Jan-2015

Research and development of novel heavy oil catalytic cracking catalyst RCC-1

With an increasing supply of heavier feedstock for the catalytic cracking unit, the FCC catalyst is required to possess a higher activity and more unobstructed porous channels in order to increase the heavy oil conversion and metal contamination resistance1-3.

Zhang Jiexiao, Xu Yun and Tian Huiping, SINOPEC Research Institute of Petroleum Processing
Zhou Yan, SINOPEC Catalyst Company Qilu Division

Article Summary

Therefore, the Y zeolite as the main active component of FCC catalyst should have such properties as intact crystal structure, proper distribution of acidic active sites, good active sites accessibility, as well as high thermal and hydrothermal stability^4-8. This study aims to firstly clean the zeolite channels followed by modification of rare earth ions to increase the effective rare earth content in the ultrastable Y zeolite in an attempt to prepare a novel hydrothermally ultrastable Y zeolite that can integrate high rare earth content with high stability and high cracking activity of the zeolite. A light oil cracking microreactor and an ACE-Model R+ type fixed fluidized bed unit have been adopted to study the performance of FCC catalyst with its active component composed of the hydrothermally ultrastable Y zeolite.

Experimental Preparation of catalyst samples
The DASY series of hydrothermally ultrastable zeoliteswere the commercial products manufactured by the Qilu Division of Sinopec Catalyst Company. At first the hydrothermally ultrastable zeolite DASY0.0 was treated with a mixed acid solution at a proper concentration to modify the zeolite structure through cleaning its pores, and then the zeolite after filtration was subjected to ion exchange with rare earths followed by filtration and drying to yield a sample labelled as MDY0-1. If the hydrothermally ultrastable zeolite DASY0.0 was directly modified through ion exchange with rare earths, followed by filtration and drying, the product obtained thereby was labeled as DY. The above-mentioned zeolite samples serving as the active component after being separately mixed with the binder, pseudo-boehmite and alumina gel, and the support kaolinite at the same proportion were subjected to spray drying to form micro-spherical catalyst in accordance with the conventional procedure for manufacture of FCC catalyst. The catalyst samples obtained thereby were calcined at 350°C for 2h, and washed with acidic water. The washed samples were dried for analytical purpose. Among these samples the catalyst made of the zeolite serving as the active component that was not modified by means of pores cleaning was denoted as the base catalyst, whereas the catalyst made of the zeolite MDY0-1 serving as the active component that was modified through pores cleaning was denoted as RCC-1.

Methods for physical and chemical analysis of catalysts
The chemical composition of catalyst samples was determined by X-ray fluorescence analysis using a Rigaku 3271E type X-ray fluorescence spectrometer. The specific surface area of catalyst was measured by the static low-temperature nitrogen adsorption volumetry using a Micromeritics ASAP2400 static nitrogen adsorption analyzer. The pore volume of catalyst was determined by the trickling water method. The attrition index of catalyst during fluidization was determined by the attrition tester.

Methods for assessing the performance of catalytic cracking catalyst
(1) Microreactor for light oil cracking
Evaluation of microreactor activity for light oil cracking (micro-activity index): The standard method RIPP 92-909 was adopted to evaluate the microreactor activity for light oil cracking. The experimental setup consisting of a WFS-1D automatic microreactor activity tester, which was manufactured by RIPP, operated on a Dagang straight-run light diesel fraction with a boiling range of 239—351°C. The microreactor was a fixed-bed reactor with a catalyst loading of 5g. The catalytic cracking reaction was conducted at a reaction temperature of 460°C, a catalyst/oil ratio of 3.2, and a WHSV of 16 h-1 along with a stripping nitrogen flow rate of 30 mL/min and a stripping duration of 10 min.

(2) Fixed fluidised-bed microreactor
The experimental setup, which was an US KTI Corporation’s ACE-Model R+ fixed fluidised-bed with a catalyst loading of 9g, operated on a VGO derived from the pipeline transported mixed crude at a reaction temperature of 500°C and a catalyst/oil ratio of 3.00-8.04.

Results and Discussion
Physicochemical properties of RCC-1 catalyst
The novel heavy oil cracking catalyst RCC-1 developed on the basis of hydrothermally ultrastable zeolite serving as the active component, which was modified through cleaning of channel pores, was prepared in the pilot plant. The chemical composition and physico-chemical properties of catalyst samples were analyzed, with the data presented in Table 1.

It can be seen from Table 1 that the chemical composition of the prepared RCC-1 catalyst including the contents of Al2O3, Na2O and Fe2O3 met the requirements for commercial catalyst, while the physicochemical properties of the catalyst including the surface area, pore volume, attrition index during fluidization, apparent bulk density, and average particle size (APS) all complied with the demand of commercial catalyst in addition to a higher micro-activity index. The test results listed in Table 1 have revealed that the chemical composition and physicochemical indicators of RCC-1 catalyst all met the specification requirements, because this catalyst featured high strength, medium bulk density, large specific surface area, large pore volume, and high catalytic activity.

Performance of novel heavy oil catalytic cracking catalyst RCC-1
Based on the concepts aimed at the development of a novel heavy oil catalytic cracking catalyst, the catalyst RCC-1 was prepared using the hydrothermally ultrastable zeolite modified through cleaning of channel pores. This novel catalyst was investigated to compare its performance with a base catalyst that was to be tested incommercial scale at a certain refinery, with the physical properties of the catalyst RCC-1 presented in Table 2. The properties of feedstock used in catalyst performance tests are presented in Table 3. The catalyst samples were subjected to ageing at 800°C for 12 h with 100% steam before performance tests. The RCC-1 catalyst along with the base catalyst were tested in the ACE microreactor unit at a reaction temperature of 500°C to compare their heavy oil cracking ability, their product distribution characteristics and coke selectivity.
 
Study on heavy oil cracking ability of novel catalyst RCC-1
The bottoms yield depending upon the changes in feedstock conversion is presented in Table 4, and the feedstock conversion depending upon the changes in catalystto- oil ratio is presented in Table 5. It can be seen from the data listed in Table 4 that in comparison with the basecatalyst the yield of unconverted bottoms over the catalyst RCC-1 was reduced. However, it can be seen from Table 5 that at the same catalyst/oil ratio adopted thereby the feedstock conversion achieved by the catalyst RCC-1 was greater than the base catalyst. The test results had revealed that compared to the base catalyst the novel heavy oil cracking catalyst RCC-1 showed a higher heavy oil cracking ability.
 
Product distribution characteristics over the RCC-1 catalyst
The product distribution characteristics obtained over the RCC-1 catalyst and the base catalyst were studied under the same reaction conditions. Table 6 shows the total liquid yield depending upon the changes in feed oil conversion, while Table 7 denotes the light oil yield depending upon the changes in feed oil conversion. It can be seen from data listed in Tables 6 and 7 that at the same feed oil conversion the total liquid yield achieved by the novel catalyst RCC-1 was always higher than that achieved by the base catalyst, and the light oils yield achieved by the novel catalyst RCC-1 was also higher that that achieved by the base catalyst. The test results had revealed that in comparison with the base catalyst the yields of valuable FCC products, especially the yield of light oils were higher as compared to those products obtained over the base catalyst.