Improved Purification and Recovery of Acetonitrile

Patentamt Europaisches || || 1 1| || || || 1 1| || || || 1 1 1| (19) J European Patent Office

Office europeen des brevets (11) EP 0 937 707 A2

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:ation: (51) |nt. ci.6: C07C 253/34, C07C 255/03 25.08.1999 Bulletin 1999/34

(21) Application number: 99300757.4

(22) Date of filing: 02.02.1999

(84) Designated Contracting States: (72) Inventors: AT BE CH CY DE DK ES Fl FR GB GR IE IT LI LU • Godbole, San jay Purushottam MC N L PT SE Solon, Ohio 441 39 (US) Designated Extension States: • Wappelhorst, Richard Lee AL LT LV MK RO SI Port Lavaca, Texas 77979 (US) • Jacobson, Paul Alan (30) Priority: 23.02.1998 US 27864 Breeksville, Ohio 44141 (US)

(71) Applicant: (74) Representative: THE STANDARD OIL COMPANY Smith, Julian Philip Howard et al Cleveland, Ohio 441 14-2375 (US) bp International Limited, Group Patents & Agreements, Chertsey Road Sunbury-on-Thames, Middlesex TW16 7LN (GB)

(54) Improved purification and recovery of acetonitrile

(57) The method of the present invention comprises lonitrile in an overhead stream exiting from the feeding crude acetonitrile containing acrylonitrile as an distillation column and recovering the crude acetonitrile impurity and water into the upper portion of a distillation substantially free of acrylonitrile impurity from the lower column, distilling the crude acetonitrile in the presence portion of the distillation column. In particular, the of the water for a time sufficient to allow substantially all method can be utilized to produce HPLC grade ace- of the acrylonitrile impurity to be vaporized in the pres- tonitrile (UV cutoff <190). ence of the water, removing substantially all of the acry- /I8

CM < o r»- r»- co o Q_ LU Printed by Xerox (UK) Business Services 2.16.7/3.6 1 EP 0 937 70737 A2 2

Description phere to remove the bulk of the HCN, (2) passing this azeotrope through a digester in which the remaining BACKGROUND OF THE INVENTION HCN is removed by treatment with an aqueous solution of base and formaldehyde, (3) performing a second dis- Field of the Invention s tillation at a pressure less than 1 atmosphere to separate the material into a bottoms product containing [0001 ] In the production of acrylonitrile by the catalytic water and a second acetonitrile/water azeotrope with ammoxidation of propylene with ammonia and oxygen, higher acetonitrile concentration, and (4) a third distilla- a crude acetonitrile co-product is produced. The term tion at a pressure above the pressure of the first distilla- "crude acetonitrile" means liquid acetonitrile containing w tion to produce purified acetonitrile as a side stream. hydrogen cyanide, water and other impurities. The other This process is described in U.S. Patent 4,362,603 impurities may include acrylonitrile, acetaldehyde, ace- assigned to the assignee of the present invention and tone, methanol, acrolein, oxazole, cis- and trans-crot- herein incorporated by reference. Acetonitrile purified ononitrile, methacrylonitrile and allyl alcohol. The by this method can contain up to several parts per mil- relative proportions of the components of the crude ace- is lion by weight of acrylonitrile, acetamide, oxazole, or tonitrile can vary over a wide range depending on vari- other UV-absorbing impurities. ous conditions. The concentration level of the organic [0004] While these two basic procedures for forming impurities in the crude acetonitrile is usually less than bulk solvent grade acetonitrile are widely accepted, their 15% with no single organic component found in greater use in producing acetonitrile for chromatographic appli- than 2 to 4 wt % concentration. Usually crude ace- 20 cations is not acceptable because the acetonitrile con- tonitrile obtained from an acrylonitrile plant contains tains a relatively high amount of UV-absorbing between 25 and 85% acetonitrile. Typically, the crude impurities. There is a distinct market for high perform- acetonitrile is composed on a weight basis of 52% ace- ance (HPLC grade) acetonitrile essentially free of UV- tonitrile, 43.6% water, 2.5% hydrogen cyanide, 0.5% absorbing impurities (UV cutoff for impurities of acrylonitrile and 1 .3% other organic impurities as men- 25 <190nm). tioned above. Originally, during the manufacture of acry- [0005] The specifications for HPLC grade acetonitrile lonitrile, the crude acetonitrile produced was disposed render the material produced by first stage purification of by incineration. However, in recent years, this mate- unacceptable, therefore requiring further processing by rial has been recovered and purified and sold to add producers of HPLC grade acetonitrile. The traditional value to the process. 30 commercial methods of acetonitrile purification to [0002] There are two basic technologies for the "first achieve this high grade of purity utilize costly multi-step stage" purification of crude acetonitrile co-product pro- processes involving, for example, permanganate oxida- duced during the manufacture of acrylonitrile. These tion, acid treatment, phosphorous pentoxide drying and processes typically produce acetonitrile of sufficient two distillations. purity for use as a bulk solvent. The first and most com- 35 [0006] More recent procedures disclosed in U.S. Pat- mon practiced technology is a batch process. In this ents 5,292,919 and 5,426,208 disclose treatment of process, crude acetonitrile is distilled to remove the bulk acetonitrile with ozone followed by passing the ace- of the HCN as a low boiling distillate. The remaining tonitrile through a series of adsorbent beds of charcoal material is allowed to react either with a mixture of or graphitized carbon, activated alumina, and/or molec- strong base, usually an aqueous sodium hydroxide 40 ular sieves. solution and formaldehyde and water, or with a strong [0007] Several other patents and literature articles base and ferrous sulfate, to remove essentially all the describe the purification of acetonitrile with acidic ion remaining HCN. (See U.S. Patents 4,328,075 and exchange resins for removal of impurities from ace- 3,201,451.) The HCN free material is then distilled to tonitrile. British Patent 1 ,223,91 5 describes the use of a produce an acetonitrile/water azeotrope containing 45 series of strong acid cation exchange resins for the about 25% water. The azeotrope is then slurried with reduction of the concentration of bases, ammonia and anhydrous calcium chloride to remove the bulk of the 3,3'-iminodipropionitrile, in aqueous acetonitrile from water in the azeotrope and produce an ace- 500 ppm each to 10 ppm and <50 ppm, respectively. tonitrile/water mixture containing about 3 to 5% water. This level of purity is still not acceptable for HPLC grade This mixture is then distilled to produce acetonitrile so acetonitrile. product having an acceptable purity for many uses. Typ- [0008] The process of the present invention is directed ically, this material contains several parts per million by to an improved procedure for easily removing substan- weight of acrylonitrile or other impurities which absorb tially all of the acrylonitrile impurity present in crude strongly in the UV spectrum. acetonitrile, in particular, crude acetonitrile produced as [0003] The second method of producing "first stage" 55 a co-product during the manufacture of acrylonitrile. In purified acetonitrile is a continuous recovery process addition, the process of the present invention results in which involves (1) first distilling crude acetonitrile in a the production of a crude acetonitrile intermediate distillation zone at a pressure of at or above 1 atmos- stream which simplifies the process for producing HPLC

2 3 EP 0 937 707 A2 4 grade acetonitrile resulting in substantial economic sav- being 148°F to 152°F) at a pressure of about 18 psia. ings. [001 9] The process of the present invention enables one to produce acetonitrile recovered from the light Summary of the Invention ends distillation column side stream which has substan- 5 tially reduced acrylonitrile impurity levels compared to [0009] It is a primary object of the present invention to previously recovered light ends distillation column side provide an improved process for the substantial removal stream acetonitrile. For example, during the practice of of acrylonitrile impurity present in crude acetonitrile. the process of the present invention the acrylonitrile [001 0] It is a further object of the present invention to impurity level of the recovered side stream acetonitrile is provide an improved process for the substantial removal 10 reduced from about 240 ppm to about 40 ppm which of acrylonitrile impurity present in crude acetonitrile represents a reduction of about 600% % from the obtained as a coproduct during the manufacture of acry- amount of acrylonitrile impurity present in typical light lonitrile. ends column side stream crude. While practicing the [001 1 ] It is a still further object of the present invention process of the present invention the solvent grade ace- to provide an improved process for the production of 15 tonitrile product obtained from the product column side HPLC grade acetonitrile. stream is decreased from a range of about 1to 3 ppm to [0012] It is another object of the present invention to a value below detection limits of 1 00 ppb. provide an improved recovery efficiency and product [0020] It has further been discovered that the practice recycle process for the production of solvent grade ace- of the process of the present invention results in a sub- tonitrile. 20 stantial economic advantage when practice in conjunc- [0013] Additional objects, advantages and novel fea- tion with the subsequent procedure of producing HPLC tures of the invention will be set forth in part in the grade acetonitrile. Since the practice of the present description which follows, and in part will become invention results in the production of a solvent grade apparent to those skilled in the art upon examination of acetonitrile product which contains no detectable acry- the following or may be learned by the practice of the 25 lonitrile compared with typical solvent grade acetonitrile invention. The objects and advantages of the invention obtained from the distillation procedures of the prior may be realized and obtained by means of the instru- process, it has been found that substantially less caus- mentalities and combinations particularly pointed out in tic (e.g. 60% to 70%) and almost no formaldehyde have the appended claims. to be added during the downstream treatment of the sol- [001 4] To achieve the foregoing objects in accordance 30 vent grade acetonitrile to produce HPLC grade ace- with the purpose of the present invention as embodied tonitrile. In fact, compared to HPLC caustic treatments and described therein, the method of the present inven- required in the previous processes the decrease in the tion comprises feeding crude acetonitrile containing caustic usage is almost 80% to 85% resulting in acrylonitrile as an impurity and water into the upper por- digester operation simplification, less polymerization tion of a distillation column, distilling the crude ace- 35 related operational problems and and substantial cost tonitrile in the presence of the water for a time sufficient savings in the overall purification process. to allow substantially all of the acrylonitrile impurity to be [0021 ] The details of the preferred production process transferred to the vapor phase by the water and, there- for the manufacture of HPLC grade acetonitrile have fore, removed in an overhead stream exiting from the been set forth in detail in copending U.S. Serial Number distillation column and recovering the crude acetonitrile 40 08/632,382 filed 4/1 0/96 assigned to the assignee of the substantially free of acrylonitrile impurity from the lower instant application and herein incorporated by reference portion of the distillation column. [0022] In accordance with another purpose of the [001 5] In a preferred embodiment of the process of present invention as embodied and described herein, the present invention the water is fed to the distillation the method of the present invention comprises (1) feed- column above the point where the crude acetonitrile 45 ing crude acetonitrile containing acrylonitrile as an enters the distillation column. impurity and water into the upper portion of a first distil- [001 6] In a further preferred embodiment of the proc- lation column affixed with a first overhead reflux loop at ess of the present invention the distillation tower is a first pressure of at least 1 atmosphere and distilling equipped with trays and the water is fed into the distilla- the crude acetonitrile in the presence of the water for a tion column at a point above the highest tray present in so time sufficient to allow substantially all of the acryloni- the column. trile impurity to be vaporized in the presence of water [001 7] In a further preferred embodiment of the proc- and removed along with HCN impurity present in the ess of the present invention the distillation tower is crude acetonitrile in an overhead stream exiting from equipped with packing. the first distillation column producing a first ace- [0018] In a still further preferred embodiment of the 55 tonitrile/water azeotrope substantially free of acryloni- process of the present invention the light ends column trile impurity and a first bottom product containing water top distillation temperature is between about 140°F to and a first bottom product containing water, (2) distilling 160°F (preferably 144°F to 155°F, especially preferred the first azeotrope in a second distillation column affixed

3 5 EP 0 937 707 A2 6 with a second overhead reflux loop at a second pres- outside this range is also satisfactory. Preferably, flow sure less than 1 atmosphere to separate the first azeo- rates are in the range of 0.2 to 50 bed volumes per hour. trope into a second bottoms product containing water Most preferably, from 0.5 to 35 bed volumes per hour. and a second acetonitrile/water azeotrope having a [0027] Lastly, a final distillation of the HPLC grade greater acetonitrile concentration than the first azeo- 5 acetonitrile is optional and may be carried out by con- trope, (3) distilling the second acetonitrile/water azeo- ventional means known in the art. Preferably, means of trope in a third distillation column affixed with a third distillation are distillation in glass or stainless steel overhead reflux loop at a third pressure above 1 atmos- equipment, although other materials of construction phere to produce a third acetonitrile/water azeotrope inert to acetonitrile and free of contaminants are within containing substantially all of the water from the second w the scope of the invention. Fractionation can be accom- azeotrope, a third bottoms product comprising ace- plished with Oldershaw columns, or columns packed tonitrile and heavy organics, and a side stream compris- with beds, helices, trays, turnings, saddles, or other ing highly pure acetonitrile, and (4) passing the highly conventional packing material known in the art. pure acetonitrile side stream through an acidic ion [0028] Suitable ion exchange resins useful in the prac- exchange resin to further purify said highly pure ace- 75 tice of the present invention include strong acid type tonitrile producing HPLC grade acetonitrile wherein the incorporating sulfonic acid functional groups, either gel reflux ratios in Steps 1 , 2 and 3 are kept at greater than form or macroreticular or macroporous form. Examples 2.7 to 1 , greater than 2.2 to 1 and greater than 3.0 to 1 , include, but are not restricted to, Amberlyst 15, Amber- respectively. lyst XN 1010, Dowex 50, Amberlite IRP-69, Amberlite [0023] The term "reflux ratio" as used above is defined 20 IR-118, and their equivalents. Also acceptable but less as follows: for the first column (light ends column), the preferred are the so-called weak acid resins incorporat- reflux ratio is defined as the ratio of overhead reflux flow ing carboxylic acid functional groups, either gel form or rate divided by the rate of feed from the column side to macroreticular or macroporous form. Examples of this the digester. For the second distillation (drying column), class of resin include, but are not restricted to, Amberlite the reflux ratio is defined as the ratio of overhead reflux 25 IRP-64 and IRC-50S. Particularly preferred are the flow rate to the rate of the overhead draw-off to the prod- strong acid resins specifically designed for non-aque- uct column. For the third distillation column (product col- ous applications, such as Amberlyst 1 5. umn), the reflux ratio is defined as the ratio of overhead reflux flow rate to the rate of acetonitrile product side Brief Description of the Drawing stream flow. 30 [0024] In a preferred embodiment of the present [0029] The Figure is a flow diagram of the practice of invention the light ends column reflux ratio is preferably the process of the present invention. greater than 4.4 to 1 , the drying column reflux ratio is preferably greater than 4.5 to 1 and the product column DETAILED DESCRIPTION OF THE INVENTION reflux ratio is preferably greater than 8.0 to 1 . Especially 35 preferred is a light ends column reflux ratio of greater [0030] In accordance with the process of the present than 5.2 to 1 , a drying column reflux ratio of greater than invention crude acetonitrile containing acrylonitrile as 5.0 to 1 and a product column reflux ratio of greater than an impurity and water are fed into the upper portion of a 10.9 to 1. distillation column. Th crude acetonitrile is then distilled [0025] The acidic ion exchange resins are used in 40 in the presence of the water for a time sufficient to allow their H+ form. Regeneration of resin beds can be carried substantially all of the acrylonitrile impurity present in out by passing sulfuric acid or hydrochloric acid solu- the crude acetonitrile to be vaporized in the presence of tions over the resin beds by any conventional procedure the water and removed in an overhead stream exiting known to the art. After regeneration, the resin bed is from the distillation column. The crude acetonitrile sub- washed with several bed volumes of acetonitrile to dry 45 stantially free of acrylonitrile impurity is recovered from the bed and remove impurities. the lower portion of the distillation column preferably as [0026] The resin treatment step can be carried out in a side stream. any mode known in the art. The resin treatment step [0031 ] In another aspect of the practice of the present can be carried out preferably as a continuous fixed bed invention the crude acetonitrile substantially free of process, although slurry mode operation in (optionally) so acrylonitrile impurity is further processed to recover stirred tank reactors, for example, is within the scope of highly pure acetonitrile. By "highly pure" acetonitrile is this invention. The adsorbent beds can be operated in a meant High Performance Liquid Chromatography continuous mode at ambient temperature or at elevated (HPLC) grade acetonitrile, acetonitrile of extremely high or reduced temperature as required, and with either purity and being sufficiently free of UV absorbing impu- upward or downward flow, with temperatures from 15 to ss rities (well below 0.1 to 0.3 ppm max) having a UV 35°C being preferred. A flow rate ranging from about 0. 1 absorbance cut off of <190 nm. The crude acetonitrile to 300 bed volumes per hour is within the scope of the which is processed in accordance with the present process of the present invention, although operating invention is any acetonitrile/water mixture containing at

4 7 EP 0 937 707 A2 8 least 15% water. Thus, the inventive process is applica- ered material is removed from digester 24 as overheads ble in the processing of various water/acetonitrile azeo- via line 27 and combined in line 18 for transport to vent tropes. The invention, however, finds broadest scrubber and waste treatment. In addition, a stream application in the processing of the crude acetonitrile comprising acetonitrile containing a small amount of streams produced by the ammoxidation of propylene 5 heavy impurities is also charged into drying column 32 with oxygen and ammonia to form acrylonitrile. As indi- via line 34 from product column 42. In drying column 32, cated above, such crude acetonitrile streams normally the acetonitrile/heavy organics and water mixture is dis- contain about 52% acetonitrile, 43.6% water, 0.5% tilled at a pressure below one atmosphere, e.g. 3.4 psi acrylonitrile, 2.5% HCN and 1.3% other minor impurities and heavy organics are discharged for waste treatment such as oxazole, allyl alcohol, acetone and propionitrile. w via line 36 with some recycled back via reboiler 39 into [0032] Crude acetonitrile recovered from an acryloni- the bottom of column 32, and a gaseous top draw com- trile plant and having the above composition can be prising a second acetonitrile/water azeotrope, the sec- conveniently processed by the present invention. Refer- ond azeotrope containing about 1 0% water, is removed ence will now be made in detail in accordance with the from column 32 via line 38. At least part of this second process flow scheme illustrated in the Figure to the 15 azeotrope is condensed through condenser 40 and process of the present invention as it applies to the refluxed back into column 32 via reflux line 37. The manufacture of HPLC grade acteonitrile. reflux ratio in this step as defined above is greater than [0033] In accordance with this preferred system, 2.2:1. crude acetonitrile via inlet line 14 and water via inlet line [0036] The second acetonitrile/water azeotrope is 12 ,or optionally via line 13, are fed into light ends col- 20 charged via line 38 into condenser 40 where it is con- umn 16 wherein the crude acetonitrile containing acry- densed, passed via line 43 through heat exchanger 44 lonitrile as an impurity are distilled at a temperature of where it is heated, and then charged via line 45 into between about 140°F to 160°F (preferably 144°F to product column 42. In product column 42, the second 155°F, especially preferred being 148°F to 152°F) at a acetonitrile/water azeotrope is distilled at high pressure, pressure of about 18 psia for a sufficient time to allow a 25 e.g. 50 psia. A bottoms product comprising acetonitrile substantial amount of the acrylonitrile impurity to be containing heavy impurities is withdrawn from the bot- vaporized by extractive distillation and removed from tom of product column 42 into reboiler 46 for partial the column via line 18. The light impurities in the crude recycling to column 42 via line 41 and drying column 32 acetonitrile, namely HCN, oxazole and acetone, are via line 34. A third acetonitrile/water azeotrope is with- also withdrawn from light ends column 16 as a vapor 30 drawn from the top of product column 42 via line 28 and draw via line 1 8 and are condensed along with the acry- condensed and recycled as reflux back to the top of lonitrile and refluxed back into the upper region of col- product column 42 via reflux line 47. The uncondensed umn 16 via reflux line 17. Preferably, the reflux ratio as vapors continue via line 28 to the azeotrope condenser defined above is greater than 2.7:1. Unrecovered over- 23 where they are mixed with the first azeotrope. Alter- heads are removed via line 18 and transported to vent 35 natively, these uncondensed vapors may be rerouted to scrubbers (not shown) or any other conventional means light ends column 16 via lines 29 and 14. Preferably, the for waste treatment. Water is recovered from the bottom reflux ratio as defined above of greater than 3.0:1 for of light ends column 16 and discharged via line 20 to this step of the process. In an alternative embodiment of waste treatment with partial recycle through reboiler 21 . the present invention, some liquid from product column A first acetonitrile/water azeotrope containing about 40 overhead stream 28 may be recycled to drying column 70% acetonitrile, 30% water, 500 ppm HCN, acryloni- 32 via line 48 or digester 24 via line 41 . Because prod- trile in the range of 40 ppm to 60 ppm and very small uct column 42 is operated at high pressure, all of the amounts of heavy organics is recovered via line 22 as a water in the second acetonitrile/water azeotrope vapor side draw condensed in condenser 23 and trans- charged into product column 42 is recovered in the ported via line 25 to digester 24. 45 overhead stream of product column 42, i.e. the third [0034] An HCN digester composition comprising an acetonitrile/water azeotrope, leaving high purity ace- aqueous solution of sodium hydroxide and formalde- tonitrile in the product column. This high purity ace- hyde is added via line 26 to digester 24 so that any tonitrile (99.8 wt % acetonitrile) is drawn off column 42 remaining HCN and acrylonitrile in the first azeotrope is as a sidestream via line 50 (This stream may be a vapor destroyed. As mentioned above, the amount of caustic so or liquid, preferably a vapor), and after cooling in heat and formaldehyde additives required is substantially exchanger 51 is discharged via line 52 into resin treat- reduced in the practice of the process of the invention ment bed 54 where it is treated to produce HPLC grade and, in fact, in the optimum practice of the process of acetonitrile which is recovered via line 56 in product the present invention it is envisioned that the use of for- tank 58. maldehyde can even be eliminated. ss [0037] The temperature for distillation in drying col- [0035] The HCN-acrylonitrile free acetonitrile/heavy umn 32 fluctuates between about 75°F to 90°F, prefera- organics and water mixture passing out of digester 24 is bly between 78°F to 88°F. The typical distillation charged via line 30 into drying column 32 and unrecov- temperature in the product column is between about

5 9 EP 0 937 707 A2 10

250°F to 260°F, preferably 255°F to 258°F. illustrative of the practice of the present invention. [0038] In a preferred embodiment of the process of the present invention, the following control scheme (not Example 1 illustrated) may be implemented. The light ends column bottoms temperature is controlled by cascading its con- s [0042] With a light ends column feed of about 1 2 gpm, trol to the feed flow control. The light ends column bot- the light ends column side stream was showing a typical toms temperature control target is set by an equation acrylonitrile concentration in the light ends column side relating it to the column bottoms pressure. The reboiler stream vapor composition of about 240 ppm. Within half steam flow controls the side draw pressure. The side an hour of adding the solvent water on the top tray with- stream vapor flow to the azeotropic condenser is used 10 out altering or making any changes to the light ends col- to control the level in the Digester. The cooling tower umn set points; the acrylonitrile concentration in the water flow to the condenser is used to control the over- light ends column side draw vapor dropped to about 40 head temperature. Then, the overhead temperature tar- ppm. This did give a reason to alter the caustic con- get is varied to maintain the light end column sumption in digester from about 120 inches of caustic / temperature profile for ensuring constant composition in is shift to about 30 inches of caustic per shift. Even with the upper section of this column. The light ends Bottoms such a drastic reduction in caustic consumption, the Level is controlled by the Bottoms blowdown flow. Such product column side stream acrylonitrile content has a control scheme, in conjunction with the solvent water decreased from about 3 ppm to below the detectable addition, ensures a more steady composition of all three limit of 100 parts per billion. streams leaving the light ends column. 20 [0043] In a typical acetonitrile purification unit opera- [0039] Once the liquid level has been established in tion, an acetonitrile product column is operating with a the Azeotrope Condenser Receiver, feed to the Digester product column liquid overhead reflux flow of 6 gpm. can be started. The rate of caustic addition is controlled Instead of recycling approximately 1 .8 gpm back to the to ensure that very little acrylonitrile enters the drying light ends column if we do recycle only 0.6 gpm, the light column feed. The caustic addition reflects the lower 25 ends column does not have to reprocess the 1 .2 gpm acrylonitrile coming forward with the solvent water addi- which was about 10% of the light ends column feed of tion. The drying column feed is manually fixed flow 12 gpm in the above quoted Example 1. This does based upon desired production rates. All other column download the light ends column by about 10% and feed rates are ultimately determined by the drying col- increases the recovery efficiency and reduces the umn fixed feed. The pressure drop in the drying column 30 energy consumption in the overall process. is controlled by varying the reboiler steam flow. Reflux flow controls the level in the reflux drum. The bottoms Claims level is controlled with the drying column bottoms blowdown. The drying column bottoms temperature is con- 1. A process for treatment of crude acetonitrile controlled with the product column feed flow. Just as in the 35 taining acrylonitrile as a impurity comprising feed- light ends column, this control scheme ensures a more ing, water and crude acetonitrile containing steady composition of the two streams leaving the dry- acrylonitrile as an impurity into the upper portion of ing column. Cascading the drying column pressure drop a distillation column, distilling the crude acetonitrile with the steam flow keeps loading constant as in the presence of the water for a time sufficient to described for the light ends column. 40 allow substantially all of the acrylonitrile impurity to [0040] The product column bottoms level is controlled be vaporized in the presence of water and removed by adjusting the product column side stream flow. The in an overhead stream exiting from the distillation product column bottoms flow is a manually set fixed column and recovering the crude acetonitrile sub- flow. The reboiler steam is fixed input as well. Reflux stantially free of acrylonitrile impurity from the lower flow controls the tray temperature in the product col- 45 portion of the distillation column. umn. Vapor recycle is fixed as well. The product column liquid recycle split between the light ends column and 2. The process of claim 1 wherein the water is fed to drying column is targeted by the amount of oxazole the distillation column above the point where the present in the recycle. It has been further discovered crude acetonitrile enters the distillation column. that changing the proportion of product column liquid so recycle going to the light ends column from 30 % to 10 3. The process of claim 1 or 2 wherein the distillation % present substantial economic advantage to the ace- tower is equipped with trays and the water is fed tonitrile recovery process. This means the amount of into the distillation column at a point above the high- product column recycle going to only the drying column est tray present in the column. increases from 70 % to 90 %. With process modeling as 55 well as the plant data, the increased recovery efficiency 4. The process of any preceding alarm wherein the and processing capacity has been demonstrated. distillation temperature is between above 140 F to [0041] The following Examples set forth below are 160 F.

6 11 EP 0 937 707 A2 12

5. A process for the manufacture of HPLC grade ace- ing distilling the purified acetonitrile recovered from tonitrile comprising (1) feeding water and crude the acidic ion exchange resin. acetonitrile containing acrylonitrile as an impurity into the upper portion of a first distillation column affixed with a first overhead reflux loop at a first 5 pressure of at least 1 atmosphere and distilling the crude acetonitrile in the presence of the water for a time sufficient to allow substantially all of the acrylonitrile impurity to be absorbed by the water and removed along with HCN impurity present in the w crude acetonitrile in an overhead stream exiting from the first distillation column producing a first acetonitrile/water azeotrope substantially free of acrylonitrile impurity and a first bottom product containing water and a first bottom product containing 15 water, (2) distilling the first azeotrope in a second distillation column affixed with a second overhead reflux loop at a second pressure less than 1 atmosphere to separate the first azeotrope into a second bottoms product containing water and a second 20 acetonitrile/water azeotrope having a greater acetonitrile concentration than the first azeotrope, (3) distilling the second acetonitrile/water azeotrope in a third distillation column affixed with a third overhead reflux loop at a third pressure above 1 atmos- 25 phere to produce a third acetonitrile/water azeotrope containing substantially all of the water from the second azeotrope, a third bottoms product comprising acetonitrile and heavy organics, and a side stream comprising highly pure acetonitrile, and 30 (4) passing the highly pure acetonitrile side stream through an acidic ion exchange resin to further purify said highly pure acetonitrile producing HPLC grade acetonitrile wherein the reflux ratios in Steps 1 , 2 and 3 are kept at greater than 2.7 to 1 , greater 35 than 2.2 to 1 and greater than 3.0 to 1 , respectively.

6. The process of claim 5 wherein the reflux ratio in step 1 is between about 4.4 to 1 . 40 7. The process of claim 5 or 6 wherein the reflux ratio in step 2 is between about 4.5 to 1 .

8. The process of any one of claims 5 to 7 wherein the reflux in step 3 is maintained between about 8.0 to 45 1.

9. The process of any one of claims 5 to 8 wherein the acidic ion exchange resin is selected to include a strong acid incorporating sulfuric acid functional so groups.

1 0. The process of any one of claims 5 to 8 wherein the acidic ion exchange resin is selected to include weak acid resin incorporating carboxylic acid func- 55 tional groups.

11. The process of any one of claims 5 to 10 compris-

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