Influence of reaction parameters and comparison of fluorinated alumina and silica supports in the heterogeneous alkylation of isobutane with olefins

The heterogeneous alkylation of i-C₄ with mixed olefins from FCC refinery streams was realized using acid-modified Al₂O₃ and SiO₂ as catalysts. The surface acidity was determined by I.R. (pyridine), Hammett indicators and NH₃-TPD, while catalytic properties were determined in a 300-ml well-mixed batch-type reactor at 0°C. The F-Al₂O₃ series was active only when mixed with acidic agents (BF₃·2H₂O), but the F-SiO₂ series was active by itself. At 0°C, the alumina based catalysts yield 13.4 wt.-% trimethylpentane (TMP) and 69.9% of C₉-C₁₀⁺ alkylate. The F-SiO₂ catalysts are more selective to C₇-C₈ alkylate, i.e. 23.7% TMP against 55.5 wt.-% C₉-C₁₀⁺. In comparison, the sulfuric acid catalyst yielded 48.8% C₉-C₁₀⁺ and 31.3% TMPs. For the solid catalysts, the increasing i-C₄/C₄⁼ ratio lowers the TMP fraction, i.e. for i-C₄/C₄⁼ = 10, the TMP proportion is only 10.2 wt.-% and C₉-C₁₀⁺ fraction reaches 76.4 wt.-% When i-C₄/C₄⁼ = 5, the TMP fraction is 16.9 wt.-% and C₉-C₁₀⁺ alkylate is 64.9 wt.-% At those low ratios the olefin dimerization could be promoted, rather than isoparaffin alkylation reactions. The surface acidity of the catalysts, i.e. those values close to H₀ = -9.6, and high pore volume (1.18 to 1.2 cm³/g) might be the most important factors for the heterogeneous reaction.