Naphtha from hydrocracking

Two stages of hydrotreatment were used to reduce further oxygen and especially nitrogen and sulfur contents in the naphtha from hydrocracking LGO. A catalyst of Ni/Mo on A1203 (Table II) was used in a 1-in. diameter trickle bed reactor at 400°C, 1500 psig, 5 M scf H2/bbl, and 4.8 LHSV in the first pass and at 450°C and 1.5 LHSV for recycle of the naphtha successively distilled off. 

The compositions of progressively processed naphtha were also determined by mass spectrographic analysis and are summarized in Table VI. These show the expected shifts from paraffins in the straight-run naphtha as well as naphtha from hydrocracking LGO to aromatics, especially benzenes in the reformate. 

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). 

Heavy naphtha from atmospheric distillation units or hydrocracking... 

For all of the hydrocracker operations, the feed properties are those of the heavy naphtha from the base crude mix blended with a specified fraction of light cycle oil from the base FCC operation. For all of the motor reformer operations, the feed properties are those of the motor naphtha from the base crude mix blended with heavy hydrocrackate from the base hydrocracker operation. For all of the BTX reformer operations, the feed properties are those of the BTX naphtha from the base crude mix blended with light hydrocrackate from the base hydrocracker operation. Finally, for each process unit, the process simulator computes the change in plant performance associated with a fixed perturbation of each feed property about the base operation. 

After hydrotreating naphtha ex hydrocracking Reformate (from naptha ex hydrocracking LGO)... 

Catalytic reforming processes gasolines and naphthas from the distillation unit into aromatics. Four major reactions occur dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to aromatics, isomerization, and hydrocracking. 

Sections 1, 2, 3, and 4 were now being used to fractionate between naphtha and hydrocracker feed. The loss in naphtha product to hydrocracker feed fell from 35% to 5%. The slurry oil pumparound draw temperature, while somewhat reduced, was still hot enough to maintain the fractionator heat balance. While this change did nothing to enhance top reflux distribution, it did bring all products back on spec without an FCCU shutdown. 

As shown in Figure 1, hydrocracking often is an in-between process. The required hydrogen comes from catalytic reformers, steam/methane reformers or both. Liquid feeds can come from atmospheric and/or vacuum distillation units delayed cokers fluid cokers visbreakers or FCC units. Middle distillates from a hydrocracker usually meet or exceed finished product specifications, but the heavy naphtha from a hydrocracker usually is sent to a catalytic reformer for octane improvement. The fractionator bottoms can be recycled or sent to an FCC unit, an olefins plant, or a lube plant. 

Thus, one might design a saturates gas plant to process the total naphtha from a crude unit plus light ends from all other sources of saturated hydrocarbons within the complex. This could include hydrotreaters, hydrocrackers, isomerizers and catalytic reformers. The unsaturates gas plant would be designed to process total light ends from all sources of unsaturated hydrocarbons. This could include... 

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. 

Naphtha is also obtained from other refinery processing units such as catalytic cracking, hydrocracking, and coking units. The composition of naphtha, which varies appreciably, depends mainly on the cmde type and whether it is obtained from atmospheric distillation or other processing units. 

Naphthas obtained from cracking units generally contain variable amounts of olefins, higher ratios of aromatics, and branched paraffins. Due to presence of unsaturated compounds, they are less stable than straight-mn naphthas. On the other hand, the absence of olefins increases the stability of naphthas produced by hydrocracking units. In refining operations, however, it is customary to blend one type of naphtha with another to obtain a required product or feedstock. 

Kerosine, a distillate fraction heavier than naphtha, is normally a product from distilling crude oils under atmospheric pressures. It may also he obtained as a product from thermal and catalytic cracking or hydrocracking units. Kerosines from cracking units are usually less stable than those produced from atmospheric distillation and hydrocracking units due to presence of variable amounts of olefinic constituents. 

This reaction is endothermic and is favored by low pressure. In practice, however, the process is conducted at a pressure of 1-3 MPa (because of a concurrent hydrocracking reaction) and a temperature of 300-450°C using Pt-based catalysts [7]. The feedstock for the reforming process must be carefully purified from S- and N-compounds (below 1 ppm), which may use up a significant portion of hydrogen produced. The typical composition of the off-gas from the catalytic reforming of naphtha is as follows (vol%) H2—82, CH4—7, C2—5, C3—4, and C4—2 [7]. 

In the hydrocracking process, this phenomenon is exploited to shift catalyst selectivity from the naphtha to the distillate products. Here the wide separation of sites is exploited to minimize the potential for secondary cracking in initial products and intermediates. This, along with the introduction of escape routes for the primary product tends to preserve the higher molecular weight hydrocarbons, thereby producing more dishllates [49, 61, 62]. 

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