Fischer-Tropsch wax catalytic cracking for the production of low olefin and high octane number gasoline: Process optimization and heat effect calculation

To produce low olefin gasoline with high octane number by Fischer-Tropsch (F-T) wax fluid catalytic cracking (FCC) process, operating conditions optimization were carried out in the pilot-scale riser and turbulent fluidized bed (TFB) FCC unit. The experimental results in the riser indicated that under the condition of low reaction temperature and regenerated catalyst temperature, large catalyst-to-oil weight ratio (C/O) and long reaction time, the gasoline olefin content could be reduced to 20.28 wt%, but there is large octane number loss owing to a great loss in high octane number olefin. Therefore, a novel FCC process using the TFB reactor was proposed to strengthen the aromatization reaction. The reaction performance of TFB reactor were investigated. The result demonstrated that the TFB reactor has more significant effect in reducing olefins and improving aromatics. At the expense of certain gasoline yield, the gasoline olefin content reduced to 23.70 wt%, aromatics content could increase to 26.79 wt% and the RON was up to 91.0. The comparison of reactor structure and fluidization demonstrated that the TFB reactor has higher catalyst bed density. The reaction heat and coke combustion heat was calculated indicating the feasibility of its industrial application of the TFB process.

Effect of Operating Conditions on Olefin Distribution in FCC Gasoline as Part of an Olefin Reduction Process

The effects of operating conditions on the distribution of olefins in the FCC gasoline, obtained during catalytic cracking reaction in the presence of the GOR-Q catalyst and conventional MLC-500 catalyst, have been studied in detail. The test results showed that the GOR-Q catalyst could obviously reduce the content of several kinds of olefins in FCC gasoline. Olefins in the FCC gasoline consist mainly of C5- C7 compounds, that are composed of C=C bond with normal or mono- branched chains. The reduction of gasoline olefin content could be achieved by decreasing the content of above-mentioned olefins. Lower reaction temperature, lower weight hourly space velocity （WHSV） and higher catalyst to oil ratio would help to reduce the content of olefins with a C = C double bond, normal olefins, mono-branched-chain olefins and diolefins. To decrease the loss of gasoline octane number, the operation for olefin reduction should be firstly focused on increasing the catalyst to oil ratio.

Effect of Olefins on Formation of Sulfur Compounds in FCC Gasoline

The effect of olefins on formation of sulfur compounds in FCC gasoline was studied in a small-scale fixed fluidized bed （FFB） unit at temperatures ranging from 400℃ to 500℃, a weight hourly space velocity （WHSV） of 10 h-1, and a catalyst/oil ratio of 6. The results showed that C4--C6 olefins contained in the FCC gasoline could react with HzS to form predominantly thiophenes, alkyl-thiophenes as well as a fractional amount of thiols, while large molecular olefins such as heptene could react with hydrogen sulfide to form benzothiophenes. The amount of sulfur compounds formed at different tem- peratures over different catalysts were in proportion to the mass fractions of olefins in the feedstock, with the amount of sulfur compounds formed over REUSY catalyst exceeding those formed over the shape selective zeolite catalyst owing to the effect of catalyst performance and the impact of catalyst on the degree of olefin conversion. The amount of sulfur compounds generated and their increase reached a maximum at 450℃ and a minimum at 400℃ because of the influence of temperature on the thermodynamic and kinetic constants for formation of sulfur compound as well as on the olefin conversion degree. Based on the above-mentioned study, a reaction network and a model for prediction of sulfur compounds generated upon reaction of olefins in FCC gasoline with HES were established.

Analysis of Factors Affecting Olefin Content in FCC Gasoline

In order to meet the urgent need for reducing olefin content in cracked naphtha, the influence of feedstock characteristics on the olefin content was discussed. The different types and performance of catalysts developed by RIPP were introduced. Moreover, some effective operation approaches in commercial units were presented to serve as a reference to the refiners for catalyst selection.

Analysis of Measures and Effect on Reducing Olefin Content in Gasoline

This article refers to major measures for reducing olefin content of automotive gasoline and the effect after adoption of these measures. The key for reducing olefin content in China's automotive gasoline pool is to reduce the olefin content of FCC naphtha. The domestic refiners apply the olefinreducing catalyst to decrease the olefin content of FCC gasoline as a convenient and cheap means to meet the national standard for automotive gasoline at the present phase. Furthermore, the novel domestic FCC reaction processes, such as the MIP, MGD, FDFCC and other processes can also apparently reduce olefin content in FCC gasoline. In order to further reduce the olefin content in gasoline to meet more stringent standard for automotive gasoline, Chinese refiners should optimize the processing scheme while aggressively disseminating hydrogenation process along with development of catalytic reforming,alkylation, etherification and other processes to completely change the simplistic composition of domestic gasoline pool.

Development of MIP Technology and Its Proprietary Catalysts

A novel catalytic cracking process named the MIP process was developed by the Research Institute of Petroleum Processing(RIPP),SINOPEC,to manufacture clean gasoline with lower olefin contents. The MIP pro-cess features a unique riser consisting of two sequential reaction zones with different radii,in which different kinds of chemical reactions are intensified respectively to achieve better product slates and product properties. In order to fully implement the MIP potentials,a proprietary catalyst RMI tailored to the needs of the MIP process was devel-oped by adopting an AIRY zeolite having improved accessibility to active sites,which could result in better heavy oil cracking,coke selectivity and olefin reduction performance compared with the conventional REUSY zeolite. Its commercial application showed that the RMI catalyst could further reduce the olefin content in gasoline and raise the gasoline octane number while increasing the total liquid yield. On the basis of the MIP process,the MIP-CGP process was also developed to significantly reduce the olefin content in FCC naphtha and to enhance the propylene yield simultaneously. As far as the MIP-CGP process itself is concerned,both the MIP-CGP process and the MIP process have the similar reactor configuration but with different reactor size and operating parameters. The proprietary catalyst CGP-1 is also proposed to tailor for the MIP-CGP process. The specific features of the CGP-1 catalyst cover the new matrix,which possesses excellent capability to accommodate coke formation in the first reaction zone;the modified Y zeolite,which exhibits high hydrogen transfer activity in the second reaction zone;and the MFI zeolite,which has good gasoline olefin cracking activity. The commercial test results of MIP-CGP process applied along with the CGP-1 catalyst showed that the olefin content of gasoline was less than 18 v% and the propylene yield was more than 8 m%. Furthermore,as compared with the conventional FCC process,the gasoline properties were improved greatly and a higher total liquid yield was obtained. The advantages and characteristics of the MIP-CGP process were fully exploited by using the CGP-1 catalyst.