Poly recycling process

R. FRANZ, F. WELLE, Post-consumer poly(ethylene terephthalate) for direct food contact application - challenge-test of an inline recycling process, Food Additives and Contaminants, 2002, 19(5), 502-511. 

In the following sections three case studies are presented where, among other LCA aspects, some of the LCI issues discussed previously are higUighted. Case Study 1 refers to solvent-based postcombustion CO2 capture processes. Case Study 2 refers to lignoceUulosic biorefmeries, and Case Study 3 refers to the poly(methyl methacrylate) recycling process. 

CASE STUDY 3 POLY(METHYL METHACRYLATE) RECYCLING PROCESS... 

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.

Figure 9 shows a schematic flow diagram and an example of the hybrid H2 PSA-SSF membrane concept. The fresh feed to the PSA process is SMROG. The PSA process cycle is an abridged version of the Poly-bed process with only two co-current depressurization steps, having a H2 recovery of 77.6%. The countercurrent depressurization effluent gas is fractionated. The initial part of this gas, which is richer in H2, is directly fed to a SSF membrane at a pressure of 3 bar. The H2 purge effluent gas is compressed to 3 bar and fed to the same membrane. The H2 enriched high pressure effluent gas from the membrane is recompressed and recycled as feed gas to the PSA process. This increased the overall H2 recovery of the hybrid process to 84.0% [23]. 

Replication of synthetic homopolyribonucleotides has been studied by Friedemann Schneider and coworkers (Schneider et al., 1979 Heinrichs and Schneider, 1980). They studied RNA-synthesis at poly(A)-poly(U) templates by the unspecific RNA polymerase from E. coli in a stirred flow reactor. In general this reaction follows an overall autokatalytic kinetics. In the flow reactor the recycling process is replaced by an influx of A and an outflux of the material in the reactor. It is worth noticing that critical slowing down has been observed experimentally in this system. 

The overall yield of the process is at least 87 mol %, and 2.3 mol of methanol per mole of final product are needed, an excess of 15% over the 2.0 theoretical amount. The methanol can be recycled from the manufacture of poly(ethylene terephthalate). Reported utilities consumptions per kilogram of product are 1.2 kg of 1400-kPa steam, 420 kj of boiler fuel, and 0.5 kWh of electricity (72). 

In America there are promising signs for certain polymers. For example, poly(ethylene terephthalate) drinks bottles can be cleaned and recycled to give an acceptable grade of PET resin in a process that is economically viable. The recycled polymer is used as carpet fibre, furniture stuffing, or insulation. Waste nylon can also be recycled profitably. 

Dissolution/reprecipitation processes were evaluated for the recycling of poly-epsilon-caprolactam (PA6) and polyhexamethyleneadipamide (PA66). The process involved solution of the polyamide in an appropriate solvent, precipitation by the addition of a non-solvent, and recovery of the polymer by washing and drying. Dimethylsulphoxide was used as the solvent for PA6, and formic acid for PA66, and methylethylketone was used as the non-solvent for both polymers. The recycled polymers were evaluated by determination of molecular weight, crystallinity and grain size. Excellent recoveries were achieved, with no deterioration in the polymer properties. 33 refs. 

R. eutropha is actually an autotrophic hydrogen-oxidizing bacterium which can also produce poly(3HB) from C02, H2, and 02 [34]. The critical factor in such autotrophic cultivation processes is to avoid possible gas explosions. Therefore, a recycled gas, closed circuit culture system equipped with several safety features was developed and the oxygen concentration in the substrate gas phase was kept below the lower limit for gas explosions. A bacterial biomass of 91.3 g 1 1 has been achieved and the poly(3HB) content reached up to 67% per cell dry weight under these oxygen-limited conditions [35]. 

Rieckmann, Th., Poly condensation and recycling of PET fibres and other PET waste by continuous processes, presentation given at the 5th Conference on Man-Made Fibres, Beijing, China, 1994. 

Partition Coefficients of nonvl-phenyl-poly-(ethoxy)-ethanol (NPE) Surfactants. The solubility of surfactants in water and hydrophobic solvents is well documented (11,12,22), but only a few attempts at measuring partition coefficients between immiscible liquids have been reported (2,4,9,10). Partition coefficients of surfactants are of theoretical interest because of their relation to observed surfactant properties such as emulsification, wetting and detergency. Partition coefficients (K ) may be also of considerable practical value for predicting surfactant recov and recycling in industrial processes. For example, in the cold water extraction of tar sand, an effective surfactant with a high Kp could be efficiently recycled in the process water and would not follow the bitumen into the upgrading stream. 

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