Catalytic Synthesis of Thiophene from Dialkyl Disulfides and n -Butane

Abstract

A modern industrial process for hydrocarbon feedstock cleaning of mercaptans is their oxidation to dialkyl disulfides with molecular oxygen in an alkaline medium in the presence of phthalocyanine catalysts [1 − 4]. The following main reactions relevant to this treatment for the removal of mercaptans occur in the material: 2 RSNa + 0.5 O 2 + H 2 O RSSR + 2 NaOH . As follows from this scheme, a byproduct of the process is a mixture of organic dialkyl disulfides RSSR, the so-called disulfide oil (DSO), a waste whose disposal from demercaptanization units is still an unresolved problem. To date, the disulfide oil has not found qualified application and is practically undisposable; meanwhile, its storage creates a safety hazard. Thus, the stock of DSO produced all over the world continuously grows. Therefore, the problem of the utilization of the disulfide oil via its processing into chemicals that are in demand is of great importance. One of the possible ways of coping with the problem is the conversion of DSO into thiophene, a compound used for the synthesis of a range of valuable drugs for human and veterinary medicine, as well as chemicals for agriculture (herbicides and pesticides) At present, according to In this work, we studied the feasibility of thiophene synthesis from organic dialkyl disulfides (disulfide oil) and n -butane using a modified magnesia-chromia-alumina catalyst. EXPERIMENTAL Feedstock components used in laboratory studies of thiophene synthesis were dimethyl disulfide containing a 99.57 wt % base substance; a mixture of organic dialkyl disulfides (disulfide oil) from the propanebutane demercaptanization unit (Orenburg gas processing plant) with dimethyl disulfide, methyl ethyl disulfide, and diethyl disulfide contents of 69.69, 24.54, and 3.15 wt %, respectively; and a grade B n -butane cut (TU (Technical Specifications) 0272-026-00151638-99) which contained 88.0 wt % n -butane (OAO Nizhnekamskneftekhim). A special catalytic system containing chromium and magnesium oxides as an active component and potassium and/or lanthanum oxides as a promoter of the general formula , where t lies in the range 5 wt %; x , y , and z are at most 3.2, 2, and 10 wt %, respectively; and the value of n ranges within 0-1, was designed for the thiophene Abstract -A promising new method for thiophene synthesis on the basis of dialkyl disulfides (byproduct of demercaptanization of hydrocarbon feedstocks) catalyzed by a modified magnesia-chromia-alumina catalyst was developed