Cracking catalysts pretreatment

A cracking catalyst is subjected to two pretreatment steps. The first step effects vanadium removal the second, nickel removal, to prepare the metals on the catalyst for chemical conversion to compounds (chemical treatment step) that can... 

Catalytic cracking is another process to benefit from hydrotreating. The benefits are similar to those for reformate pretreatment longer runs, better cracking selectivity, and better product quality. Another advantage is reduced sulfur laydown on the cracking catalyst. Then, catalyst regeneration will contribute less sulfur dioxide to the atmosphere. 

An important recent catalyst development is related to the nondestructive framework substitution of Si for A1 in the Y zeolite, described above. Using this recently disclosed mild aqueous chemistry, silicon-enriched forms of the Y zeolite structure (called LZ-210) have been synthesized, greatly improving the thermal and hydrothermal stability of the Y crystal. Cracking catalysts prepared from these silicon-rich zeolites show substantially increased cracking activity retention, following severe steaming pretreatments. In addition. 

Hatanaka, S. Yamada, M., and Sadakane, O., HDS of Catalytic Cracked Gasoline. 3. Selective Catalytic Cracked Gasoline HDS on the Co-Mo/AL203 Catalyst Modified by Coking Pretreatment. Ind. Eng. Chem. Res, 1998. 37 p. 1748. 

The effects of heavy oils on cracking can be met by process modifications, feed pretreatment or by the use of specially designed catalysts. 

Catalytic cracking was performed by a conventional pulse technique. The catalyst was pretreated with helium at 723 K for 2 hr. 0.8 mm of octane isomers mixture was injected, and the products were analyzed using a liquid paraffin column operating at room temperature to 373 K. Na-mordenlte was converted into the decationlzed form before the cracking. 

Evidence that the presence of water is important in these reactions has been obtained by Hansford (82). Pretreatment of the catalyst with a stream of predried air at 500°C resulted in a marked decrease in the rate of cracking. Further, if deuterium oxide was substituted for the water in the catalyst a large percentage of the deuterium exchanged with hydrogen atoms contained in the hydrocarbon undergoing reaction. Hansford also pointed out that effective catalysts for cracking reactions are always prepared from one or more hydrous oxides. 

The catalytic test of isohexane cracking was carried out by a pulse method. Nitrogen, purified by flowing through MS 13X trap at dry-ice temperature, was used as a carrier gas (20 ml min 1). The catalyst (typically 40 mg) was placed in a quartz tube and pretreated in flowing nitrogen at 873 K. A pulse of isohexane (0.1 pi) was injected into a flow of carrier gas, and the reaction products were analyzed with an on-line gas chromatography equipped with FID. 

The coke deposited on the catalyst is burned off in the regenerator along with the coke formed during the cracking of the gas oil fraction. If the feedstock contains high proportions of metals, control of the metals on the catalyst requires excessive amounts of catalyst withdrawal and fresh catalyst addition. This problem can be addressed by feedstock pretreatment. 

The distribution of A1 spedes of varying coordination (tetrahedral, pentacoordinated and octahedral) can be influenced by changing the conditions of hydrothermal pretreatment of amorphous silica-alumina catalysts. However, for a given composition, activity per unit surface area and selectivity were independent of pretreatment conditions. Thus, gas oil cracking activity and selectivity in amorphous silica-alumina cannot be... 

Catalytic Cracking Test. A standard microactivity test (MAT) was used to evaluate the conversion and selectivity of catalyst samples. The tests were done at the University of Pittsburgh s Applied Research Center (former Gulf Research Laboratory), a qualified laboratory for MAT evaluations. A standard method, developed by Gulf, was used without modification. A Cincinnati gas oil was cracked under the following conditions cat/oil=3, 16 h 1 WHSV, and 516°C. Prior to charging the reactor, all samples underwent a standard thermal pretreatment. Solids were first heat shocked for 1 h at 593°C. Next, selected materials were impregnated with 3000 ppm Ni and 6000 ppm V, as naphthenates. Then all samples were calcined for 10 h at 538°C. Finally, each material was steamed at 732°C for 14 h in a fluidized bed to produce a catalyst in a simulated equilibrium state. 

Resid hydrotreating catalysts, developed in 1987 have been used together with a scale-and iron-removing catalyst for (1) the cracking and desulfurization of atmospheric residue, (2) the pretreatment of RFCC and (3) the cracking of vacuum residue. Approximately 7000 tons of industrial catalysts have been used in commercial units so far. 

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