Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/006—Removal of residual monomers by chemical reaction, e.g. scavenging

Definitions

• This invention relates to the production of substantially dry polyacrylamide particles having reduced levels of acrylamide monomer contamination.
• EP-A-329,325 can be very effective in reducing acrylamide monomer content, but requires a maintenance period of at least 10 minutes, usually at least 30 minutes, between contacting the aqueous gel particles with the amidase and drying the aqueous gel particles.
• Such a process can be difficult to incorporate into an industrial scale process.
• hot gel particles are produced, either direct from polymerisation or from a comminution stage, and pass almost immediately to a drying stage at high temperature. It can be difficult to incorporate an extended maintenance period between these two points.
• Heat treatment in the exemplified processes is of the order of 1 or 2 hours. Only treatment of polymer latex is demonstrated. In all the systems exemplified the amidase is contacted with the polyacrylamide latex for at least 30 minutes, and in some cases at least 2 or 3 hours.
• the present invention is concerned with providing substantially dry polyacrylamide particles having low levels of acrylamide monomer contamination.
• the invention provides in a first aspect a process for the production of substantially dry particles of a polyacrylamide comprising providing aqueous polyacrylamide gel particles contaminated with acrylamide monomer. applying amidase enzyme to the aqueous gel particles whilst they are at a temperature of from 50 to 95°C, and substantially immediately passing the aqueous gel particles to a drying stage and subjecting them in that stage to a temperature of at least 60°C so as to produce substantially dry particles of polyacrylamide.
• This process has the significant advantage that it may be carried out on a plant already adapted for the production of substantially dry polyacrylamide particles. There is no need for a residence time of half an hour or more before the particles pass to the drying stage. We have also found unexpectedly that this process can lead to the production of acceptably low levels of residual acrylamide monomer contamination in very convenient manner. It would be expected that without a maintenance period the amidase would have little chance to affect the acrylamide monomer levels in the aqueous polyacrylamide gel particles before being denatured in the high temperature drying stage. We have found surprisingly that this is not the case.
• the amidase enzyme preferably has a very low value of Km for acrylamide. This is normally measured at pH 7 and 20°C. Generally it is below 10 and frequently below 5 and most preferably below 2 mmolar. Preferred enzymes have Km 0.5 to 2.5, most preferably 0.5 to 1.5 mmolar. The Km value can be below 0.5 mM, for instance 0.1 mM or 0.01 mM.
• amidases may be used in the process.
• all amidases Preferably have the low Km value for acrylamide discussed above.
• amidases which have been proposed in the literature for treating polyacrylamides do not have a sufficiently low Km value to give the particular preferred results achievable with the invention but others do.
• a particularly preferred amidase is the amidase produced by the microorganism which has been deposited under the deposit number NCIMB 40756. This and other suitable amidases are described in more detail in our copending International Application No. PCT/GB96/01951.
• the amidase is not inhibited by materials normally present in a process of producing substantially dry polymer particles from aqueous gel or in the growth medium for the microorganism which produces the amidase.
• the amidase is preferably not inhibited by ammonia.
• the amidase enzyme may be applied to the aqueous polyacrylamide gel particles in any suitable form. Normally it is applied in the form of a liquid suspension or solution. For instance it may be applied in the form of an aqueous solution of amidase or as a reverse phase emulsion of amidase. It may be applied in the form of an aqueous suspension.
• the amidase is be present in the suspension in the pure (molecular) form.
• Amidase may be applied in any suitable manner.
• One suitable method of application is spraying the particles of aqueous gel with the liquid suspension or solution of amidase.
• Dosage of amidase may be at any suitable level, for instance from 0.1 to 10 U/g (activity units per gram dry solids content of polymer), preferably 0.5 to 7 U/g, for instance 1 to 3 U/g.
• the particles of aqueous polyacrylamide gel preferably have size at least 50 wt%, often at least 70 wt%, from 0.1 to 8 mm.
• Particle size can be from 2 up to 4 or 6 mm, and can be for instance 0.2 to 1 or 2 mm.
• One way of making the aqueous gel particles is by reverse phase bead polymerisation followed by distilling off the water and oil so as to provide hot particles typically having a temperature of 50 to 90°C, often around 80°C, and typically having a size 0.1 to 1 mm.
• aqueous gel particles are by bulk gel polymerisation to form a rigid gel having a polymer solids content normally of 20 to 50%, often 30 to 45% by weight, followed by comminution to a particle size at least 50%, and usually at least 70%, from 0.1 to 6 or 8 mm.
• the comminution leads to an average particle size in the range 0.2 to 4 mm, often around 2 mm.
• Standard comminution systems can be used, including lubricant if desired.
• aqueous gel particles typically are contaminated with significant amounts of acrylamide monomer, often in the range 500 to 2,000 ppm.
• the processes of the invention are particularly suitable for treating aqueous gel particles contaminated with levels of acrylamide monomer above 400 or 500 ppm. It is advantageous to be able to provide a process which can reduce levels of acrylamide monomer from these levels to acceptably low levels, for instance below 200 or 100 ppm or even substantially zero, in particular because the manufacturer is given greater freedom in the first stage of the process. That is, it is possible to carry out the initial polymerisation stage to form the aqueous gel and to allow levels of acrylamide monomer in this gel to be 400 or 500 ppm or greater, in the knowledge that these levels will be reduced in the amidase application stage of the process. The need to control polymerisation conditions very carefully so as to ensure that the lowest possible acrylamide monomer levels are present in the aqueous gel is removed.
• the aqueous gel particles are produced by bulk gel polymerisation and comminution and the amidase is applied, preferably by spraying the particles, during the comminution stage.
• application of amidase preferably by spraying the particles
• the aqueous gel particles have a temperature in the range 50 to 95°C when amidase is applied, preferably 70 to 90°C.
• the process of the invention is carried out on particles of a polyacrylamide, ie a polymer formed from monomers comprising acrylamide.
• the polyacrylamide may be a homopolymer of acrylamide. Alternatively it may be a copolymer with other monomers, which may be anionic, non ⁇ ionic or cationic.
• the polyacrylamide when anionic or non-ionic, preferably has such high molecular weight that its intrinsic viscosity is at least 6 or 10 dl/g and frequently at least 15, 20 or even 30 dl/g. It is usually not above 50 dl/g.
• intrinsic viscosity is generally above 8 and usually above 10 or 12 dl/g, typically above 14 dl/g. Generally it is not above 20 or 25 dl/g.
• the polymer may be a non-ionic homopolymer of acrylamide or it may be a copolymer of acrylamide with anionic or cationic monomers, usually in an amount of 3 to 90% by weight, often below 70% and preferably below 50%, by weight based on the total weight of monomers.
• anionic monomers may be used such as ethylenically unsaturated carboxylic or sulphonic monomers, especially acrylic acid (including water-soluble salts thereof) .
• Any of the conventional cationic monomers may be used such as diallylammonium monomers for instance DADMAC or cationic esters such as DMAEA or DMAEMA (often as acid addition or quaternary ammonium salts) or cationic amides such as DMAPMA.
• DADMAC diallylammonium monomers
• cationic esters such as DMAEA or DMAEMA (often as acid addition or quaternary ammonium salts) or cationic amides such as DMAPMA.
• DMAPMA cationic amides
• the polymer may be linear or cross-linked, in conventional manner.
• the aqueous gel particles are carried to the drying stage substantially immediately after application of amidase is complete.
• substantially immediately we mean a time which is as short as is convenient in the context of an in-line production process, typically below 5 minutes, often 10 seconds to 2 minutes, often around 1 minute or less.
• the drying stage may be any standard drying system, for instance a fluid bed drier or other drying oven.
• the particles are subjected to temperatures of 60°C and greater, for instance 70 to 100°C, preferably 75 or 80 to 95°C.
• the particles are normally produced in a continuous process, although they can be produced batchwise. In the process any given aqueous gel particle will tend to spend not more than 1 hour, often not more than 30 minutes, in the drying stage.
• the particles are subjected to the drying stage so that they are substantially dry. That is, they have a final water content of below 20%, usually below 10% by weight. They generally have a final size at least 90 wt% above 30 ⁇ m, and often below lmm. They suitably have a size of 90 wt% between 70 and 700 ⁇ m.
• Generally content of acrylamide monomer in the substantially dry polymer particles is below 300 ppm calculated on the basis of the dry weight of polymer. Preferably it is below 200 ppm and most preferably below 100 ppm. Best products have values below 50 ppm and can show values of 0 ppm, ie an amount below measurable levels, up to 20 ppm. "Lowest measurable levels" in this specification are those measurable by standard techniques used in the industry. The precise level can vary with the type of polymer. We find that the lowest measurable level of acrylamide for the polymers used in the invention is normally below 5 or 10 ppm.
• a process for the production of substantially dry particles of a polyacrylamide comprising providing aqueous polyacrylamide gel particles contaminated with acrylamide monomer, applying amidase enzyme which has a Km for acrylamide of not more than 10 mM, preferably not more than 5 mM, to the aqueous gel particles whilst they are at a temperature of 50 to 95°C, holding the aqueous gel particles to which amidase has been applied in a holding stage at a temperature of from 20 to 70°C for not more than 30 minutes, and then passing the particles to a drying stage and subjecting them in that stage to a temperature of at least 60°C so as to produce substantially dry particles of polyacrylamide, the process being carried out such that the final content of acrylamide monomer in the substantially dry particles is below measurable levels.
• Such a process is particularly suitable for producing acrylamide polymer particles which are substantially dry and which have extremely low levels of residual acrylamide monomer. This is achieved in this aspect of the invention by the choice of a combination of an amidase enzyme having very low Km for acrylamide and a moderate holding period after treatment. This moderate holding period can also be incorporated into an industrial process without the very long maintenance periods, for instance more than 10 hours, which are required in certain other prior art processes.
• the duration of the holding stage is not more than 30 minutes. It may be for instance at least 2 minutes, preferably around 10 to 20 minutes.
• the aqueous gel particles to which amidase has been applied are held in the holding stage at a temperature of from 20 to 70°C, often around 30 to 50°C, for instance about 40°C.
• this may be achieved by cooling the particles during the latter stages of application of amidase to the aqueous gel particles (for instance by spraying) and then holding the treated particles at the required temperature for the duration of the holding stage (for instance 10 to 15 minutes) .
• the holding stage may be in the cold zone of a fluid bed drier, after which the particles are then fed into the hot zone of the fluid bed drier and subjected to conventional drying in the drying stage.
• This aspect of the invention leads to extremely low levels of monomer content in the final product. They are below measurable levels of acrylamide monomer.
• a process for the production of substantially dry particles of a polyacrylamide comprising providing aqueous polyacrylamide gel particles contaminated with acrylamide monomer, applying amidase enzyme which has a Km for acrylamide of not more than 10 mM, preferably not more than 5 mM, to the aqueous gel particles whilst they are at a temperature of 50 to 95°C, holding the aqueous gel particles to which amidase has been applied in a holding stage in the cold zone of a fluid bed drier at a temperature of from 20 to 70°C for not more than 30 minutes, and then passing the particles to a drying stage in the hot zone of a fluid bed drier and subjecting them in that stage to a temperature of at least 60°C so as to produce substantially dry particles of polyacrylamide.
• any of the additional process features described above for the first and second aspects of the invention may be used.
• a copolymer of 90% acrylamide and 10% sodium acrylate is formed by bulk gel polymerisation to give high IV and a content of around 1,000 ppm acrylamide free monomer. This is comminuted in conventional manner down to a final comminution stage which gives a particle size of around 0.5 m. In another process comminution gives a particle size of around 2 mm. During this final comminution stage, an aqueous suspension of cells of the type NCIMB 40756 is sprayed onto the particles at the rate of about 1 litre of the aqueous suspension to 40 kg of the aqueous particles. At this stage the particles have a temperature of about 80°C.
• the particles are immediately passed into a fluid bed drier where they are dried in a conventional manner and they are optionally subsequently comminuted.
• Such particles can easily have a free acrylamide monomer content of below 100 ppm and often below 50 ppm.
• the particles are either cooled before spraying or are cooled immediately after spraying and are held for about 15 minutes at a temperature of around 40°C before being fed into the fluid bed drier and then dried.
• Such particles optionally after comminution, typically have a free acrylamide monomer content which is so low as to be not measurable, ie 0 ppm acrylamide.
• Polyacrylamide gel was formed by bulk solution polymerisation from monomer mixture comprising 30 wt% sodium acrylate and 70 wt% acrylamide.
• the gel had a polymer solids content of 32%.
• the gel was heated to 80°C and then subjected to a lubricated comminution stage in a Waring blender.
• Amidase from the microorganism deposited under number NCIMB 40756 having Km l.l mM in the form of a 39% solids suspension in water was applied to the gel during the comminution stage. Amidase was added at various levels given in U/g below. Immediately comminution was finished the comminuted treated gel was transferred to a laboratory fluid bed drier in which the temperature had been stabilised at 80°C.
• amidase itself could migrate through the polymer gel because of the high molecular weight of the amidase (generally above 200,000) and the high polymer content of the aqueous gel particles and the high molecular weight of the polymer. Indeed, we believe the amidase does not migrate through the gel to any significant extent. Further, it would not be expected that an amidase which had Km values such as those indicated above, for instance around 1 mmolar, would be capable of reducing the free acrylamide monomer content to the low levels which are obtained in the invention.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Preparation Of Compounds By Using Micro-Organisms (AREA)

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Citations (4)

• 1996
  • 1996-02-07 GB GBGB9602415.3A patent/GB9602415D0/en active Pending
• 1997
  • 1997-02-04 PL PL97328372A patent/PL328372A1/xx unknown
  • 1997-02-04 BR BR9707271A patent/BR9707271A/pt unknown
  • 1997-02-04 JP JP9528270A patent/JP2000504057A/ja active Pending
  • 1997-02-04 EP EP97902470A patent/EP0879252A1/en not_active Withdrawn
  • 1997-02-04 WO PCT/GB1997/000317 patent/WO1997029136A1/en not_active Ceased
  • 1997-02-04 AU AU16109/97A patent/AU1610997A/en not_active Abandoned
  • 1997-02-07 ZA ZA9701021A patent/ZA971021B/xx unknown
• 1998
  • 1998-08-06 MX MX9806357A patent/MX9806357A/es unknown
  • 1998-08-06 NO NO983613A patent/NO983613L/no unknown

Patent Citations (4)

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