Study on phenol sulfonation by concentrated sulfuric acid: Kinetics and process optimization

Abstract

Sulfonation process usually exhibit high reaction rate and low yield and selectivity of product in common reactors for its insufficient micromixing. This work employed a rotating packed bed (RPB) to intensify the micromixing of the phenol sulfonation process to improve the yield and selectivity of p-hydroxybenzenesulfonic acid (p-HBSA). Experiments and kinetic study on the sulfonation of phenol by concentrated sulfuric acid were carried out in a stirred tank reactor (STR). The reaction rate constant k and activation energy E at certain temperature was tested. The values of pre-exponential factor and activation energy were obtained as follows: k1 = 5.74 × 103, E1 = 8.17 kJ/mol, k-1 = 6.95 × 103, E-1 = 6.18 kJ/mol, k2 = 1.43 × 1010, E2 = 69.35 kJ/mol, k-2 = 0.05 × 103, E-2 = 14.17 kJ/mol. The effects of various operating conditions including reaction temperature (T), sulfuric acid/phenol molar ratio (η), solvent/phenol molar ratio (ζ), concentrated sulfuric acid feeding rate (Q′), stirring speed (P), ageing time (τ), on the content of p-HBSA were investigated in an attempt to obtain the optimal operating conditions in the STR. The yield of p-HBSA is 89.85% at the optimal operating conditions. On the basis of the results in STR, further experiments were performed in a rotating packed bed (RPB) to improve the sulfonation reaction selectivity and p-HBSA yield. The effects of rotation speed (N), cycle time (t) and concentrated sulfuric acid feeding rate (Q) were investigated. Results show that the yield of p-HBSA can reach up to 96.52% in RPB at the optimal operating conditions of N = 2250 rpm, Q = 300 mL/min, T = 100 °C, η = 1.1, τ = 25 min, ζ = 1.25 and t = 3 min. The yield of p-HBSA obtained in the RPB is 6.67% higher than that in the STR. The research exhibits that RPB can obviously improve the yield of p-HBSA.