Dispersible antifouling agent for acrylonitrile

Abstract

A method for preventing the deposition of fouling-causing substances in the process for the production of acrylonitrile, comprising the addition to a fluid phase of the production process of an effective antifouling quantity of a styrenesulfonate polymer comprising the following formula of the repeating unit: wherein M is hydrogen, alkali metals or ammonium or a mixture thereof, R is hydrogen, alkyl, aryl, alkylaryl, arylalkyl, R may contain heteroatoms and n is an integer, characterized in that the styrenesulfonate polymer has a molar mass of 50,000 to 1,000,000 Daltons.

Description

Cross-reference to related applications

[0001] No. Declaration on federally funded research or development

[0002] Not applicable. Background of the invention

[0003] This invention relates to a process for producing acrylonitrile and, more particularly, to a process in which an antifouling agent comprising a polymer of styrenesulfonate is added to at least one step in the quench, recovery and waste water processes of a process for producing acrylonitrile.

[0004] Typically, the production of acrylonitrile comprises three stages: the reaction stage, the recovery stage, and the purification stage. In the reaction stage, propylene undergoes ammoxidation, forming acrylonitrile by reaction with ammonia and oxygen. This is often a catalytic gas-phase reaction at elevated temperature. The resulting acrylonitrile-containing effluent is then quenched with water, and unreacted ammonia is neutralized with sulfuric acid. In the recovery stage, the quenched product of the reaction stage undergoes a water absorption process to capture acrylonitrile and a recovery process to separate the acrylonitrile from water and other heavy components also formed in the reaction stage. Water is recycled within the recovery stage. The isolated acrylonitrile is then passed on to the purification stage.

[0005] During the recovery stage, fouling compounds tend to form and accumulate in the circulating water. These fouling compounds include both inorganic and organic compounds in the form of monomers, oligomers, prepolymers, and polymers in various combinations. These fouling compounds form deposits on some of the recovery stage equipment, such as heat exchangers, reboilers, and columns. When these fouling compounds are deposited on the heat exchange surfaces of the heat exchangers and reboilers, they reduce the efficiency of the heat exchange equipment. Furthermore, the deposition of fouling substances creates flow resistance in the affected equipment and even blockages in the production stream.As a result, the equipment used to remove fouling substances must be shut down periodically, resulting in production losses, cleaning costs, operational difficulties, and safety and environmental problems.

[0006] Known methods addressing this problem include adding a dispersant antifouling agent to problematic equipment. The dispersant acts as a colloidal stabilizer, keeping fouling agents suspended in the process stream and preventing fouling agents from depositing on equipment surfaces. One such example is disclosed in U.S. Patent No. 3,691,226, which describes the use of lignosulfonate metal salts to minimize the deposition of fouling agents on the heat transfer surface of heat exchangers used to cool circulating water. Another example is U.S. Patent No. 5,650,072, which teaches the use of a naphthalenesulfonate-formaldehyde condensate polymer to prevent heat exchanger fouling in an acrylonitrile stripper.

[0007] For example, DE 10 2007 001 427 A1 discloses a process for producing bisphenols with a purity of greater than 99.7%, in which a phenol is reacted with acetone in the presence of an acid catalyst.

[0008] DE 69819061 T2 discloses a method for preventing the formation of fouling in the manufacturing process of acrylonitrile by adding a dispersant, e.g., styrenesulfonates.

[0009] JP H08-29977 discloses styrenesulfonate polymers as dispersants.

[0010] The art described in this section is not intended to be an admission that any patents, publications, or other information cited herein constitute "prior art" with respect to this invention unless specifically identified as such. Furthermore, this section should not be construed to imply that a search has been conducted or that no other pertinent information, as defined at 37 CFR § 1.56(a), exists. All patents and patent applications cited in this application are incorporated herein by reference in their entirety. Brief description of the invention

[0011] At least one embodiment of the invention relates to a process according to claim 1. Further disclosed is a process for mitigating or eliminating the fouling problem in the quenching and recovery stages in the production of acrylonitrile by introducing a dispersing styrenesulfonate polymer antifouling agent having a repeat unit formula according to formula I:

[0012] This dispersant prevents the deposition of fouling compounds on the equipment in the quenching and recovery stages. Experimental data demonstrate that the dispersant is superior to the state of the art. Brief description of the drawings

[0013] A detailed description of the invention is given below, with express reference to the drawings, in which: Fig. Figure 1 is a general illustration of the process for producing acrylonitrile using the dispersant of the invention; Fig. Figure 2 is a more detailed illustration of a configuration in a recovery stage of the production of acrylonitrile in which the dispersant of the invention is used; Fig. Figure 3 is a more detailed illustration of another configuration in a recovery stage of acrylonitrile production using the dispersant of the invention. Detailed description of the invention

[0014] With reference to Fig. Figure 1 now shows a general illustration of the three usual steps of the process for producing acrylonitrile, to which the dispersant of the invention is added. It will be appreciated by those skilled in the art that many variations of the process for producing acrylonitrile are known, and that Fig. 1 is representative of these known variations. The three stages are the reaction stage (25), the recovery stage (24), and the purification stage (23). In the reaction stage (25), fed propylene (15) reacts with oxygen or air (16) and ammonia (14) within a reactor (1) in an ammoxidation reaction to form acrylonitrile. The exiting reaction medium then passes to a quenching tower (2), where it is quenched with circulating water (18) and where unreacted ammonia is neutralized with sulfuric acid. After the quenching process, the products pass to the recovery stage, where they enter an absorber column (3). In the absorber column (3), acrylonitrile and heavy components are purified from light components (such as O2, CO, CO2, and unreacted propylene, etc.) with regenerated water (26).The acrylonitrile-containing bottoms product of the absorber column, referred to as enriched water (27), is passed to the recovery column (4), while the light components are stripped (17) through the top of the absorber column (3) and burned. In the recovery column (4), the enriched water undergoes extractive distillation. Acrylonitrile and hydrogen cyanide are removed via a top section of the recovery column (4) together with their azeotropes and water. Most of the water contained in the enriched water stream is withdrawn at the bottom of the recovery column (4) and returned to the absorber column (3) as regenerated water. Dissolution water also passes to the top section. A small portion of the water from the recovery column (4) is drained from the bottom of the recovery column (4) and either returned to the quench column or sent to a wastewater process for disposal. In . Fig. 1, the distillation process in the recovery column is supported by reboiler heat exchangers connected to the recovery column (4).

[0015] The acrylonitrile-containing overhead stream then passes to the purification stage (23), where hydrogen cyanide (19), water (20), and heavy substances are separated from the acrylonitrile product (21). The purification stage (23) comprises a recovery overhead decanter (5), a light ends column (6), a drying column (7), a light ends / dry decanter (8), and a product column (9). Further information on the ammoxidation reaction to form acrylonitrile can be found in US Patent 3,691,226.

[0016] For the purposes of this application, enriched water is defined as water passed from the absorber column to the recovery column and is enriched in acrylonitrile. For the purposes of this application, regenerated water is the water remaining after the enriched water has been passed through a recovery column and no longer contains acrylonitrile. Regenerated water is recycled to the absorber column and passed through the column countercurrent to the stripped components. For the purposes of this application, dissolution water (26) is the water remaining after the enriched water has also been passed through a recovery column and therefore no longer contains acrylonitrile. The dissolution water is fed to the upper section of the recovery column to reduce contamination of the acrylonitrile stream entering the decanter (5).

[0017] In acrylonitrile plants, variations in configuration are very common. Fig. 2 and Fig. 3 illustrate two different configurations of extraction and wastewater treatment. In the configuration of Fig. 2, a separate stripping column (10) is added, which strips acetonitrile (22) and light components from the solution water (26). In Fig. 3, a multi-stage evaporation-wastewater process (11 and 12) is used to remove water from the purge stream at the recovery bottom, thus minimizing wastewater disposal. The overhead water (28) is recycled to the quench, and the bottoms product (29) is sent to the wastewater treatment plant.

[0018] As regenerated water and solvent water are recycled through the recovery stage, and the purge stream from the recovery bottom passes through the stripping column or a multi-stage wastewater distillation process, they undergo various physical and chemical changes that lead to the formation of fouling substances in various components, vessels, and equipment of the recovery stage and wastewater process. For the purposes of this application, fouling substances are defined as a deposit of material that deposits on equipment during the operation of a manufacturing and / or chemical process, which may be undesirable and impair the operation and / or efficiency of the process. The accumulation of fouling substances hinders and blocks throughput, particularly through recovery columns.Fouling substances are particularly detrimental when they accumulate along the heat exchangers for cooling the regenerated and solution water and the reboilers or stripping columns because the poor thermal conductivity of the fouling substances leads to a decrease in the efficiency of these components.

[0019] At least one embodiment of the invention comprises adding a styrenesulfonate polymer to one or more of the liquid streams of the process for producing acrylonitrile. The styrenesulfonate polymer is a polymeric material comprising the following repeating units: where M is hydrogen, alkali metals, or ammonium, or a mixture thereof; R is hydrogen, alkyl, aryl, alkylaryl, or arylalkyl; R may contain heteroatoms; n is an integer; and the styrenesulfonate polymer has a molecular weight of 50,000 to 1,000,000 Daltons.

[0020] In at least one embodiment, the styrenesulfonate polymer is introduced into one or more of the liquid streams of the quench column and recovery stage, as well as the wastewater process, where it serves as a dispersant, preventing deposition of fouling substances and even facilitating the removal of previously deposited fouling substances. Previous examples of dispersants used in various manufacturing processes include: sulfonated oils, sulfonated fatty acids, sulfated oils, sulfated fatty acids, naphthalenesulfonate formaldehyde, sulfonic acids, dodecylbenzenesulfonic acid, and lignosulfate metal salts (described in U.S. Patents 5,650,072, 4,650,072, 5,746,924, and 3,691,226). However, experimental data demonstrate that styrene sulfonate polymer has superior dispersing properties to all these previous dispersants in the recovery stage of acrylonitrile production.

[0021] At lower pH and / or higher impurity concentrations, where prior art dispersants tend to become ineffective, the styrenesulfonate polymer exhibits superior dispersing behavior. In at least one embodiment, the dispersant has a molecular weight of 100,000 to 1,000,000 Daltons.

[0022] There are several ideal locations in the liquid circuits of the quench, recovery, and wastewater processes where the styrene sulfonate polymer dispersant can be introduced. These include, but are not limited to, the quench column recycle streams, the regenerated water circuit before the regenerated water cooler / heat exchanger, the solution water circuit before or after the solution water cooler / heat exchanger, the feed line to the reboiler, the feed to the stripping column, and the feed to the multi-stage distillation wastewater process. In particular, introducing the dispersant immediately before a heat exchanger or reboiler is effective because it ensures that the heat exchanger or reboiler is supplied with intact and sufficient amounts of dispersant. Depending on the severity of fouling and the economics of the treatment, the effective dosage ranges from 1 to 10,000 ppm by weight.In practice, a preferred dosage ranges from 5 to 1000 ppm, and the most preferred dosage is from 10 to 200 ppm.

[0023] The styrenesulfonate polymer dispersant itself is generally present as a solid, and a solvent is generally used to dissolve it and create a liquid formulation. This is generally done during the preparation of the styrenesulfonate polymer. Although styrenesulfonate polymer is soluble in many solvents, water is the most commonly used solvent for obvious reasons. A highly concentrated styrenesulfonate polymer formulation is generally desirable for economic reasons. Co-solvents can be used with water to improve solubility and to enhance the stability and handling of the product.

[0024] The following examples are provided to describe embodiments and benefits of the invention and should not be construed as limiting the invention unless otherwise stated in the claims. EXAMPLES

[0025] Example 1A. Dispersion test simulating the fouling of the solution water cooler: A sample of the deposited fouling material was taken from the heat exchanger for cooling the recovery solution water of an acrylonitrile plant. The sample of fouling substances was dried and ground into a powder. A solution of the fouling substances was prepared by dissolving the powder of the fouling substances in an organic solvent. 15 ml of the recovery column solution water stream from a recovery column of the same acrylonitrile plant was added to a 15 ml centrifuge tube. 1 ml of the fouling substance solution prepared above was added to the centrifuge tube. The contents of the tube were shaken well, and then the tube was allowed to stand at room temperature. A precipitate formed in the tube. After 2.5 h, approximately 0.5 ml of precipitate was observed at the bottom of the tube.

[0026] Example 2A. Sample treated with the styrenesulfonate polymer of the invention: The same procedure as in Example 1A was performed, except that 39 ppm of the styrenesulfonate polymer of the invention was added to the contents of the tube prior to adding the solution of fouling substances. No precipitate was observed in this tube during the 2-day duration of this experiment. This example illustrates that the styrenesulfonate polymer of the invention is an effective dispersant in the fouling situation.

[0027] Example 3A. Sample treated with state-of-the-art dispersants: The same procedure as in Example 1A was performed, except that 57 ppm of a naphthalenesulfonate polymer was added to the contents of the tube prior to adding the solution of the fouling substances. No precipitate occurred during the first 20 hours of settling. Three days later, approximately 0.2 ml of solid precipitate was measured at the bottom of the tube. The naphthalenesulfonate polymer is only partially effective in this fouling situation.

[0028] Example 1B. Dispersion test simulating fouling on the extraction soil: A sample of the fouling deposited material was taken from the recovery reboiler of an acrylonitrile plant. The sample of fouling substances was dried and ground to a powder. A solution of the fouling substances was prepared by dissolving the powder of the fouling substances in an organic solvent. 15 ml of the soil purge stream was added to a 15 ml centrifuge tube. a recovery column from the same acrylonitrile plant. This stream from the bottom of the recovery column had a higher concentration of impurities and a lower pH than the solution water stream. An aliquot of the fouling substance solution prepared above was added to the same centrifuge tube. The contents of the tube were shaken well, and then the tube was allowed to stand at room temperature. A precipitate formed within 5 minutes. After 30 minutes, approximately 3 ml of precipitate was observed at the bottom of the tube.

[0029] Example 2B. Sample treated with styrene sulfonate polymer: The same procedure as in Example 1B was performed, except that 39 ppm of the styrenesulfonate polymer of the invention was added to the contents of the tube prior to adding the solution of fouling substances. No precipitate was observed in this tube during the 3-day duration of this experiment. This example illustrates that the styrenesulfonate polymer of the invention is an effective dispersant in fouling situations. Example 3B. Sample treated with state-of-the-art dispersants

[0030] The same procedure as in Example 1B was performed, except that 57 ppm of a naphthalenesulfonate polymer was added to the contents of the tube before adding the solution of the fouling substances. After a few minutes, a precipitate appeared. After 30 minutes, approximately 3 ml of precipitate was observed at the bottom of the tube. The naphthalenesulfonate polymer is ineffective in this fouling situation. Example 1C. Dispersion test simulating fouling of the recovery reboiler

[0031] A sample of the fouling deposited material was taken from the recovery column reboiler of an acrylonitrile plant. The sample of fouling substances was dried and ground to a powder. A solution of the fouling substances was prepared by dissolving the fouling substance powder in an organic solvent. 8 ml of the bottom purge stream from the recovery column of an acrylonitrile plant was placed in a 10-ml centrifuge tube. 2 µl of glacial acetic acid was added to the contents to lower its pH. 50 µl of the fouling substance solution prepared above was added to the same centrifuge tube. The tube was shaken well and then allowed to stand at elevated temperature. At approximately 70 °C, a precipitate appeared in the untreated tube.

[0032] Example 2C. Sample treated with a prior art lignosulfonate dispersant: The same procedure as in Example 1C was performed, except that 39 ppm of a lignosulfonate dispersant was added to the tube contents prior to adding the fouling substance solution. No precipitate was observed in this tube at 70 °C. However, precipitate was observed when the temperature was increased to 90 °C. This example illustrates the limited effectiveness of the lignosulfonate dispersant.

[0033] Example 3C. Sample treated with a prior art naphthalenesulfonate resin dispersant: The same procedure as in Example 1C was carried out, except that before adding the solution of the fouling substances to the 57 ppm of a naphthalenesulfonate polymer were added to the tube. No precipitate was observed at 70 °C and 90 °C. Then, another 3 µl of acetic acid was added to the contents. A precipitate was immediately observed. This example demonstrates that the naphthalenesulfonate polymer has a limited dispersing effect in this fouling situation.

[0034] Example 4C. Sample treated with the styrene sulfonate polymer dispersant of the invention: The same procedure as in Example 3C was performed, except that the contents of the tube were treated with 57 ppm of the styrenesulfonate polymer dispersant of the invention. No precipitate was observed at 70 °C and 90 °C. No precipitate was observed even upon addition of 3 µl of acetic acid. This example illustrates that the styrenesulfonate polymer is a more effective dispersant than those of the prior art in this fouling situation.

[0035] While this invention may be embodied in many different forms, specific preferred embodiments of the invention are illustrated in the drawings and described herein.

[0036] The present disclosure is an illustration of the principles of the invention and should not be construed as limiting the invention to the specific embodiments illustrated. The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to those skilled in the art. It is intended that all such alternatives and variations be included within the scope of the claims, where the term "comprising" means "including, but not limited to." Those skilled in the art may recognize other equivalents to the specific embodiments described herein, and it is intended that these equivalents also be included within the claims.

[0037] This concludes the description of the preferred and alternative embodiments of the invention. Those skilled in the art will recognize other equivalents to the specific embodiments described herein, and it is intended that these equivalents be included in the appended claims.

Claims

[1] A method for preventing deposition of fouling substances in the process for producing acrylonitrile, comprising adding to a fluid phase of the production process an effective antifouling amount of a styrenesulfonate polymer comprising the following formula of the repeating unit:wherein M is hydrogen, alkali metals or ammonium or a mixture thereof, R is hydrogen, alkyl, aryl, alkylaryl, arylalkyl, R may contain heteroatoms and n is an integer, characterized by that the styrenesulfonate polymer has a molecular weight of 50,000 to 1,000,000 Dalton. [2] The process according to claim 1, wherein the fluid phase originates from the ammoxidation reaction of propylene, ammonia and oxygen and / or air. [3] The process of claim 1, wherein the manufacturing process further comprises adding the styrene sulfonate polymer to an element selected from the list consisting of: a recovery stage, a water recycle line, a multi-stage wastewater distillation process, a quench column, a heat exchanger, a reboiler, and a stripping column, and any combination thereof, wherein at least one selected element is in sealable fluid communication with the other elements. [4] The process of claim 1, further comprising a quench column that cools the medium exiting the ammoxidation reactor with a circulating aqueous stream, and wherein the styrenesulfonate polymer is added to the circulating aqueous stream. [5] The process of claim 1, further comprising a recovery stage which itself comprises at least one absorber and at least one recovery column, all of which are in sealable fluid communication with each other, wherein enriched water with a high acrylonitrile concentration is formed in the absorber by absorption in regenerated water, in the recovery column, acrylonitrile is isolated by separation by distillation, the styrenesulfonate polymer is added to at least one member selected from the list consisting of the absorber column and the recovery column. [6] The method of claim 1, further comprising at least one recirculating water line receiving water from one part of the manufacturing process and recirculating it by directing it to another part of the manufacturing process, wherein the styrene sulfonate polymer is added to the recirculating water line. [7] The method of claim 6, wherein the water conducted from the circulating water line comprises solution water circulated to the top of a recovery column, and the styrene sulfonate polymer is added to the solution water. [8] The method of claim 6, wherein the water supplied from the recirculating water line comprises regenerated water and the styrene sulfonate polymer is added to the regenerated water. [9] The process of claim 1, further comprising a wastewater processing section in which the purge stream from the bottom of the recovery column is processed by a multi-stage distillation process and the styrene sulfonate polymer is added to the feed of the wastewater processing section. [10] The process according to claim 1, wherein the styrenesulfonate polymer is added in a dosage of 1 to 10,000 ppm. [11] The process according to claim 1, wherein the styrenesulfonate polymer is added in a dosage of 10 to 1000 ppm. [12] The process according to claim 1, wherein the styrenesulfonate polymer is added in a dosage of 20 to 200 ppm. [13] The process according to claim 1, wherein the styrene sulfonate polymer is used in combination with other antifouling agents such as dispersants and polymerization inhibitors, corrosion inhibitors, antifoaming agents either by separate or joint injection. [14] The process of claim 1, wherein the styrenesulfonate polymer is a solid dissolved in a solvent. [15] The method of claim 14, further comprising a co-solvent. [16] The process of claim 14, wherein water is the solvent.

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