Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-04-26
2002-06-25
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S005000, C522S024000, C522S028000, C522S030000, C522S060000, C522S061000, C522S001000, C522S150000, C522S151000, C522S152000, C522S175000, C522S173000
Reexamination Certificate
active
06410610
ABSTRACT:
The invention relates to a process for the production of water-soluble, powdered, cationic polyelectrolytes based on non-ionogenic and cationic monomers.
Copolymers of acrylamide and cationic monomers are used in waste water treatment and paper manufacturing, for example. It is their purpose to coagulate colloidal particles in aqueous suspensions to form mechanically stable flakes which settle readily or can easily be filtrated.
It is desirable for economic reasons to achieve high settling rates and high filtration rates of the coagulated particles with a minimum of polyelectrolyte input. High effectiveness in the clarification of aqueous suspensions is presented by high molecular weight cationic polyelectrolytes having good solubility.
High molecular weight cationic water-soluble copolymers are obtained when the polymerization of the aqueous monomer solution is performed at a polymerization temperature as low as possible and with small amounts of initiator.
As the viscosity of the monomer solution increases after initiating the polymerization, and a solid gel is present after a short period of polymerization, controlled heat removal is not possible, i.e., the exothermic reaction proceeds in a virtually adiabatic fashion. In order to keep the maximum polymerization temperature as low as possible, the temperature of the monomer solution at the time of initiation must be selected low at a given monomer concentration. In summary, this means that in order to produce high molecular weight cationic polymers by polymerization in aqueous solution, not only the initiation temperature and the amount of initiator, but also the monomer concentration must be kept low, the amount of initiator ranging approximately between 0.02 and 5 wt.-% and the monomer concentration approximately between 25 and 45 wt.-%. Such preconditions result in extensive problems when producing water-soluble, high molecular weight copolymers from non-ionogenic and cationic monomers because:
1) initiator systems consisting of an oxidizing agent and a reducing agent (redox system) which are sufficiently active to initiate polymerization at temperatures below 20° C., preferably below 0° C., are available in only a limited range;
2) redox systems initiating polymerization at low input and low initiation temperature are not capable of directing the polymerization to high conversion;
3) low amounts of initiator require exceedingly long periods of polymerization which do not permit a continuous design of the polymerization process;
4) low amounts of initiator result in poorly reproducible initiation and progress of the polymerization because even minor variations in the monomer quality or oxygen content of the monomer solution will give rise to significant interference with the process;
5) polymerization at low monomer concentrations not only deteriorates the space-time yield but also impedes breaking up of the hydrous, gelled polymer into separate particles, hampering the subsequent drying.
To overcome the above-demonstrated problems in the production of high molecular weight, water-soluble polymers, the EP 0,296,331 suggests initiation of the polymerization at temperatures below 0° C. in the presence of dispersed monomer crystals. The polymerization is initiated using the well-known redox system consisting of ammonium persulfate and ammonium iron(II) sulfate which reacts sensitively to traces of oxygen. This redox system does not provide sufficient conversion, however, and for that reason 2,2′-azobis(2-amidinopropane) dihydrochloride (ABAH) is also added, which provides free radicals by thermal decomposition. The thermal decomposition of this azo initiator becomes apparent by an accelerated polymerization from about 45° C. on, and as a consequence, the molecular weight of the polymers formed decreases with increasing polymerization temperature. The residual monomer content of acrylamide is 970 ppm, and such high values in the polymer cannot be accepted for toxicological reasons.
In order to produce high molecular weight polyacrylamides by polymerizing acrylamide or acrylamide including other comonomers in aqueous solution, the U.S. Pat. No. 4,455,411 claims an initiator system consisting of a peroxodisulfate and the sodium formaldehyde sulfoxylate (=sodium hydroxymethanesulfinic acid=Rongalit C®) reducing agent, as well as the 2,2′-azobis(2-amidinopropane) dihydrochloride (ABAH) already mentioned above. Also, the initiator system appears to be insensitive to varying purity of the monomer used. Example 8 describes the production of a cationic polyelectrolyte. The copolymerization of acrylamide with quaternized dimethylaminoethyl methacrylate is initiated with the redox system at 20° C. and carried on to high conversion by using 403 ppm. of ABAH.
As has been illustrated, the production of high molecular weight, well-soluble polyelectrolytes necessarily requires a low initiation temperature, i.e., a temperature of the monomer solution of below 20° C., preferably below 10° C.
In contrast to redox polymerization, the photopolymerization of a monomer solution in the presence of an initiator providing free radicals by irradiation with UV light is largely independent of the initiation temperature (Chemical Reviews, Vol. 68, No. 2, Mar. 25, 1968). The disadvantage of photopolymerization results from the Lambert-Beer Law which states that the light intensity in the irradiated monomer solution decreases exponentially with increasing layer thickness. For this reason, photochemical reactions should be stirred vigorously in order to replace reacted product in the reaction zone by new substrate.
In continuous processes for producing high molecular weight, water-soluble polymers, such as described in EP 0,296,331 A2, Example 4, intimate mixing of the polymerizing solution is not possible because immediately after starting the polymerization initiated by a redox initiator system of iron ammonium sulfate/ammonium persulfate with addition of an azo initiator, it would solidify to give a solid gel which can no longer be stirred.
The DOS 27 16 606 suggests performing the continuous production of water-soluble acrylic polymers by photopolymerization, preferably at a layer thickness of the monomer solution of from 3 to 8 mm on a mobile support. In order to decrease the residual monomer content of the polymers obtained compared to those polymers obtained according to the process of DAS 2,050,988, it is necessary according to claim 1
d
) to irradiate the polymer layer after removal from the support for preferably another 40 to 90 minutes. According to Example 4, the residual content of acrylamide in the polymer is 600 ppm despite the use of 240 ppm of benzoin propyl ether and 75 minutes irradiation time. Such long polymerization periods with thin layer thickness result in poor space-time yields. The tackiness of the polymers obtained as determined by the applicant is a consequence of the thin polymerizing layer, i.e., the unfavorable ratio of volume to surface results in an increase of low molecular weight tacky components forming at the phase boundary, particularly towards the gaseous phase.
To produce water-soluble, low molecular weight polymers, the DOS 22 48 715 suggests performing the photopolymerization in a thin layer using benzoin propyl ether and an accelerator. The accelerator consists of azobisisobutyronitrile or the persulfate/bisulfite redox system.
A process for the continuous production of polymers and copolymers of water-soluble monomers is known from EP 0,228,638 A1, wherein polymerization of the aqueous monomer solution takes place between −10° C. and 120° C. on a mobile conveyor belt, initiated by chemical initiation and/or high-energy radiation/light. Polymers having a low content of residual monomer and gel have not been described.
Cationic copolymers of acrylamide and dimethylaminopropylacrylamide as flocculant can be inferred from EP 0,228,637 B1. The initiation of polymerization can be triggered using redox systems, thermally decomposing initiators, or free radicals formed by photochemical
McClendon Sanza L
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seidleck James J.
Stockhausen GmbH & Co. KG
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