Europaisches Patentamt 19 European Patent Office Office europeen des brevets (fi) Publication number: 0 432 876 B1 12 EUROPEAN PATENT SPECIFICATION @ Date of publication of patent specification (st) Int. CI.5: C01C3/02 03.11.93 Bulletin 93/44 (2j) Application number: 90310040.2 (22) Date of filing : 13.09.90 (54) Process for production of hydrogen cyanide from crude acetonitrile. (§) Priority : 15.12.89 US 451477 (56) References cited : PATENT ABSTRACTS OF JAPAN vol. 9, no. 96 (C-278)(1819) 25 April 1985, & JP-A-59 227718 (43) Date of publication of application (MITSUBISHI KASEI KOGYO KK) 21 December 19.06.91 Bulletin 91/25 1984, (45) Publication of the grant of the patent : @ Proprietor : BP AMERICA INC. 03.11.93 Bulletin 93/44 200 Public Square 7A Cleveland Ohio 44114 2375 (US) @ Designated Contracting States : AT BE DE ES GB IT NL (72) Inventor : Dio, Susan Bay Meado Subdivision, P.O. Box 978 Port Lavaca, Texas 77979 (US) Inventor Paul (56) References cited : : Wachtendorf, DE-A- 2 856 876 7545 Chippewa Road US-A- 3 516 789 Lodi, Ohio 44251 (US) US-A- 4 136 156 PATENT ABSTRACTS OF JAPAN vol. 10, no. 258 (C-370)(2314) 4 September 1986, & JP-A-61 @) Representative : Crack, Richard David et al 086416 (MITSUBISHI CHEM IND LTD) 1 May BP INTERNATIONAL LIMITED Patents 1986, Division Chertsey Road Sunbury-on-Thames Middlesex TW16 7LN (GB) CO CO 00 CM CO Note : Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been LU filed until the opposition fee has been paid (Art. 99(1) European patent convention). Jouve, 18, rue Saint-Denis, 75001 PARIS EP 0 432 876 B1 Description BACKGROUND OF THE INVENTION 5 The present invention relates to a process for the preparation of hydrogen cyanide from acetonitrile. In par- ticular, it relates to a process for preparing hydrogen cyanide from crude acetonitrile produced during the man- ufacture of an unsaturated nitrile such as acrylonitrile. As is well known, hydrogen cyanide is an important substance which is frequently employed as a starting material for various organic reactions, and its consumption is expected to increase more and more. 10 Industrially, hydrogen cyanide has been mainly produced by ammoxidation of methane and is also obtained as a co-product in the preparation of acrylonitrile by the catalytic ammoxidation of propylene in the well known Sohio Acrylonitrile Process developed by the assignees of the instant application. U.S. Patent 3,51 6,789 discloses a process for the manufacture of hydrogen cyanide by reacting acetonitrile over an ammoxidation catalyst. The preferred procedure of this patent is the reaction of the acetonitrile pro- is duced during the manufacture of acrylonitrile by recycling the acetonitrile through the ammoxidation reactor over the ammoxidation catalyst. Moreover, U.S. Patent 3,911 ,089 discloses the preparation of hydrogen cya- nide by the addition of methanol to the ammoxidation reactor using the production of acrylonitrile to further increase the yield the hydrogen cyanide. Both of these patents have disadvantages which are overcome by the process of the present invention. 20 SUMMARY OF THE INVENTION It is the primary object of the present invention to provide an economical process for the production of hy- drogen cyanide from crude acetonitrile which has been vaporized. 25 It is a further object of the present invention to provide a process for the production of hydrogen cyanide from crude acetonitrile obtained as a coproduct from an acrylonitrile plant. The term "crude acetonitrile" as used in this application means liquid acetonitrile containing various im- purities and water. One of these impurities should be HCN which is usually present in amounts no greater than 2% by weight. 30 Additional objects and advantages of the invention will be set forth in part in the description that follows and in part will be obvious from the description or may be learned by practicing the invention. The objects and advantages of the invention may be realized and attained by means of instrumentalities and combinations par- ticularly pointed out in the appended claims. To achieve the foregoing objects and in accordance with the purposes of the invention as embodied and 35 broadly described herein, the process of the present invention comprises manufacturing hydrogen cyanide from gaseous acetonitrile comprising reacting the acetonitrile in the presence of an oxygen containing gas in contact with an oxidation/ammoxidation catalyst at an elevated temperature wherein the improvement com- prises producing said gaseous acetonitrile from a mixture of crude acetonitrile and a polymerization inhibiting agent. 40 In a further preferred embodiment, the process of producing hydrogen cyanide of the present invention comprises mixing a polymerization inhibiting agent with crude acetonitrile to form a mixture, heating said mix- ture to a temperature sufficient to vaporize said acetonitrile, feeding the vaporized acetonitrile into a fluid bed reactor containing an oxygen containing gas and an oxidation/ammoxidation catalyst to produce hydrogen cy- anide, and recovering the hydrogen cyanide. 45 DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the present preferred embodiments of the invention. While the invention will be described in connection with the preferred embodiments, it will be understood so that it is not intended to limit the invention to that embodiment. On the contrary it is intended to cover all al- ternatives, modifications and equivalents as may be included within the scope of the invention defined by the appended claims. The process of the present invention is directed to the production to hydrogen cyanide from crude aceto- nitrile. In particular, the process comprises catalytically reacting gaseous acetonitrile at an elevated tempera- 55 ture over an oxidation/ammoxidation catalyst in the presence of an oxygen containing gas to produce hydrogen cyanide wherein the improvement comprises producing said gaseous acetonitrile from a mixture of crude acet- onitrile and a polymerization inhibiting agent. The crude acetonitrile can be obtained from any conventional source. However, in the preferred embodi- 2 EP 0 432 876 B1 mentof the present invention the crude acetonitrile is a coproduct of an acrylonitrile plant and comprises acet- onitrile/waterazeotrope containing impurities which must include HCN. Normally, the level of HCN impurity in the crude acetonitrile is no greater than 2 weight percent. Typically, this acetonitrile/water azeotrope contains 5 between 50-60% acetonitrile. The preferred process for producing the gaseous acetonitrile is by heating the crude acetonitrile in a va- porization/superheater unit. Prior to the feeding the crude acetonitrile to the vaporization unit for vaporization of the acetonitrile a polymerization inhibiting agent is added to the crude acetonitrile to prevent or substantially minimize the fouling problems which occur during vaporization. It has been found that the HCN in the crude 10 acetonitrile even at the impurity level creates fouling problems in the vaporization unit due to polymerization. The addition of the polymerization inhibiting agent prevents the HCN impurity from polymerizing and substan- tially eliminated fouling of the vaporization unit. Typically, organic acids are used as the polymerization inhib- iting agent. In particular, carboxylic organic acids such as glycolic acid and acetic acid. The crude acetonitrile is heated to a temperature sufficient to vaporize the acetonitrile in the vaporiza- 15 tion/superheater unit (approximately 110-130°C) followed by superheating to about 135-140°C in the super- heater unit. Any conventional vaporization/superheater unit may be utilized in the practice of the present in- vention. In a further preferred embodiment of this aspect of the present invention a slipstream of unvaporized or- ganics (10-25% by weight of the feed stream going into the vaporizing unit) is taken out of the vaporization/su- 20 per heater unit to help further reduce potential fouling of the system and allowing for the maintenance of a con- stant reactor feed composition going into the reactor. The superheated gaseous acetonitrile is then introduced into a fluid bed reactor where it is mixed with an oxygen containing gas (preferably air) and brought into contact with an oxidation catalyst. In a further modifi- cation to the process of the present invention an inert gas such as nitrogen can be used to dilute the reactant 25 feeds into the reactor. The gaseous acetonitrile catalytically reacts in the reactor as it passes over the oxida- tion/ammoxidation catalyst to produce hydrogen cyanide which is subsequently recovered from the reactor by conventional means (e.g., condensation). In a preferred aspect of the process of the present invention the hydrogen cyanide which is produced in the reactor is recovered as an overhead from the reactor and is fed directly into an ongoing acrylonitrile process 30 plant for recovery of the HCN and recycle of unreacted acetonitrile. The vaporization/superheater unit is operated at an elevated temperature between 110-140°C and also at an elevated pressure of between 182.7-272.4 KPa (12-25 psig). Preferrably the temperature range for vapor- ization is between 125-130°C and superheating of the acetonitrile vapors in the vaporization takes place at about 1 35-140°C. The pressure range is between 203.4-341 .3 KPa (15-35 psig) preferrably being 237.9-306.9 35 KPa (20-30 psig), especially preferred being 272.4-306.9 KPa (25-30 psig). The polymerization inhibiting agent, as stated previously, is added to prevent or substantial eliminate the polymerization of the HCN impurity in the crude acetonitrile. The organic carboxylic acid utilized in a preferred embodiment of the invention controls the pH of the liquid feed to the vaporization unit vhich prevents polymer- ization thereby alleviating fouling problems.