Study On The Vanadium-based Catalysts For Oxidative Dehydrogenation Of Propane To Propylene In The Presence Of Carbon Dioxide

Propylene is important petroleum chemical raw materials, mainly for theproduction of polypropylene, acrylonitrile, acrylic acid, propylene oxide and otherchemical products. Due to the variety of downstream products, increasing demand forpropylene as a by-product of from catalytic cracking, steam cracking and cokingproduction plant of propylene cannot meet the market demand.Our country has rich resources of propane, turning it into propylene has hugemarket prospect and value. Propane dehydrogenation to propylene catalyzed processhas achieved industrialization. The main disadvantage of this process is due to theconstraint of thermodynamics and need the reaction conditions of high temperature,large energy consumption, and catalyst deactivation quickly. CO2as a kind of activemild oxidant, is used in the reaction of propane oxidative dehydrogenation to improvethe activity of propane oxidative dehydrogenation to propylene reaction, effectivelyinhibit the oxidation depth, improve the selectivity of propylene, reduce the surfacearea of carbon, improve the stability of the catalyst，consume CO2as a greenhouse gasto a certain extent. It is a kind of green energy chemical industry while co-productionof carbon monoxide.This paper introduced the research progress of propane dehydrogenation topropylene technology, discussed the detailed manufacturing technique of propanedehydrogenation to propylene production and analyzed the mechanism of propaneoxidative dehydrogenation and the commonly used catalysts. This paper included theselection of vanadium catalysts to oxidation dehydrogenation of propane to propylenereaction in the presence of carbon dioxide, the choices of catalyst supports, solventand complexing agent, the synthesis of catalysts by impregnation method andone-step hydrothermal Synthesis method. The main research contents and the conclusions are as follows:(1)Metalvanadium loading six supports such as MCM-41, SBA-15，ZSM-5, a-AI2O3, SiCh and SiCh (nm) have catalytic role in oxidative dehydrogenation，ofwhich MCM-41, SBA-15and ZSM-5performed well. Mesoporous materials havelarger specific surface area, in favour of the dispersion of metal vanadium. And theyhave so good thermal stability to maintain their structure characteirstics and to avoidagglomeration of metal oxide. Investigation of the changing of CO2partial pressureon the reaction of propane dehydrogenation，the results showed that the right amountof CO2promoted the propane dehydrogenation reaction as oxidizing agent. Theexperiment adopted the volume of a gas ratio of C3H8： CO2： Ar=1:1:4.(2)The experiment selected citric acid as complexing agent to improve thestructure of catalyst by changing the amount of citric acid. It was found that propaneoxidation dehydrogenation reaction performed well when NH4NO3： CeHsCh moleratio was1:1. The addition of citric acid could form complex maximumly withammonium vanadate, highly disperse in the solvent. The expeirment selecteddeionized water and different concentrations of ammonia as solvent contrastexperiment in the process of catalysts preparation. Results showed that the catalystwith deionized water as solvent dissolving in60。C performed best.(3)Heteroatom molecular sieve was synthesized with vanadium, silicon, alkali,template agent and deionized water by hydrothermal method. The catalysts werecharacterized by XRD，BET，FESEM，TEM testing means, and the result showed thatheteroatom molecular sieve was synthesized successfully with uniform six-partychannel structure, and the specific surface area reached1000m2/g. The catalyticactive site of active material, the metal base reducibility of catalyst and catalyst acidicsites were tested by XPS，H2-TPR，NH3-TPD test. The results can be concluded thatthe catalytic propane oxidation dehydrogenation reaction were highly dispersive fourligand VO34" active species. To evaluate the different vanadium addition amount ofimpurity atoms molecular sieve catalytic propane dehydrogenation reaction, of which8.8%V-MCM-41had good catalytic activity, propylene yield can reach52.2%.Toparaphrase regeneration performance of catalysts was investigated. Results indicated that the recycling after four times of catalyst samples still remained good catalyticactivity of propane oxidative dehydrogenation to propylene reaction.