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Study on Catalytic Cracking of Light Hydrocarbons and Catalyst Deactivation

Author: LuZuoZuo
Tutor: ChenFengQiu
School: Zhejiang University
Course: Industrial Catalysis
Keywords: Light hydrocarbons catalytic cracking mechanism coke deactivation
CLC: TQ221.2
Type: Master's thesis
Year: 2012
Downloads: 39
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Abstract

With the continually growing demands of ethylene and propylene, more and more countries began to pay attention to catalytic cracking of light hydrocarbons to prepare olefins. There are a lot of influencing factors of catalytic cracking process, including catalysts, operating conditions and raw materials, making the catalytic cracking mechanism and the product composition vary. In light hydrocarbons’s catalytic cracking process, the catalyst deactivation phenomenon is inevitable.In this thesis, X-ray diffraction, surface area and pore structure analysis, and acid analysis were used to analyze the1#and2#catalysts provided by Institute of Shanghai Petrochemical. Then evaluated the catalysts’ activity, stability in a fixed bed-gas chromatography combined equipment. The results showed that, compared with1#catalyst,2#catalyst had a greater surface area and more microporous and mesoporous distribution.1#catalyst had more acid density, weak acid and average acid amount than2#catalyst, but2#catalyst had a small amount of strong acid.2#catalyst had a better activity than1#catalyst, but1#catalyst had a better stability than2#catalyst.Studied different conditions of catalytic cracking process, and that were the effect of reaction temperature, WHSV and water oil ratio on the yield of diene. The results showed that the rise of reaction temperature was benefit to improving the yield of ethylene and propylene. The WHSV affected greatly on the cracking reaction. On1#catalyst, with the increase of water oil ratio, the yield of propylene rose, and ethylene didn’t change much; on2#catalyst, when the water oil ratio was in0-2, the yield of ethylene and propylene increased with the water oil ratio rising. But if added more water, the yield reduced.Respectively, used n-heptane,2-methyl pentane, cyclohexane as the straight chain alkane, branched chain alkane and cycloalkane model compounds. Investigated reactivity and mechanism of catalytic cracking of different materials on1#and2#catalysts. The results showed that n-heptane was the easiest to be catalytic cracked while cyclohexane was the most difficult one. On the same temperature, n-heptane had the highest ethylene yield and2-methyl pentane had the highest yield of propylene. Cyclohexane had the least diene yield. Cracking mechanism ratio increased with temperature rising.1#catalyst had a higher catalytic cracking mechanism ratio than2#catalyst. Under the same condition, the n-heptane had the highest cracking mechanism ratio, that meant it was most prone to cracking in a single molecule mechanism, and2-methylpentane had the lowest cracking mechanism ratio, indicating relatively more bimolecular reaction ratio.Through regeneration and re-evaluation of2#catalyst, it could be found that its relative poor stability was caused by coke deactivation. Three different materials deactivated catalysts were characterized by elemental analysis, thermal analysis, specific surface area and pore structure analysis, IR and GC-MS analysis. The amounts of coke, coke location, coke composition were analyzed. The results showed that, under the same condition, n-heptane catalyst coke had the highest hydrogen-carbon ratio but the minimum amount of coke.2-methylpentane catalyst had the lowest hydrogen-carbon ratio, but its amount of coke was highest. Cyclohexane had the fastest carbon removal rate. The coke was mainly formed from the mesoporous of the catalyst and its main formation was2to4aromatic rings compounds, and the2-methyl pentane and cyclohexane coke also contained long-chain alkanes with more than10carbons.

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