This patent describes a PTC process for manufacturing bis(trialkoxysilylpropyl) polysulfides. In addition to a high yield S-alkylation, a key aspect of this patent is a brine-recycle strategy that retains catalyst and unreacted starting materials in the aqueous phase, reduces fresh water consumption, minimizes chloride discharge, and lowers total catalyst make-up per batch.
Polysulfide anions are generated in aqueous phase from sodium hydroxide (or carbonate), sodium hydrosulfide, and elemental sulfur. A quaternary ammonium catalyst, typically TBAB, transfers these anions into the organic silane phase, where SN2 substitution on 3-chloropropyltrialkoxysilane forms the bis(trialkoxysilylpropyl) polysulfide with controlled sulfur-chain distribution. The system operates as a multiphase slurry followed by warm phase separation and thin-film evaporation to isolate the product.
The strength of the process lies in how the PTC system is managed. Recycled brine replaces fresh water, carrying dissolved catalyst and residual reactants forward into the next batch. Portion-wise or continuous catalyst addition reduces onium residence time, limiting decomposition and lowering overall catalyst consumption. The unwanted byproducts go into the solid salt cake. The useful components stay in solution. This makes sulfide handling easier and reduces downstream treatment. The result is lower water usage, reduced distillation and treatment energy, smaller equipment demand, and improved environmental compliance in regions with strict chloride limits.
From a PTC standpoint, the system leverages classic ion-transfer behavior: hydrated polysulfide anions are transported into the organic silane phase, where reduced hydration and looser ion pairing enhance effective nucleophilicity and enable efficient substitution under mild conditions. The silane serves as the organic phase, eliminating the need for polar aprotic solvents while maintaining practical cycle times.
