Monomer Recycle

Nylon-6,6 monomers, recycling, 544 Nylon-6,6 products, depolymerized, 533 Nylons, 19, 135. See also Nylon PA entries Polyamides (PAs) depolymerization of, 566-571 solvolysis reactions for, 535... 

PET industrial synthesis, 70 PET monomers, recycling of, 539-541 PET products, recycled and depolymerized, 531-532 PETRA, 532... 

Finally, the HDPE slurry from the second reactor is sent to the postreactor (3) to reduce dissolved monomer, and no monomer recycling is needed. In the decanter (4), the polymer is separated from the dispersing medium. The polymer containing the remaining hexane is dried in a fluidized bed dryer (5) and then pelletized in the extrusion section. The separated and collected dispersing medium of the fluid separation step (6) with the dissolved co-catalyst and comonomer is recycled to the polymerization reactors. A small part of the dispersing medium is distilled to maintain the composition of the diluent. 

Continuous solution Free radical (backmixed reactor) Styrene monomer Recycled solvent W or W/O initiator Good Temperature Control Good for copolymers Good clarity and color Uniform product Limited in final conversion Limited in product range Pumping difficulties High capital Low-cost process for high-volume GP... 

Catalyst removal steps can be eliminated in very efficient processes (Section 9.5) in which the residual catalyst concentration is negligible. Conversion levels are generally higher than in the free-radical, high-pressure polymerization process, and less monomer recycle is therefore required. The reaction temperature in a typical slurry processes is controlled by refluxing the solvent. 

P = polymer product rate and monomer feed rate R — monomer recycle rate G = monomer-polymer recycle rate Ti side arm neat exchange temperature T2 = reactor temperature... 

It is perhaps worth noting that the monomer recycle vapor condenser is also a heat exchanger for the reactor. In the above discussion, the recycled monomer was considered to be at 30° C. For this condition the condenser removes not only the heat put in by the devolatilizer, but cools the monomer considerably below the reactor temperature. 

Efficient heat transfer is also obtained in the monomer recycle condenser where viscosity is no problem. 

Acrylonitrile/Butadiene/Styrene (ABS) Acry-lonitrile/butadiene/styrene (ABS) polymers are not true terpolymers. As HIPS they are multipolymer composite materials, also called polyblends. Continuous ABS is made by the copolymerization of styrene and acrylonitrile (SAN) in the presence of dissolved PB rubber. It is common to make further physical blends of ABS with different amounts of SAN copolymers to tailor product properties. Similar to the bulk continuous HIPS process, in the ABS process, high di-PB (>50%, >85% 1,4-addition) is dissolved in styrene monomer, or in the process solvent, and fed continuously to a CSTR where streams of AN monomer, recycled S/AN blends from the evaporator and separation stages, peroxide or azo initiators, antioxidants and additives are continuously metered according to the required mass balance to keep the copolymer composition constant over time at steady state. 

For many reactions, the step reactions, to even form polymer, the extent of reaction must be 0.99+ or over 99 percent complete. For all commercial polymerizations, if the extent of reaction is not above 90 percent, the polymer can only be made with extensive monomer recycle and the cost of the polymerized product may be prohibitively high. In general then, the extent of reaction of a polymerization, both in terms of the mrmber of repeat units added, i,... 

Figure 13.7 Block flow diagram of current polyfmethyl methacrylate) (PMMA) monomer recycling process. MIB, Methyl isobutyrate MA, methyl acrylate MMA dimer, 1,4-cyclohexane dicarboxylic acid dimethyl ester [87]. Modified from Kikuchi Y, Hirao M, Sugiyama H, Papadokonstantakis S, Hungerbuehler K, Ookubo T, et al. Design of recycling system for poly(methyl methacrylate) (PMMA). Part 2 process hazards and material flow analysis. Int J Life Cycle Assess 20i4 i9(2) 307—19.

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