The Weight Change of SAPO-34 Catalyst During MTO Process in TGA Reactor
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The Weight Change of SAPO-34 Catalyst During MTO Process in TGA Reactor Hao Hu, Weiyong Ying*, Fahai Cao and Dingye Fang Engineering Research Center of Large Scale Reactor Engineering and Technology, Ministry of Education; State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai, 200237, China. E-mail: [email protected] ABSTRACT The Thermax 700 thermo gravimetric analysis (TGA) instrument is introduced for the investigation of the weight change of SAPO-34 catalyst during methanol-to-olefin (MTO) process. By the use of a special sample basket with screen bottom, the TGA instrument can be viewed as fixed-bed reactor, while the weight change of SAPO-34 during MTO reaction can be recorded online. It is noticed that the SAPO-34 catalyst experiences a procedure of dehydration as furnace temperature rises; hence the weight increase of SAPO-34 during MTO reaction should be calculated based on the weight after dehydration. It is checked that the increase of weight is mainly coke ignore of adsorbates. In the range of 648~773K temperature and 7.08~35.9h-1 (WHSV) space velocity, the maximum coke deposition is roughly 25% independent of reaction condition. The coke formation experiences a stage of fast increase soon after reaction initiates, while slows down apparently after 18% coke is deposited on the catalyst. Higher temperature, space velocity and methanol partial pressure accelerate the coking rate. Temperature plays an important role in the type of coke formation, which can be distinguished directly by the colour of completely deactivated catalyst. The deactivated catalyst in lower temperature experiences a weight loss with partly recovery of catalyst activity as temperature rises in the hydrothermal atmosphere. The phenomenon of weight loss with catalyst regeneration will not occur as reaction temperature decreases for deactivated catalyst, as well as the different DTA curves for coke burning, are also evidences for the different type of coke formation on SAPO-34 catalyst in different reaction temperature. INTRODUCTION Methanol-to-Olefins (MTO) reaction was first discovered in 1970s. The invention of small-pore molecular-sieve [1] named SAPO-34 was utilized as catalyst for its special structure and higher selectivity to light olefins later [2]. The deposition of coke leads to a sharp decrease of activity for zeolite catalyst [3]. Because of the chabazite structure with small pore size, SAPO-34 experiences a fast coking stage soon after the reaction initiates [2]. Investigation of the behavior of coke deposition belongs to fundamental study for catalyst property. However, ordinary methods such as determining coke content by weighing catalyst outside reactor [4, 5] or detecting carbon mass by burning off coke
inside reactor [6], would lead into extra operating error obviously. TEOM (Tapered Element Oscillating Microbalance) reactor was introduced for the study of deactivation and adsorption phenomena in MTO reaction over SAPO-34 catalyst by Chen et.al.[7], and was proved to
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