Hydroconversion

The main feedstock for catalytic reforming is heavy gasoline (80 to 180°C) available from primary distillation. If necessary, reforming also converts byproduct gasoline from processes such as visbreaking, coking, hydroconversion and heart cuts from catalytic cracking. 

Feedstocks are light vacuum distillates and/or heavy ends from crude distillation or heavy vacuum distillates from other conversion processes visbreaking, coking, hydroconversion of atmospheric and vacuum residues, as well as deasphalted oils. 

The residue hydroconversion process applies to both atmospheric and vacuum residues. 

Typical Feedstocks Performance and product properties from residue hydroconversion (to be continued). 

Intermediate feedstock preparation processes such as direct hydroconversion of vacuum residues, solvent deasphalting, improved coking will also make their appearance. 

American Petroleum Institute atmospheric residue atmospheric residue hydroconversion American Society for Testing and Materials Association pour la Valorisation des Huiles Lourdes Anstalt fur Verbrennungskraftmaschinen List Bureau of Mines Correlation Index bromine number... 

Another hydrogenation process utilizes internally generated hydrogen for hydroconversion in a single-stage, noncatalytic, fluidized-bed reactor (41). Biomass is converted in the reactor, which is operated at about 2.1 kPa, 800°C, and residence times of a few minutes with steam-oxygen injection. About 95% carbon conversion is anticipated to produce a medium heat value (MHV) gas which is subjected to the shift reaction, scmbbing, and methanation to form SNG. The cold gas thermal efficiencies are estimated to be about 60%. 

In the other market areas, lead naphthenates are used on a limited basis in extreme pressure additives for lubricating oils and greases. Sodium and potassium naphthenates are used in emulsiftable oils, where they have the advantage over fatty acid soaps of having improved disinfectant properties. Catalyst uses include cobalt naphthenate as a cross-linking catalyst in adhesives (52) and manganese naphthenate as an oxidation catalyst (35). Metal naphthenates are also being used in the hydroconversion of heavy petroleum fractions (53,54) and bitumens (55). 

Schematic representation of a typical two-stage hydroconversion unit. The reactors contain multiple catalyst beds and quench zones. The second stage reactor is a recycle reactor.

Huybrechts, W., Mijoin, J., Jacobs, P.A. et al. (2003) Development of a fixed-bed continuous-flow high-throughput reactor for long-chain n-alkane hydroconversion. Appl. Catal. A Gen., 243, 1. 

There are commercial processes for the direct upgrading of residues under high severe hydroconversion conditions. Other alternatives consider the previous hydrotreatment of the residue, so that the hydrocracking stage does not need to be so harsh. Otherwise, residue conversion could also proceed via carbon rejection methods, these processes fall out the scope of the present book and will not be considered here. However, it is important to mention than VR coking is seen as a more economical alternative than HDP, especially for the more heavy crudes, for which concentrations of metals and nitrogen would require the toughest conditions. 

Gray, M. R., and McCaffrey, W. C., Role of Chain Reactions and Olefin Formation in Cracking, Hydroconversion, and Coking of Petroleum and Bitumen Fractions. Energy Fuels, 2002. 16(3) pp. 756-66. 

Bearden, R. Jr., MICRO CAT-RCTM Technology for the hydroconversion upgrading of petroleum residua. Book of Abstracts, 213th ACS National Meeting, San Francisco, April 13-17, 1997 p. PETR-021. 

Ramirez de Agudelo, M. M., and Galarraga, C., Catalytic system for the hydroconversion of heavy oils. Patent No. US4888104, 1989. Dec. 19, 12pp. 

Gas chromatography is especially useful for gas-phase analysis of partial oxidation, hydrogenation, or hydroconversion products as in many cases a full carbon balance (educts, products, and all side products), in order to evaluate sample performance. As the detection and quantification of permanent gases such as N2, 02, CO, and C02 and also of higher boiling compounds are standard separation problems for gas chromatography, it is wise to employ the method regarding this problem. 

Hydroconversion of Nonhydrocarbon Constituents Sulfur and nitrogen in gas oils (14, 15)... 

For hydroconversion of nonhydrocarbon constituents, catalysts with weak acidity are used where cracking is undesirable. Strong hydrogenation activity is needed, particularly with heavy feedstocks containing high molecular weight aromatics. 

Figure 8. Effect of feed molecular weight on hydroconversion rates using moderately and weakly acidic catalysts...

From the foregoing dicussion it is apparent that residuum hydroconversion processes can be influenced adversely by pore diffusion limitations. Increasing the catalyst porosity can alleviate the problem although increased porosity is usually accompanied by a decrease in total catalytic surface area. Decreasing the catalyst particle size would ultimately eliminate the problem. However, a different type of reaction system would be required since the conventional fixed bed would experience excessive pressure drops if very fine particles were used. A fluidized system using small particles does not suffer from this limitation. However, staging of the fluidized reaction system is required to minimize the harmful effects that backmixing can have on reaction efficiency and selectivity. 

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