WO2014210191A1

WO2014210191A1 - Improved process for refining nitriles

Info

Publication number: WO2014210191A1
Application number: PCT/US2014/044145
Authority: WO
Inventors: Milind V. Kantak
Original assignee: Invista Technologies S.A R.L.
Priority date: 2013-06-26
Filing date: 2014-06-25
Publication date: 2014-12-31
Also published as: EP3013793A1; TW201504204A

Abstract

The present invention provides an improved process for preferentially concentrating 2-methylglutaronitrile from mixtures comprising 2-methyl-glutaronitrile and other C6 nitriles having very close relative volatilities, for example, 2-ethylsuccinonitrile and adiponitrile, in a particular integrated, continuous distillative refining process, advantageously utilizing a carefully staged distillation apparatus train and by operating in an optimized window for effective separation.

Description

IMPROVED PROCESS FOR REFINING NITRILES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority filing date of U.S. provisional application serial number 61/839,435, filed June 26, 2013, the disclosures of which are specifically incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

[0002] The present invention relates to an improved process for preferentially concentrating 2-methylglutaronitrile from mixtures comprising 2-methylglutaronitrile and other C₆ nitriles having very close relative volatilities ranging from 0.9 to 1.2 in the pressure range of 10 to 300 mmHg and temperature range of 170 to 210°C. More particularly, the invention relates to an improved process for preferentially concentrating 2-methylglutaronitrile from mixtures comprising 2-methylglutaronitrile and other C₆ nitriles having very close relative volatilities, for example, 2-ethylsuccinonitrile and adiponitrile, in a particular integrated, continuous distillative refining process, advantageously utilizing a carefully staged distillation apparatus train and by operating in an optimized window for effective separation.

BACKGROUND OF THE INVENTION

[0003] In current commercial processes for production of adiponitrile, the starting reactants are butadiene and hydrogen cyanide. The adiponitrile intermediate is an important chemical for its commercial versatility and finds application in the industrial production of nylon polyamides that are used in forming films, fibers and molded parts. The chemical thermodynamics of such a process usually favors several other co-product species during adiponitrile synthesis. While the objective is always to minimize production of such co-products and boost the desired product yield, some of these unique co-products have highly specialized markets of their own. One of these co-products is a branched six-carbon dinitrile labeled 2-methylpentanedinitrile, commonly known as 2- methylglutaronitri le . [0004] It is desirable to collect the co-product crude containing 2-methyl- glutaronitrile and further process it to its highest purity form (e.g., 99.1 wt. % minimum). This product is commercially known as DYTEK® MGN (2-methylglutaronitrile), which is a high-boiling specialty intermediate used in the fibers, solvent and polymer industries.

[0005] Several impurities are purged from the adiponitrile synthesis process, which end up in this crude dinitrile stream in various concentrations. These include different forms of trivalent and pentavalent phosphorus species, glycols, phenols, cresols, and catechol along with other substituted nitriles and dinitriles. In the adiponitrile synthesis process starting from butadiene and hydrogen cyanide, tert-butyl catechol ("TBC"), used as a butadiene stabilizer, and boron-containing catalyst promoter subsequently interact to form TBC ester of phenyl boronic acid. The 2-methylglutaronitrile rich crude thus formed in the adiponitrile synthesis process is continuously analyzed for these low- and high-boiling impurities.

[0006] Catalytic hydrogenation of high purity 2-methylglutaronitrile, such as DYTEK^® MGN, is an important chemical process. Since the impurities accompanying 2- methylglutaronitrile produced in an adiponitrile synthesis process severely deactivate hydrogenation catalysts, it is desirable to separate them from 2-methylglutaronitrile. Further, some of the impurities interfere with downstream chemistries, thereby negatively impacting the desired product yield and/or separation. Of primary importance in this regard is the impurity, 2-ethylsuccinonitrile ("ESN"), which is present in significant quantity and a very close boiler with 2-methylglutaronitrile.

[0007] U.S. Patent No. 5,312,959A discloses a method for purification of 2- methylglutaronitrile or adiponitrile which contain boron residues from the process of butadiene reacting with hydrogen cyanide using a nickel catalyst and a boron compound as a promoter. The method comprises adding an alcohol selected from the group consisting of amino alcohols and glycols, and then recovering the nitrile by distillation. When 2-methylglutaronitrile is being purified, the single distillation column would normally be run at a pressure in the range of 10 to 300 mmHg, and at a temperature in the range of 70 to 160°C.

[0008] U.S. Patent Nos. 3,496,218; 4,330,483; and 4,339,395 disclose manufacturing nitriles by the boron-promoted catalyzed reaction between butadiene and hydrogen cyanide. The product mixtures thus formed contain, among desired nitrile products, varying levels of organo-boron as well as other hydrocarbon impurities. Removal of these impurities is essential to effectively process the desired nitrile products downstream.

[0009] U.S. Patent No. 7,501,045 B2 discloses a method for the separation of a group of dinitrile compounds from a medium originating from hydrocyanation of unsaturated mononitriles. In this publication, the separation within the group of dinitriles itself, i.e., between adiponitrile, methylglutaronitrile and ethylsuccinonitrile, is not disclosed. The present invention involves in detail this complex separation between the dinitrile group compounds having very close relative volatilities.

[00010] U.S. Patent No. 8,247,561 B2 discloses a chemical conversion process for the manufacture of 2-methylpentamethylenediamine ("MPMD") and 3-methylpiperidine ("MPP") from hydrogenation of enriched methylglutaronitrile or its mixture with other dinitriles. It is well-known that hydrogenation of an enriched but not purified stream of methylglutaronitrile would lead to a synthesis product consisting of MPMD and MPP. The present invention involves a selective method of purifying methylglutaronitrile to at least 99.1 wt. % with < 0.5 wt. % other dinitrile impurities. This would be a much improved hydrogenation feed material with the highest MPMD yield.

[00011] The above described methods can add complexity, processing limitations, and/or cost to a process for preferentially concentrating 2-methylglutaronitrile from mixtures comprising 2-methylglutaronitrile and other C₆ nitriles having very close relative volatilities, for example, ESN and adiponitrile. One of the most desirable and demanding chemical steps is the separation of crude 2-methylglutaronitrile for making high purity DYTEK^® MGN that is essentially free of these impurities. Purification of this linear/substituted dinitrile crude stream is not trivial or obvious from the available literature. A simple economical process for preferentially concentrating 2- methylglutaronitrile from such mixtures is needed.

SUMMARY OF THE INVENTION

[00012] The present invention provides an economical improved integrated continuous process for preferentially concentrating 2-methylglutaronitrile in high purity from mixtures comprising 2-methylglutaronitrile and other C₆ nitriles having very close relative volatilities, for example, ESN and adiponitrile, by way of an optimized distillation apparatus arrangement and operation. An embodiment of the invention process involves the steps of: a) providing a feedstock mixture comprising about 75 to about 90 wt. % 2-methylglutaronitrile, about 2 to about 25 wt. % other C₆ nitriles, and about 0 to about 8 wt. % other lighter impurities, b) feeding the feedstock mixture of step a) to the upper half of a first distillation column comprising at least five packed sections providing the equivalent of at least 50 theoretical distillation stages, c) passing process vapors from the top of the first distillation column of step b) overhead to a first condensing device maintained at a condensing temperature, for example about 30 to about 50°G, whereby the process vapors are cooled to become resulting liquid and purge material, d) passing a portion of the resulting liquid of step c) to the top of the first distillation column of step b) and removing a portion of the resulting purge material of step c), e) passing liquid from the bottom of the first distillation column of step b) to a first boiling device maintained at a boiling temperature, for example, about 180 to about 220°C, whereby the liquid is heated to become saturated vapors and enriched liquid, f) passing the saturated vapors of step e) to the bottom of the first distillation column of step b) and passing enriched liquid of step e) to the middle of a second distillation column comprising at least three packed sections providing the equivalent of at least 20 theoretical distillation stages, g) passing process vapors from the top of the second distillation column of step f) overhead to a second condensing device maintained at a condensing temperature, for example, about 30 to about 40°C, whereby the process vapors are cooled to become second resulting liquid and second purge material, h) passing a portion of the second resulting liquid of step g) to the top of the second distillation column of step f), i) recovering the remaining portion of the second resulting liquid of step g) as product comprising at least 99.1 wt. % 2-methylglutaronitrile and < 0.5 wt. % other C₆ nitriles, j) passing liquid from the bottom of the second distillation column of step f) to a second boiling device maintained at a boiling temperature, for example, about 200 to about 220°C, whereby the liquid is heated to become second saturated vapors and second enriched liquid, and k) passing the second saturated vapors of step j) to the bottom of the second distillation column of step f) and removing the second enriched liquid of step j). [00013] Another embodiment of the present invention is wherein the feedstock mixture of step a) above also comprises about 1 to about 12 wt. % ESN, about 1 to about 15 wt. % adiponitrile, and the product recovered in step i) above comprises < 0.4 wt. % ESN and < 0.1 wt. % adiponitrile.

[00014] Another embodiment of the present invention is wherein the feedstock mixture of step a) above also comprises about 0 to about 5 wt. % phenols and cresols, about 0 to about 10 wt. % water, about 0 to about 2 wt. % pentenenitrile, about 0 to about 1000 ppm boronate esters or glycols, about 0 to about 100 ppm hydrogen cyanide, and about 0 to about 100 ppm benzene. Another embodiment is wherein the first distillation column of step b) above comprises at least five packed sections providing the equivalent of about 50 to about 60, for example, about 57, theoretical distillation stages. Another embodiment of the present invention is wherein the second distillation column of step f) above comprises at least three packed sections providing the equivalent of about 20 to about 30, for example, about 24, theoretical distillation stages.

[00015] Another embodiment of the present invention comprises the optional step of passing a portion of the enriched liquid of step e) above to the first distillation column of step b) with the feedstock mixture, and/or the optional step of passing a portion of the second enriched liquid of step j) above to the second distillation column of step f) with the enriched liquid of step e).

[00016] Another embodiment of the present invention comprises the optional step of passing a portion of the resulting liquid of step c) above along with the feedstock mixture of step a) above to the first distillation column of step b), and/or the optional step of passing a portion of the second resulting liquid of step g) above along with the enriched liquid of step e) to the second distillation column of step f).

BRIEF DESCRIPTION OF THE DRAWINGS

[00017] Fig. 1 shows a diagrammatic view of an embodiment of the present process involving first and second distillation columns configured as required in the present invention. [00018] Fig. 2 shows a diagrammatic view of a preliminary non-limiting embodiment of the present process.

DETAILED DESCRIPTION OF THE INVENTION

[00019] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement "about X to Y" has the same meaning as "about X to about Y," unless indicated otherwise. Likewise, the statement "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z," unless indicated otherwise.

[00020] The term "about" as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[00021] As a result of intense research in view of the above, we have found that we can economically and effectively preferentially concentrate 2-methylglutaronitrile from mixtures comprising 2-methylglutaronitrile, other Ce nitriles and other impurities. The process avoids the problems associated with the presence of impurities accompanying 2- methylglutaronitrile produced in an adiponitrile synthesis process. The process of this invention involves preferentially concentrating 2-methylglutaronitrile in high purity from mixtures comprising 2-methylglutaronitrile and other C₆ nitriles having very close relative volatilities, for example, ESN and adiponitrile, by way of an optimized distillation apparatus arrangement and operation.

[00022] The term 2-methylglutaronitrile ("MGN"), also known as 2- methylpentanedinitrile, represents the compound with a formula N≡C-CH(-CH₃)-CH₂- CH₂-C≡N, with a normal boiling point of 273.6°C. The term 2-ethylsuccinonitrile ("ESN") represents the compound with a formula N≡C-CH(-C₂H₅)-CH₂-C≡N, with a normal boiling point of 264.3°C. The term adiponitrile ("ADN"), also known as 1,4- dicyanobutane, represents the compound with a formula N≡C-CH₂-CH₂-CH₂-CH₂-C≡N, with a normal boiling point of 304.4°C. Percentages are in weight % unless otherwise indicated.

[00023] The vessels for use as the distillation columns in the present invention must conform to the particular assemblies described herein. The first distillation column will comprise at least five packed sections providing the equivalent of at least 50, such as from about 50 to about 60, e.g., about 57, theoretical stages. The second distillation column will comprise at least three packed sections providing the equivalent of at least 20, such as from about 20 to about 30, e.g., about 24, theoretical stages. The packed sections of the first distillation column will be from about 8 to about 25 feet in height, and the packed sections of the second distillation column will be from about 10 to about 20 feet in height. The total packing height in the first distillation column will be from about 40 to about 125 feet, and the total packing height in the second distillation column will be from about 30 to about 60 feet.

[00024] The packing material for use in the first and second distillation columns may be such materials commonly used for this purpose, such as, for example, industrial structured or random packing of all available types and shapes. Non-limiting examples of such materials include Norton #1.5T, Norton #2T, Norton IMTP, Koch FlexiPack, Koch-Glitch 352 Series, SS dumped saddle and other high efficiency packing materials. It is known to those skilled in the art of distillative separation that all forms and types of gas-liquid contacting stages, e.g., packed, plates, trays, and a combination thereof, would be suitable forms of providing the necessary theoretical separation stages in the process of this invention. Also, the conventional and improved forms of sub-cooled, heated and two-phase feed introduction, radial and axial distribution, and re-collection thereof shall apply to this application.

[00025] The condensing device for use in each distillation column shall be of indirect heat exchanger type with sufficient heat transfer surface and minimal in-line pressure drop to effectively carry out the vapor-to-liquid condensation process with no vapor carry-over.

[00026] The boiling device for use in each distillation column shall be of indirect heat exchanger type and sufficient circulation rate with wetted heat transfer surface so as to yield no drying of the surface due to over-temperature, thereby, causing thermal decomposition of the C6 dinitriles.

[00027] The comingled liquid feedstock to the first distillation column will comprise about 75 to about 90 wt. % MGN and about 2 to about 25 wt. % other C₆ nitriles, and possibly other impurities, such as, for example, about 0 to about 5 wt. % phenols and cresols, about 0 to about 10 wt. % water, about 0 to about 2 wt. % pentenenitrile, about 0 to about 1000 ppm boronate esters or glycols, about 0 to about 100 ppm hydrogen cyanide, and about 0 to about 100 ppm benzene. The other C₆ nitriles may comprise ESN and ADN, such as, for example, about 1 to about 12 wt. % ESN and about 1 to about 15 wt. % ADN.

[00028] Conditions in the first distillation column may include a temperature of about 125 to about 220°C and pressure of about 10 to about 200 mniHg, such as, for example, a temperature of about 150 to about 200°C and pressure of about 10 to about 120 mmHg. Conditions in the second distillation column may include a temperature of about 150 to about 230°C and pressure of about 10 to about 200 mmHg, such as, for example, a temperature of about 170 to about 220°C and pressure of about 50 to about 110 mmHg. Conditions in the first condensing device as3sociated with the first distillation column may include a condensing temperature of, for example, about 30 to about 50°C, and conditions in the first boiling device associated with the first distillation column may include a boiling temperature of, for example, about 180 to about 220°C. Conditions in the second condensing device associated with the second distillation column may include a temperature of, for example, about 30 to about 40°C, and conditions in the second boiling device associated with the second distillation column may include a temperature of, for example, about 200 to about 220°C.

[00029] Referring more particularly to the drawing, Fig.l shows a non-limiting example embodiment of the present invention involving first and second distillation columns conformed as required herein. As shown in Fig. 1, crude stream 9, either directly from an ADN production facility or having been processed by distillation following an ADN production facility, is collected in a feed storage vessel 40. In one embodiment, crude stream 9 may be pre-treated to be free of organo boron impurities as shown in, for example, U.S. Patent No. 5,312,959A, incorporated herein by reference. In another embodiment, stream 17 is a crude feed collected and transported from an offsite location and added to the feed storage vessel 40. The co-mingled liquid of vessel 40 is fed to first distillation column 60 via stream 19 at a tray location in the upper half of column 60.

[00030] Optionally and according to a preliminary embodiment of the disclosed process, stream 19 may undergo a pre-treatment via column 50 (Fig. 2) and the resultant treated stream 56 (Fig. 2) may comprise feed pre-treated to be free of organo boron impurities as shown in, for example, U.S. Patent No. 5,312,959A, directly therefrom.

[00031] Column 60 comprises at least five packed sections providing the equivalent of at least 50, for example about 50 to about 60, such as about 57, theoretical distillation stages. The vapor-liquid traffic in first distillation column 60 is adjusted by refluxing and boil-up according to the quality and quantity of feed from stream 19. The process vapors from first distillation column 60 are collected overhead and fed via stream 31 to first condensing unit 62 and cooled to a temperature in the range of about 30 to about 50°C. A portion, such as about 80 to about 95 %, of the cooled liquid from unit 62 is refluxed back to column 60 via stream 38 and a small purge, such as about 5 to about 20 %, is drawn out of this stage via stream 34. The enriched liquid from the bottom of first distillation column 60 is fed to the bottom first boil-up apparatus 65 via stream 33. The liquid is heated in apparatus 65 to a temperature in the range of about 180 to about 220°C. The saturated vapors from apparatus 65 are fed back to the bottom of column 60 via stream 35 to maintain the vapor traffic in first distillation column 60. From about 5 to about 15 % of enriched liquid from apparatus 65 is fed continuously to the second distillation column 70 via stream 66. A provision is made to optionally recycle a portion, such as about 0 to about 100 %, for example, about 20 to about 70 %, of the enriched liquid from apparatus 65 back to column 60 at the feed entry point via stream 63. The remainder of the enriched liquid from apparatus 65 is drawn out of this stage via stream 37.

[00032] Enriched liquid from apparatus 65 is fed continuously to the second distillation column 70 via stream 66 at a tray location in the middle section of column 70. Column 70 comprises at least three packed sections providing the equivalent of at least 20, for example about 20 to about 30, such as about 24, theoretical distillation stages. The vapor-liquid traffic in second distillation column 70 is adjusted via refluxing and boil-up relative to the quality and quantity of feed from stream 66. The process vapors from second distillation column 70 are collected overhead and fed via stream 41 to second condensing unit 72 and cooled to a temperature in the range of about 30 to about 40°C. A portion, such as about 50 to about 70 %, of the cooled liquid from unit 72 is refluxed back to column 70 via stream 48. The remaining cooled liquid from unit 72, such as about 10 to about 50%, is drawn out of this stage via stream 78 as the desired product meeting or exceeding the target purity. Optionally and in certain off-normal operation, a very small purge of the cooled liquid from unit 72, such as less than 5%, can be drawn out via stream 44 to maintain the impurity control in this purification stage. The enriched liquid from the bottom of second distillation column 70 is fed to the bottom second boil-up apparatus 75 via stream 43. The liquid is heated in apparatus 75 to a temperature in the range of about 200 to about 220°C. The saturated vapors from apparatus 75 are fed back to the bottom of column 70 via stream 45 to maintain the vapor traffic in second distillation column 70. A provision is made to optionally recycle a portion, such as from about 0 to about 100 %, for example about 20 to about 70 %, of the enriched liquid from apparatus 75 back to column 70 at the feed entry point via stream 73. The remainder of the enriched liquid from apparatus 75 is drawn out of this stage via stream 47.

[00033] Fig. 2 shows a non-limiting preliminary embodiment of the present invention involving an optional column 50 conformed as required herein. As shown in Fig. 2, crude stream 9, either directly from an ADN production facility or having been processed by distillation following an ADN production facility, is collected in a feed storage vessel 40. In one embodiment, stream 17 is a crude feed collected and transported from an offsite location and added to the feed storage vessel 40. The co-mingled liquid of vessel 40 is fed to column 50 via stream 19 at a tray location in the lower half of column 50.

[00034] Column 50 may be a structured packed column or a tray column and may provide a minimum of 15 theoretical stages. Feed 19 enters column 50 at a tray location about two-thirds from the top, which provides a minimum of ten equivalent theoretical stages above the feed entry point and about five equivalent theoretical stages below the feed entry point serving as stripping stages. [00035] The column 50 temperature profile is maintained such that the column base is in the range from about 180°C to about 215°C, preferably in the range from about 190°C to about 210°C, and more preferably in the range from about 195°C to about 205°C. The column head temperature is maintained to be below 100°C. The column pressure profile is maintained in the range from about 75 mmHg to about 150 mmHg, particularly in the range from about 85 mmHg to about 130 mmHg, and more particularly in the range from about 95 mmHg to about 125 mmHg.

[00036] The vapor-liquid traffic in column 50 is adjusted by refluxing in the range from about 1:10 to about 5:1 (stream 28 : stream 24) and boil-up in the range from about 1:10 to about 5:1 (stream 25 : stream 56) according to the quality and quantity of feed from stream 19. The process vapors from column 50 are collected overhead and fed via stream 21 to condensing unit 52 and cooled to a temperature in the range of about 30 to about 50°C. A portion, such as about 50 to about 80 %, of the cooled liquid from unit 52 is refluxed back to column 50 via stream 28 and a small purge, such as about 0.1- about 10%, is drawn out of this stage via stream 24.

[00037] The enriched liquid from the bottom of column 50 is fed to the boil-up apparatus 55 via stream 23. The liquid is heated in apparatus 55 to a temperature in the range of about 195 to about 205°C. The saturated vapors from apparatus 55 are fed back to the bottom of column 50 via stream 25 to maintain the vapor traffic in column 50. From about 50 to about 80 % of enriched liquid from apparatus 55 is fed continuously to column 60 via stream 56. A provision is made to optionally recycle a portion, such as about 0 to about 100 %, for example about 20 to about 70 %, of the enriched liquid from apparatus 55 back to column 50 at the feed entry point via stream 53. The remainder of the enriched liquid from apparatus 55 is drawn out of this stage via stream 27.

[00038] In column 50, several low-boiling species including cresols, boron esters, phenol and other impurities from the feed stream 19 are removed from the feed via stream 24. Typical component splits that may be achieved in one embodiment are given below: Table 1

(1) Phenols and Cresols

(3) Boronate Esters and Glycols

(4) Benzene

[00039] In the non-limiting example embodiment shown in Fig.l, compositions of various streams are shown in Table 2. The optional stream, if any, pre-treated to be free of organo boron impurities as shown in, for example, U.S. Patent No. 5,312,959A, directly therefrom fed with stream 19 is shown as " 56 [Fig.2]" in Table 2. Percentages are in weight percent.

Table 2

(1) Phenols and Cresols

(2) Pentenenitrile

(3) Boronate Esters and Glycols

(4) Benzene

[00040] The following Example further demonstrates the present invention and its capability for use. The invention is capable of other and different embodiments, and its several details are capable of modifications in various apparent respects, without departing from the scope and spirit of the present invention. Accordingly, the Example is to be regarded as illustrative in nature and not as restrictive. All percentages are by weight unless otherwise indicated.

Example 1

[00041] This experiment demonstrates an embodiment of the present process with reference to Fig. 1 using process simulation with known experimental vapor-liquid information. Stream 19 comprising of 85 % MGN, 10 % ESN, 5 % ADN and other trace impurities is fed to first distillation column 60 at a continuous rate of 10,000 lb hr at 30°C. The liquid feed entry point in first distillation column 60 is between the top and first packing section which is equivalent to the 11^th theoretical stage measured from the top of the column. Therefore, there are ten equivalent theoretical stages above the feed entry point and forty-five equivalent theoretical stages below the feed entry point serving as stripping stages. The head pressure in column 60 is maintained at 50 mmHg while the total pressure drop under operating conditions is about 70 mmHg. This makes the base pressure in column 60 about 120 mmHg. Correspondingly, the head and bottom temperatures are maintained in the 170 tol80°C and 200 to 220°C ranges, respectively. The vapor-liquid traffic is set at the reflux ratio (i.e., stream 38/stream 34) in the 10 tol5 range while the boil-up rate (i.e., stream 35/stream 66) is in the 10 tol2 range. The overhead condenser 62 sub-cooling of about 15 MMBTU/hr is required and the balancing base boil-up apparatus 65 is about 16 MMBTU/hr.

[00042] Stream 19 is effectively fractionated in column 60 into MGN-enriched bottoms liquid outlet stream 33 containing about 90 % MGN, less than 20 % ADN and less than 0.5 % ESN. The overhead condensed liquid concentrates ESN in approximately 30:70 ESN: MGN mass balance. The achieved split of stream 34 versus stream 66 is about l/3^r versus 2/3^r . In this experiment, about 3,345 lb/hr of overhead material is collected from about 10,000 lb/hr of feed. Other low-boiling impurities concentrate in the overhead and are continuously purged via stream 34.

[00043] The MGN-enriched bottoms stream 66 is fed to second distillation column 70 which concentrates the product in the overhead by stripping MGN from the heavy impurities. The feed enters column 70 between the middle and bottom packed sections to allow approximately fourteen theoretical stages above the feed location and another ten theoretical trays below it. The head pressure in column 70 is 50 mmHg while the total pressure drop under operating conditions is about 55 mmHg. This makes the base pressure in column 70 about 105 mmHg. Correspondingly, the head and bottom temperatures are maintained in the 170 tol 80°C and 200 to 220°C ranges, respectively. The vapor-liquid traffic is set at the reflux ratio (i.e., stream 48/stream 78) in the 1 to 5 range. The boil-up rate (i.e., stream 45/stream 47) is in the 50 to 60 range. The overhead condenser 72 sub-cooling of about 7 MMBTU/hr is required and the balancing base boil- up apparatus 75 is about 6 MMBTU/hr.

[00044] Stream 66 is effectively fractionated in column 70 into purified Dytek^® MGN stream 78 with 99.5 % purity containing 0.4 % ESN and 0.1 % ADN as acceptable impurities. Stream 47 is essentially free of ESN and contains mostly ADN. The achieved split of stream 78 to stream 47 is about 92 to 8. In this particular experiment, about 6,100 lb/hr of overhead pure DYTEK^® MGN material is collected from about 6,700 lb/hr of stream 66 entering column 70. Overall in this experiment, we achieve about 0.6 to 0.62 pure DYTEK^® MGN product yield (defined as a ratio of stream 78 to stream 19) and about 0.7 to 0.72 contained MGN yield (defined as a ratio of MGN present in stream 78 to MGN present in stream 19).

[00045] All patents, patent applications, test procedures, priority documents, articles, publications, manuals, and other documents cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for all jurisdictions in which such incorporation is permitted.

[00046] When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. [00047] While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and may be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims hereof be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which the invention pertains. For instance, regarding cited concentration ranges, operating conditions such as column temperatures and pressures and condensing and boiling device temperatures, as well as reflux ratios, those skilled in distillative separations procedures will appreciate that broader and different ranges, temperatures, pressures and ratios are included in the spirit and scope of the present invention as claimed. It will be understood, for instance, that the present invention is flexible and offers the opportunity to use broader compositional ranges by adjusting the operation of one or both columns.

Claims

CLAIMS What is claimed is:

1. An improved process for preferentially concentrating 2-methylglutaronitrile from mixtures comprising 2-methylglutaronitrile and other C nitriles, comprising the steps of: a) providing a feedstock mixture comprising about 75 to about 90 wt. % 2- methylglutaronitrile, about 2 to about 25 wt. % other C6 nitriles, and about 0 to about 8 wt. % other impurities:

b) feeding the feedstock mixture of step a) to the upper half of a first distillation column comprising at least five packed sections providing the equivalent of at least 50 theoretical distillation stages;

c) passing process vapors from the top of the first distillation column of step b) overhead to a first condensing device maintained at a condensing temperature, whereby the process vapors are cooled to become resulting liquid and purge material;

d) passing a portion of the resulting liquid of step c) to the top of the first distillation column of step b) and removing a portion of the resulting purge material of step c);

e) passing liquid from the bottom of the first distillation column of step b) to a first boiling device maintained at a boiling temperature, whereby the liquid is heated to become saturated vapors and enriched liquid;

f) passing the saturated vapors of step e) to the bottom of the first distillation column of step b) and passing enriched liquid of step e) to the middle of a second distillation column comprising at least three packed sections providing the equivalent of at least 20 theoretical distillation stages;

g) passing process vapors from the top of the second distillation column of step f) overhead to a second condensing device maintained at a condensing temperature, whereby the process vapors are cooled to become second resulting liquid and second purge material;

h) passing a portion of the second resulting liquid of step g) to the top of the second distillation column of step f); i) recovering the remaining portion of the second resulting liquid of step g) as product comprising at least 99.1 wt. % 2-methylglutaronitrile and < 0.5 wt. % other C6 nitriles;

j) passing liquid from the bottom of the second distillation column of step f) to a second boiling device maintained at a boiling temperature, whereby the liquid is heated to become second saturated vapors and second enriched liquid; and k) passing the second saturated vapors of step j) to the bottom of the second

distillation column of step f) and removing the second enriched liquid of step j).

2. The process of claim 1 wherein the feedstock mixture also comprises about 0 to about 5 wt. % phenols and cresols, about 0 to about 10 wt. % water, about 0 to about 2 wt. % pentenenitrile, about 0 to about 1000 ppm boronate esters or glycols, about 0 to about 100 ppm hydrogen cyanide, and about 0 to about 100 ppm benzene.

3. The process of claim 1 wherein the other C₆ nitriles comprise 2- ethylsuccinonitrile and adiponitrile.

4. The process of claim 1 wherein the first distillation column of step b) comprises at least five packed sections providing the equivalent of about 50 to about 60 theoretical distillation stages.

5. The process of claim 4 wherein the first distillation column of step b) comprises five packed sections providing the equivalent of about 57 theoretical distillation stages.

6. The process of claim 1 wherein the second distillation column of step f) comprises at least three packed sections providing the equivalent of about 20 to about 30 theoretical distillation stages.

7. The process of claim 6 wherein the second distillation column of step f) comprises three packed sections providing the equivalent of about 24 theoretical distillation stages.

8. The process of claim 1 comprising the optional step of passing a portion of the enriched liquid of step e) to the first distillation column of step b) with the feedstock mixture, and/or the optional step of passing a portion of the second enriched liquid of step j) to the second distillation column of step f) with the enriched liquid of step e).

9. The process of claim 1 wherein the packed sections of the first distillation column are each from about 8 to about 25 feet high, and the packed sections of the second distillation column are each from about 10 to about 20 feet high.

10. The process of claim 1 wherein total packing height of the first distillation column is about 40 to about 125 feet, and total packing height of the second distillation column is about 30 to about 60 feet.

11. The process of claim 1 wherein conditions in the first distillation column include a temperature of about 125 to about 220°C and pressure of about 10 to about 200 mmHg, conditions in the second distillation column include a temperature of about 150 to about 230°C and pressure of about 10 to about 200 mmHg, condensing temperature of the first condensing device is about 30 to about 50°C, boiling temperature of the first boiling device is about 180 to about 220°C, condensing temperature of the second condensing device is about 30 to about 40°C, and boiling temperature of the second boiling device is about 200 to about 220°C.

12. An improved process for preferentially concentrating 2-methylglutaronitrile from mixtures comprising 2-methylglutaronitrile, 2-ethylsuccinonitrile and adiponitrile, comprising the steps of:

a) providing a feedstock mixture comprising about 75 to about 90 wt. % 2- methylglutaronitrile, about 1 to about 12 wt. % 2-ethylsuccinonitrile, about 1 to about 15 wt. % adiponitrile;

c) passing process vapors from the top of the first distillation column of step b) overhead to a first condensing device maintained at condensing conditions, whereby the process vapors are cooled to become resulting liquid and purge material;

h) passing a portion of the second resulting liquid of step g) to the top of the second distillation column of step f);

i) recovering the remaining portion of the second resulting liquid of step g) as

product comprising at least 99.1 wt. % 2-methylglutaronitrile, < 0.4 wt. % 2- ethylsuccinonitrile and < 0.1 wt. % adiponitrile,

13. The process of claim 12 wherein the feedstock mixture also comprises about 0 to about 5 wt. % phenols and cresols, about 0 to about 10 wt. % water, about 0 to about 2 wt. % pentenenitrile, about 0 to about 1000 ppm boronate esters or glycols, about 0 to about 100 ppm hydrogen cyanide, and about 0 to about 100 ppm benzene.

14. The process of claim 12 wherein the first distillation column of step b) comprises at least five packed sections providing the equivalent of about 50 to about 60 theoretical distillation stages.

15. The process of claim 14 wherein the first distillation column of step b) comprises five packed sections providing the equivalent of about 57 theoretical distillation stages.

16. The process of claim 12 wherein the second distillation column of step f) comprises at least three packed sections providing the equivalent of about 20 to about 30 theoretical distillation stages.

17. The process of claim 16 wherein the second distillation column of step f) comprises three packed sections providing the equivalent of about 24 theoretical distillation stages.

18. The process of claim 12 comprising the optional step of passing a portion of the enriched liquid of step e) to the first distillation column of step b) with the feedstock mixture, and/or the optional step of passing a portion of the second enriched liquid of step j) to the second distillation column of step f) with the enriched liquid of step e).

19. The process of claim 12 wherein the packed sections of the first distillation column are each from about 8 to about 25 feet high, and the packed sections of the second distillation column are each from about 10 to about 20 feet high.

20. The process of claim 12 wherein total packing height of the first distillation column is about 40 to about 125 feet, and total packing height of the second distillation column is about 30 to about 60 feet.

21. The process of claim 12 wherein conditions in the first distillation column include a temperature of about 125 to about 220°C and pressure of about 10 to about 200 mmHg, conditions in the second distillation column include a temperature of about 150 to about 230°C and pressure of about 10 to about 200 mmHg, condensing temperature of the first condensing device is about 30 to about 50°C, boiling temperature of the first boiling device is about 180 to about 220°C, condensing temperature of the second condensing device is about 30 to about 40°C, and boiling temperature of the second boiling device is about 200 to about 220°C.