Volatility hydrocracking

Upgrading of natural-gas liquids to motor fuels with customary technology used in the petroleum industry (isomerization, hydroisomerization, etc.) represents difficulties. One reason is that the volatility of motor fuels cannot be increased, thus limiting treatments such as hydrocracking. 

The volatile products from the soaking drum enter the fractionator where the distillates are fractionated into desired product oil streams, including a heavy gas oil fraction. The cracked gas product is compressed and used as refinery fuel gas after sweetening. The cracked oil product after hydrotreating is used as fluid catalytic cracking or hydrocracker feedstock. The residuum is suitable for use as boiler fuel, road asphalt, binder for the coking industry, and as a feedstock for partial oxidation. 

Figure 2.9 shows the species-specific evolution profiles for (a) paraffin (b) olefin and (c) alkyl aromatic volatile products for the PE-PtHZSM-5 sample heated in hydrogen. As expected, paraffins dominated the hydrocracking volatile product slate and olefin and alkyl aromatic yields were greatly reduced compared with results obtained when the same sample was heated in helium. The paraffin profile for the PE-PtHZSM-5 sample heated in hydrogen exhibited two maxima. Below 200°C, volatile product mixtures were composed entirely of paraffins. As the sample temperature increased, a wide range of... 

Sour water (hydrogen sulfide in water) is also obtained as aqueous condensate from the fractionation of the volatile products of refinery operations, such as the fluid catalytic cracker (FCC), hydrotreater, hydrocracker, or coker. In fact, in a refinery, which is endeavoring to minimize water use, sour waters may make up as much as 25% of the total aqueous effluent discharged. 

In the past, only ester- or PAO-based formulations could meet these performance criteria. Recently it has been demonstrated that compressor oils based on solvent-refined, hydrotreated or hydrocracked base stocks formulated with low-volatility, thermally stable antioxidants can also fulfil these targets. 

Base stocks falling in the group II category will, in the vast majority of cases, be hydrocracked stocks, since the low sulfur and high saturates limits (low aromatics of less than 10%) are otherwise difficult to attain. The majority of group II stocks produced have Vis of 95 to 105. Group 11+ is a commonly used industry subset (not a formal part of the API classification) defined by a VI in the range of 110 to 120 and created because of the current demand for the low volatility that accompanies these Vis. 

Gas-liquid reactions catalyzed by a solid catalyst are carried out in multiphase reactors. These reactors are usually used when the gaseous reactant is too volatile to liquefy or when the liquid reactant is too nonvolatile to vaporize. Typical examples are hydrogenation, desulfurization, and hydrocracking of petroleum feeds. Many different reactor configurations can result depending on the mode of feeding and the manner in which the catalyst is placed in the reactor. The two most common multiphase reactors are slurry and trickle-bed reactors, which have been described in some detail in Chapter 7. Since other reactor configurations can be analyzed in a similar manner as for slurry and trickle-bed reactors, attention here will be focused on these reactors. 

The gas phase consists of hydrocarbons vaporized by distillation processes and/or formed by cracking or other decomposition of fluids. Sulfur compounds, such as hydrogen sulfide and volatile mercaptans, often present in the gas phase, may be components of the original feed to the unit of interest, e.g. the crude still they may be formed by thermal degradation of disulfides, thiophenes, etc., or they may be the result of various hydrogenation processes such as hydrodesulfurizing, hydrocracking, etc. 

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