Plastic wastes hydrogenation

Considering the preservation or saving of the material, the material recycling is the most effective procedure. The usable fractions are about 70 to 80 % [6]. Also raw-material recycling processes achieve an output of 70 up to 80 %, exceptional the pyrolysis of mixed plastics waste. Hydrogenation of a clean... 

Feedstock recycling is examined as a method of plastics recovery. The range of techno logics currently employed are described, and include pyrolysis, hydrogenation, gasification, and chemolysis. Methods for the recycling of mixed plastics wastes are discussed, which include work by BP Chemicals, VEBA Oil, Shell Chemicals and Leunawerke. 

Current methods of feedstock recovery are reviewed. Brief details are given of pyrolysis, hydrogenation, gasification, and chemolysis. Activities of some European companies are briefly discussed in the areas of recycling mixed plastics waste and closed-loop recycling. 

Activity of these catalysts depends on the balance between the hydrogenation and acidic functions. For example, it was found that HZSM-5 was effective for the hydrocracking of HDPE and plastic waste [24]. But the liquid product contained much less n-paraffins and a greater amounts of aromatics (34%) and naphthenes (21.7%) because of a lack of sufficient hydrogenation function. The reaction mechanism over HZSM-5 can be considered as follows ... 

Based on the above results, it can be mentioned that the catalyst having both hydrogenation and acidic functions can successfully convert heavy oil derived from plastic wastes (relatively clean) into environmentally acceptable transport fuels. However, for the heavy oils containing impurities, the dual functional hydrocracking catalysts still need to be improved. In the hydrocracking process over the acidic catalyst, nitrogen content in feed is limited because basic nitrogen compounds poison the acidic sites of the catalyst. 

Thermal cracking often yields a low-value mixture of hydrocarbons with a very broad volatility range that can extend from hydrogen to coke. It is therefore important to determine the optimal pyrolysis conditions and/or the most advantageous catalyst to obtain marketable products (e.g. diesel fuel) from mixed plastic wastes. 

A major shortcoming of zeolite-type catalysts is their sensitivity to hydrogen chloride and HCl acid, which canses destrnction of a catalyst in concentrations above 200 ppm HCl. Considering the fact, plastic wastes often contains PVC the application of expensive zeolite-type catalysts is disadvantageons. 

High-temperature pyrolysis (650-800°C) of plastic waste, fed into the rotary kiln via a screw feeder. Solid cokes and pyrolytic vapours are sent to further treatments in gasification or hydrogenation plant... 

Co-pyrolysis of wood biomass and plastic wastes of different origin under the pressure of argon and hydrogen... 

Unused reactants can be recycled and off-specification product reprocessed. Integrated processes can be selected the waste from one process becoming the raw material for another. For example, the otherwise waste hydrogen chloride produced in a chlorination process can be used for chlorination using a different reaction, as in the balanced, chlorination-oxyhydrochlorination process for vinyl chloride production. It may be possible to sell waste to other companies, for use as raw material in their manufacturing processes for example, the use of off-specification and recycled plastics in the production of lower grade products, such as the ubiquitous black plastic bucket. 

For the pyrolysis of plastic waste with a high PVC content, it is probably better to first dehydrohalogenize it in a reactor with added sand. Tests have shown that hydrogen chloride gas can be produced from PVC at temperatures of between 350 and 400°C, which is up to 99 % pure and, after adsorption of the residual hydrocarbons, may be used to make very pure hydrochloric acid. After treating PVC for 20 minutes at a temperature of 350°C, more than 90 % of the bound chloride has split off. This time is reduced to less than 10 minutes if the temperature is increased to 400°C (13). ... 

If the PVC content of the plastic waste is low, the hydrogen chloride produced can be absorbed either directly in the fluidized bed to which calcium oxide or magnesium oxide is added, or in a separately connected fluidized bed. This method has proved satisfactory, at least for the absorption of hydrogen fluoride in the pyrolysis of PTFE-containing plastic wastes and for hydrogen sulfide in the pyrolysis of rubber. 

Oxidation of waste plastics, such as polyethylene, polypropylene, polystyrene, poly (alkyl acrylates), and nylon 6,6, with NO/O2 for 16 h at 170°C, led to mixtures of carboxylic acids, for which uses would have to be developed if this method was applied to large volumes of waste plastics.180 Hydrogenation of polyethylene at 150C>C for 10 h over a sil-ica/alumina-supported zirconium hydride catalysts gave a 100% conversion to saturated oligomers.181 Polypropylene gave a 40% conversion to lower alkanes at 190°C for 15 h. It is not clear what use these materials would have, other than serving as a feedstock for a petroleum refinery. 

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