GB2114118A - Method for removing aldehyde impurities in acrylonitrile and acrylamide - Google Patents

Abstract

Aldehyde impurities, such as acrolein, in acrylonitrile and acrylamide formed therefrom are removed by contacting with a gel type weak base ion exchanger having primary and/or secondary amine functionality. Low quality acrylamide catalytic monomer can be upgraded to produce polymers of satisfactory commercial molecular weight for use as flocculants in water treating applications, as measured by standard viscosity, in contrast to such untreated monomers which result in polymers of limited usefulness. The preferred ion exchange is a weakly basic gel type polystyrene-polyamine type anion exchange resin having a styrene- divinylbenzene matrix and primary and/or secondary functional groups.

Description

SPECIFICATION Method for removing aldehyde impurities in acrylonitrile and acrylamide Background of the invention This invention relates to acrylonitrile and acrylamide prepared from acrylonitrile and, particularly, to the removal of aldehyde impurities therein.

Acrylamide prepared from aldehyde contaminated acrylonitrile may be unsatisfactory, when polymerized, in that it contains large amounts of insoluble material and/or results in polymer with extremely reduced molecular weight. As a consequence, such polyacrylamide polymers are rendered commercially unsatisfactory in most water treating applications where they would be desirably used as flocculants.

Any aldehyde in aqueous acrylamide is a potential cross-linking agent source. Acrolein, which has been identified as an impurity in acrylonitrile at levels from about 2 to about 20 parts per million (ppm), may act as a cross-iinker itself or as an alkylol adduct with acrylamide. The addition of measured quantities of acrolein to aqueous solutions of crystalline acrylamide has demonstrated the strong effect of this aldehyde and its adduct with acrylamide on acrylamide polymers. Even impurity levels of acrolein in acrylamide of less than 20 parts per million will yield polymers having the unsatisfactory reduced molecular weight.

Several methods for reducing or removing acrolein from acrylonitrile have been proposed.

Japanese Patent Application 53-60040 (Publication No. 54-151915) of Mitsui Toatsu Chemicals. Inc.

discloses the use of a porous-type ion exchange resin which possesses a primary and/or secondary amine to remove acrolein from acrylonitrile. That patent application compares the use of a porous type free base resin, available under the name Diaion WA 20, with a gel type free base resin, available under the name Amberlite IRA-45, and concludes that the gel type cannot be used to remove acrolein. Thus, acrylonitrile containing 2.5 ppm acrolein is said to be purified to a level below the detection limit (0.1 ppm) with the porous type resin while still containing 2.1 to 2.3 ppm after treatment with the gel type resin.Japanese Patent Application 75/139,341 (Publication No. 77-68118) of Yoshiakilto eft at discloses stirring acrylonitrile containing acrolein for three hours with acetyl acetone, dimethylaminoethanol and 10 percent aqueous ferric chloride solution followed by distillation to give pure acrylonitrile. In co-pending application, Serial No. 258,104, filed April 1981,for "Purification of Acrylonitrile", assigned to the assignee of the present invention, the acrolein content in acrylonitrile is disclosed as being greatly reduced by adding an effective amount of a compound which contains at least one -B-H moiety, that is, a borane compound for a sufficient time to reduce the acrolein content.

Nevertheless, there remains a need for alternate methods for removing aldehyde impurities in acrylonitrile and in acrylamide formed therefrom.

Summary of the invention Aldehyde impurities, such as acrolein, in acrylonitrile and acrylamide formed therefrom can be removed by contacting with a weak base ion exchanger having primary and/or secondary amine functionality. Low quality acrylamide catalytic monomer can be upgraded to produce polymers of satisfactory commercial molecular weight for use as flocculants in water treating applications, as measured by standard viscosity, in contrast to such untreated monomers which result in polymers of limited usefulness.

The preferred ion exchangers for use in the present invention are weakly basic gel type polystyrene-polyamine type anion exchange resins having a styrene-divinylbenzene matrix and primary and/or secondary functional groups. A commercially available example of this type of anion exchange resin is that sold under the name Amberlite IRA-45 by Rohm and Haas Company.

Description of the preferred embodiments The effect of acrolein on aqueous solutions of acrylamide was observed by adding measured quantities of acrolein to 50 percent aqueous acrylamide solutions, ageing, and measuring the standard viscosity of the monomer converted to polymer as an indication of effective molecular weight. The percentage of insolubles, in the solution polymerization process, was also determined. The results are set forth in Table 1 , for emulsion polymerization, and Table 2, for solution polymerization, below.

Table 1 Emulsion polymerization Acrolein in 50% aqueousAMD Std. Vis.* Days PPM acrolein/AMD CPS 1 O/AMD 5.90 1 20/AMD 5.53 1 200/AMD 3.12 27 0/AMD 6.17 27 20/AMD 2.76 27 200/AMD 1.35 *0.1 g of polymer in a 1 N NaCI aqueous solution at pH 8 measured by a Brookfield viscometer with a UL adaptor at 250C.

Table 2 Solution polymerization Acrolein in 50% aqueous AMD Std. Vis.* Insolubles Days PPMAcrolein/AMD CPS 5 O/AMD 3.64 0.06 5 20/AMD 2.88 15.6 5 200/AMD 1.10 70.27 31 O/AMD 3.51 0.17 31 20/AMD 1.36 58.80 31 200/AMD 1.01 74.70 *.08 g of polymer in a 1 N NaCI aqueous solution at pH 8 measured by a Brookfield viscometer with a UL adaptor at 250C.

A crude adduct of acrolein and acrylamide was prepared and isolated and added to an impurityfree 50 percent aqueous acrylamide solution and polymerized without ageing. The viscosity was measured at various acrolein impurity levels. The results, as set forth in Table 3 below, show that less than 1 0 parts per million of acrolein as an alkylol adduct with acrylamide would render the polymerized acrylamide unsatisfactory, because of reduced molecular weight, as a flocculant in water treating applications.

Table 3 PPMAcrolein/AMD Std. Vis. (CPS) O/AMD 4.08 10/AMD 2.82 40/AMD 1.65 The following examples illustrate preferred embodiments of this invention.

Example 1 Acrylonitrile was treated with a gel type weak base ion exchanger having primary and/or secondary amine functionality to determine its effectiveness in removing acrolein as an impurity. The acrylonitrile treated contained approximately 20 to 25 parts per million acrolein. The weak base ion exchanger was that commercially available under the name of Amberlite IRA-45 from Rohn and Haas Company. Amberlite IRA-45 is a gel type, weakly basic, polystyrene-polyamine type anion exchange resin having a styrene-divinylbenzene matrix and primary or secondary amine, R-NH3+ or R2NH2+ functional groups. The ion exchanger is in spherical bead form having a size, based on a wet screen analysis, of 1 6-50 mesh. The method of treatment was as follows.

A fixed bed of the ion exchange resin was formed by adding 1 2 milliliters of wet ion exchange resin particles to a vertical glass column having a 0.5 inch diameter and 12 inches in length.

Acrylonitrile containing approximately 20 to 25 parts per million of acrolein, was pumped to the top of the column at flow rates comprising 1 0, 30 and 300 milliliters per hour to provide contact times of 30, 10 and 1 minute, respectively. The acrylonitrile which passed through the column was collected at the bottom and the amount of acrolein determined. The initial acrolein contents of about 20 to 25 ppm were shown to be reduced to less than 1 ppm.

It will be understood that the ability of the ion exchanger to remove acrolein is dependent upon the contact time which will vary with bed size and/or pump rate as well as total throughput. The capacity of the resin for the foregoing conditions was determined and the results are set forth in Table 4 below as illustrative. The greater the total throughput, the more capacity of the ion exchange resin to remove acrolein is diminished.

Table 4 FinalAcrolein content (ppm) Acrolein content Flow rate (ml/hr)/ at throughout, liters ppm contact time (min) 2 4 6 8 21.2 300/1 5 11.2 16.6 - 19.5 30/10 - 1 3.8 9 25.6 10/30 - .5 3 7.4 Example 3 A 50 percent aqueous solution of catalytic acrylamide containing aldehyde and impurities and having an emulsion polymer standard viscosity of 3.30 cps, was passed through a 2.8 centimeter diameter glass column, packed to a height of 100 centimeters with the ion exchange resin Amberlite IRA-45, at varying rates and quantities and with and without recycle. The resin was washed with 10 liters of deionized water at a rate of 2500 milliliters per hour. The first few hundred milliliters of treated acrylamide were discarded after which the remainder was collected.In one run, the acrylamide solution was trickled through the resin with an air purge. The effects of the rates of passage through the resin on monomer purity, as determined by emulsion polymer standard viscosity, are set forth in Table 5.

Table 5 Resin passage Std. Vis.

Rate Ouantity Procedure (CPS) 2500 ml/hr 700 ml 22 hr (recycle loop) 4.86 250 800 Single pass same 5.10 2500 800 resin for both 4.17 250 1500 Single pass same 5.06 500 4000 resin for both 4.79 As can be seen, the standard viscosity is 3.30 CPS for the untreated emulsion polymerized acrylamide and 4.17 to 5.10 CPS for that treated with the ion exchange resin indicating that the low quality monomer can be upgraded by the treatment to produce polymer of useful molecular weight in water treating applications.

Example 4 Acrylonitrile containing acrolein was treated with a macro reticular type weak base ion exchanger having tertiary amine functional groups, R-N-(CH3)2, on a polystyrenedivinylbenzene matrix and commercially available under the name Amberlite IRA-93 from Rohm and Haas Company. This ion exchanger was not effective to remove acrolein from acrylonitrile.

Example 5 A field test was conducted to determine the effectiveness of the gel type weak primary and secondary amine ion exchange resin treatment of acrylonitrile in a plant stream known to contain acrolein impurities and then subsequently catalytically converting the purified acrylonitrile to acrylamide. The field test verified the laboratory results. After several days of operation, the results of treatment were evident in that the level of insolubles, in percentage, generally decreased tenfold to less than half of a percent while the standard viscosity also increased.

Claims (7)

Claims

1. A method for removing aldehyde impurities in acrylonitrile and acrylamide prepared therefrom comprising contacting the acrylonitrile or acrylamide with a gel type weak base ion exchange resin having primary and/or secondary amine functionality.

2. A method as claimed in Claim 1 wherein the ion exchange resin is a gel type weakly basic, polystyrenepolyamine type anion exchange resin having a styrenedivinylbenzene matrix and primary and/or secondary amine functional groups.

3. A method as claimed in Claim 1 or 2 wherein the aldehyde impurity is primarily acrolein.

4. A method as claimed in Claim 1 or 2 wherein the contacting comprises passing the acrylonitrile or acrylamide through a bed of the particles of the ion exchange resin.

5. A method for treating catalytic acrylamide monomer to remove aldehyde impurities comprising passing impure aqueous acrylamide monomer through a bed of particles of a weakly basic, polystyrene-polyamine type anion exchange resin having a styrene-divinylbenzene matrix and primary and/or secondary amine functional groups and recovering an upgraded monomer which, upon polymerization, exhibits a reduced amount of insolubles and an increased molecular weight, as measured by standard viscosity, compared to a polymer similarly made from the impure untreated monomer.

6. A method as claimed in Claim 5 wherein the anion exchange resin is a gel type resin.

7. A methods claimed in Claim 5 or 6 wherein the aldehyde impurity is primarily acrolein.