Coke combustion kinetics of spent Pt-Sn/Al 2 O 3 catalysts in propane dehydrogenation
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Coke combustion kinetics of spent Pt-Sn/Al2O3 catalysts in propane dehydrogenation Pajri Samsi Nasution*,‡, Jae-Won Jung*,‡, Kyeongseok Oh**, and Hyoung Lim Koh*,† *Department of Chemical Engineering, RCCT, Hankyong National University, Anseong 456-749, Korea **Chemical and Environmental Technology Department, Inha Technical College, Inha-ro 100, Michuhol-gu, Incheon 22212, Korea (Received 16 December 2019 • Revised 20 February 2020 • Accepted 8 March 2020)
AbstractThe kinetics of coke combustion was investigated by using a thermogravimetric analyzer (TGA) of coked catalysts which was used for propane dehydrogenation to determine the activation energy. Apart from the Pt/Al2O3 catalyst, four different Pt-Sn/Al2O3 catalysts were prepared by varying the Pt/Sn ratio from 3 : 0.5 to 3 : 3 by weight. The catalytic activity was measured by propane dehydrogenation at 620 oC. The reactant mixture consisting of C3H8 (30 ml/ min) and H2 (30 ml/min) was fed into the reactor for 5 h. A thermogravimetric analyzer in the presence of air was used to determine the amount of coke deposited and calculate the kinetic parameters for coke combustion. Three nonisothermal models (Friedman, Flynn-Wall-Ozawa (FWO), and Kissinger-Akahira-Sunose) were used to determine the activation energy and the best model to fit the experimental data. The FWO model provided the best fit for 3Pt/Al2O3 and 3Pt-0.5Sn/Al2O3. The three models were equivalent for fitting the data for 3Pt-1Sn/Al2O3, 3Pt-2Sn/Al2O3, and 3Pt3Sn/Al2O3. The activation energy increased with increasing Sn addition in the 3Pt/Al2O3 catalyst. Differences in the locations and the qualitative features of the cokes were suggested to interpret the results. Keywords: Coke Combustion, Propane Dehydrogenation, Pt-Sn/Al2O3, Thermogravimetry, Activation Energy
be converted to either aromatic or pre-graphite. Though unconfirmed, the metal dispersion might affect the coke generation. In our previous study [7], the metal dispersion was changed by varying the treatment temperature from 450 to 600 oC in the range of direct reduction. From a qualitative study of the coke location, we reported that the so-called drain effect may provide indirect evidence that differences in the coke combustion observed by differential thermal analysis (DTA) are caused by the coke location. A split of the DTA peak was observed at 400-500 oC and was unique in case of bimetallic Pt-Sn catalysts. With addition of Sn, peak splits were clearly observed in the DTA analysis. The observed peak splits were attributed to the migration of coke. However, there was no evidence that the type of coke differed with the addition of a Sn promoter. More coke was also noticed on the metal catalyst when it was suspected that the Pt3Sn alloy was present and coke accumulation was more active. Kinetic studies on the combustion of coke are important in the design of PDH regenerator in which PDH catalyst can be regenerated by burning the coke on the catalyst. Since
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