(19) TZZ _T

(11) EP 2 254 859 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.: of the grant of the patent: C07C 253/34 (2006.01) 09.01.2013 Bulletin 2013/02 (86) International application number: (21) Application number: 09717270.4 PCT/US2009/036111

(22) Date of filing: 05.03.2009 (87) International publication number: WO 2009/111605 (11.09.2009 Gazette 2009/37)

(54) IMPROVED PROCESS TO CO-MANUFACTURE AND VERBESSERTES VERFAHREN ZUR GEMEINSAMEN HERSTELLUNG VON ACRYLNITRIL UND CYANWASSERSTOFF PROCEDE AMELIORE DE CO-FABRICATION D’ACRYLONITRILE ET DE CYANURE D’HYDROGENE

(84) Designated Contracting States: • STIMEK, Richard, T. AT BE BG CH CY CZ DE DK EE ES FI FR GB GR Old Hickory, TN 37138-1016 (US) HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK TR (74) Representative: Towler, Philip Dean Dehns (30) Priority: 05.03.2008 US 74775 St Bride’s House 10 Salisbury Square (43) Date of publication of application: London 01.12.2010 Bulletin 2010/48 EC4Y 8JD (GB)

(73) Proprietor: E. I. du Pont de Nemours and Company (56) References cited: Wilmington, DE 19898 (US) US-A- 3 185 636 US-A- 6 084 121 US-B1- 6 296 739 US-B1- 6 355 828 (72) Inventors: • BASHAM, Brent, E. Cordova Tennessee 38016 (US)

Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 2 254 859 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 2 254 859 B1 2

Description commonly referred to as "synthesis gas" or "syn-gas." The syn-gas then undergoes an additional high temper- FIELD OF THE INVENTION ature reaction to yield methanol. It is desirable to avoid the inefficiencies of an intermediate step to convert meth- [0001] This invention relates to a process for the co- 5 ane to methanol while increasing production of HCN in manufacture of acrylonitrile and hydrogen cyanide with an ACRN reaction system. improved control and efficiency. [0008] Other alcohols and ketones have been added to increase production of HCN in an acrylonitrile process. BACKGROUND OF THE INVENTION While such processes increase the HCN to ACRN ratio, 10 the total pounds of acrylonitrile is reduced, and adding [0002] Acrylonitrile (ACRN) is an important monomer additional alcohols and ketones to the reactor, further for the synthesis of various polymers including acrylic accelerates catalyst deactivation. fibers, synthetic rubbers, nylons, and is the starting ma- [0009] HCN is a highly toxic and flammable gas. At terial for acrylic acids and acrylaminde. Processes to pre- high concentrations, risk increases for exothermic runa- pare acrylonitrile are well known, and include the so-15 way reaction through polymerization and decomposition, called "Sohio Process" in which propylene/ propane react which is a potentially explosive situation. Therefore, it is with and oxygen (air) over a catalyst at elevated critical in any process which uses and/or produces HCN temperatures ("ammoxidation"). Hydrogen cyanide that safety must be of highest priority. Thus, when in-

(HCN) and acetonitrile (CH3CN) are produced as by- creasing concentration of HCN of a process, extreme products. 20 caution is needed to ensure safe operation of the proc- [0003] HCN is a valuable by- product due to it vast uses ess. as a starting material or as an intermediate. HCN is used, [0010] High concentrations of HCN in acrylonitrile sys- for example, as a starting material for the synthesis of tems are relatively unstable, and solid polymeric HCN various polymers, including polyamides, and chemicals. can form in the heads column, reducing column pressure. HCN is the starting material for metal cyanides including 25 The heads column is the distillation column in which HCN sodium cyanide and potassium cyanide, two compounds and ACRN are separated. The pressure drop raises the important in metallurgy for recovery of gold and the hard- column temperature further favoring HCN polymeriza- ening of steel. tion. Solid polymerization products plug equipment, such [0004] To increase HCN yield in the Sohio process, a as relief systems, valves, instruments, and piping, which technique commonly referred to as "methanol injection" 30 in turn, increase risks associated with HCN. may be employed. Methanol injection involves adding [0011] Downtime associated with cleaning of the solids methanol gas to the acrylonitrile reactor or feed to the and other downstream process equipped is increased reactor to increase HCN production. A conventional So- and results in substantial costs and loss production of hio process produces a ratio of acrylonitrile to HCN of ACRN and HCN. In U.S. Patents 6,296,739 and about 9 to 1, whereas using methanol injection, this ratio 35 6,793,776, Godbole discloses methods to reduce the risk can be decreased to 8 to 1. In a typical plant, use of of HCN polymerization based on reducing the amount of methanol injection can result in an increase of about 10 aqueous layer in the heads column. Godbole’s methods million pounds of HCN per year with coproduction of include increasing the reflux ratio of HCN to ACRN by about 360 to 400 million pounds of acrylonitrile per year. adding recycled or pure HCN to the heads column to [0005] Methanol injection has several disadvantages. 40 reduce the likelihood of polymer formation, among oth- Due to the burden placed on the system, overall yield of ers. Common practice is to reduce column pressure thus acrylonitrile can be reduced by as much as 5%. Methanol lowering the column temperature. reduces propylene content of the reactor, resulting in less [0012] There remains a need for co- production of acry- acrylonitrile being produced. High heat released at the lonitrile and HCN, wherein the ratio of ACRN and HCN catalyst surface as methanol reacts leads to catalyst de- 45 is less than that provided in a conventional Sohio proc- activation resulting in more frequent catalyst replace- ess. It is further desired to be able to vary this ratio. It is ment. Methanol can also react with ammoxidation inter- still further desired to avoid any negative effects on the mediates to form reactive intermediates that can lead to acrylonitrile process, such as catalyst deactivation, and polymer formation and fouling in downstream equipment. on downstream recovery and purification operations. It [0006] Methanol also reacts with oxygen in the system, 50 is further desired to have efficient conversion of consuming this reagent, and forming undesired by- prod- to HCN, or at least avoid equipment and energy cost of ucts, such as carbon oxides. producing methanol. It is further desired to maintain ef- [0007] Less obvious disadvantages of methanol injec- ficiency of oxygen consumption and to minimize forma- tion process are increased cost for equipment and energy tion of undesired by-products. It is still further desired to due to the need to convert methane to methanol. Meth- 55 use existing acrylonitrile recovery and purification equip- anol is typically produced by reaction of methane with ment. It is further critical that any increase in HCN con- steam under high temperatures and pressures over a centration be performed in a manner that does not com- copper catalyst yielding carbon monoxide and hydrogen, promise safety. The present invention meets these

2 3 EP 2 254 859 B1 4 needs. comprising hydrogen cyanide and the acrylonitrile prod- uct stream in an absorber column with water, to produce SUMMARY OF THE INVENTION a combined product stream, having a ratio of the acrylo- nitrile product stream to the stream comprising hydrogen [0013] 1. The present invention is a process for co- 5 cyanide of about 9 to 1 or less; (d) treating the combined manufacture of acrylonitrile and hydrogen cyanide com- product stream sequentially in a recovery column, a de- prising (a) combining a stream comprising hydrogen cy- canter having an aqueous layer and an organic layer, anide and an acrylonitrile reactor product stream, in an and a heads column, wherein pH is controlled by addition absorber column with water to produce a combined prod- of an acid at pH of 7.0 or less in the absorber column and uct stream, having a ratio of acrylonitrile to hydrogen cy- 10 the recovery column, and at pH less than 4.5 in the de- anide of about 9 to 1 or less; and (b) treating the combined canter and heads column; and (e) separating a crude product stream sequentially in a recovery column, a de- HCN stream from a crude acrylonitrile stream in the canter having an aqueous layer and an organic layer, heads column, treating the crude HCN stream in a HCN and a heads column, wherein pH is controlled by addition distillation column, and treating the crude acrylonitrile of an acid at pH of 7.0 or less in the absorber column and 15 stream in a drying column, wherein pH is controlled in the recovery column, and at pH less than 4.5 in the de- the HCN distillation column at pH less than 4.5. canter and heads column. The ratio of and at pH less than 4.5 in the decanter and heads column; and (e) sep- Acrylonitrile Reactor Product Stream arating a crude HCN stream from a crude acrylonitrile stream in the heads column, treating the crude HCN20 [0018] Acrylonitrile is produced in the present inven- stream in a HCN distillation column, and treating the tion, for example, and preferably, by the Sohio process. crude acrylonitrile stream in a drying column, wherein pH In this process, propylene, propane or a combination is controlled in the HCN distillation column at pH less thereof, reacts with ammonia and oxygen over a catalyst than 4.5. at elevated temperatures. Hydrogen cyanide and ace- [0014] Thus, there is provided a process for hydrogen 25 tonitrile are produced as by-products. Any source of ox- cyanide and acrylonitrile recovery and purification from ygen can be used. Typically, the oxygen source is air. which greater amounts of hydrogen cyanide are recov- Useful catalysts are known and are generally based on ered relative to a conventional Sobio acrylonitrile proc- bismuth-molybdates. ess. The relative ratio of acrylonitrile to hydrogen cyanide [0019] The reaction is carried out a temperature of be- can be controlledby controlling the feedrate of thestream 30 tween about 260°C and 600°C, preferably 310°C to comprising hydrogen cyanide in the process. 510°C, more preferably 400°C to 510°C. The pressure [0015] Essential, according to the present invention, is typically 5 to 30 psig (34 to 207 kPa). The contact time an acrylonitrile process and a hydrogen cyanide process is generally in the range of 0.1 to 50 seconds. can be operated in parallel and the product streams from [0020] The acrylonitrile product stream (reactor efflu- the individual processes are combined in a single recov- 35 ent) is a gas stream comprising unreacted reactants, ery/purification operation. Surprisingly, at relatively high acrylonitrile, hydrogen cyanide, acetonitrile and water. concentrations of hydrogen cyanide in the process, HCN The acrylonitrile product stream passes through a polymerization is substantially prevented and the proc- quencher into which water is fed to lower the temperature ess is operated in a safe manner. In addition, surprisingly of this stream and to remove any unreacted ammonia. the added HCN the process can be simply combined with 40 The unreacted ammonia can be recycled back into the ACRN product stream for recovery and purification, with- process as a reactant. Alternatively, sulfuric acid may be out need for a separate purification system added with the water to produce ammonium sulfate, which is removed as an aqueous stream. BRIEF DESCRIPTION THE DRAWINGS [0021] It is understood that other ways of acrylonitrile 45 manufacture are also possible, and the present invention [0016] is not limited to the Sohio process described above.

Figure 1 is a flow diagram of the process of this in- Stream Comprising Hydrogen Cyanide vention. 50 [0022] The stream comprising hydrogen cyanide can DETAILED DESCRIPTION OF THE INVENTION be obtained from any source of hydrogen cyanide. Con- veniently, hydrogen cyanide stream is provided as hy- [0017] Provided herein is a process for manufacture drogen cyanide product stream from a hydrogen cyanide of acrylonitrile and hydrogen cyanide in parallel from sep- synthesis reactor. arate reactor systems comprising (a) producing acrylo- 55 [0023] Hydrogen cyanide can be produced as a stand nitrile and providing an acrylonitrile product stream; (b) alone process, from the reaction of natural gas (meth- producing hydrogen cyanide and providing a stream ane), ammonia, and oxygen over platinum, platinum- rho- comprising hydrogen cyanide; (c) combining the stream dium, or a platinum-iridium alloy catalyst in gauze form

3 5 EP 2 254 859 B1 6 at atmospheric pressures and at temperatures greater refers to a distillation column. In the heads column, the than 1000°C in the Andrussow Process. Alternatively, crude HCN is separated from the crude ACRN, and sent hydrogen cyanide can be produced from methane and to an HCN distillation column for further purification and ammonia passed through porous ceramic tubes lined or then sent for additional reaction and/or to storage. The coated with platinum, at about 1300°C in the Degussa 5 crude ACRN is sent from the heads column to a drying BMA Process. Detailed descriptions of these processes column then to a product column for further purification are provided, for example, in the Encyclopedia of Chem- and storage. A detailed description of a typical recovery ical Technology (Fourth Edition, Volume 7, pp 753 to 782) and purification process is known to those skilled in the edited by Kirk-Othmer. It is understood that alternate art and is disclosed in U.S. Patent 4,234,510 and Ency- methods of HCN production exist, and the present inven- 10 clopedia of Chemical Technology (Fourth Edition, Vol- tion is not limited to those referred to hereinabove. ume 7, pp 753 to 782) edited by Kirk- Othmer. [0024] A hydrogen cyanide product stream comprises [0029] As will be appreciated by those skilled in the art, hydrogen cyanide and may also comprise unreacted re- appropriate materials of construction should be used in actants, such as but not limited to methane, oxygen, ni- the recovery and purification equipment, such as stain- trogen, and additional impurities, such as but not limited 15 less steel rather than carbon steel, to protect equipment to hydrogen. against higher concentrations of HCN relative to those of conventional Sohio acrylonitrile processes. Combined Product Stream [0030] Flammable gases, such as methane and hydro- gen, relative to a standard ACRN product stream are [0025] In the present invention, an acrylonitrile product 20 present in the absorber column as part of the combined stream and a stream comprising hydrogen cyanide are product stream. Hydrogen, methane, and oxygen, as well combined to create a combined product stream. The con- as other non-absorbing gases, are separated from the centration of the each component in the combined prod- combined product stream and removed as off-gas from uct stream can be varied to produce a ratio of acrylonitrile the top of the absorber column for incineration, or further to hydrogen cyanide ranging from 9 to 1, which is the 25 separation. As part of this invention it should be recog- typical ratio of acrylonitrile to hydrogen cyanide produced nized by those skilled in the art, that the concentration of in a standard Sohio process, to 2 to 1 and may be be- oxygen in the absorber column can become elevated and tween 2 to 1 and 5 to 1. Conveniently, this ratio can be care should be taken to maintain an oxygen concentra- adjusted by increasing or decreasing the rate of HCN tion below the explosion limit, for example, by adjusting being fed, such as increasing or decreasing rate of pro- 30 the ratio of air to propylene being feed into the acrylonitrile duction from a HCN synthesis reactor. The combined reactor. Sensors and control systems are known and product stream is introduced into a recovery and purifi- available commercially to make these adjustments. cation system. [0031] In the present invention, the concentration of [0026] The acrylonitrile product stream and the stream HCN present in the adsorber column is increased, for comprising hydrogen cyanide are combined in an ab- 35 example up to about 3% by weight, relative to a typical sorber column of a recovery/purification operation. The Sohio process where the concentration of HCN is 1% by streams are combined with water in the absorber column weight at the same location. Moreover, HCN concentra- to provide an aqueous stream comprising hydrogen cy- tion in the decanter can be as high as 20-30% by weight. anide acrylonitrile, having a ratio of acrylonitrile to hydro- Therefore, for safe operation, at the high HCN concen- gen cyanide of about 9 to 1 or less; 40 trations, conditions must be maintained to prevent HCN [0027] A typical process of this invention can yield 360 polymerization and/or decomposition. to 400 million pounds (163,000 to 181,000 metric tons) [0032] In the process of this invention to accommodate of acrylonitrile and 40 to 150 million pounds (18,000 to the higher concentrations of HCN, there is provided a 68,000 metric tons) of hydrogen cyanide per year. While control system to monitor pH and temperature along the additional hydrogen cyanide is produced, surprisingly 45 recovery/purification system. Specifically, through a there is no substantial loss in yield of acrylonitrile. That combination of temperature control and pH control, con- is, HCN and acrylonitrile can form adducts, which would ditions are maintained to prevent HCN polymerization decrease yield of acrylonitrile and it is surprising that giv- from occurring. More specifically, in circulating aqueous en high concentration of HCN, no yield loss occurs. In streams, as are present in the absorber column, recovery addition, unlike methanol injection, there is no affect on 50 column, and decanter, these streams are maintained at capacity of the acrylonitrile reactor. a pH of pH 7 or less. The aqueous feed to the absorber column generally has a pH of 5.5 to 7.0. The absorber Recovery and Purification column is preferably maintained at pH of 5.0 to 6.5, which is then fed to the recovery column. pH is monitored in [0028] The process of this invention comprises pass- 55 the absorber column and acid is added if needed to lower ing the combined product stream into an absorber col- pH, as described below. umn, recovery column, a decanter and a heads column. [0033] Preferably the pH of the recovery column is near As is known to those skilled in the art, "column" herein neutral pH, that is, pH of 6.8 to 7, for example, pH 6.8 to

4 7 EP 2 254 859 B1 8 control acrolein in the system. If needed, a base, such need to convert methane to methanol then to HCN im- as soda ash is added to the recovery column to raise pH. proving the overall carbon balance of raw materials to [0034] Temperatures are also adjusted based on pH, final product. Another advantage of this invention is the as HCN polymerization is affect by a combination of pH ability to process large concentrations of HCN in the re- and temperature. 5 covery and purification process while still preventing po- [0035] Similarly, in organic streams, such as in the de- lymerization of HCN. Since risk of HCN polymerization canter, heads column and HCN column from which is increases with increasing HCN concentration it is sur- recovered crude HCN, pH is controlled at pH less than prising that the relatively high concentrations of HCN in 4.5, preferably at pH 3.8 to 4.2. Temperature is similarly the process of the present invention can be achieved with controlled in combination with pH. For example, the de- 10 substantially no HCN polymerization, and maintaining canter preferably has a temperature of less than about safe operation. 50°C and a pH of 3.8 to 4.2. [0042] Previous attempts to prevent polymerization [0036] The control system can be any standard control added significant equipment and costs or reduced pres- systemsuch as adistributed control system or other feed- sures which also can reduce total output. Using a process back control system. Devices are installed in the recov- 15 of this invention, downtime is reduced and plant output ery/purification system, particularly on the decanter as is consistent with a typical acrylonitrile process with min- part of the control system, to monitor and control the tem- imal equipment costs. perature and pH. The devices may include thermocou- ples, pH meters, feedback controllers, and control devic- Detailed Description of Drawing es to adjust temperature, e.g., by increasing or decreas- 20 ing coolant to a column and to adjust pH, e.g., by adding, [0043] Figure 1 is a general diagram of a hydrogen increasing or decreasing flow of an acid to one or more cyanide (HCN) and acrylonitrile (ACRN) process of this of the absorber column, recovery column, decanter, invention. An ACRN product stream 4 is obtained by the heads column and HCN column. Under conventional op- ammoxidation of propylene, ammonia, and air in ACRN eration, HCN concentrations are relatively low and acid 25 reactor 1. A HCN product stream 3 is obtained by reaction addition was performed only in the heads column and in of methane, ammonia, and air in a HCN reactor 2, such HCN distillation column. as an Andrussow reactor. The ACRN product stream 4 [0037] The acid can be any acid capable of reducing is transferred to a quench column 5 where the hot ACRN the pH to below 4.5, preferably below 3.8. Preferably the product stream is cooled with water spray containing sul- acid is glycolic acid, acetic acid, phosphoric acid, succinic 30 furic acid fed through line 6 to neutralize the unreacted acid, lactic acid, formic acid, glyceric acid, citric acid, fu- ammonia in the ACRN product stream to produce am- maric acid, citraconic acid, maleic acid, sulfamic acid, monium sulfate which is removed from quench column esters of these acids, and combinations of two or more 5 through line 8 to waste water column9. Recovered thereof. More preferably, the acid is glycolic acid. HCN/ACRN is cycled back to quench column 5 through [0038] In addition to pH, temperature is controlled. The 35 line 7. A waste water purge stream 10 is take from waste temperature of the decanter should be less than 50°C, water column 9. preferably between 38°C and 42°C. Process cooling is [0044] The cooled ACRN product stream11 is then normally controlled by cooling water circulation including combined with the HCN product stream 3 in the absorber in the decanter. It is understood that others methods of column 12, where the HCN and ACRN form a combined cooling is acceptable provided it is compatible with the 40 product stream as they are absorbed into an aqueous materials of construction and does not interfere with the solution. Water is provided to the absorber column recovery and purification. through line 13. Non-absorbed compounds are separat- [0039] The present invention has various advantages ed and removed as off-gas 15. compared to currently practiced co-manufacture of acry- [0045] The aqueous solution containing the combined lonitrile and hydrogen cyanide. The first advantage is the 45 product stream 14 is then transferred to a recovery col- quantity of ACRN and HCN produced. ACRN reactor pro- umn 16 for product purification. The combined product duction is not decreased and the full potential of the plant stream 21 is fed to decanter 22. Water from stripper col- is realized, while HCN production can be increased from umn 18 is fed through line 13 to absorber column. 40 millions pounds (18,000 metric tons) of HCN in a typ- [0046] A separate stream 17 is taken from the recovery ical non-methanol injection process, and from 50 m illion 50 column 16 and fed to stripper column 18from whichcrude pounds (23,000 metric tons) per year in methanol inject- acetonitrile 19 is recovered and remaining aqueous edprocess toranges of 110to 150 millionpounds (50,000 stream 20 is fed back into recovery column16. Crude to 68,000 metric tons) per year! acetonitrile 19 can be recovered or sent to incineration. [0040] The quantity of HCN can also be selectively pro- [0047] The product stream 21 from recovery column duced based on market need and can be reduced or 55 16 is transferred to decanter 22 where the stream sepa- increased without affecting the ACRN catalyst or process rates, forming an organic layer and an aqueous layer. conditions. The aqueous layer is separated and returned as reflux [0041] An additional advantage is the elimination of the flow 29 to recovery column 16. The organic layer is trans-

5 9 EP 2 254 859 B1 10 ferred through line 28 to heads column 30 where it is 6000 pph (3000 kgph) of HCN in a Sohio ammoxidation separated into crude ACRN 31 and crude HCN 32. process. The effluent from the ACRN facility was an [0048] The crude HCN 32 is sent to a HCN column 33, ACRN product stream having a temperature of about where the HCN is further purified and sent for storage 450°C, which was fed to a quench column. After addition (not shown) through line 40. Recovered ACRN 41 from 5 of sulfuric acid and water to remove unreacted ammonia, HCN column 33 is returned to quench column 5 (line for a stream at a temperature of 46°C was fed to an absorber return of recovered ACRN 41 from HCN column 33 to column, to a recovery column to a decanter, wherein an quench column 5 is not shown). aqueous layer was separated from an organic layer, with [0049] Crude ACRN 31 is sent to a drying column 34, the aqueous layer recycled to the recovery column and fromwhich water is removed through line 37. Dried ACRN 10 the organic layer fed to a heads column where crude 35 is transferred to ACRN product column 36 for further HCN was separated from crude ACRN. Crude ACRN purification before being sent through line 39 to storage was removed from the bottom of the heads column and (not shown) from which waste material is removed from sent to a drying column and further purification and pack- ACRN product column 36 through line 38. aging.Crude HCN was removed fromthe top of the heads [0050] Acetonitrile waste water stream 42 is combined 15 column and sent to an HCN distillation column for further with other waste water streams as combined waste water purification, reaction, if desired, and packaging. stream 43, which is collected and treated as needed. [0054] In this Comparative Example, the pH was mon- [0051] Acid to control pH between pH 3.8 and 4.4 is itored and controlled at the heads column, HCN column added through any of lines 23, 25, 26, or 27 to absorber and drying column by adding glycolic acid to the column. column 12, recovery column 16, decanter 22, heads col- 20 [0055] The product ratio of ACN to HCN after purifica- umn 28, and HCN column 31. An appropriate control sys- tion was 9 to 1. tem (not shown) is used to monitor pH and temperature at each location where HCN concentration is sufficiently Example 1 high, that is, greater than 1% by weight, that there is increased risk of HCN polymerization. 25 [0056] The process of the Comparative Example was repeated, with the following changes. A hydrogen cya- EXAMPLES nide reactor was operated producing an HCN product stream, which was combined with quenched stream from [0052] The following Examples were performed in a the ACRN process in the ACRN recovery/purification flow system as illustrated in Figure 1. For the Compara- 30 system used in the Comparative Example and as de- tive Example, there was no HCN synthesis reactor and scribed above. ACRN was produced at the same rate as no HCN product stream present. The ACRN product was produced in the Comparative Example. The amount stream (reactor effluent from acrylonitrile synthesis reac- of HCN produced from the ACRN reactor and hydrogen tor) was treated in a quench column to reduce tempera- cyanide reactor was about 2.5 times the amount pro- ture to 46°C and then fed to an absorber column. The 35 duced in Comparative Example. HCN product stream (in Examples 1 and 2 only) was [0057] High concentration of HCN in the streams, es- similarly quenched to a temperature of about 55°C was pecially in the recovery column and decanter provide combined with the ACRN product stream in the absorber greatest concern for safety, where there are high con- column. The product stream (ACRN or combined stream) centrations of HCN in organic phases, susceptible to po- passed from the absorber column to a recovery column 40 lymerization. In this Example 1, the pH was monitored to a decanter, wherein an aqueous layer was separated and controlled at the absorber column, recovery column, from an organic layer, with the aqueous layer recycled decanter, heads column, and drying column by adding to the recovery column and the organic layer fed to a glycolic acid to the column or decanter, as needed to heads column where crude HCN was separated from stabilize against polymerization. crudeACRN. Crude ACRN was removed from the bottom 45 [0058] Temperature was also monitored and control- of the heads column and sent to a drying column and led in each of these vessels by controlling flow of cooling then further purification and packaging. Crude HCN was water to the cooling system of each vessel. removed from the top of the heads column and sent to [0059] Afterpurification, theratio of acrylonitrileto HCN an HCN distillation column (HCN column) for further pu- was 3 to 1 with no substantially no polymerization of HCN. rification, reaction, if desired, and packaging. 50 Example 2 Comparative Example [0060] The process of Example 1 was repeated, but [0053] For a nominal ACRN facility, capable of produc- the amount of HCN produced was varied to provide ratios ing 180 million pounds (82 million kg) per year of acrylo- 55 of ACRN to HCN of 2 to 1, 4 to 1 and 5 to 1 to show the nitrile and 20 million pounds (9 million kg) of hydrogen ability to vary rate of co-manufacture of HCN and ACRN. cyanide, the facility produced about 50,000 pounds per In this Example, the pH was monitored and controlled at hour, pph (23,000 kg per hour, kgph) of acrylonitrile and the absorber column, recovery column, decanter, heads

6 11 EP 2 254 859 B1 12 column, and drying column by adding glycolic acid to the 7. A process according to claim 2, wherein the concen- column or decanter, as needed to stabilize against po- tration of hydrogen cyanide in the absorber column lymerization. Thus, the process of this invention can pro- is between 1 and 3% by weight and wherein the con- vide varying amounts of HCN relative to ACRN with min- centration of hydrogen cyanide in the decanter is be- imal need for added investment in recovery and purifica- 5 tween 20 and 30% by weight. tion operations. Polymerization of HCN was substantially prevented. 8. A process according to claim 1 or 4 wherein the acid is glycolic acid, acetic acid, phosphoric acid, succinic acid, lactic acid, formic acid, glyceric acid, citric acid, Claims 10 fumaric acid, citraconic acid, maleic acid, sulfamic acid, esters of these acids, or a combination of two 1. A process for manufacture of acrylonitrile and hydro- or more thereof. gen cyanide in parallel from separate reactor sys- tems comprising (a) producing acrylonitrile and pro- 9. A process according to claim 8 wherein the acid is viding an acrylonitrile product stream; (b) producing 15 glycolic acid. hydrogen cyanide and providing a stream compris- ing hydrogen cyanide; (c) combining the stream comprising hydrogen cyanide and the acrylonitrile Patentansprüche product stream in an absorber column with water, to produce a combined product stream, having a ratio 20 1. Verfahren zur Herstellung von Acrylnitril und Cyan- of the acrylonitrile product stream to the stream com- wasserstoff parallel aus getrennten Reaktorsyste- prising hydrogen cyanide of about 9 to 1 or less; (d) men, umfassend (a) das Herstellen von Acrylnitril treating the combined product stream sequentially und das Bereitstellen eines Acrylnitrilproduktstroms; in a recovery column, a decanter having an aqueous (b) das Herstellen von Cyanwasserstoff und das Be- layer and an organic layer, and a heads column,25 reitstellen eines Stroms, der Cyanwasserstoff um- wherein pH is controlled by addition of an acid at pH fasst; (c) das Kombinieren des Stroms, der Cyan- of7.0 or less inthe absorber column andthe recovery wasserstoff umfasst, und des Acrylnitrilprodukt- column, and at pH less than 4.5 in the decanter and stroms in einer Absorbersäule mit Wasser, um einen heads column; and (e) separating a crude HCN kombinierten Produktstrom herzustellen, der ein stream from a crude acrylonitrile stream in the heads 30 Verhältnis des Acrylnitrilproduktstroms zu dem Cy- column, treating the crude HCN stream in a HCN anwasserstoff umfassenden Strom von etwa 9 zu 1 distillation column, and treating the crude acryloni- oder weniger aufweist; (d) das Behandeln des kom- trile stream in a drying column, wherein pH is con- binierten Produkstroms sequentiell in einer Rückge- trolled in the HCN distillation column at pH less than winnungssäule, einem Dekanter, der eine wässrige 4.5. 35 Schicht und eine organische Schicht aufweist, und einer Kopfproduktsäule, wobei der pH-Wert durch 2. A process according to claim 1 wherein the ratio of Zusatz einer Säure auf einen pH-Wert von 7,0 oder the acrylonitrile product stream to the stream com- weniger in der Absorbersäule und der Rückgewin- prising hydrogen cyanide in the combined product nungssäule und einen pH-Wert von weniger als 4,5 stream is between 2 to 1 and 9 to 1. 40 im Dekanter und der Kopfproduktsäule eingestellt wird; und (e) das Abtrennen eines Roh- HCN-Stroms 3. A process according to claim 1 wherein the ratio the von einem Rohacrylnitrilstrom in der Kopfprodukt- acrylonitrile product stream to the stream comprising säule, das Behandeln des Roh- HCN-Stroms in einer hydrogen cyanide in the combined product stream HCN-Destillationssäule und das Behandeln des is between 2 to 1 and 5 to 1. 45 Rohacrylnitrilstroms in einer Trocknungssäule, wo- bei der pH-Wert in der HCN-Destillationssäule bei 4. A process according to claim 2 wherein the stream einem pH-Wert von weniger als 4,5 kontrolliert wird. comprising hydrogen cyanide is provided as a hy- drogen cyanide product stream from a hydrogen cy- 2. Verfahren nach Anspruch 1, wobei das Verhältnis anide synthesis reactor. 50 des Acrylnitrilproduktstroms zu dem Strom, der Cy- anwasserstoff umfasst, in dem kombinierten Pro- 5. A process according to claim 1 wherein pH is con- duktstrom zwischen 2 zu 1 und 9 zu 1 liegt. trolled in the absorber column at pH 5.5 to 7.0, pH is controlled in the recovery column at pH 6.8 to 7.0; 3. Verfahren nach Anspruch 1, wobei das Verhältnis and pH is controlled in the decanter at pH 3.8 to 4.2. 55 des Acrylnitrilproduktstroms zu dem Strom, der Cy- anwasserstoff umfasst, in dem kombinierten Pro- 6. A process according to claim 5 wherein the temper- duktstrom zwischen 2 zu 1 und 5 zu 1 liegt. ature in the decanter is less than 50°C.

7 13 EP 2 254 859 B1 14

4. Verfahren nach Anspruch 2, wobei der Strom, der dans la colonne de tête, le traitement de l’écoule- Cyanwasserstoff umfasst, als Cyanwasserstoffpro- ment de HCN brut dans une colonne de distillation duktstrom aus einem Cyanwasserstoffsynthesere- de HCN, et le traitement de l’écoulement d’acryloni- aktor bereitgestellt wird. trile brut dans une colonne de séchage, dans lequel 5 le pH est contrôlé dans la colonne de distillation de 5. Verfahren nach Anspruch 1, wobei der pH-Wert in HCN à un pH inférieur à 4,5. der Absorbersäule bei einem pH-Wert von 5,5 bis 7,0, der pH-Wert in der Rückgewinnungssäule bei 2. Procédé selon la revendication 1, dans lequel le rap- einem pH-Wert von 6,8 bis 7,0 und der pH-Wert im port de l’écoulement de produit acrylonitrile à l’écou- Dekanter bei einem pH- Wert von 3,8 bis 4,2 kontrol- 10 lement comprenant du cyanure d’hydrogène dans liert wird. l’écoulement combiné de produit est compris entre 2 à 1 et 9 à 1. 6. Verfahren nach Anspruch 5, wobei die Temperatur im Dekanter weniger als 50 °C beträgt. 3. Procédé selon la revendication 1, dans lequel le rap- 15 port de l’écoulement de produit acrylonitrile à l’écou- 7. Verfahren nach Anspruch 2, wobei die Konzentrati- lement comprenant du cyanure d’hydrogène dans on von Cyanwasserstoff in der Absorbersäule zwi- l’écoulement combiné de produit est compris entre schen 1 und 3 Gew.% liegt und wobei die Konzen- 2 à 1 et 5 à 1. tration von Cyanwasserstoff im Dekanter zwischen 20 und 30 Gew.-% liegt. 20 4. Procédé selon la revendication 2, dans lequel l’écou- lement comprenant du cyanure d’hydrogène est 8. Verfahren nach Anspruch 1 oder 4, wobei die Säure fourni comme écoulement de produit de cyanure Glycolsäure, Essigsäure, Phosphorsäure, Bern- d’hydrogène à partir d’un réacteur de synthèse de steinsäure, Milchsäure, Ameisensäure, Glycerin- cyanure d’hydrogène. säure, Zitronensäure, Fumarsäure, Citraconsäure, 25 Maleinsäure, Sulfaminsäure, Ester dieser Säuren 5. Procédé selon la revendication 1, dans lequel le pH oder eine Kombination von zwei oder mehreren da- est contrôlé dans la colonne absorbante au pH 5,5 von ist. à 7,0, le pH est contrôlé dans la colonne de récupé- ration au pH 6,8 à 7,0; et le pH est contrôlé dans le 9. Verfahren nach Anspruch 8, wobei die Säure Gly- 30 décanteur au pH 3,8 à 4,2. colsäure ist. 6. Procédé selon la revendication 5, dans lequel la tem- pérature dans le décanteur est inférieure à 50°C. Revendications 35 7. Procédé selon la revendication 2, dans lequel la con- 1. Procédé de fabrication d’acrylonitrile et de cyanure centration du cyanure d’hydrogène dans la colonne d’hydrogène en parallèle à partir de systèmes de absorbante est comprise entre 1 et 3 % en poids et réacteur séparés comprenant (a) la production dans lequel la concentration du cyanure d’hydrogè- d’acrylonitrile et la fourniture d’un écoulement de ne dans le décanteur est comprise entre 20 et 30 % produit acrylonitrile; (b) la production de cyanure40 en poids. d’hydrogène et la fourniture d’un écoulement com- prenant du cyanure d’hydrogène; (c) la combinaison 8. Procédé selon la revendication 1 ou 4, dans lequel del’écoulement comprenant le cyanure d’hydrogène l’acide est l’acide glycolique, l’acide acétique, l’acide et l’écoulement de produit acrylonitrile dans une co- phosphorique, l’acide succinique, l’acide lactique, lonne absorbante avec de l’eau, pour produire un 45 l’acide formique, l’acide glycérique, l’acide citrique, écoulement combiné de produit, ayant un rapport de l’acide fumarique, l’acide citraconique, l’acide maléi- l’écoulementde produit acrylonitrile sur l’écoulement que, l’acide sulfamique, les esters de ces acides ou comprenant du cyanure d’hydrogène d’environ 9 à une combinaison de deux ou plusieurs d’entre eux. 1 ou moins; (d) le traitement de l’écoulement com- biné de produit de manière séquentielle dans une 50 9. Procédé selon la revendication 8, dans lequel l’acide colonne de récupération, un décanteur ayant une est l’acide glycolique. couche aqueuse et une couche organique, et une colonne de tête, dans lequel le pH est contrôlé par addition d’un acide au pH de 7,0 ou moins dans la colonne absorbante et la colonne de récupération, 55 et à un pH inférieur à 4,5 dans le décanteur et la colonne de tête; et (e) la séparation d’un écoulement brut de HCN d’un écoulement d’acrylonitrile brut

8 EP 2 254 859 B1

9 EP 2 254 859 B1

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• US 6296739 B [0011] • US 4234510 A [0028] • US 6793776 B, Godbole [0011]

Non-patent literature cited in the description

• Encyclopedia of Chemical Technology. vol. 7, 753-782 [0023] [0028]

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