ZA200507199B - Process for recovering acrylonitrile or methacrylonitrile - Google Patents
Process for recovering acrylonitrile or methacrylonitrile Download PDFInfo
- Publication number
- ZA200507199B ZA200507199B ZA200507199A ZA200507199A ZA200507199B ZA 200507199 B ZA200507199 B ZA 200507199B ZA 200507199 A ZA200507199 A ZA 200507199A ZA 200507199 A ZA200507199 A ZA 200507199A ZA 200507199 B ZA200507199 B ZA 200507199B
- Authority
- ZA
- South Africa
- Prior art keywords
- column
- improvement
- ammonium
- alkaline compound
- water
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims description 36
- 230000008569 process Effects 0.000 title claims description 31
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 title claims description 21
- GYCMBHHDWRMZGG-UHFFFAOYSA-N Methylacrylonitrile Chemical compound CC(=C)C#N GYCMBHHDWRMZGG-UHFFFAOYSA-N 0.000 title claims description 11
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 41
- 239000001099 ammonium carbonate Substances 0.000 claims description 30
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 29
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 claims description 27
- 150000002825 nitriles Chemical class 0.000 claims description 24
- 239000000178 monomer Substances 0.000 claims description 22
- 229910021529 ammonia Inorganic materials 0.000 claims description 20
- 235000012501 ammonium carbonate Nutrition 0.000 claims description 20
- 238000011084 recovery Methods 0.000 claims description 15
- 150000001875 compounds Chemical class 0.000 claims description 13
- 239000007864 aqueous solution Substances 0.000 claims description 12
- 238000004821 distillation Methods 0.000 claims description 12
- 238000010791 quenching Methods 0.000 claims description 12
- BVCZEBOGSOYJJT-UHFFFAOYSA-N ammonium carbamate Chemical compound [NH4+].NC([O-])=O BVCZEBOGSOYJJT-UHFFFAOYSA-N 0.000 claims description 9
- KXDHJXZQYSOELW-UHFFFAOYSA-N carbonic acid monoamide Natural products NC(O)=O KXDHJXZQYSOELW-UHFFFAOYSA-N 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 9
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 8
- 235000012538 ammonium bicarbonate Nutrition 0.000 claims description 8
- 229910000013 Ammonium bicarbonate Inorganic materials 0.000 claims description 7
- 125000005263 alkylenediamine group Chemical group 0.000 claims description 7
- 239000002904 solvent Substances 0.000 claims description 7
- PIICEJLVQHRZGT-UHFFFAOYSA-N Ethylenediamine Chemical compound NCCN PIICEJLVQHRZGT-UHFFFAOYSA-N 0.000 claims description 5
- 238000000895 extractive distillation Methods 0.000 claims description 5
- 239000007788 liquid Substances 0.000 claims description 5
- 239000001569 carbon dioxide Substances 0.000 claims description 4
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 4
- 238000004519 manufacturing process Methods 0.000 claims description 4
- KWYHDKDOAIKMQN-UHFFFAOYSA-N N,N,N',N'-tetramethylethylenediamine Chemical compound CN(C)CCN(C)C KWYHDKDOAIKMQN-UHFFFAOYSA-N 0.000 claims description 3
- 238000011065 in-situ storage Methods 0.000 claims description 3
- 239000000047 product Substances 0.000 description 18
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 12
- 239000000654 additive Substances 0.000 description 11
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 description 9
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 9
- LELOWRISYMNNSU-UHFFFAOYSA-N hydrogen cyanide Chemical compound N#C LELOWRISYMNNSU-UHFFFAOYSA-N 0.000 description 9
- HGINCPLSRVDWNT-UHFFFAOYSA-N Acrolein Chemical compound C=CC=O HGINCPLSRVDWNT-UHFFFAOYSA-N 0.000 description 8
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical group [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 8
- 239000000356 contaminant Substances 0.000 description 8
- 238000007792 addition Methods 0.000 description 7
- 230000000996 additive effect Effects 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 7
- 239000006096 absorbing agent Substances 0.000 description 6
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 6
- 150000003839 salts Chemical class 0.000 description 6
- 239000002351 wastewater Substances 0.000 description 6
- -1 for example Substances 0.000 description 5
- 230000007935 neutral effect Effects 0.000 description 5
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 4
- 235000011054 acetic acid Nutrition 0.000 description 4
- 229960000583 acetic acid Drugs 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 239000008346 aqueous phase Substances 0.000 description 4
- 239000003518 caustics Substances 0.000 description 4
- 238000007278 cyanoethylation reaction Methods 0.000 description 4
- 229930195733 hydrocarbon Natural products 0.000 description 4
- 150000002430 hydrocarbons Chemical class 0.000 description 4
- 239000012535 impurity Substances 0.000 description 4
- 235000017550 sodium carbonate Nutrition 0.000 description 4
- 229910000029 sodium carbonate Inorganic materials 0.000 description 4
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical class OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 3
- 239000004215 Carbon black (E152) Substances 0.000 description 3
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- 230000003113 alkalizing effect Effects 0.000 description 3
- 239000006227 byproduct Substances 0.000 description 3
- 230000003472 neutralizing effect Effects 0.000 description 3
- 239000012074 organic phase Substances 0.000 description 3
- 238000000746 purification Methods 0.000 description 3
- 238000007086 side reaction Methods 0.000 description 3
- 235000011121 sodium hydroxide Nutrition 0.000 description 3
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 150000007513 acids Chemical class 0.000 description 2
- 150000001412 amines Chemical class 0.000 description 2
- PRKQVKDSMLBJBJ-UHFFFAOYSA-N ammonium carbonate Chemical class N.N.OC(O)=O PRKQVKDSMLBJBJ-UHFFFAOYSA-N 0.000 description 2
- 235000011162 ammonium carbonates Nutrition 0.000 description 2
- 230000003139 buffering effect Effects 0.000 description 2
- 150000004985 diamines Chemical class 0.000 description 2
- HPNMFZURTQLUMO-UHFFFAOYSA-N diethylamine Chemical compound CCNCC HPNMFZURTQLUMO-UHFFFAOYSA-N 0.000 description 2
- NAQMVNRVTILPCV-UHFFFAOYSA-N hexane-1,6-diamine Chemical compound NCCCCCCN NAQMVNRVTILPCV-UHFFFAOYSA-N 0.000 description 2
- NNPPMTNAJDCUHE-UHFFFAOYSA-N isobutane Chemical compound CC(C)C NNPPMTNAJDCUHE-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000006116 polymerization reaction Methods 0.000 description 2
- 239000001294 propane Substances 0.000 description 2
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 2
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- GETQZCLCWQTVFV-UHFFFAOYSA-N trimethylamine Chemical compound CN(C)C GETQZCLCWQTVFV-UHFFFAOYSA-N 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- VQTUBCCKSQIDNK-UHFFFAOYSA-N Isobutene Chemical group CC(C)=C VQTUBCCKSQIDNK-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 150000001242 acetic acid derivatives Chemical class 0.000 description 1
- 150000001299 aldehydes Chemical class 0.000 description 1
- 150000001335 aliphatic alkanes Chemical class 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000003973 alkyl amines Chemical class 0.000 description 1
- 125000000217 alkyl group Chemical group 0.000 description 1
- 150000003863 ammonium salts Chemical class 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical class N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 150000008064 anhydrides Chemical class 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001728 carbonyl compounds Chemical class 0.000 description 1
- 125000002915 carbonyl group Chemical group [*:2]C([*:1])=O 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000010960 commercial process Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 229940083124 ganglion-blocking antiadrenergic secondary and tertiary amines Drugs 0.000 description 1
- 239000001282 iso-butane Substances 0.000 description 1
- 239000010808 liquid waste Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- KVKFRMCSXWQSNT-UHFFFAOYSA-N n,n'-dimethylethane-1,2-diamine Chemical compound CNCCNC KVKFRMCSXWQSNT-UHFFFAOYSA-N 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 238000010641 nitrile hydrolysis reaction Methods 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 235000021317 phosphate Nutrition 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 150000003141 primary amines Chemical class 0.000 description 1
- AOHJOMMDDJHIJH-UHFFFAOYSA-N propylenediamine Chemical compound CC(N)CN AOHJOMMDDJHIJH-UHFFFAOYSA-N 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000008439 repair process Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000013638 trimer Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 238000009279 wet oxidation reaction Methods 0.000 description 1
Landscapes
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Description
Lo WO 2004/063145 PCT/US2003/038691
PROCESS FOR RECOVERING ACRYLONITRILE OR METHACRYLONITRILE
) 5 Background of the Invention ; This invention is directed to an improved process for the recovery of nitrile monomer
N from the reactor effluent from a hydrocarbon ammoxidation reactor. More particularly, the invention is directed to an improved process for the recovery of nitrile monomer contained in the effluent stream from the ammoxidation of propylene, propane, isobutane or isobutylene in the production of acrylonitrile or methacrylonitrile.
The processes widely used in commercial practice for recovering the products of hydrocarbon ammoxidation generally comprise the steps of: a) contacting the effluent from an ammoxidation reactor in a quench tower with an aqueous quench liquid to cool the gaseous effluent; b) contacting the quenched effluent with water in an absorber, forming an aqueous solution comprising the ammoxidation products; c) subjecting said aqueous solution to extractive distillation with water in the recovery column to separate the crude monomer as an overhead vapor stream and collect water soluble, less volatile contaminants in a liquid waste stream from the bottom of the column; and d) condensing an overhead vapor stream to form an organic phase comprising nitrile monomer and an aqueous phase, and decanting the organic phase containing crude monomer. Further purification of the nitrile monomer may be accomplished by passing said organic phase to a second distillation column to remove at least some impurities from the crude nitrile monomer, and further distilling the partially purified nitrile in a third distillation column to obtain the purified acrylonitrile or methacrylonitrile.
Processes for recovery and purification of acrylonitrile and methacrylonitrile are well known and widely described in the art, for example, in U.S. Pat. Nos. 6,107,509, 4,234,510, 3,885,928, 3,459,639, 3,352,764, and 3,198,750. The entire disclosure of each of said patents is incorporated herein by reference.
Hydrocarbon ammoxidation, particularly of alkanes, is typically conducted using substantial excesses of ammonia. Ammonia that is not consumed in the ammoxidation exits the reactor in the effluent, together with nitrile monomer and reaction by-products including hydrocyanic acid, cyanoalkane and the corresponding aldehyde and the like. The by-products react with nitrile monomer in the presence of unreacted ammonia, or with one another. It is therefore necessary to separate the ammonia from the effluent stream immediately after the stream exits the ammoxidation reactor. Conventionally, the unreacted ammonia is removed in the form of a salt as a part of the quench operation, step a, by including sufficient acid, for example, sulfuric acid, in the aqueous quench liquid to neutralize and capture the excess
Co WO 2004/063145 PCT/US2003/038691 and control the addition of the several reaction components and the reaction parameters, substantially all of the excess ammonia will be captured in the quench step.
The aqueous solution obtained from the absorber in the subsequent absorption step (step b) will comprise the water soluble components of the effluent including nitrile monomer, : 5 the corresponding coproducts including alkylnitrile and hydrocyanic acid, together with minor amounts of contaminants. For example, in an acrylonitrile process, the solution will include : acrylonitrile, acetonitrile and HCN, together with a minor amounts of acrolein and other carbonyl compounds, residual ammonia, cyanohydrins and other contaminants. The pH will vary, depending in part upon the relative levels of HCN and residual ammonia.
Acrylonitrile and valuable coproducts including acetonitrile are separated in the recovery column. The separation is greatly affected by the pH of the system, which will preferably be maintained in the range of from about 5.5 to about 7.5, more preferably from about 6 to about 7. Within the preferred pH range, acrolein and other carbonyl contaminants react with water and HCN, forming high molecular weight, water soluble products that remain with the aqueous phase. Maintaining the system pH in the preferred range will also neutralize other volatile contaminants including nitrogen oxides, removing them from the product stream.
A more alkaline condition promotes formation of HCN trimers and polymers, and leads to loss of product through nitrile hydrolysis and polymerization of nitrile monomer. Side reactions form high molecular weight products that may be carried into the column and lead to fouling of the column. At a low pH, acrolein and other volatile contaminants may escape to the overhead and contaminate the product stream.
The recovery column may be maintained at a near neutral pH by monitoring the pH and adding an appropriate amount of an alkaline compound to the system as required. The addition may be made at any convenient point; typically, the addition will be to the aqueous phase in the overhead decanter and to the solvent water fed to the column.
A variety of water soluble caustic additives including alkali metal hydroxides such as potassium hydroxide and sodium hydroxide have been disclosed in the art for this use, as have ammonia, alkyl amines and the like. However, these additives tend to react with one or more of the products. Contacting the product stream with strong caustics may initiate polymerizations and other side reactions; to avoid these difficulties, the caustic will be well- diluted with water, further adding to the disposal problem. Ammonia and water soluble alkyl . amines undergo cyanoethylation by the nitrile monomer, and amines may be sufficiently soluble in acrylonitrile to be carried into the product stream. . Salts of weak acids, for example, alkali metal and alkaline earth metal carbonates, bicarbonates, acetates, phosphates and the like have also been disclosed for this use, for example, in U.S. Pat. No. 3,896,740. These mildly alkaline compounds may be added directly
Co WO 2004/063145 PCT/US2003/038691 to the column or to a process stream without causing significant product loss. The additive most commonly employed in commercial processes for this purpose is soda ash, in part because of its low cost and ready availability. The residual salts resulting from the neutralization accumulate in the still bottoms and are eventually purged from the process as
N 5 wastewater. Where the neutralizing additive is soda ash or caustic soda, the wastewater will necessarily contain a high level of sodium salts. \ Acrylonitrile plants generate a significant volume of wastewater containing organic compounds, ammonia, and inorganic salts. Methods for treating or disposing of these streams include thermal or catalytic incineration, biotreatment, wet oxidation and reduction, and deep welling. These disposal methods represent current general industry practice.
Producers of acrylonitrile are, however, studying alternative methods of wastewater handling.
Currently, much of the wastewater generated by acrylonitrile plants in the United States is disposed of by the deep welling of streams with low levels of contaminants and the incineration of streams with higher levels of impurities.
Incineration of aqueous wastes containing high levels of sodium gives rise to serious corrosion problems, including erosion of the incinerator furnace refractory liner. Periodic shut- downs of the plant are needed to allow repair of the incinerator and replacement of the refractory, substantially adding to operating costs. Substantially reducing the level of sodium in effluent wastewater, thereby reducing damage to the incinerator and increasing the time between shutdowns, would thus provide a significant economic benefit.
The present invention is directed to an improved process for the recovery of acrylonitrile or methacrylonitrile from an aqueous product stream comprising nitrile monomer : and coproducts produced by an ammoxidation process. More particularly, the invention is directed to an improved extractive distillation process for the recovery of acrylonitrile or methacrylonitrile wherein the pH of the recovery column is maintained near neutral with an additive selected from ammonium carbonate, ammonium carbamate, mixtures comprising ammonium carbonate and ammonium carbamate, and alkylene diamines.
More fully described, the nitrile monomer recovery process will comprise: contacting an effluent containing acrylonitrile or methacrylonitrile from an ammoxidation reactor with an aqueous quench liquid in a first column (quench); contacting the gaseous quench effluent with . water in a second column (absorber), thereby forming an aqueous solution comprising nitrile monomer and coproducts; and subjecting said aqueous solution to a water extractive . distillation in a distillation column (recovery) while maintaining the pH of said distillation column in the range of from about 5.5 to about 7.5, preferably in the range of from about 6 to © about 7, by adding at least one alkaline compound selected from ammonium carbonate,
oo WO 2004/063145 PCT/US2003/038691 ammonium bicarbonate, ammonium carbamate, and alkylene diamines to the system.
Typically, the absorber column and recovery column are maintained at a pressure in the range of from 0 to 20 psig.
Further purification may be accomplished by passing the overhead vapor stream of 8 5 nitrile to a second distillation column (heads column) to remove at least some of the impurities from the crude nitrile, and further distilling the partially purified nitrile in a third distillation \ column (product column) to obtain product acrylonitrile or methacrylonitrile. in a preferred embodiment of the present invention, the reactor effluent is obtained from the reaction zone of a catalyzed ammoxidation of propane or propylene, ammonia and oxygen in the production of acrylonitrile. in another preferred embodiment, the alkaline compound is selected from ammonium carbonate, ammonium bicarbonate, ammonium carbamate and mixtures thereof.
In another preferred embodiment, the alkaline compound is generated in situ by adding ammonia and carbon dioxide to at least one of the solvent water employed in the extractive distillation and the aqueous phase of the overhead decanter.
In the improved process of this invention, an aqueous solution comprising nitrile monomer and coproducts, for example the aqueous product stream from the adsorption column of an ammoxidation process, is fed to a distillation column and subjected to a water extractive distillation wherein solvent water is introduced at the top of said column. A first overhead vapor stream comprising nitrile monomer with some water will be removed from the top of the column and condensed to an overhead decanter, and a first liquid stream containing water and water soluble coproducts and impurities will be taken from the bottom of said column.
Typically, the aqueous product stream from the adsorption column will comprise acrylonitrile or methacrylonitrile together with reaction byproducts including acrolein, acetonitrile (or methyl-substituted analogs), HCN, and ammonium salts, typically ammonium sulfates. Various contaminants such as cyanohydrins, nitrogen oxides and the like arising from side reactions may also be present. The pH will vary, depending in part upon several process factors, including the ability to accurately meter the addition of the several reaction components and to control the ammoxidation reaction parameters. Excursions in the process . control may create larger-than-anticipated deviations in the ammonia content of the reactor effluent. If not completely removed in the quench step, ammonia may be carried into the . recovery column, alkalizing the column and the overhead decanter.
The distillation column is maintained at a near-neutral pH in the range of from about 5.5 to about 7.5, more preferably in the range of from about 6 to about 7, to minimize loss of
Co WO 2004/063145 PCT/US2003/038691 product. The art discloses the use of caustic soda and a variety of other caustics for neutralizing excess acidity in the column. Where ammonia is present in the process stream, alkalizing the column and requiring the addition of an acidic compound to adjust the pH, the art further discloses the use of acetic acid and the like as additives. - 5 In the improved process of this invention, maintaining the distillation column at a near neutral pH will be accomplished by adding an alkaline compound selected from the group . consisting of ammonium carbonate, ammonium carbamate, alkylene diamines, and mixtures thereof, to the water being recovered and cycled to the column as solvent water.
The acidity of a process stream from the quench column, and thereby the acidity of the 10 aqueous solution can vary widely with time. Adding ammonium carbonate to the aqueous stream in the column will a carbonate/bicarbonate mixture. The buffering ability of ammonium carbonate/bicarbonate mixtures serves to maintain the pH near neutral, whether a deviation in the process stream causes an increase or a decrease in the acid components. Thus, ammonia present in the process stream may be absorbed by the ammonium bicarbonate to 15 form ammonium carbonate, avoiding the need to provide for the use of an acid additive.
Moreover, aqueous solutions of ammonium carbonate are only mildly alkaline; a modest excess of ammonium carbonate will be tolerated by the system without risk of product loss by alkalizing the column.
Ammonium carbonate and its anhydride, ammonium carbamate, are readily available 20 from commercial sources, as is ammonium bicarbonate. The commercial grade of ammonium carbonate is said to be a double salt of ammonium bicarbonate and ammonium carbamate,
NH,HCO,-NH,CO,NH,. Alternatively, ammonium carbonates are conveniently prepared by contacting aqueous ammonia and carbon dioxide, preferably in an absorption apparatus, and controlling the exothermic process with appropriate cooling means. 25 Alkylene amines, for example, ethylene diamine, propylene diamine, hexamethylene diamine and the like, as well as cyclic analogs thereof, are also water soluble difunctional bases capable of forming buffered aqueous solutions. A wide variety of suitable diamines are readily available from commercial sources, and these may also be found useful, singly or in combination, to provide buffered systems for neutralizing the aqueous solution from the 30 absorber. Both the alkylene diamine and the corresponding mono- and di-amminium salts that result on titrating with acidic components of the process stream are necessarily water soluble. Secondary and tertiary amines such as, for example, N,N'-dimethyl ethylene diamine, N,N,N'N’-tetramethy! ethylene diamine and the like, are less susceptible to being cyanoethylated, and thus may be preferred. 35 The amount of the alkaline compound added will be sufficient to maintain the pH of the recovery column near neutral. Diamines and ammonium carbonates may conveniently be
K Wo 2004/063145 PCT/US2003/038691 “added to the overhead decanter of the distilling column and to the solvent water.
Alternatively, ammonium carbonate may be generated in situ by separately adding appropriate quantities of ammonia and carbon dioxide to the cycle water.
EXAMPLES v 5 Seven samples of acidic column feed collected from the absorber column were neutralized by adding sufficient amounts of an alkaline additive to produce a pH of 7. The : additives and the quantities used are summarized in the following Table 1.
A portion of each was allowed to stand at room temperature for 20 hrs. to determine the amount of pH drift. The results are summarized in Table 1.
Separate portions of each were treated with equal amounts of acetic acid. The change in pH for each is summarized in Table 1.
The cyanoethylation rate, relative to diethyl amine, was also determined for each additive. The results are summarized in Table 1.
Table 1. .
Relative pH Aceticacid Rel. rate
Example Additive moles drift H shift cyanoeth. 1 Ammonium carbonate 2.08 0.06 0.37 0.040 2 HoNCH,CH;NH, 1.22 0.08 0.38 1.75 3 (CH3),NCH,CH,N(CHj3). 1.33 0.06 0.37 .003
Comp. 1 | ammonia 2.36 0.11 0.73 0.018
Comp. 2 | diethyl amine 2.76 0.41 1.23 1.00
Comp. 3 | trimethyl amine 2.79 0.22 0.85 0.003
Comp. 4 | sodium carbonate 1.00 0.07 0.45 <0.003
Though twice the molar amount of ammonium carbonate, compared with sodium carbonate, is required to produce a pH of 7, the buffering ability of ammonium carbonate is greater, as reflected in the lower shift in pH with the addition of acetic acid.
Loss in acrylonitrile due to cyanoethylation will be seen to be acceptably low for ammonium carbonate and for N,N,N’, N'-tetramethyl ethylene diamine. The cyanoethylation rate for ethylene diamine, a primary amine, is very much greater, causing an unacceptable loss in acrylonitrile.
The methods and process steps of the invention are described and illustrated in terms of particular embodiments in connection with the ammoxidation of hydrocarbons in the production of nitrile monomers. However, those skilled in the art will recognize that many ] alternatives, modifications and variations of the described methods may be found suitable for use in the practice of this invention. Such modifications and additions, as well as compositions, formulations and apparatus embodying them, are cont&hipiated ts lie within the scope of the invention, which is defined and set forth in the following claims.
Claims (7)
1. In a process for the manufacture of nitrile monomer selected from the group consisting of acrylonitrile and methacrylonitrile, said process comprising contacting a gaseous effluent comprising nitrile monomer from an ammoxidation reactor with an aqueous . 5 quench liquid in a first column; contacting the gaseous quench effluent from said first column with water in a second column, thereby forming an aqueous solution ’ comprising nitrile monomer and coproducts; and subjecting said aqueous solution to a water extractive distillation in a recovery distillation column employing solvent water and collecting said nitrile monomer together with water in an overhead decanter wherein the pH of the contents of said distillation column is maintained in the range of from about 5.5 to about 7.5 by adding an alkaline compound, the improvement wherein said alkaline compound is selected from the group consisting of ammonium carbonate, ammonium bicarbonate, ammonium carbamate, alkylene diamines, and mixtures thereof.
2 In the process of Claim 1, the improvement wherein said pH is maintained in the range of from about 6 to about 7.
3. in the process of Claim 1, the improvement wherein said alkaline compound is ammonium carbonate.
4. In the process of Claim 1, the improvement wherein said alkaline compound is a mixture comprising ammonium bicarbonate and ammonium carbamate.
5. In the process of Claim 2, the improvement wherein said ammonium carbonate is generated in situ by adding ammonia and carbon dioxide to said solvent water.
6. In the process of Claim 1, the improvement wherein said alkaline compound is an alkylene diamine.
7. In the process of Claim 1, the improvement wherein said alkaline compound is an alkylene diamine selected from the group consisting of ethylene diamine and an N,N,N’ N'-tetraalkyl ethylene diamine.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US43783604P | 2004-01-03 | 2004-01-03 |
Publications (1)
Publication Number | Publication Date |
---|---|
ZA200507199B true ZA200507199B (en) | 2006-06-28 |
Family
ID=38291141
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
ZA200507199A ZA200507199B (en) | 2004-01-03 | 2005-09-07 | Process for recovering acrylonitrile or methacrylonitrile |
Country Status (1)
Country | Link |
---|---|
ZA (1) | ZA200507199B (en) |
-
2005
- 2005-09-07 ZA ZA200507199A patent/ZA200507199B/en unknown
Similar Documents
Publication | Publication Date | Title |
---|---|---|
EP1165499B1 (en) | Improved process for the recovery of acrylonitrile and methacrylonitrile | |
US5840955A (en) | Waste minimization and product recovery process | |
EP1093389B1 (en) | Process for recovery of acrylonitirle | |
US7250527B2 (en) | Process for recovering acrylonitrile or methacrylonitrile | |
EP0811609B1 (en) | Improved acrylonitrile recovery process | |
KR100994094B1 (en) | Ammoxidation of carboxylic acids to a mixture of nitriles | |
ZA200504177B (en) | Method for inhibiting polymerization during the recovery and purification of unsaturated mononitriles. | |
ZA200507199B (en) | Process for recovering acrylonitrile or methacrylonitrile | |
US20160167975A1 (en) | Hydrogen cyanide manufacturing process with second waste heat boiler | |
EP1332177B1 (en) | Nitrile process | |
RU2113430C1 (en) | Method for stabilization of unpurified acetonitrile and method for production of hydrogen cyanide | |
MXPA98007379A (en) | Process of minimization of residues and recovery of produ |