DE4397378B3 - High purity acetonitrile usable as a module-solvent for liq. chromatography - purified by bringing into contact with nascent oxygen@ and basic substances successively in a simple method. - Google Patents

Abstract

A high purity acetonitrile used as a module phase solvent for liq. chromatography has a low absorption in the uv wavelength region of 200-400 nm. A purification method of the crude acetonitrile comprises a first step of bringing the crude acetonitrile into contact with nascent oxygen and a second step of bringing the acetonitrile thus obtained into contact with at least one of a basic compound or an adsorbing reagent.

Description

TECHNICAL AREA

The invention relates to a process for the purification of crude acetonitrile. More particularly, the invention relates to a simple and easy process for purifying crude acetonitrile, and to a purification process for producing high purity acetonitrile which has an absorbance of not more than 0.05 in the ultraviolet range at a wavelength of 200 to 400 nm and which is suitable for use as Solvent for the mobile phase is suitable in industrial liquid chromatography.

TECHNICAL BACKGROUND

Commercially available acetonitrile is mainly produced by purifying crude acetonitrile, which is obtained as a by-product in the production of acrylonitrile or methacrylonitrile by catalytic ammoxidation of propylene or isobutene with ammonia and molecular oxygen. Since the acetonitrile formed as a by-product contains many impurities, the following various purification methods have already been proposed, which are carried out in a conventional manner.

Known processes for removing allyl alcohol from crude acetonitrile include reaction with sulfuric acid and subsequent distillation ( JP-A-51-23218 the term "JP-A" used means "unexamined published Japanese patent application"), the extractive distillation in the presence of water ( JP-A-55-143949 ) and the reaction with an aqueous solution of an alkali metal or alkaline earth metal hypochlorite ( JP-A-55-32518 ). Known methods for removing oxazole from crude acetonitrile include reaction with molecular chlorine and subsequent separation ( JP-A-59-10556 ) and the extractive distillation in the presence of water ( JP-A-55-143950 ).

Known processes for the purification of crude acetonitrile include the reaction with a basic compound and subsequent distillation ( JP-A-56-5449 ) and distillation with the aid of three distillation columns ( JP-A-58-124751 ). In short, the by-produced acetonitrile contains allyl alcohol, oxazole, acrylonitrile, etc. as main impurities, and in order to remove these impurities, it is necessary to combine some of these previously proposed methods, thereby complicating the entire purification process. In addition, the inventors experimentally confirmed that none of these known methods can achieve acetonitrile having an absorption of not more than 0.05 at 200 to 400 nm.

WO 93/23366 discloses a process which comprises contacting crude acetonitrile with nascent oxygen and contacting the resulting acetonitrile with an adsorbent.

DD 243 492 discloses a method for purifying acetonitrile, which comprises contacting crude acetonitrile with nascent oxygen and a base, and carrying out a distillation step.

The DD-A1-217212 discloses an excellent purification process in which crude acetonitrile is contacted with ozone to simultaneously decompose allyl alcohol, oxazole, acrolein, etc., and the purified acetonitrile is separated by distillation. However, as a result of attempts to follow-up this process, the inventors have found that while the process can indeed achieve some reduction in absorption at 200 to 400 nm, it does not reach as low as 0.05 or less.

Commercially available acetonitrile is therefore unsuitable as a solvent of the mobile phase for liquid chromatography, in particular for HPLC, due to its high UV absorption (at 200 to 400 nm). There is therefore a need to develop an industrially valuable process for producing acetonitrile of sufficient purity to be suitable as a mobile phase solvent for liquid chromatography.

The UV absorption of crude acetonitrile at 200 to 400 nm is mainly due to the double bonds of the impurities resulting from the manufacturing process. For example, compounds having a carbon-carbon double bond, a carbonyl group (C = O), a carboxyl group (COOH), an aldehyde group (CHO), a carbon-nitrogen double bond, a nitroso group (N = O), a nitro group (NO ₂ ) or similar bonds or functional groups absorption in this wavelength range. Examples of compounds having such a bond or functional group are allyl alcohol, oxazole, acrylonitrile, methacrylonitrile, cis- and trans-crotonitrile, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, acetic acid, acrolein, methacrolein and acetone. It is very difficult to remove these compounds in order to reduce the absorption at 200 to 400 nm to 0.05 or less. Specifically, in order to reduce the absorption of acetonitrile at 200 nm to 0.05 or less, the allyl alcohol content of acetonitrile must be 1.5 ppm or less, its oxazole content be 0.8 ppm or less, and its acrylonitrile content must be 0 , 2 ppm or less, its methacrylonitrile content to 0.2 ppm or less, its cis-crotonitrile content to 0.2 ppm or less, its acrylic acid content to 0.2 ppm or less, its methyl acrylate content can be reduced to 0.2 ppm or less and its acetic acid content can be reduced to 30 ppm or less. The same strict requirements apply to other contaminants. Since crude acetonitrile usually contains not less than two of these compounds, the critical content of each compound is practically lower than the above value. It is therefore recognized that the production of highly purified acetonitrile places high technical demands.

The object of the invention is to provide a simple and easy process for the purification of crude acetonitrile, as well as a process for the preparation of highly purified acetonitrile, which has a UV absorption of not more than 0.05 at 200 to 400 nm and which is suitable as a solvent for the mobile phase of industrial liquid chromatography, especially HPLC.

As a result of extensive studies on contact treatment of acetonitrile with ozone, the inventors have found that treatment by contact with ozone forms acids and permanganate reducing substances and that these substances can be removed by contact with an adsorbent. Based on these findings, a simple and easy process for purifying acetonitrile has been completed. It has also been found the surprising fact that highly purified acetonitrile having an absorption of not more than 0.05 at a wavelength of 200 to 400 nm can be obtained by contacting a liquid formed after contact treatment with ozone in contact with at least one of base and an adsorbent-selected substance, and thereafter compounds having lower and higher boiling points than acetonitrile (hereinafter referred to simply as low-boiling compounds and high-boiling compounds) are removed. On the basis of these findings, the present invention has been conceived.

DESCRIPTION OF THE INVENTION

• (1) eine erste Stufe, in der rohes Acetonitril mit naszierendem Sauerstoff in Kontakt gehalten wird, und
• (2) eine zweite Stufe, in der das Acetonitril aus Stufe (1) mit mindestens einem Anionenaustauscherharz in Kontakt gebracht wird, sowie, erforderlichenfalls,
• (3) eine dritte Stufe, in der niedersiedende Verbindungen und hochsiedende Verbindungen aus dem Acetonitril entfernt werden, oder
• (4) ein Verfahren, bei dem das Acetonitril aus Stufe (1), der Stufe (3) unterworfen und danach der Stufe (2) unterworfen wird.

The present invention provides a process for the purification of crude acetonitrile which comprises:

• (1) a first stage in which crude acetonitrile is kept in contact with nascent oxygen, and
• (2) a second stage in which the acetonitrile of step (1) is contacted with at least one anion exchange resin and, if necessary,
• (3) a third stage in which low boiling compounds and high boiling compounds are removed from the acetonitrile, or
• (4) a method in which the acetonitrile of the step (1) is subjected to the step (3) and then subjected to the step (2).

The crude acetonitrile, which can be purified by the method of the present invention, includes crude acetonitrile having an absorption of not less than 0.1 at a wavelength of 200 nm. The crude acetonitrile may be acetonitrile, which has been formed as a by-product in the production of acrylonitrile or methacrylonitrile by the ammoxidation of propylene, isobutene or t-butanol with ammonia and molecular oxygen.

As the kind of the crude acetonitrile having a UV absorption of not less than 0.1 at 200 nm, crude acetonitrile having a UV absorption of 0.1 to 5, and more preferably 0.1 to 3 at 200 nm is preferable ,

The nature of the crude acetonitrile is not particularly limited, and species prepared by other methods may also be used. For example, it may be obtained by the ammoxidation reaction of a saturated hydrocarbon compound such as ethane, propane, butane, isobutane or pentane, carbon monoxide, an aromatic compound such as toluene or xylene, etc.

By the method of the present invention, acetonitrile having a UV absorption of not more than 0.05 at 200 to 400 nm can be obtained from crude acetonitrile having a UV absorption of not less than 0.1 at 200 nm.

Although the method can be applied to crude acetonitrile having a UV absorption of less than 0.1 at 200 nm, the effect achieved is small and is not so attractive from an economic point of view.

The term "UV absorption (or simply absorption)" as used in the present invention means a value measured in a quartz cell having an optical path of 10 mm at the prescribed measuring wavelength using distilled water for liquid chromatography as a reference.

Stage (1) of the process according to the invention consists in the contact treatment of crude acetonitrile with nascent oxygen. The purpose of step (1) is the decomposition of double bond impurities which are difficult to remove by distillation, adsorption or by reaction, especially allyl alcohol, oxazole and acrylonitrile, by contact with nascent oxygen to convert it into compounds that are easily separated and removed in the subsequent stage. Compounds capable of forming nascent oxygen include permanganic acid or its salts (eg potassium permanganate), peroxides (eg hydrogen peroxide, sodium peroxide and barium peroxide), oxo acids or their salts (eg sodium hypochlorite, potassium hypochlorite , Sodium hypoiodite, potassium hypoiodite, sodium hypobromite, potassium hypobromite, sodium chlorate, potassium chlorate, sodium iodate, potassium iodate, sodium bromate, potassium bromate, sodium perchlorate, potassium perchlorate, perchloric acid, periodic acid, sodium periodate and potassium periodate), and ozone-containing gases, with an ozone-containing gas being preferred. By step (1), the efficiency of separation and removal of impurities in the subsequent step is remarkably improved.

The ozone-containing gas which can be used in step (1) is obtained by supplying air, oxygen or an oxygen-containing gas into an ozone generator. The ozone-containing gas can be used diluted with nitrogen, carbon dioxide, air, etc. The ozone concentration in the ozone-containing gas is 0.01 to 5.0% by volume, and preferably 0.1 to 2.0% by volume. If it is too low, the contact time or the size of the reactor must be increased, or the loss of acetonitrile by discharge with the exhaust gas is increased, resulting in only a reduction in the efficiency. Due to the performance of the ozone generator, it is difficult to increase the ozone concentration above 5% by volume.

The contact temperature is -40 to 80 ° C, and preferably 10 to 40 ° C. At lower temperatures, the reaction is delayed or trace constituents are precipitated. At too high temperatures, the reaction proceeds excessively, reducing only the yield of acetonitrile.

The contact may be carried out under reduced pressure, at atmospheric pressure or under pressure, and is preferably conducted under a pressure between atmospheric pressure and 1 MPa (10 atm). The contact can be made either in a batch system or a continuous system. The contact in a discontinuous system can be carried out by means of a single-stage or multi-stage, equipped with a stirrer contact container or a gas bubble scrubbing tower. In order to ensure efficient gas-liquid contact, a contact vessel equipped with a stirrer is preferred. In addition, to achieve a good gas-liquid contact, the ozone-containing gas is preferably introduced from at least one nozzle in the form of small bubbles in the crude acetonitrile. The ozone-containing gas is preferably introduced at a location below or adjacent to a stirrer blade. The optimum position and number of the nozzles are determined depending on the structure of the container and the stirring blades and depending on the observation of the stirring state of the acrylonitrile.

A contact treatment in a batch system is suitably carried out by adding an ozone-containing gas in an amount corresponding to 1 to 10,000 times, preferably 10 to 1000 times, the volume of the crude acetonitrile for a period of 1 to 300 minutes , preferably from 10 to 120 minutes, being varied depending on the amount of impurities in the crude acetonitrile. If the initiation time is too short, the reaction between ozone and the impurities is insufficient and the loss of acrylonitrile by discharge is increased at an increased flow rate of the gas. Too long an introduction period has no value in terms of productivity.

The introduction time of the ozone-containing gas can also be determined by analyzing the ozone concentration in the exhaust gas. In this case, the supply is continued until the ozone concentration in the exhaust gas reaches at least 80%, preferably at least 90% of that of the introduced gas. The ozone concentration can be determined analytically using a continuous analyzer using iodometric titration, ultraviolet photometric titration or chemiluminescent analysis.

The contact treatment in a continuous system can be carried out in a packed column, a falling film column, a gas bubble washing column and the like. A packed column is preferred. Suitable packings include Rasching rings, Lessing rings, Berl saddles, interlock saddles, Terralet fillers, Pole rings, MacMahon fillers, Dixon rings and the like made of porcelain, metals, plastic, Carbon and the like can exist. The contact can be either in a countercurrent system or in the DC system, with a countercurrent system being preferred. When using a packed column, a liquid distribution plate may be provided at a suitable height to improve the efficiency of the gas-liquid contact. The volume ratio of ozone-containing gas to crude acetonitrile is selected in the range of 1 to 10,000, and preferably 10 to 1,000, so that no flooding is caused.

Step (2) consists of bringing the acetonitrile of step (1) into contact with at least one anion exchange resin. The purpose of the Step (2) is the conversion of the impurities contained in the acetonitrile of step (1) into readily separable compounds or the adsorption and separation of the impurities.

The contact between the acetonitrile and the anion exchange resin is carried out at a temperature of from -40 to 80 ° C, preferably from 5 to 60 ° C and especially from 10 to 40 ° C.

Anion exchange resins include strongly basic or weakly basic porous or gel-type anion exchange resins. Both ion exchange resins for aqueous solutions and those for nonaqueous solutions can be used. Strongly basic anion exchange resins are preferably used in the form in which their exchange group, for example a dimethylammonium group or a dimethylethanol group, is converted into the OH form or CO ₃ form by a regeneration treatment. Weakly basic anion exchange resins are preferably used in a form in which their exchange group, for. For example, a primary, secondary or tertiary amino group has been regenerated with NaOH, NH ₄ OH and the like. It is recommended that these anion exchange resins, after being treated with a regenerant, beforehand washed with a large amount of acetonitrile to remove water or impurities present.

The anion exchange resin may be handled in powder form or in the form of particles having a particle size of 0.001 to 100 mm, and preferably 0.01 to 20 mm. An anion exchange resin may be formed into a cylindrical or spherical shape by, for example, tableting.

The contact between the anion exchange resin and the acetonitrile can be in either a continuous system or a discontinuous system. For the treatment on an industrial scale, a continuous system is recommended.

The contact treatment in a continuous system can be carried out by passing acetonitrile at a space velocity of 0.001 to 1000 l / min, and preferably from 0.01 to 100 l / min, through a column or tube packed with an anion exchange resin.

A contact treatment in a batch system may be carried out in a contact tank and the like equipped with a stirrer or a shaker. The contact time is 0.1 to 1000 minutes, and preferably 1 to 120 minutes.

Since the anion exchange resin is a solid, separation from the acetonitrile is not required, and thus the object of the invention, the performance of a simple purification process for acetonitrile, can be achieved without step (3). In this case, purified acetonitrile can be obtained simply by passing acetonitrile through a packed layer of an anion exchange resin without using a distillation tower as described in U.S. Pat DD-A-217212 is required. In order to obtain highly purified acetonitrile having a UV absorption of not more than 0.05 at a wavelength of 200 to 400 nm according to the second object of the invention, it is necessary to add the acetonitrile of step (1) or (2) additionally according to step ( 3) to treat.

Step (3) according to the invention is a step in which low-boiling compounds and high-boiling compounds present in the acetonitrile coming from step (1) or (2) are separated and removed. The purpose of the step (3) is to remove impurities including compounds causing UV absorption to give highly purified acetonitrile having an absorption of not more than 0.05 at 200 to 400 nm.

The separation of these impurities can be carried out by distillation or membrane separation. For industrial separation, distillation is preferred.

Distillation towers or columns that can be used in step (3) include plate columns and packed columns. Examples of suitable plate columns include cross-flow contact plate columns with reflux tubes and countercurrent contact columns without reflux tubes. The bottoms of the plate columns include bubble trays, perforated trays and valve trays. The number of trays is usually at least 10, and preferably 30 to 80.

Examples of suitable fill column fillings are Rasching rings, Lessing rings, Pol rings, Berl saddles, Interlock saddles, Terralet fillers, MacMahon fillers and Dixon rings made of porcelain, metals, plastics, carbon and the like can exist. The efficiency of the gas-liquid contact can be improved by arranging a liquid distribution plate at an appropriate height.

Step (3) can be carried out by means of two distillation towers connected in series. In this case, especially low-boiling compounds are removed at the head of a first tower and high-boiling compounds are withdrawn from the bottom end of a second tower, with purified Acetonitrile is recovered at the top. Alternatively, high boiling compounds are taken from the bottom end of a first tower and low boiling compounds are separated at the top of a second tower, with purified acetonitrile being recovered from the bottom end of the second tower or overlying part. To improve the quality of the acetonitrile, it is preferred to first separate its water content as an azeotrope with acetonitrile, after which acetonitrile is recovered at the top of a second tower. That is, low boiling compounds are separated at the top of a first tower and high boiling compounds are taken off the bottom of a second tower to recover purified acetonitrile at the top of the second tower. The above water content includes water originally present in the crude acetonitrile and water by-produced by the ozone oxidation.

The removal of the low-boiling compounds and the high-boiling compounds can also be carried out using a single distillation tower. Specifically, acetonitrile is introduced into the middle part of a distillation tower and low boiling point compounds are withdrawn from the top and high boiling point compounds are recovered from the bottom end while recovering purified acetonitrile at a point which is above or below, preferably above the point at which acetonitrile is introduced ,

In carrying out the distillation, the reflux ratio and the rates of stripping low-boiling compounds and high-boiling compounds are selected depending on the desired degree of purification. The rate at which the distillate containing the low-boiling compound and the bottoms product containing the high-boiling compounds are withdrawn is at least 1% and preferably at least 5%, based on the acetonitrile fed. When the rate of head-off or bottom-end stripping is less than 1%, the recovered acetonitrile sometimes has a UV absorbance of more than 0.05 at 200 to 400 nm due to trace amounts of residual impurities.

The removal of low-boiling compounds and high-boiling compounds can also be carried out using three or more distillation towers, but this has no economic advantage.

The above-mentioned distillation may be carried out under reduced pressure, atmospheric pressure or under pressure, and is usually and preferably carried out under a pressure of normal pressure to 10 atm.

The three stages described above should be carried out under close and high technical control, especially if acetonitrile is to be prepared which is suitable as a solvent for the mobile phase for HPLC. Such process control can be effectively maintained by, for example, monitoring the physical properties of the raw acetonitrile used as the starting material as well as the product of each step by near infrared IR spectrophotometry.

When a solid base and / or an adsorbent is used in carrying out the above-mentioned three steps, the objects of the invention can be achieved even if the order of the step (2) and the step (3) is reversed.

BRIEF DESCRIPTION OF THE DRAWINGS

1 shows the ultraviolet absorption spectrum of purified acetonitrile.

2 shows an ultraviolet absorption spectrum of crude acetonitrile.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will now be explained in more detail by way of examples, but it is to be understood that the invention is not intended to be so limited.

EXAMPLE 1:

Crude acetonitrile having a UV absorbance of 1.560 at 200 nm containing 2.8 ppm of acrylonitrile, 5.0 ppm of allyl alcohol and 1.5 ppm of acids as impurities and exhibiting a permanganate stain rate of 29% was used as the starting material.

In step (1), at the upper end of an ozone contact tower having a diameter of 30 mm, which was filled at a height of 410 mm with porcelain Rasching rings (outer diameter 5 mm, inner diameter 2 mm, height 5 mm) was crude acetonitrile under atmospheric pressure introduced at 20 ° C at a rate of 300 ml / h and at the lower end was an ozone-containing gas with an ozone concentration of 0.24 vol .-% (5.1 g / Nm ³ , wherein "Nm ³ ""m ³ At 0 ° C and 1 atm) at a rate of 180 Nl / h ("Nl" means liters at 0 ° C and 1 atm), the gas: liquid ratio being 600. From the bottom of the tower acetonitrile, which had come into contact with ozone, was withdrawn. It was found that the thus obtained acetonitrile showed an acid concentration increased to 105 ppm and a permanganate staining rate increased to 100%, and that neither acrylonitrile nor allyl alcohol could be detected.

In step (2), the acetonitrile from step (1) was then passed at 20 ° C into a 20 mm diameter column filled with 50 ml of a non-aqueous type "Aberlist A21" porous, weak base anion exchange resin. The final acetonitrile had a UV absorbance at 200 nm of 1.620, an acid concentration of 0.9 ppm, and a permanganate stain rate of 0%. The contents of acrylonitrile and allyl alcohol were below the detection limit by gas chromatography. From the above results, it can be seen that in the step (1), the decomposition of acrylonitrile and allyl alcohol is caused, but the amount of acid and permanganate reducing substances is increased and that the acid and the permanganate reducing substances are removed in the step (2). The process described above could be carried out easily and stably in a continuous procedure for 200 hours. The recovery of purified acetonitrile in this continuous procedure was high and was 90% based on the crude acetonitrile charged. A UV absorption spectrum was measured using a quartz cell with an optical length of 10 mm, with distilled water as reference substance and using a Spectrophotometer 288A from Hitachi Ltd. measured. Gas chromatography was performed using the device HP-5890 manufactured by Yokokawa KK, with a capillary column (inner diameter 0.25 mm, length 50 m) filled with Silicon OV-1. The column temperature was maintained at 40 ° C for 5 minutes and then increased to 200 ° C at a rate of 10 ° C / min, maintaining the column at this temperature for 10 minutes. The acid concentrations were measured according to JIS K8001, 5.6 (1). The content of permanganate reducing substances was determined by referring to JIS K8032 as follows. To 10 g of a sample was added 0.1 ml of 0.1 N potassium permanganate, followed by shaking, and the mixture was allowed to stand for 30 minutes in a cool and dark place. The absorbance at 545 nm was measured by the apparatus "UV 2000" manufactured by SHIMADZU CORPORATION immediately at the beginning of standing and after standing for 30 minutes, whereby the permanganate staining rate as an indication of the presence of permanganate reducing substances was determined according to the following equation : Permanganate staining rate (%) = (1 - (A / B)) × 100 where A is the absorption after standing for 30 minutes and B is the absorption at the beginning of standing.

Example 2: (not included within the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 1 except that the anion exchange resin used in Step (2) was replaced with 35 g of silica-alumina as an adsorbent prepared by mixing aluminum nitrate and silica sol in an atomic ratio of Al: Si were mixed 1: 1, the mixture was evaporated to dryness and the residue was fired at 500 ° C. The resulting purified acetonitrile had a UV absorbance at 200 nm of 1.480, an acid concentration of 1.0 ppm and a permanganate stain rate of 7%.

EXAMPLE 3 (not included in the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 1 except that 50 ml of activated carbon was used as the adsorbent in step (2). The resulting purified acetonitrile had a UV absorbance at 200 nm of 1,500, an acid concentration of 1.2 ppm, and a permanganate stain rate of 5%.

EXAMPLE 4

Crude acetonitrile having a U.V. absorption of 1.703 at 200 nm containing 3.5 ppm of acrylonitrile, 8 ppm of methacrylonitrile, 8 ppm of allyl alcohol and 2 ppm of oxazole as impurities was used as the starting material.

In step (1), at the upper end of an ozone contact tower having a diameter of 30 mm, which was filled up to a height of 410 mm with porcelain Rasching rings (outer diameter: 5 mm, inner diameter: 2 mm, height: 5 mm) the crude acetonitrile was introduced under atmospheric pressure at 20 ° C at a rate of 300 ml / h and from the bottom an ozone-containing gas having an ozone concentration of 0.24% by volume (5.1 g / Nm ³ , "Nm ³ "Means" m ³ "at 0 ° C and 1 atm) at a rate of 180 Nl / h (Nl means liters at 0 ° C and 1 atm) in a gas: liquid ratio of 600. From the bottom of the tower acetonitrile was withdrawn, which had come into contact with ozone.

Then, in step (2), the acetonitrile of step (1) was passed into a 20 mm diameter column filled with 50 ml of a nonaqueous type "Amberlist A21" porous, weakly basic anion exchange resin at 20 ° C ,

In step (3), the acetonitrile of step (2) was finally fed to the 10th tray of a distillation tower (diameter 40 mm) having a total of 65 perforated plates, maintaining a pressure of atmospheric pressure at the top of the tower and a reflux ratio was complied with by 16. Acetonitrile containing low-boiling compounds was distilled off at the head end at a rate of 20% based on the supplied acetonitrile, and acetonitrile containing high-boiling compounds was withdrawn at the bottom end at a rate of 10% based on the acetonitrile charged. while purified acetonitrile was recovered on the 40th tray at a rate of 70% based on the added acetonitrile.

The recovered purified acetonitrile had a UV absorption at 200 nm of 0.021 and at 210 to 400 nm of not more than 0.013. As a result of gas chromatography, it was found that the proportions of acrylonitrile, methacrylonitrile, allyl alcohol and oxazole were below the respective detection limit.

The procedure described above could be continued stably and without difficulty for more than 200 hours to give purified acetonitrile having stable physical properties. All stages were monitored by on-line system control using a near-infrared infrared spectrometer Model 6500 from NIR Systems Co.

The ultraviolet absorption spectrum of the purified acetonitrile and the crude acetonitrile is in 1 or in 2 shown.

EXAMPLE 5

Purified acetonitrile was prepared in the same manner as in Example 4, except that in step (2), a strongly basic gel-type anion exchange resin of "IRA-400" whose exchange group was converted to the OH form was used as the base. The UV absorption of the resulting purified acetonitrile was 0.040 at 200 nm and not more than 0.025 at 210 to 400 nm.

Example 6: (not included in the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 4, except that in step (2), 30 g of particulate CaCO _{3 was} used as the base. The UV absorbance of the resulting purified acetonitrile was 0.034 at 200 nm and not more than 0.021 to 210 to 400 nm.

Example 7: (not included in the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 4 except that in the step (2), as the base, silica having 5.0% by weight of MgO (total weight 40 g) was used. The UV absorption of the resulting purified acetonitrile was 0.030 at 200 nm and not more than 0.019 at 210 to 400 nm.

EXAMPLE 8 (not included in the scope of the present invention)

The same operation as in Example 4 was carried out up to the step (2) except that the solid base used in the step (2) was activated carbon loaded with 2.0 wt% KOH (total weight 50 g) ,

In stage (3), 2 distillation towers each with a diameter of 32 mm and a total of 60 perforated plates were used in series. The acetonitrile from step (2) was introduced at a rate of 250 ml / hr at the 40th tray of the first tower and distilled at atmospheric pressure at a top end of the tower at a reflux ratio of 12. From the bottom of the first tower, acetonitrile was withdrawn at a rate of 80% based on the supplied acetonitrile and then introduced to the 20th tray of a second tower and distilled at a reflux ratio of 3. In this way, purified acetonitrile was recovered at the top of the second tower in a yield of 70%, based on the acetonitrile used. The UV absorption of the resulting acetonitrile was 0.043 at 200 nm and not more than 0.026 at 210 to 400 nm.

EXAMPLE 9: (not included in the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 4, except that 35 g of silica-alumina obtained by mixing aluminum nitrate and silica sol in an Al: Si atomic ratio of 1: 1, evaporating the mixture to dryness and firing the mixture Residue was prepared at 500 ° C, was used as adsorbent in step (2). The resulting purified acetonitrile had a UV absorbance of 0.039 at 200 nm and not more than 0.024 at 210 to 400 nm.

COMPARATIVE EXAMPLE 1

Crude acetonitrile was purified in the same manner as in Example 4 except that step (1), that is, contact with ozone, was not carried out has been. The resulting acetonitrile had a UV absorption of 1.601 at 200 nm.

COMPARATIVE EXAMPLE 2

Crude acetonitrile was purified in the same manner as in Example 4, except that step (2), d. H. the treatment with a solid base, was not performed. The resulting acetonitrile had a UV absorption of 0.157 at 200 nm.

COMPARATIVE EXAMPLE 3

Crude acetonitrile was purified in the same manner as in Example 4, except that step (3), d. H. the distillation was not carried out. The resulting acetonitrile had a UV absorption of 1.451 at 200 nm.

The results of the above-described three comparative examples show that the omission of any of the steps (1) to (3) according to the invention results in that it is not possible to obtain acetonitrile having an absorption of not more than 0.05 to 200 nm.

COMPARATIVE EXAMPLE 4

Acetonitrile was purified in the same manner as in Example 4 except that the process was carried out in the following order: Step (2), Step (3) and Step (1). The resulting acetonitrile had a UV absorption of 1.655 at 200 nm.

COMPARATIVE EXAMPLE 5

Acetonitrile was purified in the same manner as in Example 4 except that the process was carried out in the order of step (2), step (1) and step (3). The resulting acetonitrile had a UV absorption of 0.219 at 200 nm.

COMPARATIVE EXAMPLE 6

Acetonitrile was purified in the same manner as in Example 4 except that the process was carried out in the order of step (3), step (1) and step (2). The resulting purified acetonitrile had a UV absorbance of 1.552 at 200 nm.

COMPARATIVE EXAMPLE 7

Acetonitrile was purified in the same manner as in Example 4 except that the process was carried out in the order of step (3), step (2) and step (1). The resulting purified acetonitrile had a UV absorption of 1.550 at 200 nm.

EXAMPLE 10 (not included in the scope of the present invention)

Crude acetonitrile formed as a by-product of the process for preparing acrylonitrile by ammoxidation of propylene, which had a UV absorbance of 0.503 at 200 nm and impurities containing 1 ppm of acrylonitrile, 2 ppm of oxazole and 20 ppm of allyl alcohol, was used as the starting material used.

In step (1), 1500 ml of the crude acetonitrile was placed in a 2-liter round-bottomed flask equipped with a stirrer, and an ozone-containing gas having an ozone concentration of 0.24 vol% (5.1 g / Nm ³ ) was poured into at a rate of 3 Nl / h for 90 minutes. The pH of an aqueous solution formed by diluting the acetonitrile obtained from this process with water to 1/10 was 6.0.

In the step (2), 3.3 g of a 50 wt% NaOH aqueous solution was added to this acetonitrile and stirred for 20 minutes. In the flask, white sticky substances separated, which were then filtered off. The pH of an aqueous solution formed by diluting the obtained acetonitrile with water to 1/10 was 7.4.

In step (3), two of the distillation apparatuses used in Example 8 were used. The acetonitrile obtained in step (2) was fed to the 40th tray of the first tower at a rate of 250 ml / hr and the process was carried out while keeping the pressure at the top of the tower at atmospheric pressure and the reflux ratio at 12. Acetonitrile was withdrawn from the bottom of the tower at a rate of 75% based on the added acetonitrile and introduced to the 20th bottom of the second tower, maintaining the reflux ratio at 3, so that purified acetonitrile was at the top at a rate of 65 %, based on the supplied acetonitrile, was distilled off. The resulting acetonitrile had a UV absorbance of 0.025 at 200 nm and not more than 0.016 at 210 to 400 nm.

As a result of gas chromatography, it was found that the proportions of acrylonitrile, oxazole and allyl alcohol were below the respective detection limit.

Example 11: (not included in the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 10 except that ethanolamine was added in the step (2) so that the pH of an aqueous solution obtained by the method described in U.S. Pat Dilution of the resulting acetonitrile with water was 9.0. The resulting purified acetonitrile had a UV absorbance of 0.027 at 200 nm and not more than 0.013 at 210 to 400 nm.

EXAMPLE 12

8 parts by weight of the same crude acetonitrile as used in Example 1 were mixed with 2 parts by weight of the acetonitrile obtained in Example 4 to give a crude acetonitrile having a UV absorption of 1.4 at 200 nm was obtained. 1500 ml of the acetonitrile thus prepared were placed in a 2 liter round bottom flask equipped with a stirrer. Gas containing 0.5% by volume of ozone was introduced into the solution at a rate of 3 l / min at 25 ° C for 240 minutes.

The acetonitrile of step (1) was treated in the same manner as in steps (2) and (3) of Example 4. The thus purified acetonitrile had a UV absorption of 0.045 at 200 nm and not more than 0.028 at 210 to 400 nm.

EXAMPLE 13

Acetonitrile formed as a by-product in the production of acrylonitrile by ammoxidation of propylene was recovered and purified so that it had a UV absorption of 0.360 at 200 nm. This was used as crude acetonitrile. 2000 ml of the crude acetonitrile was placed in a 3 liter round bottom flask equipped with a stirrer and gas containing 0.24 vol% of ozone was introduced at 20 ° C at a rate of 3 Nl / min. The supply of the ozone-containing gas was stopped when the ozone concentration in the exhaust gas reached 0.20% by volume, which was 83% of the content of the supplied gas. The resulting acetonitrile was treated in the same manner as in steps (2) and (3) of Example 4 to give purified acetonitrile having a UV absorbance of 0.040 at 200 nm and not more than 0.026 at 210 to 400 nm.

EXAMPLE 14

Purified acetonitrile was obtained in the same manner as in Example 4 except that in the step (1), one liter of the acetonitrile and 1.09 g of potassium permanganate (product of Wako Pure Chemicals Co., Ltd.) were used as the nascent oxygen-forming compound a 2 liter round bottom flask equipped with a stirrer, followed by stirring at 60 ° C for 2 hours to form acetonitrile containing no potassium permanganate. Then, the same procedure as in steps (2) and (3) was carried out. The resulting purified acetonitrile had a UV absorbance of 0.045 at 200 nm and not more than 0.027 at 210 to 400 nm.

Example 15: (not included in the scope of the present invention)

Purified acetonitrile was prepared in the same manner as in Example 10 except that 10 g of silica-alumina obtained by mixing aluminum nitrate and silica sol under an Al: Si atomic ratio of 1: 1 was used as the adsorbent in step (2) Evaporation of the mixture to dryness and firing of the residue at 500 ° C had been obtained. The resulting purified acetonitrile had a UV absorbance of 0.020 at 200 nm and not more than 0.010 at 210 to 400 nm.

Example 16: (not included within the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 13, except that 50 ml of the synthetic zeolite "Molecular Sieve 4A" was used as the adsorbent in the step (2). The purified acetonitrile had a UV absorption of 0.011 at 200 nm and not more than 0.005 at 210 to 400 nm.

The resulting purified acetonitrile was used experimentally for lipid analysis and purification of peptides. In studies of phospholipids exhibiting physiological activity at the molecular level, it is necessary to analyze traces of lipids in various biological preparations with high sensitivity and high accuracy, and it is therefore required that acetonitrile has high purity when in the mobile phase the HPLC should be used. Similarly, acetonitrile is required to be highly purified if it is to be used as a mobile phase for preparative liquid chromatography for peptide purification.

However, commercial acetonitrile for liquid chromatography and that in Comparative Example 2 were DD-A-217212 produced acetonitrile unsuitable for lipid analysis or peptide purification because of their high levels of impurities. In contrast, the acetonitrile obtained according to the invention with a UV absorption of 0.011 at 200 nm proved to be suitable for both lipid analysis and peptide purification due to its remarkably reduced levels of impurities.

Example 17: (not included in the scope of the present invention)

Purified acetonitrile was obtained in the same manner as in Example 11 except that 50 ml of activated carbon was used as the adsorbent in step (2). The purified acetonitrile had a UV absorbance of 0.013 at 200 nm and not more than 0.006 at 210 to 400 nm.

EXAMPLE 18

Purified acetonitrile was obtained in the same manner as in Example 4 except that the process was carried out in the order of step (1), step (3) and step (2). The resulting purified acetonitrile had a UV absorbance of 0.048 at 200 nm and not more than 0.028 at 210 to 400 nm.

As described in Examples 4 to 18, highly purified acetonitrile having a UV absorption of not more than 0.05 at 200 nm could be obtained by a simple procedure.

POSSIBILITIES OF INDUSTRIAL APPLICATION

According to the invention, acetonitrile having a reduced content of acids and permanganate reducing substances can be easily obtained by bringing crude acetonitrile into contact with nascent oxygen and passing the thus treated acetonitrile through a filled column filled with an anion exchange resin. The process requires no cooling devices, heat source or strict Temperaturregellung as they are for in the DD-A-217212 In addition, highly purified acetonitrile having an absorption of not more than 0.05 at an ultraviolet wavelength of 200 to 400 nm, which may be used as a solvent, may be used mobile phase is suitable for HPLC, obtained by a process comprising a step (1) in which crude acetonitrile is contacted with nascent oxygen, a step (2) in which the acetonitrile is reacted with at least one anion exchange resin in And a step (3) in which low-boiling compounds and high-boiling compounds are separated and removed, or by a process comprising step (1), step (3) and step (2) in the latter order.

Claims (19)

A process for purifying crude acetonitrile which comprises: (1) a step in which crude acetonitrile is contacted with nascent oxygen, and (2) a step in which the acetonitrile of step (1) is contacted with at least one anion exchange resin. A process for purifying crude acetonitrile according to claim 1 which additionally comprises: (3) a step of removing low-boiling compounds and high-boiling compounds from the acetonitrile of step (2), wherein the step (3) can also be carried out after step (1) and before step (2). The method of claim 2, wherein the crude acetonitrile has an absorption of not less than 0.1 at a wavelength of 200 nm. Process according to claims 1 and 2, wherein the crude acetonitrile is acetonitrile, which is obtained as a by-product in the production of acrylonitrile or methacrylonitrile by catalytic ammoxidation of propylene, isobutene or t-butyl alcohol with ammonia and molecular oxygen. Process according to claims 1 and 2, wherein the nascent oxygen is nascent oxygen formed from at least one compound selected from permanganic acid or a salt thereof, an oxo acid or a salt thereof, a peroxide and an ozone-containing gas. The method of claim 5, wherein the peroxide is selected from hydrogen peroxide, sodium peroxide and barium peroxide. A process according to claim 6, wherein the oxo acid or its salt is at least one compound selected from sodium hypochlorite, potassium hypochlorite, sodium hypoiodite, potassium hypoiodite, sodium hypobromite, potassium hypobromite, sodium chlorate, potassium chlorate, sodium iodate, potassium iodate, sodium bromate, potassium bromate, potassium bromate, sodium perchlorate, potassium perchlorate, perchloric acid, Periodic acid, sodium periodate and potassium periodate is selected. The method of claim 1 and 2, wherein the contact with nascent oxygen at a temperature of -40 to 80 ° C is carried out in a batch system or a continuous. The method of claim 8, wherein the nascent oxygen is an ozone-containing gas having an ozone concentration of 0.01 to 5.0% by volume. The method of claim 9, wherein the contact with the ozone-containing gas is carried out in a batchwise system, wherein the ozone-containing gas in an amount corresponding to 1 to 10,000 times the volume of the crude acetonitrile for a period of 1 to 300 minutes at least one nozzle is introduced into the liquid, crude acetonitrile. The method of claim 9, wherein the contact with the ozone-containing gas is carried out in a batch system, wherein the ozone-containing gas is introduced until the ozone concentration in the exhaust gas reaches a value of at least 80% of the value of the supplied gas. The process according to claim 9, wherein the contact with the ozone-containing gas is carried out in a continuous system in a packed column or tray column, wherein the crude acetonitrile from the top end and the ozone-containing gas are supplied from the bottom end of the column, wherein the volume ratio of gas to Liquid is 1 to 10,000. A process according to claims 1 and 2, wherein the contact with the anion exchange resin is carried out at a temperature of -40 to 80 ° C. A process according to any one of the preceding claims, wherein the anion exchange resin is a porous or gel type strongly basic anion exchange resin having an exchange group in the OH form or CO ₃ form or a porous or gel type weakly basic anion exchange resin as exchange group has a primary, secondary or tertiary amino group. The process of claim 2, wherein the step of removing low boiling compounds and high boiling compounds is carried out by means of at least one of the methods selected from distillation and membrane separation. The process according to claim 15, wherein the step of removing low-boiling compounds and high-boiling compounds in a tray column or a packed column is conducted under a pressure of 0.5 to 10 atm. The process of claim 15, wherein the step of removing low boiling compounds and high boiling compounds is carried out in two distillation columns, wherein low boiling point compounds are separated from the top of a first column and high boiling point compounds from the bottom end of a second column. The process of claim 15, wherein the step of removing low boiling compounds and high boiling compounds is conducted in a single distillation column, wherein acetonitrile is introduced into the middle part of the column and low boiling point compounds are separated from the bottom end of the column while purified Acetonitrile is recovered at a location which is higher than the site of introduction of acetonitrile. The method of claim 1 or 2, wherein each step is controlled by near infrared spectrophotometry.

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