Feedstock recycling product yield

Characteristics of feedstock quality, recycle ratio, and drum pressure affect the coke yield. Highly aromatic feedstock contains more carbon per feed volume and typically produces a high coke yield. Heavy coker gas oil can be recycled back into the coker feedstock to help improve the coke yield. Also, increasing the coking drum pressure tends to increase the coke yield. Typically, a higher coke yield results in a reduced liquid product yield. 

The detailed analysis of the derived oil/wax and gas products from the pyrolysis of plastics in relation to process conditions and different types of plastic is essential in providing data for the assessment of the feedstock recycling process. In addition, the yields and composition of gases and oils from the pyrolysis of mixed plastic waste are important in assessment of the process and to determine the possibility of any interactions between the plastics during pyrolysis. 

Product Yield from the Feedstock Recycling of Single Plastics... 

With methyl acetate at 200 C and 34.5 MPa and a Co-LiI-NPh3 catalyst the acetaldehyde yield is nearly quantitative. In the reductive carbonyiation of CH3OH, the product mixture contains a wide variety of compounds including methyl acetate, acetic acid, 1,1-dime-thoxyethane and copious amounts of H2O. Separating acetaldehyde from this mixture is difficult. In contrast, with a methyl ester feedstock, the product mixture is anhydrous and acetaldehyde is readily distilled from RC(0)OH. RC(0)OH is esterified in a separate step and recycled. The simplified reaction mechanism for methyl acetate is ... 

The severe limitations on the mechanical recycling of plastic wastes highlight the interest and potential of feedstock recycling, also called chemical or tertiary recycling.17,18 It is based on the decomposition of polymers by means of heat, chemical agents and catalysts to yield a variety of products ranging from the starting monomers to mixtures of compounds, mainly hydrocarbons, with possible applications as a source of chemicals or fuels. The products derived from the plastic decomposition exhibit properties and quality similar to those of their counterparts prepared by conventional methods. 

Table 2.2 lists the pyrolysis product yields for different feedstocks treated at very high severity with recycle of the ethane produced or unconverted at the inlet of the reaction section. Indeed, ethane is an ideal raw material for the formation of the lower olefins. It may be observed that the relative production of ethylene decreases as the feedstock becomes heavier. Also worth noting is that the ratio of the ethylene and propylene yields (C2J CJ ratio) decreases steadily from ethane to the gas oils, whereas the percentage of pyrolysis gasoline (CS-20G°C cut) increases simultaneously. As to the butadiene yield, this varies slightly with the type of feedstock in the treatment of liquid petroleum fractions. 

The most interesting variant on the basic thermochemical liquefaction process involves the addition of an overpressure of carbon monoxide and hydrogen to the reaction, which is also performed in a non-aqueous solvent (anthracene oil or recycled product oil). Yields of oil up to 70% of the weight of the Douglas fir wood feedstock have been reported in an investigation by Elliott (4-8), Elliott and Walkup ( and Elliott and Giacoletto (10). This process variant (also known as the Albany, PERC, or CO-Steam Process) is described in more detail in the Results and Discussion section. 

The ideal HMF production process would use raw biomass as its feedstock, without the necessity for extensive drying or pretreatment (apart fi om mechanical reduction to particle sizes which do not suffer mass transfer limitations). Reactions would proceed in high yield over short time scales under mild conditimis in inexpensive media and use simple, non-foulable catalysts. The HMF product would be isolated without recourse to distillation or protracted solvent extraction, and all materials would be easily recyclable. Except for product yield, none of these objectives has currently been met in such a way as to be reducible to practice on an industrial scale. In the end, it is a matter of economics. When the dust settles, only the most competitive, industrially viable processes will be left standing, and the rest will be consigned to history. 

Table 6.6.1 Product yields (wt%) in the steam cracker process as a function of the feedstock applied (high severity cracking) -the figures in the table assume that all light alkanes (C2-C4) are recycled to the cracker (Crantom eta ., 1987 HaertI eta ., 1996).

In a single stage with liquid recycle, total conversion to products lighter than the feedstock is possible. The yield of kerosene plus diesel is between 70 and 73 weight %. 

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

The recovery area of the plant employs fractionation to recover and purify the phenol and acetone products. Also in this section the alpha-methylstyrene is recovered and may be hydrogenated back to cumene or recovered as AMS product. The hydrogenated AMS is recycled as feedstock to the reaction area. The overall yield for the cumene process is 96 mol %. Figure 1 is a simplified process diagram. 

Methane, chlorine, and recycled chloromethanes are fed to a tubular reactor at a reactor temperature of 490—530°C to yield all four chlorinated methane derivatives (14). Similarly, chlorination of ethane produces ethyl chloride and higher chlorinated ethanes. The process is employed commercially to produce l,l,l-trichloroethane. l,l,l-Trichloroethane is also produced via chlorination of 1,1-dichloroethane with l,l,2-trichloroethane as a coproduct (15). Hexachlorocyclopentadiene is formed by a complex series of chlorination, cyclization, and dechlorination reactions. First, substitutive chlorination of pentanes is carried out by either photochemical or thermal methods to give a product with 6—7 atoms of chlorine per mole of pentane. The polychloropentane product mixed with excess chlorine is then passed through a porous bed of Fuller s earth or silica at 350—500°C to give hexachlorocyclopentadiene. Cyclopentadiene is another possible feedstock for the production of hexachlorocyclopentadiene. 

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