Clays and Clay Minerals, Vol. 45, No. 2, 213 220, 1997. CONDENSATION OF OLEFINS ON CLAYS. GAS-SOLID SYSTEMS. PART I: GRAVIMETRIC METHODS EDUARDO CHOREN, ALEXANDER MORONTA, GUSTAVO VARELA, ARNEDO ARTEAGA AND JORGE SANCHEZ Centro de Superficies y Cat~ilisis, Facultad de Ingenierfa, Universidad del Zulia, Apartado 15251, Maracaibo 4003A, Venezuela Abstract--The adsorption-condensation of olefins was studied on 7 adsorbents: 2 commercial clays, a natural clay and its protonated form, ~-alumina and porous and nonporous silicas. These adsorbents were characterized by X-ray diffraction (XRD), chemical analysis, thermogravimetric analysis (TGA), differ- ential thermal analysis (DTA) and determination of specific surface area measurement by the BET method. The experiments were carried out gravimetrically, in gas- or vapor-solid systems, at 25 ~ and on ad- sorbents dried at 120 ~ Adsorption-condensation of olefins are fast processes, diffusion controlled. Alumina and silicas adsorb olefins and paraffins only reversibly, but are unable to condense olefins. The water polarized by the countercations is the source of BrCnsted acid sites. When the gas phase is evacuated or swept with inert gas, the condensation terminates. On clays, paraffins are reversibly adsorbed but no condensation was observed. Key Words--Adsorption, Clays, Condensation, Olefins, Oligomerization, Paraffins. INTRODUCTION A benzene alkylation plant with hydrogen fluoride (HF) as catalyst encountered a problem with the final product, because it had a concentration of olefins above specification. The proposed solution was the se- lective adsorption of these olefins onto clays. A num- ber of commercial clays were tested by percolating the impure product, in a colunm 0.8 cm in diameter by 10 cm long, packed in a glass tube. The results were ex- cellent: an initial drop of the bromine number to a tenth or less and a high processing capacity. A stream of hot benzene and drying with warm air were enough to reactivate the clay. During the run, clays changed colors: greenish, brownish and finally a black front started at the top of the column and descended until all of the column turned black. The activity remained for some time until the Br number marked the end of the run. All of these effects have been described in numer- ous papers on clays exchanged with salts of all the metal groups, or organic complexes of them, or pil- lared clays, published during the last 30 years. But few of those papers addressed the reactions of olefins in the range 20-25 ~ on clays dried at 120 ~ The aim of this study is to identify and evaluate the different factors and steps in olefin adsorption-conden- sation processes using vapor-solid or gas-solid sys- tems. "Condensation", in this work, involves all of the reactions that generate products of higher molec- ular weight, such as etherifications and oligomeriza- tion. EXPERIMENTAL Adsorbates Adsorbates were propylene, Scott, >99.5%; 1-bu- tene, Matheson, >99.0%; cis-2-butene, Linde, Copyright 9 1997, The Clay Minerals Society >99.0%; cyclohexane, Baker, >98.0%; cyclohexene, Baker, B.P. 82-84 ~ 2,2-dimethylbutane, Fluka, >99.0%; and 2,3-dimethyl-2-butene, Fluka, >99.5%. All liquid adsorbates were purified by the freezing- thaw method before adsorption. Adsorbents Adsorbents were: 1) Two similar commercial activated clays from Fil- trol-Harshaw, Filtrol 24 (F24) and Filtrol 124 (F124). 2) A Venezuelan clay (T1) from Tinaquillo, State of Cojedes, purified as described in Choren et al. (1996). 3) A protonated form of the T1 clay (TIH), pre- pared by treatment with a hot NH4NO3 solution, 1.5 M as indicated by Lunsford (1968). The derivative clay was washed with distilled water, dried and heat- ed to 300 ~ to decompose the salt. The very small variation in the MgO content of this clay (Table 1) suggests that Mg is a structural component and not a free ion. 4) Cabosil, a high-purity silica aerogel from Cabot, Inc. The particles of Cabosil are nonporous spheres with homogeneous radii. High-purity -y-alumina from Rh6ne-Poulenc, G.ES.C. High-purity silica-gel, Baker Reagent, 60-200 mesh. All of the adsorbents were ground to pass through a 200 sieve. The pretreatments are indicated herein. X-ray powder diffraction traces of the clays were potentiometrically recorded using a Philips PW-1720 diffractometer with Co anode. The chemical compo- sition of clays was determined by atomic absorption and emission spectroscopies and conventional chemi- cal analysis. The TGA was carried out in a Cahn D-200 electro- balance. Samples of 100-150 mg were subjected to a heating program ([3 = 10 ~ in a He flow (30- 213