Waste liquefaction, solid

This paper discusses in depth advanced technologies for recycled materials from solid waste streams. Chemical depolymerisation, thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification, partial oxidation, and feedstock compatibility are all explained. The economic feasibility of the methods are considered. 

Kaufman, J.A. and Weiss, A.H., "Solid Waste Conversion Cellulose Liquefaction", Report No. EPA-670/2-75-031, Nat. Environmental Research Center, Office of R D, U.S. Environmental Protection Agency, Cincinnati (1975). 

Figure 3.17 Flowsheet of a waste plastic liquefaction plant based on thermal cracking and subsequent catalytic reforming [102]. (Reproduced by permission of the International Solid Waste Association (ISWA))...

According to a US patent [46], cracking or liquefaction of waste plastics is realized in a sequential three- or four-screw extruder system with increasing process temperature. Similarly, the catalyst (if used) is discharged with coke and mineral residue. At the end of the process, the distillable hydrocarbon fraction is separated from solid residue and coke. 

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). 

Ruynal, J., Delgenes, J. P., and Moletta, R. (1998). Tow phase anaerobic digestion of solid waste by a multiple liquefaction reactors process. Bioresour. Technol. 65, 97-103. 

Jones, J.L., Phillips, R.C., Takaoka, S., and Lewis, F.M., "Pyrolysis, Thermal Gasification, and Liquefaction of Solid Wastes and Residues - Worldwide Status of Processes," Presented at the ASME 8th Biennial National Waste Processing Conference, Chicago, May 1978. 

White. D. H. et al. Fundamentals of Direct Liquefaction of Municipal Solid Waste In a Seml-Contlnuous Microprocessor-Controlled Autoclave Argonne National Laboratory, ANL/CNSV-TM-180 (1986). 

Solid Waste Streams from Coal Liquefaction Processes... 

A coal liquefaction plant generates three main types of solid-waste materials ash and slag from the reactors, sludge from various waste-water treatment units, and spent catalysts from the various catalytic units (Table 25.5). 

Kaufman, J.A. Weiss, A.H. (1975). Solid Waste Conversion Cellulose Liquefaction. Report prepared for the US National Environmental Research Centre by the Worcester Polytechnic Institute, USA... 

The ORC flash pyrolysis process has been used with minor modifications to process municipal and industrial solid wastes. The emphasis is on liquid yield. More preparation of the feed is involved than for coal gasificaltion or coal liquefaction. A process schematic is shown in Figure 3. In addition to grinding and drying, an air classification process and screening are used... 

Waste materials such as municipal solid waste, scrap tires, and waste plastics have traditionally been placed in sanitary landfills. However, with landfill space rapidly decreasing in the United States and worldwide, an alternative disposal method for these waste materials becomes imperative. The recycling of solid wastes is a challenging problem, with both economic and environmental constraints. Recently, two broad approaches have been attempted to reclaim solid wastes. The first approach relies on thermal or catalytic conversion of waste materials into fuel and valuable chemical feedstocks. Examples of this approach include gasification, pyrolysis, depolymerization, and liquefaction. The second approach relies on the physical recovery of valuable ingredients in the waste materials. 

In conclusion, the technology of total liquefaction of apple allows to work with a continuous process with less labour and faster than with a classical one, to get a high and constant yield during the whole processing season at a very high level (93- 95%), to get a pulp with a low content of solids (about 20% in volume) which can be centrifuged instead of pressed (lower investment in equipment), to decrease the quantity of waste pomace, to decrease the production costs. Liquefaction technology allows to process different fruits with the same process, at last to liquefy fruits for which no equipment had been developed to extract the juice or for which the use of pectinases did not allow to get juice such as tropical fruits. 

Various catalysts were examined to increase the products obtained from thermochemical reaction of biomass. Appell and co-workers demonstrated that solid organic materials, including urban refuse, agricultural wastes, wood and bovine manure, can be converted directly to heavy fuel oil in the presence of a catalyst such as sodium carbonate. Since then, a great number of works have been reported on the direct liquefaction of biomass in the presence of suitable catalysts. Recent publication, the addition of Na2C03 greatly increased the reaction rate. Minowa et... 

---