Pyrolysis and Hydroprocessing

Although direct liquefaction of waste plastic looked promising, problems associated with impurities (paper, aluminum, etc.) and chlorine derived from PVC caused operational difficulties. Consequently, it currently appears that the first step of any feedstock recycling process for waste plastics or tires should be pyrolysis, which allows much easier separation of solid impurities and chlorine. Research on pyrolysis of post-consumer plastic has been carried out by Kaminsky and co-workers [17, 18], Conrad Industries [19, 20], and Shah et al. [21]. Shah et al. [21] conducted pyrolysis experiments on relatively dirty post-consumer waste plastic obtained from the DSD. The pyrolysis oils were then subjected to hydroprocessing to convert them into high-quality transportation fuels (gasoline, kerosene, diesel). 

Chlorine derived from PVC is the impnrity of most concern in oil prodnced from waste plastic. Because the DSD plastic contained 1.26 wt% Cl, measnres were reqnired to remove it in these experiments. To lower the chlorine content of the oil prodncts, small additions (2-3 wt%) of sodinm carbonate were made to both the pyrolysis and 

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N. Shah, J. Rockwell and G. P. Huffman. Conversion of waste plastic to oil direct liquefaction versus pyrolysis and hydroprocessing. Energy and Fuels, 13, 832-838 (1999). 

Production of Premium Oil Products from Waste Plastic by Pyrolysis and Hydroprocessing... 

Figure 27.3 Rotary kiln pyrolyzer [2], 1 thermometer 2 bearing 3 gear transmission 4 electric furnace 5 rotary kiln 6 temperature controller 7 seal 8 two-step condenser 9 filter 10 total flowmeter 11 computer 12 gas sampler 13 feed and discharge opening 14 adjustable-speed motor. (Adapted from Shah, N., Rockwell, J. and Huffman, G.P., Conversion of Waste Plasticto Oil Direct Liquefaction versus Pyrolysis and Hydroprocessing, Energy Fuels, 13, 832-838 (1999))...

Elliott, D.C., 2013. Transportation fuels from biomass via fast pyrolysis and hydroprocessing. WIRES Energy and Environment, http //dx.doi.org/10.l(X)2/wene.74. 

Soltes, E.J. Lin, S-C.K. Sheu, Y-H.E. "Catalyst specificities in high pressure hydroprocessing of pyrolysis and gasification tars." In Production. Analysis and Upgrading of Oils from Biomass. Vorres,... 

Elliott, D.C., Wang, H., French, R., Deutch, S., lisa, K., 2014. Hydrocarbon liquid production from biomass via hot-vapor filtered fast pyrolysis and catalytic hydroprocessing of the biooil. Energy Fuels 28, 5909—5917. 

The liquefaction of solid biomass followed by hydrotreating is viewed as an attractive route to the production of petroleum like liquid fuels [1], While liquefaction processes (e.g. high pressure liquefaction or fast pyrolysis) have already been demonstrated at a relatively large scale [2], the hydroprocessing step still requires development and demonstration. 

Figure 13.4 Simdist analysis of pyrolysis oil from DSD waste plastic before and after thermal or catalytic hydroprocessing. (Reproduced by permission of the American Chemical Society)...

Transportation fuel. For mixed post-consumer plastic (PCP) that contains significant amounts of paper, inorganics, and chlorine, the best approach appears to be pyrolysis followed by hydroprocessing. Batch mode pyrolysis at 600°C, followed by thermal or... 

Other types of biomass pyrolysis oil produced under less specified conditions, typically longer residence time or lower temperature, will have a different chemical composition and will therefore have different chemical and physical properties. Such Uquids will also be produced in lower yields in conjunction with higher gas and solid byproducts. The hydroprocessing described in this chapter has been developed to address the properties of fast pyrolysis bio-oil. A more detailed discussion of fast pyrolysis can be found in chapter Catalytic fast pyrolysis for improved liquid quality . 

The future for hydrothermal liquefaction and subsequent hydrotreating may be more straightforward. Although the biomass conversion process development lags years behind fast pyrolysis, the increasing interest in the R D community and the perception of a more simple hydroprocessing step is likely to move the technology forward more quickly. 

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