Asphaltenes catalyst selection

The asphaltenes are selectively converted with a low hydrogen consumption decreasing significantly the metal content in the product. Catalyst was tested during a six-month period, processing various heavy feedstocks and showing a stable performance. The yields and product quality reported indicated almost complete conversion of the feed and total metal removal. The net effect of the ABC pretreatment was found to be an increase in catalyst life, higher metal quality of the product oil, and increase distillate yields. 

The results of this study showed that flash pyrolysis subbituminous coal tar can be hydrorefined. Ni-Mo supported on alumina was the most effective catalyst for hydrorefining flash pyrolysis subbituminous coal tar among the five types of catalysts tested. The removal of asphaltenes and preasphaltenes was easy to achieve. Catalyst selection should emphasize heteroatoms removal efficiency and hydrogen consumption. The catalyst life is an equally important selection criterion although this program has not completed catalyst-life studies. It will be determined in the future. 

The effect of conversion on the structure of an asphaltene molecule has been reported to depend on the operating conditions and on the presence or not of a catalyst. The effect of thermal processing reaction of a vacuum residue resulted in the selective cracking of the aliphatic or naphthenic side chains of the molecule, leaving the highly condensed aromatic core structure almost intact (see Fig. 16) [116]. 

All of these problems are related to the performances of the catalysts used in coal liquefaction. Very active, durable, recoverable, and regenerable catalysts are most wanted in the primary liquefaction stage, where catalyst poisons from asphaltenes and minerals are most severe. Multifunctional catalysts should be designed by selecting supports with specific functions, such as strong but favorable interactions with catalytic species, resistance to poisons, and improved properties to allow easy recovery, while maintaining high activity. 

The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions. 

Feedstock Characteristics. Several important feed characteristics considered in H-Oil desulfurization are (1) the character of the residuum, i.e., whether vacuum, atmospheric, deasphalter bottoms, cracked tars, or blends (2) the asphaltene and metal content (3) the sulfur level and degree of desulfurization required. These feed characteristics ultimately infiuence the selection of operating temperature, hydrogen partial pressure, space velocity, and catalyst type and usage. 

The catalyst used was Topsoe TK-751. It is a general purpose HDS catalyst for residual feedstocks. Their functions are desulphurization, demetallation and asphaltenes and Conradson carbon reduction. It is recommended for HDS of residua with moderate metals content and for 2 stage catalyst in composite fillings. It has good HDS activity, good HDM selectivity and capacity for metals uptake. It is Ni/Mo type. 

IMP process. Developed by the Mexican Institute of Petroleum. It uses FBR in series with selective catalyst for removal of metals and sulfur, as well as hydrocracking of asphaltenes. The operation of reactors is at moderate severity, thus minimizing the formation of sediments. It employs proprietary catalysts that are designed according to the type and quality of heavy crude oil to be upgraded. Proper selection of feed preparation, reaction conditions, reactor arrangement, and catalyst properties assure the process to operate continuously (Ancheyta et al., 2010). 

---