Selectivity feedstocks

A detailed study of the properties of the potential products is of prime technical and economic importance, because it allows the refiner to have a choice in selecting feedstocks for his different units for separation, transformation and conversion, to set their operating conditions, in order to satisfy the needs of the marketplace in the best ways possible. 

The question then lies in the selection of more appropriate feedstocks for these two processes. The cost of hydrocracking leads to selecting feedstocks that are the easiest to convert as for catalytic cracking, its flexibility and extensive capabilities lead to selection of heavier feedstocks. 

The feedstock is usually extracted toluene, but some reformers are operated under sufftciendy severe conditions or with selected feedstocks to provide toluene pure enough to be fed directiy to the dealkylation unit without extraction. In addition to toluene, xylenes can also be fed to a dealkylation unit to produce benzene. Table 20 Hsts the producers and their capacities for manufacture of benzene by hydrodealkylation of toluene. Additional information on hydrodealkylation is available in References 50 and 52. 

Estimated Costs of Producing Ethanol from Selected Feedstocks for a 40 Million-Gal Facility ( /gal of ethanol)... 

In the particular reactor system employed, structure of the black is more easily controlled by injecting the selected feedstock as a liquid, rather than as a vapor or gas. In this case, the distribution of the oil injected into the combustion chamber can be controlled by mechanical means. The point of initiation of the reaction can also be moved along a line in the reactor to make it short or long at will. Structure then is more dependent upon the feedstock, its boiling range and preheat temperature, and the point within the reactor selected for reaction initiation. Structure can also, of course, be altered downward through the use of feedstock additives. 

The data presented suggest the possibility of selecting feedstock or raw materials for a specific product mix. The quality of both the liquid and gaseous products indicates the advantages of indirect reactions with applied microwave power. 

In order to carry out the transformation of selected feedstock into the target molecule the criteria of efficiency, availability and effect of the reagent used must be kept in mind. Some of the green reagents are as follows. 

Needle coke, a premium grade with distinctive needle-shape particles, produced by delayed coking from selected feedstocks with low concentration of insolubles. It is used in applications requiring high thermal-shock resistance and low electrical resistivity. 

Greater flexibility, particularly with regard to selecting feedstock... 

Table 5.15 gives some physical-chemical characteristics of selected main refinery streams capable of being added to the diesel fuel pool. Also shown is the weight per cent yield corresponding to each stock, that is, the quantity of product obtained from the feedstock. 

For the refiner, the main problem is to meet the specifications for kinematic viscosity and sulfur content. Dilution by light streams such as home-heating oil and LCO, and selection of feedstocks coming from low-sulfur crude oils give him a measure of flexibility that will nevertheless lead gradually to future restrictions, most notably the new more severe antipollution rules imposing lower limits on sulfur and nitrogen contents. 

Solvent deasphalting. This is an extraction of the heaviest fractions of a vacuum residue or heavy distillate. The extract is used to produce the bitumen. The separation is based on the precipitation of asphaltenes and the dissolution of the oil in an alkane solvent. The solvents employed are butane or propane or a butane-propane mixture. By selecting the proper feedstock and by controlling the deasphalting parameters, notably temperature and pressure, it is possible to obtain different grades of bitumen by this process. 

Liquefied gas fractions (propane, propylene, butanes, butenes) that will be able to provide feedstocks to units of MTBE, ETBE, alkylation, dimerization, polymerization after sweetening and/or selective hydrogenation. 

In two stages with recycle to the second stage, the conversion per pass is approximately 50 wt. % and the selectivity to middle distillates is maximal 75 to 80 wt. %. However, the investment is clearly higher and is justified only when feedstocks are difficult to convert and that their content in nitrogen is high. Figure 10.11 represents two variants of the hydrocracking process. 

Simple conventional refining is based essentially on atmospheric distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used. 

The mole fractions of various dyads in the vinylidine chloride (Mi)-isobutylem (Mj) system were determinedf by NMR spectroscopy. A selection of the value obtained are listed below, as well as the compositions of the feedstocks fron which the copolymers were prepared ... 

Cyclohexane, produced from the partial hydrogenation of benzene [71-43-2] also can be used as the feedstock for A manufacture. Such a process involves selective hydrogenation of benzene to cyclohexene, separation of the cyclohexene from unreacted benzene and cyclohexane (produced from over-hydrogenation of the benzene), and hydration of the cyclohexane to A. Asahi has obtained numerous patents on such a process and is in the process of commercialization (85,86). Indicated reaction conditions for the partial hydrogenation are 100—200°C and 1—10 kPa (0.1—1.5 psi) with a Ru or zinc-promoted Ru catalyst (87—90). The hydration reaction uses zeotites as catalyst in a two-phase system. Cyclohexene diffuses into an aqueous phase containing the zeotites and there is hydrated to A. The A then is extracted back into the organic phase. Reaction temperature is 90—150°C and reactor residence time is 30 min (91—94). 

Olefin Feedstock Selection. The selection of feedstock and severity of the cracking process are economic choices, given that the specific plant has flexibiUty to accommodate alternative feedstocks. The feedstock prices are driven primarily by energy markets and secondarily by supply and demand conditions ia the olefins feedstock markets. The prices of iadividual feedstocks vary widely from time to time as shown ia Figure 2, which presents quarterly prices of the various feedstocks ia the United States from 1978 through 1991 ia dollars per metric ton (1000 kg) (4). 

Alternative feedstocks for petrochemicals have been the subject of much research and study over the past several decades, but have not yet become economically attractive. Chemical producers are expected to continue to use fossil fuels for energy and feedstock needs for the next 75 years. The most promising sources which have received the most attention include coal, tar sands, oil shale, and biomass. Near-term advances ia coal-gasification technology offer the greatest potential to replace oil- and gas-based feedstocks ia selected appHcations (10) (see Feedstocks, coal chemicals). 

Feedstock Development. Most of the research in process in the United States in the early 1990s on the selection of suitable biomass species for energy appHcations is limited to laboratory studies and small-scale test plots. Many of the research programs on feedstock development were started in the 1970s or early 1980s. 

An early source of glycols was from hydrogenation of sugars obtained from formaldehyde condensation (18,19). Selectivities to ethylene glycol were low with a number of other glycols and polyols produced. Biomass continues to be evaluated as a feedstock for glycol production (20). 

Naphtha at one time was a more popular feed, and alkah-promoted catalysts were developed specifically for use with it. As of 1994 the price of naphtha in most Western countries is too high for a reformer feed, and natural gas represents the best economical feedstock. However, where natural gas is not available, propane, butane, or naphtha is preferentially selected over fuel oil or coal. 

Process Technology Evolution. Maleic anhydride was first commercially produced in the early 1930s by the vapor-phase oxidation of benzene [71-43-2]. The use of benzene as a feedstock for the production of maleic anhydride was dominant in the world market well into the 1980s. Several processes have been used for the production of maleic anhydride from benzene with the most common one from Scientific Design. Small amounts of maleic acid are produced as a by-product in production of phthaHc anhydride [85-44-9]. This can be converted to either maleic anhydride or fumaric acid. Benzene, although easily oxidized to maleic anhydride with high selectivity, is an inherently inefficient feedstock since two excess carbon atoms are present in the raw material. Various compounds have been evaluated as raw material substitutes for benzene in production of maleic anhydride. Fixed- and fluid-bed processes for production of maleic anhydride from the butenes present in mixed streams have been practiced commercially. None of these... 

The 0x0 process is employed to produce higher alcohols from linear and branched higher olefins. Using a catalyst that is highly selective for hydroformylation of linear olefins at the terminal carbon atom. Shell converts olefins from the Shell higher olefin process (SHOP) to alcohols. This results in a product that is up to 75—85% linear when a linear feedstock is employed. Other 0x0 processes, such as those employed by ICI, Exxon, and BASE (all in Europe), produce oxo-alcohols from a-olefin feedstocks such alcohols have a linearity of about 60%. Enichem, on the other hand, produces... 

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