| Method for making caprolactam from impure 6-aminocapronitrile -> Monitor Keywords |
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Method for making caprolactam from impure 6-aminocapronitrileRelated Patent Categories: Organic Compounds -- Part Of The Class 532-570 Series, Azo Compounds Containing Formaldehyde Reaction Product As The Coupling Component, Carbohydrates Or Derivatives, The Hetero Ring Contains Seven Members Including Nitrogen And Carbon, Chalcogen Double Bonded Directly To A Ring Carbon Adjacent To The Ring Nitrogen (e.g., Caprolactam, Etc.), Cyclization To Form The Hetero Ring, Reactant Contains A Cyano GroupMethod for making caprolactam from impure 6-aminocapronitrile description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080009618, Method for making caprolactam from impure 6-aminocapronitrile. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to the field of production of lactams from aminonitriles, and in particular to the production of .epsilon.-caprolactam by the vapor phase hydrolytic cyclization of 6-aminocapronitrile. BACKGROUND OF THE INVENTION [0002] .epsilon.-Caprolactam is a precursor for the preparation of Nylon-6. Nylon-6 was first made in 1899 by heating 6-aminohexanoic acid. Commercially feasible synthesis from .epsilon.-caprolactam (CL) was discovered by Paul Schlack at I. G. Farbenindustrie in 1938. Currently, approximately 95 wt % of the world's .epsilon.-caprolactam is produced from cyclohexanone oxime via the Beckmann rearrangement. The starting material for cyclohexanone can be cyclohexane, phenol, or benzene. Then, through a series of reductions and/or oxidations, cyclohexanone is formed. The latter is then reacted with a hydroxylamine salt, usually the sulfate, to form the oxime and ammonium sulfate. The oxime is rearranged in concentrated sulfuiric acid, and the resulting lactam sulfate salt is neutralized with ammonia to form .epsilon.-caprolactam and more ammonium sulfate. Subsequently, pure .epsilon.-caprolactam is obtained by a number of separation and purification steps. Currently, this process is extremely capital intensive and generates large quantities of waste. [0003] An economically attractive method of production of .epsilon.-caprolactam uses 6-aminocapronitrile (ACN). U.S. Pat. No. 2,301,964 (E. I. Du Pont de Nemours & Company) discloses the production of lactams from aminonitriles and water in a liquid-phase method. Hydrolysis and concurrent lactam formation proceed rapidly when aminonitrile is reacted in a weak aqueous solution. Temperatures of from 200.degree. C. to 375.degree. C. are employed. The aminonitrile and water are maintained at this reaction temperature for not more than 1 hour. The reaction is preferably catalyzed with hydrogen sulfide. [0004] U.S. Pat. No. 2,357,484 (issued to Martin, E. I. Du Pont de Nemours & Company) discloses a vapor-phase catalytic process for preparing N-substituted amides. The process comprises passing a vaporized mixture of water and an aliphatic aminonitrile, containing at least one aminonitrile moiety, over a dehydration-type catalyst at a temperature of typically from 150.degree. C. to 500.degree. C. for not more than 1 minute. When an open-chain aliphatic aminonitrile is used, in which the amino and nitrile groups are separated by at least two carbon atoms in contiguous relation, the product obtained is a lactam. [0005] In recent years, inexpensive adiponitrile (ADN) has been made by the direct hydrocyanation of butadiene. This has led to a renewed interest in the Martin CL process because inexpensive ADN can be partially hydrogenated and refined to produce an impure product that comprises ACN. This product may contain some byproducts of the hydrogenation reaction, notably tetrahydroazepine (THA). [0006] U.S. Pat. No. 6,716,977 discloses a method for making CL from impure ACN containing THA, comprising the following steps: [0007] (1) Contacting the impure ACN with water at elevated temperature in the presence of a dehydration catalyst, both the impure ACN and the water being in the vapor phase, to produce a vapor phase reaction product that comprises CL, ammonia, water, ACN, and THA; [0008] (2) Separating the ammonia and a major portion of the water from the vapor phase reaction product to produce a crude liquid CL comprising CL, ACN and THA; [0009] (3) Introducing the crude liquid CL into a low boiler distillation column and removing a major portion of both the THA and ACN as a low boiler column distillate, and removing CL, high boilers and at most a minor portion of both the THA and ACN as a low boiler column tails; and [0010] (4) Introducing the low boiler column tails into a high boiler distillation column and removing CL and at most a minor portion of the high boilers as a high boiler column distillate product and removing a major portion of the high boilers as a high boiler column tails. [0011] In this method, separation of ACN & THA from CL requires a considerable number of stages in the low boiler column due to the difficulty of separation. A large number of stages in this column will cause increased pressure drop and excessively high temperature in the base of the column. It would, therefore, be desirable to have a process to make CL from ACN in which the impurities in the crude caprolactarn product were converted into species having a higher vapor pressure, which would require fewer distillation stages. SUMMARY OF THE INVENTION [0012] In the present invention, a crude liquid caprolactam comprising .epsilon.-caprolactam (CL), 6-aminocapronitrile (ACN) and water obtained from a vapor phase cyclization reaction of ACN is contacted with hydrogen in the presence of a hydrogenation catalyst to convert the ACN in the crude liquid caprolactam to a product comprising hexamethylenediamine (HMD) and hexamethyleneimine (HMI). Tetrahydroazepine (THA) is converted to HMI during this hydrogenation. The HMD and HMI have lower boiling points compared to ACN and thus are more easily separated from CL in the subsequent distillation operations. Thus a process to make CL from ACN with fewer distillation stages (hence lower pressure drop and lower base temperature) is accomplished. The present invention is, therefore, a method for making .epsilon.-caprolactam (CL) from 6-aminocapronitrile (ACN), comprising: [0013] (a) contacting a vaporized mixture of ACN and water in a reactor comprising a dehydration catalyst to produce a vapor phase reaction product comprising CL, ammonia, water and ACN; [0014] (b) separating the ammonia and a major portion of the water from the vapor phase reaction product to produce a crude liquid caprolactam comprising CL, ACN and a minor portion of the water; [0015] (c) contacting the crude liquid caprolactam with hydrogen in the presence of a hydrogenation catalyst to produce a hydrogenated crude caprolactam comprising CL, HMI, HMD and water; [0016] (d) removing water and HMI from the hydrogenated crude caprolactam in a dehydration column to produce an anhydrous crude caprolactam comprising CL and HMD; [0017] (e) introducing the anhydrous crude caprolactam into a low boiler distillation column, wherein the low boiler column distillate comprises HMD, and the low boiler column tails comprises CL and high boilers; and [0018] (f) introducing the low boiler column tails into a high boiler distillation column, wherein and the high boiler column distillate comprises CL and the high boiler column tails comprises high boilers. BRIEF DESCRIPTION OF THE DRAWING [0019] The Drawing consists of two figures, FIGS. 1 and 2, which are flow diagrams illustrating two alternative embodiments of the process of the present invention. DETAILED DESCRIPTION OF THE INVENTION Continue reading about Method for making caprolactam from impure 6-aminocapronitrile... Full patent description for Method for making caprolactam from impure 6-aminocapronitrile Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for making caprolactam from impure 6-aminocapronitrile patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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