Ind. Eng. Chem. Res. 1992,31, zyxwvu 1283-1288 1283 Industrial Regeneration of Naphtha Reforming Catalysts Contaminated by Sulfate Ions: Effect of Sulfate Level Teresita F. Garetto, Armando Borgna, and Carlos R. Apesteguia* Instituto de Investigaciones en Catdlisis y Petroquimica (INCAPE), FIQ- UNL-CONICET, Santiago del Estero 2654, 3000 Santa Fe, Argentina Jean Claude Lavalley Laboratoire de Spectrochimie, U.A. 414, I.S.M.Ra, Universitt? de Caen, 14032, Caen C&dex, France When naphtha reforming catalysts are sulfur contaminated, a special procedure is employed during catalyst regeneration to diminish the sulfation of the support. Thus, from an industrial point of view it is important to know the effect of the sulfate level on the naphtha reforming process. In this paper, most of the results were obtained on a Pt-Re/A1203 catalyst taken from commercial reforming reactors. Fresh Pt-Re/A1203 catalyst was also employed. The effect of the sulfate level on naphtha reforming was studied through an accelerated deactivation zyx run at reforming conditions zy using a naphtha feed. Correlations were established through the analysis of parameters such as octane number, volumetric liquid yield, percentage of gases, percentage of aromatics in the liquid, and coke formation. The results showed that for sulfate levels higher than 0.08-0.1 % S the rate of deactivation is increased as a consequence of enhanced coke formation. Such an increase of the coke formation results from (a) the difficulty of restoring the chlorine level on the support because of the blockage of the Lewis acid sites of the alumina by sulfate ions and (b) excessive sulfidation of the metallic fraction by H2S produced during the reduction of the sulfated catalysts with H2. Introduction Naphtha reforming catalysts are sensitive to the pres- ence of sulfur compounds which are present as impurities in the hydrocarbon feed. Catalyst poisoning typically results from strong chemisorption of sulfur compounds on the surface of the metal. During commercial practice feed is previously treated in a hydrodesulfurization (HDS) unit to reduce the sulfur concentration before reaching the reforming unit. The maximum sulfur level admissible in the feed depends upon the catalysts used. For standard Pt/Al2O3 catalysts, the preferred sulfur levels have been outlined (Ciapetta, 1971). When a conventional Pt-Re (atomic ratio Re/Pt = 1) catalyst is employed, the sulfur level must be as low as 1 ppm (Menon et al., 1982). New %kewed" catalysts containing higher Re/Pt ratios are even more sensitive to the sulfur compounds. For these cata- lysts, a maximum sulfur level of 0.5 ppm is allowed (Mc Lung, 1988). Because of these high-severity limits re- garding sulfur poisoning, an additional sulfur-guard unit is often incorporated before the industrial reforming re- actors to eliminate almost completely sulfur compounds in the feed. The loss of catalytic activity caused by sulfur poisoning occurs through two main mechanisms: (i) during the re- ducing conditions of the operation cycle, sulfur can be slowly incorporated to the catalyst by adsorption of H2S onto metallic sites; (ii) during catalyst regeneration, oxi- dized sulfur species can be adsorbed onto the support poisoning the acid sites (Franck and Martino, 1982). Since during industrial operation sulfur concentration in the feed is maintained at low values, this first mecha- nism is unlikely to occur. However, during the operation cycle sulfur is accumulated as iron sulfide on the reactors walls, in hot spots, and mainly in granulated metal pro- duced by corrosion. When coke burning is carried out, the iron sulfide is oxidized to gaseous SO2 and/or SO3 which can be fixed as sulfate ions by the support. If a high *To whom correspondence should be addressed. Present ad- dress: Exxon Research & Engineering zyxwvuts Co., Route 22 East, An- nandale, NJ, 08801. 0888-5885 zyxwvutsr f 92 f 263l-l283$03.Oo/O 0 amount of sulfates is accumulated, the catalytic perform- ance is adversely affected. In spite of the large bibliography regarding sulfur poi- soning of naphtha reforming catalysts, few investigations have been specifically focused on the poisoning by sulfate under industrial conditions and on the special regeneration procedures needed to eliminate it. From an industrial point of view it is important to determine the maximum sulfate content allowable on the catalyst without inter- fering in a successful regeneration. In this paper we report the effecta that the sulfate level has upon catalyst chlorine regulation and catalytic activity during naphtha reforming. Experimental Section A set of fresh (BF) and used (BU) samples of a com- mercial Pt-Re/A1203-C1catalyst of 0.31% Pt and 0.32% Re was employed. Fresh samples have 0.85% C1,80 ppm S, 170 m2 g-l BET specific area (Sg), and 0.45 cm3 g-l pore volume. Used samples were obtained after industrial use in a reforming unit composed of four endothermic reactors in series. Samples were removed from reactors during the fifth industrial regeneration. The length of the fifth op- erating cycle was 185 days. A high-purity A1203 powder (Cyanamid Ketjen CK 300) was also employed. Alumina CK 300 has 180 m2g-' BET specific area and 0.49 cm3 g-l pore volume and contains 50 ppm sulfur. Catalytic reforming activity was measured by meam of an accelerated deactivation test using bench-scale equip- ment (Apesteguia et al., 1984). The standard run utilizes three test periods. Initial operation was carried out under industrial reforming conditions zyx (P = 15 atm; H2:naphtha molar ratio = 4) during 8 h (period I). Then, pressure was decreased during 8 h to 1 atm (period 11). In period I11 the conditions of period I were restored. During all the periods temperature, weight hourly space velocity (WHSV) and H2:naphthamolar ratio were kept at 505 OC, 5 h-l, and 4, respectively. The severe conditions of period 11 produce a deactivation similar to long reaction time under the conditions of period I. The commercial hydrotreated naphtha contained less than 1 ppm sulfur and had the following properties: re- 1992 American Chemical Society