Conventional recycling processes

The table shows that the process can eliminate volatile compounds much more efficiently than non-volatile substances. Volatiles, like toluene and chlorobenzene, are already efficiently removed by step (ii) alone. Toluene was no longer measurable at a detection limit of 0.4 ppm. The other volatile, chlorobenzene, was recovered at 5.5 % of the initial concentration after the extrusion step. After the post-condensation step, the amount of toluene in the final product was likely to be far below the limit of detection since the detection limit was already determined after the extrusion step. Chlorobenzene also could not be found above the limit of detection. These results show very impressively that a conventional recycling process (consisting of steps (i) and (ii)) for post-consumer PET removes volatile real-life contaminants very efficiently, for example solvents and fuel. An additional vacuum treatment during solid-phase post-condensation further decreases any level of volatile compounds in the final product. 

Lewis acids, such as the haUde salts of the alkaline-earth metals, Cu(I), Cu(II), 2inc, Fe(III), aluminum, etc, are effective catalysts for this reaction (63). The ammonolysis of polyamides obtained from post-consumer waste has been used to cleave the polymer chain as the first step in a recycle process in which mixtures of nylon-6,6 and nylon-6 can be reconverted to diamine (64). The advantage of this approach Hes in the fact that both the adipamide [628-94-4] and 6-aminohexanoamide can be converted to hexarnethylenediarnine via their respective nitriles in a conventional two-step process in the presence of the diamine formed in the original ammonolysis reaction, thus avoiding a difficult and cosdy separation process. In addition, the mixture of nylon-6,6 and nylon-6 appears to react faster than does either polyamide alone. 

The impact of micro reactor processing on the recycle ratio cannot be predicted in a straightforward manner. As this is somehow linked to mass transfer and mixing, improvements are possible actually this was found experimentally, e.g. recycle ratios below 2 were used for micro flow processing (instead of 17 in the conventional industrial processing, see below) [64],... 

The conventional technique for removing zinc from the spinning acid wastestream has been direct lime precipitation to -pH 10, with no zinc recovery. The economics of this approach are compared to the American Enka zinc recycle process. 

Plants to produce low-sulfur fuels from coal, oil shale, tar sands or heavy oil frequently are conceived to use the Claus process to produce byproduct sulfur. Using coal gasification as an example, it is seen that the conventional Claus process is not well suited to the usual problem of processing H2S at a concentration of 20% or lower. A new process, recycle Selectox, is very suitable to process H2S in concentrations up to 40%, provided the acid gas is free of olefins up to 95% recovery is possible, even with very dilute feed. 

This microwave-assisted reaction was carried out on a 3-g scale in a glass vessel placed in a bath of alumina/magnetite. The anthraquinone (m.p. 284°C) produced was collected as it sublimed from the reactor. Further, o-benzoylbenzoic acid was added and the reaction repeated. The main advantage of the microwave-assisted reaction lies in the recycling of the catalyst. The yield in the conventional heating process falls to 50% after four uses of catalyst, whereas in the microwave-assisted process the yield is still 84% after fifteen uses. 

Characterization tests reported here were performed on combinations of materials needed to evaluate the predicted performance of typical pavements made from conventional asphaltic concrete with limestone aggregate, sulfur-asphalt concrete with limestone aggregate, sulfur-asphalt concrete with beach sand aggregate, and recycled asphaltic concrete pavement with sulfur added during the recycling process. The data... 

Equation 10 shows that for the conventional process (no recycle) the value of 6c is equal to the hydraulic retention time (0), Thus, effluent quality and treatment efficiency for a given waste are determined by the choice of a value of 0. The ability to vary 6c independently of 0 in the recycle process (Equation 11) is the principal advantage of the recycle process compared with the conventional process. This capability allows one to maintain a certain value of 6c and hence microbial growth rate chosen according to the desired effluent quality by varying the rate of return of microorganisms to the reactor. This can be accomplished with a short 6 and hence small reactor volume. 

Fig. 2.2-1. Flow sheet of a conventional solution recycling process for urea manufacture. [Taken from Fromm, D. and Liitow, D., Modern Processes in the Heavy Chemicals Industry Urea , Chemie in unserer Zeit 13, 78-81 (1979).]...

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