GB1593857A - Preparation of acrylic copolymers - Google Patents

Description

(54) THE PREPARATION OF ACRYLIC COPOLYMERS (71) We, ROHM AND HAAS (UK) LIMITED, a British Company, of Lennig House, 2 Mason's Avenue, Croydon CR9 3NB, England, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns a polymerization process for preparation of a high molecular weight polymer flocculant.

The present invention is based on the discovery that the presence, in minute amounts, of furfural in acrylic or methacrylic acid prolongs to a commercially unacceptable extent the polymerization taken in the formation of high molecular weight polymer flocculants from a monomer charge containing one or both of these acids.

The polymerization time retardant effect of furfural is surprising. Thus, for example, minute amounts of aliphatic or aromatic aldehydes in purified acrylic acid, notably formaldehyde, acetaldehyde and benzaldehyde which can and do occur in commercially produced purified acrylic acid, exhibit no significant effect upon the time of polymerization taken to produce high molecular weight polymer flocculants; also no significant retardant effects have been observed with minute amounts of compounds contaning the furan nucleus such as furan, 2-furoic acid and 2-furfuryl alcohol.

Yet again, the observation has been made that long polymerization times result from the use of furfural-free distilled glacial acrylic acid notwithstanding the fact that such glacial acid has been derived from crude acid which has itself been treated, e.g.

with o-phenylenediamine, to eliminate furfural in detectable amounts.

In accordance with this invention there is provided a process for the preparation of a high molecular weight water-soluble or water-dispersible copolymer flocculant which comprises copolymerizing, in the presence of less than 1000 ppm (based to the total weight of polymerizable monomer) of polymerization initiator, and preferably less than 100 ppm (based to the total weight of polymerizable monomer) of a redox initiator system, a monomer charge containing (based to the total weight of polymerizable monomer) at least 80 wt. % of a mixture of (A) acrylamide and/or methacrylamide and (B) acrylic acid/or methacrylic acid in free acid or salt form, wherein component (B) of the monomer charge is, or is derived from, acrylic and/or methacrylic acid which (I) has been pretreated to reduce the furfural therein to an amount which in any event is less than the weight of initiator used in the copolymerization and which is preferably less than 20 ppm (based on the weight of acrylic and/or methacrylic acid) or (II) is acid containing less than 100 ppm furfural and which has been prepared by the vapour phase catalytic oxidation of a feed giving rise to the acid. The furfural contents given above and subsequently may be measured by GLC/mass spectroscopy.

Component (B) of the monomer charge referred to above will usually have a furfural content, if any, of < 10 ppm, preferably < 5 ppm and even more preferably 0 - < 1 ppm.

The process of the invention is particularly applicable to the preparation of ultra-high molecular weight polymer flocculants having viscosity average molecular weights of 10 million or more. Typical polymerization procedures which may be utilized in the present invention are those employing a redox initiator system which is present, based on the total weight of polymerizable monomer in amounts such as (a) < 150 ppm, (b) (100 ppm, (c) < 75 ppm, (d) < 50 ppm, (e) < 25 ppm, and (f) (15 ppm. Such typical polymerization procedures may be carried out by the emulsion or solution technique and usable polymerization temperatures are from -10 C to +25 C, particularly -5"C to +50C.

The monomer charge subjected to polymerization may contain in addition to the monomers specified above, up to 20% by weight (based on the total weight of polymerizable monomer) of one or more other monoethylenically unsaturated comonomers.

When component (B) of the monomer charge (whether or not pretreated to remove furfural) is, or, is derived from (e.g. in the case of a salt of acrylic or methacrylic acid), acrylic and/or methacrylic acid which has been prepared by the vapour phase catalytic oxidation or oxydehydrogenation of a feed giving rise to the desired unsaturated acid(s), the latter feed will most commonly be one containing propane, propylene, butanes, e.g. isobutane, butylene, e.g. isobutylene, acrolein and methacrolein. Component (B) of the monomer charge is preferably glacial acrylic acid prepared by the distillation of crude acrylic acid formed by the vapour phase catalytic oxidation of acrolein which in turn has been formed by the vapour phase catalytic oxidation of propylene. As conventionally practised, propylene, air and steam are passed through a first catalytic reactor and the total acrolein-containing effluent from the first reactor is passed through a second catalytic reactor wherein the acrolein is converted to acrylic acid.

When component (B) of the monomer charge has been pretreated to remove furfural, the unsaturated acids subjected to the pretreatment may typically contain amounts of furfural such as (a) < 200 ppm, (b) < 150 ppm, (c) < 120 ppm, (d) < 100 ppm, (e) < 75 ppm and (f) < 50 ppm.

The furfural removal is generally achieved by treatment of the unsaturated acid with an agent which acts upon, e.g. by combining with, the furfural to give a product which is then separated from the unsaturated acid. An example of such an agent is a compound which complexes or reacts with the aldehyde group in furfural to give a separable product, preferably a product which is higher boiling than the unsaturated acid and which is thermally stable up to 90"C. so that it can be easily removed by distillation. Agents which can be used for the removal of furfural may be selected from phenolic compounds and primary amines, examples being phloroglucinal, ophenylenediamine and Nnitrosophenylhydroxylamine ammonium salt. The phenolic compounds or amines may, in general, be used in an amount from 500 to 5,000 ppm based on the weight of unsaturated acid to be purified. When the furfural removing agent is phloroglucinol the latter is used in conjunction with a strong acid such as sulphuric or hydrochloric.

It follows from what has been stated above that the agent used to treat the unsaturated acid to effect removal of furfural should act upon the furfural to give a product which is separable, preferably by distillation, from the acid. In this connection, it has been observed that, while o-phenylenediamine and phloroglucinol/ acid do indeed reduce to non-detectable amounts the furfural content in crude undistilled acid from the vapour phase catalytic oxidation of acrolein, these agents appear to result in the formation of some unidentified product (a) which is present in the glacial acrylic acid subsequently produced by distillation and (b) which acts as a polymerization retardant. However, these two agents give perfectly acceptable results when used in the formation of glacial acrylic acid which is then subjected to yet a further distillation step i.e. when double distillation is carried out.

Aniline (plus a strong acid such as sulphuric) is an example of a treating agent which has been used successfully to treat furfural-containing crude undistilled acrylic acid resulting from the vapour phase catalytic oxidation of acrolein. Crude acid thus treated contained no detectable amount of furfural and the glacial acid resulting from subsequent distillation was satisfactory for use in forming ultra-high molecular weight polymers. Apparently, aniline reacts with furfural in the crude acid to cause ringopening of the furan nucleus and the reaction products are removed during the subsequent distillation. Aniline may be used in amounts from 0.2 to 1%, e.g. 0.5%, by weight (based on the crude acid) in conjunction with a strong acid such as about 1% of sulphuric acid based on the weight of crude acid.

It will be understood of course that where the furfural removal treatment is such as to be liable to result in polymerization of the unsaturated acid, there should be used a polymerization inhibitor such as the monomethyl ether of hydroquinone (MEHQ) and/or phenothiazine (PTZ).

When using o-phenylenediamine for furfural removal. the use of a polymerization inhibitor is particularly indicated because the diamine is itself a polymerization in itiator.

The following examples illustrate typical acrylic acid purification procedures and the use of the purified acrylic acid in the preparation of high molecular weight copolymer flocculants by adiabatic polymerization.

Example 1 (A) In this example 525 g. of glacial acrylic acid (GAA) was flask distilled at reduced pressure in a 3-necked flask fitted with a 11/4" 5-plate Oldershaw column fitted with a reflux head and a receiver. The GAA used contained about 125 ppm furfural and 200 ppm MEHQ inhibitor and had been prepared by the distillation of crude acrylic acid formed by the catalytic vapour phase oxidation of acrolein. The GAA charge to the flask was mixed with 0.1% by weight of phloroglucinol, 0.1% by weight of PTZ and 0.2% by weight of sulfuric acid. The distillation was run for a period of 5 hours, under a pressure of 2 mm. Hg and using a head temperature of 27"C. and a bottom temperature from 42-100"C. The purified acrylic acid distillate contained less than 1 ppm furfural.

(B) 18 g. of GAA, purified by the procedure of Part A of this example, was added to 10 g. of AR sodium hydroxide dissolved in 22 ml. of water. The pH of the mixture was adjusted to pH 7-8.5, the mixture cooled to 0 C. and there was then dissolved therein pure acrylamide (94g.).

The mixture was then cooled to -10"C., transferred to a Dewar flask, purged with nitrogen for 10 minutes and there were added ferrous sulphate (1.4 ml. of a fresh 0.1 wt. % aqueous solution), ammonium persulphate (2.75 ml. of a fresh 0.1 wt. % aqueous solution) and isopropanol (3.4 ml.

of a fresh 1 wt % aqueous solution). The mixture in the flask was then again purged with nitrogen for a further 10 minutes, azobisisobutyronitrile (0.126 g.) was added and the mixture further purged with nitrogen for 10 minutes. The mixture was then left to undergo an exothermic polymerization and ultra-high molecular weight copolymer flocculant resulted in two hours.

Attempts to prepare copolymer by the above procedure, but using unpurified GAA contaning about 125 ppm furfural, require polymerization times of from 7-34 hours for the production of copolymer flocculant of comparable molecular weight.

Example 2 Parts A and B of Example 1 are repeated except that, in Part A, the sulphuric acid is omitted, the phloroglucinol is replaced by the same amount of o-phenylenediamine and 1000 ppm of PTZ is dissolved in the GAA prior to the addition of the diamine.

This PTZ addition is necessary to inhibit polymerization of the GAA by the diamine which acts as an initiator. Results similar to those of Example 1 are obtained.

WHAT WE CLAIM IS: 1. A process for the preparation of a high molecular weight water-soluble or water-dispersible copolymer flocculant which comprises copolymerizing, in the presence of less than 1000 ppm (based on the total weight of polymerizable monomer) of polymerization initiator, a monomer charge containing (based on the total weight of polymerizable monomer) at least 80 wt. % of (A) acrylamide and/or methacrylamide and (B) acrylic and/or methacrylic acid in free acid or salt form, wherein component (B) of the monomer charge is, or is derived from, acrylic and/or methacrylic acid which (I) as been pretreated to reduce the furfural therein to an amount which in any event is less than the weight of the initiator used in the copolymerization or (II) is acid containing less than 100 ppm furfural and which has been prepared by the vapour phase catalytic oxidation of a feed giving rise to the acid.

2. A process according to claim 1, wherein there is used less than 100 ppm (based on the total weight of polymerizable monomer) of a redox initiator system.

3. A process according to claim 1 or 2, wherein component (B) of the monomer charge is, or is derived from, acid which has been pretreated to reduce the furfural therein to an amount which is less than 20 ppm (based on the weight of acrylic and/or methacrylic acid).

4. A process according to any one of the preceding claims, wherein the furfural removal pretreatment involves treatment (if necessary in the presence of a polymerization inhibitor for the unsaturated acid) of said acid with an agent which acts upon the furfural to give a product which is then separated from said acid.

5. A process according to claim 4, wherein said agent is a compound which complexes or reacts with the aldehyde group in furfural to give a product which is separated from said acid.

6. A process according to claim 5, wherein said product separated from said acid is one which is higher boiling than the acid and which is thermally stable up to 90"C.

7. A process according to claim 4, wherein said agent is a phenolic compound or an aromatic amine.

8. A process according to claim 7, wherein said agent is phloroglucinol (used in conjunction with a strong acid) or ophenylenediamine and the acid is treated in distilled glacial acrylic acid which after treatment is further purified by distillation.

9. A process according to claim 7 or 8,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. itiator. The following examples illustrate typical acrylic acid purification procedures and the use of the purified acrylic acid in the preparation of high molecular weight copolymer flocculants by adiabatic polymerization. Example 1 (A) In this example 525 g. of glacial acrylic acid (GAA) was flask distilled at reduced pressure in a 3-necked flask fitted with a 11/4" 5-plate Oldershaw column fitted with a reflux head and a receiver. The GAA used contained about 125 ppm furfural and 200 ppm MEHQ inhibitor and had been prepared by the distillation of crude acrylic acid formed by the catalytic vapour phase oxidation of acrolein. The GAA charge to the flask was mixed with 0.1% by weight of phloroglucinol, 0.1% by weight of PTZ and 0.2% by weight of sulfuric acid. The distillation was run for a period of 5 hours, under a pressure of 2 mm. Hg and using a head temperature of 27"C. and a bottom temperature from 42-100"C. The purified acrylic acid distillate contained less than 1 ppm furfural. (B) 18 g. of GAA, purified by the procedure of Part A of this example, was added to 10 g. of AR sodium hydroxide dissolved in 22 ml. of water. The pH of the mixture was adjusted to pH 7-8.5, the mixture cooled to 0 C. and there was then dissolved therein pure acrylamide (94g.). The mixture was then cooled to -10"C., transferred to a Dewar flask, purged with nitrogen for 10 minutes and there were added ferrous sulphate (1.4 ml. of a fresh 0.1 wt. % aqueous solution), ammonium persulphate (2.75 ml. of a fresh 0.1 wt. % aqueous solution) and isopropanol (3.4 ml. of a fresh 1 wt % aqueous solution). The mixture in the flask was then again purged with nitrogen for a further 10 minutes, azobisisobutyronitrile (0.126 g.) was added and the mixture further purged with nitrogen for 10 minutes. The mixture was then left to undergo an exothermic polymerization and ultra-high molecular weight copolymer flocculant resulted in two hours. Attempts to prepare copolymer by the above procedure, but using unpurified GAA contaning about 125 ppm furfural, require polymerization times of from 7-34 hours for the production of copolymer flocculant of comparable molecular weight. Example 2 Parts A and B of Example 1 are repeated except that, in Part A, the sulphuric acid is omitted, the phloroglucinol is replaced by the same amount of o-phenylenediamine and 1000 ppm of PTZ is dissolved in the GAA prior to the addition of the diamine. This PTZ addition is necessary to inhibit polymerization of the GAA by the diamine which acts as an initiator. Results similar to those of Example 1 are obtained. WHAT WE CLAIM IS:

1. A process for the preparation of a high molecular weight water-soluble or water-dispersible copolymer flocculant which comprises copolymerizing, in the presence of less than 1000 ppm (based on the total weight of polymerizable monomer) of polymerization initiator, a monomer charge containing (based on the total weight of polymerizable monomer) at least 80 wt. % of (A) acrylamide and/or methacrylamide and (B) acrylic and/or methacrylic acid in free acid or salt form, wherein component (B) of the monomer charge is, or is derived from, acrylic and/or methacrylic acid which (I) as been pretreated to reduce the furfural therein to an amount which in any event is less than the weight of the initiator used in the copolymerization or (II) is acid containing less than 100 ppm furfural and which has been prepared by the vapour phase catalytic oxidation of a feed giving rise to the acid.

2. A process according to claim 1, wherein there is used less than 100 ppm (based on the total weight of polymerizable monomer) of a redox initiator system.

3. A process according to claim 1 or 2, wherein component (B) of the monomer charge is, or is derived from, acid which has been pretreated to reduce the furfural therein to an amount which is less than 20 ppm (based on the weight of acrylic and/or methacrylic acid).

4. A process according to any one of the preceding claims, wherein the furfural removal pretreatment involves treatment (if necessary in the presence of a polymerization inhibitor for the unsaturated acid) of said acid with an agent which acts upon the furfural to give a product which is then separated from said acid.

5. A process according to claim 4, wherein said agent is a compound which complexes or reacts with the aldehyde group in furfural to give a product which is separated from said acid.

6. A process according to claim 5, wherein said product separated from said acid is one which is higher boiling than the acid and which is thermally stable up to 90"C.

7. A process according to claim 4, wherein said agent is a phenolic compound or an aromatic amine.

8. A process according to claim 7, wherein said agent is phloroglucinol (used in conjunction with a strong acid) or ophenylenediamine and the acid is treated in distilled glacial acrylic acid which after treatment is further purified by distillation.

9. A process according to claim 7 or 8,

wherein said agent is used in an amount from 500-5,000 ppm based on the weight of unsaturated acid to be purified.

10. A process according to claim 4, wherein crude undistilled acrylic acid is treated with aniline and a strong acid to effect furfural removal and the treated acid is purified by distillation to form glacial acrylic acid.

11. A process according to any one of the preceding claims, wherein component (B) of the monomer charge is, or is derived from, acrylic acid which has been prepared by the vapour phase catalytic oxidation of acrolein and which has then been pretreated to reduce the furfural therein to an amount which is less than 1 ppm (based on the weight of acrylic acid).

12. A process according to claim 11, wherein said acrolein has been prepared by the vapour phase catalytic oxidation of propylene.

13. A process according to claim 1 carried out substantially as hereinbefore described with reference to foregoing Example 1 or 2.

14. Copolymer flocculants when prepared by a process according to any one of the preceding claims.