Chapter 16
Deactivation of Light Naphtha Aromatization Catalyst 1
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S. Fukase , N. Igarashi , K. Aimoto , and K. Kato
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Petroleum Refining Research and Technology Center, Japan Energy Corporation, 3-17-35 Niizo-Minami, Toda-shi, Saitama 335, Japan Petroleum Refining Department, Japan Energy Corporation, Toranomon, Minato-ku, Tokyo 105, Japan
Downloaded by CORNELL UNIV on September 14, 2016 | http://pubs.acs.org Publication Date: June 6, 1996 | doi: 10.1021/bk-1996-0634.ch016
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Deactivation of light naphtha aromatization catalyst based on zeolite was studied, by kinetic analysis, micropore volume analysis and model reactions. Coke accumulates at the entrance of zeolite channel, blocks it and hinders reactant molecule to access active sites in zeolite channel. Our own stabilization technique passivates coke-forming sites at the external surface of the zeolite. This minimizes the coke formation at the entrance of zeolite channel and increases on-stream stability. The stabilized catalyst enabled us to develop a new light naphtha aromatization process using an idle heavy naphtha reformer that is replaced by CCR process. Aromatics are produced mainly by the catalytic reforming of heavy naphtha in the petroleum refining industry. In recent years, light hydrocarbons have become an alternative source of aromatics. Several processes have been developed for this reaction : Cyclar (7 ), Z-former (2 ) and Aroformer (3 ). Zeolitic catalysts with MFI structure are generally chosen for this reaction, because of their lower coking tendency. However the operating conditions required for the process results in a catalyst carbon lay-down rate which is unsuitable for a conventional fixed bed catalytic operation. Thus development of those processes was directed towards continuous or swing-type regeneration because of rapid decline of catalyst activity. The economics of light hydrocarbon aromatization processes do depend on the initial investment cost, mainly construction cost, and the price difference between the feedstock and aromatics. Due to the massive construction cost and no expected widening in the feedstock/BTX price difference, the payout years of a construction cost would be lengthy. One solution of this problem is to develop a new aromatization process using a conventional fixed bed, thus avoiding the need to construct CCR type or swing type reactor unit. Currently in many refineries, conventional "semi-regenerated type" heavy naphtha reformers have been replaced by CCR reformers. A number of these units are currently unused and available for another use of light naphtha aromatization. Modernization of these units to aromatize light naphtha may prove economically justifiable. The objective of the development of "LNA" process, thus, is to develop a new catalyst having extended stability which enables us to use conventional fixed bed reactors, minimizing initial construction cost. The deactivation of acid zeolite catalysts is mainly due to the coke deposit within 0097-6156/96/0634-0219$15.00/0 © 1996 American Chemical Society
O'Connor et al.; Deactivation and Testing of Hydrocarbon-Processing Catalysts ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
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DEACTIVATION AND TESTING OF HYDROCARBON-PROCESSING CATALYSTS
the pores or on the external surface of the crystallites. The prevention of coke deposit is the key to success for the development of LNA process. Under these circumstances, Japan Energy Corporation has conducted extensive research on the development of a new aromatization catalyst that exhibits high activity and excellent inhibition of coke formation (4,5). On the basis of this fundamental research, we have operated the LNA demonstration plant. The present work describes the phenomena responsible for the deactivation of LNA catalyst.
Downloaded by CORNELL UNIV on September 14, 2016 | http://pubs.acs.org Publication Date: June 6, 1996 | doi: 10.1021/bk-1996-0634.ch016
Experimental. Catalyst. Zinco-aluminosilicates (Si/Al = 30) were prepared by the method described elsewhere (6 ). Subsequently, the zeolites were stabilized by our proprietary technique of steaming. HZSM-5 having Si/Al ratio of 40 obtained from PQ Zeolite (CBV 8020) was also used to study the effect of steaming on deactivation. Catalytic Activity Measurement. The reaction was carried out in a stainless steel microflow reactor. In each run, 2 g catalyst was placed in the reactor and heated to 520 °C under a nitrogen stream. The nitrogen stream was replaced by a light naphtha vapor fed by a micro plunger pump. The reaction was carried out at 520 °C, under various pressures and WHSVs without any hydrogen addition. The products were analyzed periodically by gas chromatography. The properties of the light naphtha are shown in Table I. Table I Properties and components of the Feedstock Density (g/cm ) 0.6591 Sulfur (ppm)
