Depolymerization “fuel

Various processes have been developed for hydrolyzing lignocellulose to its major constituents, i.e., to sugars and (partly) depolymerized lignin. The lignin is usually precipitated from the aqueous solution and either used as chemical feedstock or burned as process fuel. The aqueous sugar solution is then applied for fermentation to ethanol after neutralization and purification. 

In the depolymerized scrap mbber (DSR) experimental process, ground scrap mbber tires produce a carbon black dispersion in oil (35). Initially, aromatic oils are blended with the tire crumb, and the mixture is heated at 250—275°C in an autoclave for 12—24 h. The oil acts as a heat-transfer medium and swelling agent, and the heat and oil cause the mbber to depolymerize. As more DSR is produced and mbber is added, less aromatic oil is needed, and eventually virtually 100% of the oil is replaced by DSR. The DSR reduces thermal oxidation of polymers and increases the tack of uncured mbber (36,37). Depolymerized scrap mbber has a heat value of 40 MJ/kg (17,200 Btu/lb) and is blended with No. 2 fuel oil as fuel extender (38). 

Bio-oil from rapid pyrolysis is usually a dark brown, free-flowing liquid having a distinctive smoky odor. It has significantly different physical and chemical properties compared to the liquid from slow pyrolysis processes, which is more like a tar. Bio-oils are multicomponent mixtures comprised of different size molecules derived primarily from depolymerization and fragmentation reactions of the three key biomass building blocks cellulose, hemicellulose, and lignin. Therefore, the elemental composition of biooil resembles that of biomass rather than that of petroleum oils. Basic properties of biooils are shown in Table 33.7. More detail on fuel-related characteristics is provided in the literature.571... 

W. Ding, J. Liang and L. L. Anderson. Depolymerization of waste plastics with coal over metal-loaded silica-alumina catalysts, Fuel Processing Technology, 49, 49-63 (1996). 

In the liquefaction step the plastic waste is cracked nnder relatively mild thermal conditions. This depolymerization results in a synthetic heavy oil and a gas fraction, which in part is condensable. The noncondensable fraction is nsed as a fuel in the process. The process is very comparable to the cracking of vacnnm residues that originate from oil recycling process. 

Neat polystyrene feedstocks will depolymerize in a pyrolysis process to give predominantly styrene monomer-a liquid fuel with good energy content. 

The ion-exchange catalyst dechlorinates the plastics (e.g. PVC) and therefore avoids issnes with HCl generation and chlorine contamination of the diesel. The company claims to have processed cable waste consisting of almost 100% PVC and the catalytic depolymerization process produced diesel fuel with a chlorine content below the detection limit. The catalyst needs to be activated before use via ion exchange using soda (sodium carbonate) and lime (calcium hydroxide) in order to insert the sodium and calcium ions... 

The Blowdec depolymerization process from Slovakia converts waste plastics into low-sulphur diesel fuel [35]. The main principle is the processing of waste plastics in a hot whirling bed of hot sand in the BLOWDEC reactor (Figure 15.19). The plastic is heated to 430°C. The process allows for simultaneous cracking of hydrocarbons and inhibition of coke formation. The fluidized sand bed products three types of cracking reactions mechano-activation thermal and catalytic (Si02/aluminosilicates). The process is covered under the US Patent 6,165,349. The process enables the economical conversion of mixed waste plastics into liquid hydrocarbons, mainly low-sulphur (25 ppm) diesel... 

---