of acrolein produced is 521 micromoles / h and the amount of acrylic acid is 23 363 micromoles / h. Example 4: A reactor configuration comprising three catalyst beds with a feed of the gas mixture comprising propylene from the top down and an intermediate feed for the glycerol solution was used. The Pyrex reactor is equipped with a sintered glass to retain the catalyst. A weight of 5 g of catalyst for the oxidation of acrolein to give acrylic acid with the reference AC54 (from Nippon Shokubai), was reduced to a powder in a particle size of 100 to 160 microns and diluted with 5 ml of carbide silicon with a particle size of 0.125 mm, was charged first than all. Subsequently, 9 ml of silicon carbide with a particle size of 0.5 mm was loaded. Subsequently, a weight of 1578 g and the catalyst for the dehydration of glycerol with the reference Z1044 (Zirconia tungstada of Dialchi Kigenso, KK), diluted with 4 ml of silicon carbide with a particle size of 0.062 mm, were loaded. Subsequently, different beds of silicon carbide were loaded, to separate the catalyst dehydration catalyst for the oxidation of propylene and to independently control its temperature, and to make possible the injection of an aqueous solution of glycerol or glycerol or glycerol hydrated between the two catalyst beds: 4 ml with a particle size of 0.125 mm, then 7 ml with a particle size of 0.5 mm and again 2 ml with a particle size of 0.125 mm. Subsequently, 6,578 g of catalyst for the oxidation of propylene to acrolein were loaded with the reference ACF4 (from Nippon Shokubai), diluted with 7 ml of silicon carbide with a particle size of 0.125 mm. Finally the reactor was filled with silicon carbide with a particle size of 0.125 mm (2 ml) and 0.5 mm, then 1.19 mm.

The reactor is subsequently connected to the test plant. The temperatures of the catalyst layers are regulated independently at 260 ° C for the lower layers for the dehydration of glycerol and for the oxidation of acrolein to acrylic acid and at 305 ° C for the top layer for the oxidation of propylene to give acrolein . The reactor is fed with a mixture of propylene gases / oxygen / helium-krypton / water in its upper part with hourly molar costs (expressed in micromoles per hour) of 30 089/55 584/288 393/76 666. The mixture of helium-krypton gases comprises 4.92% krypton, which acts as an internal standard. A water-glycerol mixture comprising 80% by weight of glycerol is fed between the catalyst layer for the oxidation of propylene and the catalyst for dehydration, with an expenditure of glycerol / water of 4530/5794 (micromoles / hour). These conditions represent a total molar expense of C3 compounds (propylene + glycerol) of 34 619 micromoles / h. The effluents are collected at the outlet of the reactor via a cold trap comprising ice and the acrolein and acrylic acid produced are determined quantitatively by means of chromatographic analysis. The effluents are accumulated in the trap for a time of 84 minutes. The non-condensable gases are analyzed during the duration of the evaluation. The amount of acrolein produced is 389 micromoles / h and the amount of acrylic acid is 26 360 micromoles / h. The residual propylene is 2613 micromoles / h. Example 5: Example 4 was repeated but using a 95% by weight glycerol solution (glycerol hydrate). The hourly molar costs (in micromoles per hour) of the constituents of the mixture are as follows: Propylene / oxygen / helium-krypton / water 30 089/33 584/288393/76 666 for the feed of the top and glycerol / water 8220/2205 for intermediate feeding. These conditions represent a total molar expense of C3 compounds (propylene + glycerol) of 38 309 micromoles / h. The effluents are accumulated in the trap for a time of 81 minutes. The non-condensable gases are analyzed during the duration of the evaluation. The amount of acrolein produced is 633 micromoles / h and the amount of acrylic acid is 29 898 micromoles / h. The residual propylene is 2805 micromoles / h.

Example 6: Example 4 was repeated but using a 70% by weight glycerol solution. The hourly molar costs (in micromoles per hour) of the constituents of the gas mixture are as follows: propylene / oxygen / helium-krypton / water 30089/55 584/288 393/76 666 for the feed of the top and glycerol / water 6350/13923. These conditions represent a total molar expense of C3 compounds (propylene + glycerol) of 36 439 micromoles / h. The effluents were collected in the trap for a time of 78 minutes. The non-condensable gases are analyzed during the duration of the evaluation. The amount of acrolein produced is 612 micromoles / h and the amount of acrylic acid is 28 212 micromoles / h. The residual propylene is 2702 micromoles / h.

Claims (7)

NOVELTY OF THE INVENTION Having described the present invention, it is considered as novelty, and therefore the content of the following is claimed as property:
1. CLAIMS 1. - A process for the preparation of acrylic acid from propylene comprising a first stage of oxidation of propylene to give acrolein and a second
2. Oxidation stage of acrolein to give acid acrylic, characterized in that it comprises a stage of dehydration of glycerol in the presence of a gas that
3. It comprises propylene. 2. - The process in accordance with the claim 1, characterized in that the gas comprising propylene is the reaction gas resulting from the oxidation stage of propylene to give acrolein. 3. - The process in accordance with the claim 1 or 2, characterized in that the dehydration reaction is carried out in the gas phase in the presence of a catalyst
4. 4. - The process of compliance with any one of the preceding claims characterized in that the Molecular oxygen is added for the dehydration stage of glycerol.
5. 5. -The process of conformity with any one of the preceding claims, characterized in that the glycerol is injected in the liquid form or in the gas form.
6. 6. - The process according to any one of the preceding claims, characterized in that pure glycerol or glycerol is used in the form of a concentrate or diluted aqueous solution.
7. 7. - The process according to any one of the preceding claims, characterized in that the oxidation of propylene is carried out in the presence of a thermal regulator.