Feed stock recycling

Since the fresh feed stock charge of the reactor is a known and constant quantity, in order to determine the recycling coefficient it is necessary to calculate the total reactor charge (fresh feed stock+recycle material) after the steady state has been reached, when for the process being considered the quantity of recycle material becomes virtually constant. 

Solvent Extraction - Solvent extraction uses solvents to dissolve and remove aromatics from lube oil feed stocks, improving viscosity, oxidation resistance, color, and gum formation. A number of different solvents are used, with the two most common being furfural and phenol. Typically, feed lube stocks are contacted with the solvent in a packed tower or rotating disc contactor. Each solvent has a different solvent-to-oil ratio and recycle ratio within the tower. 

To set up and operationalize DTCs, an estimated time of 2-2.5 months would be required by PROs once they are selected. To import the recycling system, erect the commission in India, the estimated time would be around 4—5 months. It is preferred that if DTCs are imported in first instance and made operational as in initial months, there would not be any feed stock available for the recycling unit. Once their operation is stabilized, one can import recycling unit and commission it. These facilities would be required to obtain necessary consent to establish and operate and also to obtain authorization from respective SPCBs in the state where they are commissioned. 

The SSP plant for repelletized PET is similar to a virgin SSP plant. It is usually smaller, because of smaller feed stock availability, and should provide the flexibility to adapt to changing product requirements. Another difference results from the IV increase rate of recycled PET, which tends to be lower. This is attributed to a lower activity of the transesterification catalyst in recycled PET. 

The necessity for regeneration arises from the fact that catalyst activity declines with time on reaction, owing to small deposits of carbonaceous material and sulfur compounds on the catalyst. This deposit, of course, varies with feed stock, catalyst, and process conditions. The regeneration is carried out by oxidizing the deposits on the catalyst with a stream of air diluted to 2 to 3% oxygen with recycled flue gas. 

The feed stock, usually topped or reduced crude oil, is heated in pipe coils (Figure 1) from about 900° to 950° F. The oil is then fed to one of two or more vertical, insulated coke drums. The coke drums are connected by valves so that they can be switched onstream for filling, then switched off-stream for coke removal. The temperature in the drum will ordinarily be 775° to 850° F. and the pressure 4 to 60 pounds per square inch gage. Hot, coke-still vapors from the coke drum pass to a fractionator where gas and gasoline, intermediate gas oil, and heavy gas oil are separated. More or less of the heavy gas oil is recycled. The ratio of recycled heavy gas oil to fresh feed is usually less than 1 but may go up to about 1.6 (5,15,28, 40). 

Carbon blacks of lower particle size can be produced by diluting natural gas with recycled hydrogen. Fine thermal blacks (FT blacks) with mean primary particle sizes of 120-200 nm are manufactured in this way. Medium thermal blacks (MT blacks) with mean particle sizes of 300-500 nm are still produced and are obtained by using undiluted feed stock. The yield of MT blacks is about 40% with respect to the amount of feedstock and fuel used. 

Chemical manufacturing companies produce materials based on chemical reactions between selected feed stocks. In many cases the completion of the chemical reactions is limited by the equilibrium between feed and product. The process must then include the separation of this equilibrium mixture and recycling of the reactants. The fundamental process steps of bringing material together, causing them to react, and then separating products from reactants are common to many processes. 

Catalytic polymerization is a leading process of the refining industry in the production of high-quality motor fuels and certain petrochemicals. The Solid Phosphoric Acid catalytic process was developed by Vladimir Ipatieff and has since been extensively modified and improved. By this method the catalyst is loaded in a chamber or placed in tubes and the heated charge is passed through it. The olefinic feed stock generally is diluted with low-olefin recycle. 

Dynamic optimisation of this type of periodic operation was first attempted and reported in the literature by Mayur et al. (1970), who considered the initial charge to the reboiler as a fresh feed stock mixed with the recycled off-cut material from the previous distillation task. Each batch cycle is then operated in two distillation tasks. During the Task 1, a quantity of overhead distillate meeting the light product specification is collected. The residue is further distilled off in Task 2 until it meets the bottom product specification. The overhead during Task 2 meets neither specifications (but the composition is usually kept close to the that of the initial charge for thermodynamic reasons) and is recycled as part of the charge for the next batch. As the batch cycle is repeated a quasi-steady state mode of operation is attained which is characterised by the identical amount and composition of the recycle (from the previous batch) and the off-cut (from the current batch). Luyben (1988) indicates that the quasi-steady state mode is achieved after three or four such cycles. 

Reactor operating conditions vary over a considerable range depending upon the particular catalyst, feed stock, and desired conversion level. Once-through motor-gasoline operations are typically at conversions of 45 to 60% in partial-recycle operations, conversions up to 75% are commonly obtained (53,236). 

Yields obtained from reduced crudes vary with the feed stock and the extent of recycling, but are typically in the following ranges ... 

The underflow of the cyclone 7 is withdrawn by an eccentric worm pump 8 and delivered to a belt filter press 9 yielding a highly dewatered cake and a filtrate consisting essentially of water but loaded with small concentrations of sulfuric acid, furfural, and by-products. This filtrate is recycled to tank 1 for preparing the feed stock slurry. Due to this scheme, most of the sulfuric acid is recovered and reutilized, the only loss being the quantity contained in the cake. This loss is replaced in tank 1. Analogously, the water leaving the system with the cyclone vapor and the cake is also replenished in tank 1 so that the overall mass balance is satisfied. 

The cyclohexane vapors are condensed, separated by distillation, and recycled in the process. Three volumes of hydrogen are recycled for every volume of feed stock, which consists of cyclohexane containing 5 mol % benzene. To initiate a design for the reactor, calculate standard heat of reaction per g mol of CeHu. 

Water can act in this environment as a Bronsted base to neutralize some of the weaker zeolite acid sites. This effect is not harmful to any appreciable extent to the beta zeolite catalyst at typical feed stock moisture levels and under normal alkylation and transalkylation conditions. This includes processing of feedstocks up to the normal water saturation condition (typically 500-1000 ppm) resulting in 10-150 ppm water in the feed to the alkylation reactor dependent on feed and/or recycle stream fractionation efficiency. 

Another alternative to recycling is pyrolysis [6], While the idea of material resource recovery is attt ctive, a mixed-feed stock generally yields a pyrolysate of complex nature. Oie has but to remember the coal pyrolysis attempts of a generation ago to appreciate the difficulty of making effective use of a mixture of hundreds of chemical intem ates. 

Because of advanced computer control (auxostat mode) and an anaerobic culture, sterilization of the feed, aseptic techniques, and sparging of the broth are not required. Using standard equipment mills, waste paper would be shredded directly into the reactor. This avoids expensive pre-suspending of the paper in a separate tank, prevents microbial contamination of the feed stock, and circumvents difficult pumping of paper slurries. Once the acetic acid has been extracted, some of the broth could be recycled back to the reactor. If the product were mixed calcium/magnesium salts, the solution could be concentrated to form crystals and sold. While the process control is sophisticated, the overall system represents a low cost approach for the production of acetic acid mixed with small amounts of other acids. The obvious application is acetate salts for deicing of highways. 

Plastics recycling using the selective dissolution process can function with possibilities (iii) and (iv). Plastics collected locally would be shredded or compacted at or near the point of collection. They would then be shipped in bulk, typically by rail or water, to central sites for processing. The use of relatively few central sites would give good economies of scale and would allow the plants to be located where chemicals and plastics are now made. Selective dissolution is a chemical process which is yet another stage in the transformation of the original feed stock. It is therefore unreasonable to expect them to be recycled by strictly mechanical means. 

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