Hydrocrackers, fractionation

Corrosion problems have also occurred in compressors, sour water valve trims, expansion bellows, and hydrocracker fractionators. Type 4140 (UNS G41400) compressor impellers have sulfide cracked in sour gas when the hardness exceeded 235 Brine)i(e>. Hardened 12Cr valve trim has sulfide cracked to prevent this problem, 18Cr-8Ni SS trim in sour water service is commonly used. Sulfide cracking has not occurred significantly in pumps. 

The effectiveness of catalysts A and B to desulfurize SRN and blend naphtha was investigated and the results are shown in Table 4. Figure 4, which shows the performance of catalyst A, illustrates that it is easier to desulfurize SRN than blend naphtha. The results also confirmed higher HDS performance with blend naphtha than SRN with both catalysts. This could be due to the refractive material in the hydrocracked fraction of the blend naphtha. With blend naphtha and catalyst A the minimum total sulfur ofO.69 ppm was obtained at 320°C, while with SRN the minimum was 0.37 ppm at 300°C. Above these temperatures, the occurrence of H2S-alkene recombination reactions increased the total sulfur. Nickel-molybdenum catalysts are known to reduce recombination reactions by hydrogenating alkenes. Higher temperatures and very active catalysts can cause cracking at the reactor outlet allowing alkenes production[13],... 

Fig. 5. Selectivity to the different hydrocracked fractions obtained at ca. 55% hydrocracking conversion over NiMo-containing catalysts ( ) NiMo/ASA. (H )NiMo/USY. ( )NiMo/ ITQ-2. Gases C1-C4. Naphtha Cs-195 C. Middle distillates 195-360"C.

Hydrocracking Fractions b.p. 165-575°C/H,. e.g. Ni/Mo or Co/Mo as sulphides on silica/alumina. Pd/zeolite for hydrocracking. 316-482°C 68-204 atm i) Carbonium ion reactions as in cat. cracking. ii) Hydrogenation of aromatics and alkenes. Wide range of hydrocarbon fractions available. 

Hydrotreating and hydrocracking differ in other ways. For a given amount of feed, hydrocrackers use more catalyst and operate at higher pressures. They also use different catalysts. Because they make large amounts of light products, hydrocracker fractionation sections must be more complex. In some hydrocrackers, unconverted oil from the fiactionation section is recycled, either back to the front of the unit or to a separate cracking reactor. 

Two areas listed in Table 1 were not discussed—hydrocarbon-water binaries and petroleum fractions. For the former systems only eight systems of experimental VLE data (ethylene, propylene, 1-butene, 1-hexene, n-hexane, cyclohexane, benzene, and n-nonane) were available. Use of solubility data and calculated VLE data added only five more systems (propane, propyne, cyclopropane, n-butane, and 1,3-butadiene). For petroleum fraction systems only three sources and seven systems have been characterized well enough to use in analytical correlations to be tested. These systems Include three naphtha-fuel oil systems, two hydrogen-hydrocrackate fractions, and two hydrogen-hydrogen sulfide-hydrocrackate fractions. No reasonable work can be done without additional data. 

Properly speaking, steam cracking is not a refining process. A key petrochemical process, it has the purpose of producing ethylene, propylene, butadiene, butenes and aromatics (BTX) mainly from light fractions of crude oil (LPG, naphthas), but also from heavy fractions hydrotreated or not (paraffinic vacuum distillates, residue from hydrocracking HOC). 

This form of limited-conversion hydrocracking is a process that selectively prepares high quality residues for the special manufacture of base oils of high viscosity index or treating residues having low BMCl for the conversion of heavy fractions to ethylene, propylene, butadiene and aromatics. 

British Coal Corp. is developing a gasoline-from-coal process at a faciUty at Point of Ayr (Scotiand). This process involves treatment with Hquid recycle solvents, digestion at 450—500°C, filtration to separate unconverted residues, and separation into two fractions. The lighter fraction is mildly hydrotreated, and the heavier one is hydrocracked (56). 

Solvents. Petroleum naphtha is a generic term appHed to refined, pardy refined, or unrefined petroleum products. Naphthas are prepared by any of several methods, including fractionation of distillates or even cmde petroleum, solvent extraction, hydrocracking of distillates, polymerization of unsaturated (olefinic) compounds, and alkylation processes. Naphtha can also be a combination of product streams from more than one of these processes. 

Catalytic Reforming. Worldwide, approximately 30% of commercial benzene is produced by catalytic reforming, a process ia which aromatic molecules are produced from the dehydrogenation of cycloparaffins, dehydroisomerization of alkyl cyclopentanes, and the cycHzation and subsequent dehydrogenation of paraffins (36). The feed to the catalytic reformer may be a straight-mn, hydrocracked, or thermally cracked naphtha fraction ia the... 

In addition to straight run naphthas, 70—190°C cuts obtained by distillation from streams produced by cracking high boiling petroleum fractions can also be used as feed to reformers. Naphthas produced by hydrocracking are particularly suitable. 

Solvents are recovered from the oil stream through distillation and steam stripping in a fractionator. The stream extracted from the solvent contains high concentrations of hydrogen sulfide, aromatics, naphthenes and other hydrocarbons, and is often fed to the hydrocracking unit. 

Product separation for main fractionators is also often called black oil separation. Main fractionators are typically used for such operations as preflash separation, atmospheric crude, gas oil crude, vacuum preflash crude, vacuum crude, visbreaking, coking, and fluid catalytic cracking. In all these services the object is to recover clean, boiling range components from a black multicomponent mixture. But main fractionators are also used in hydrocracker downstream processing. This operation has a clean feed. Nevertheless, whenever you hear the term black oil, understand that what is really meant is main fractionator processing. 

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