Currently available commercial pervaporation membranes are limited by their stability, in especially strong organic solvents and under acidic conditions. In recent publications the unprecedented stability of HybSi® membrane technology is reported.
HybSi membranes are suitable for demanding separations using pervaporation at temperatures up to at least 190°C, in aggressive aprotic solvents including N-methyl-2-pyrrolidone (NMP), and down to a pH value of ~2. The continuous measurements lasted for periods of months to 1,000 days. The results show that HybSi membranes have a very wide operation window.
Membranes are well known to be able to shift the equilibrium of reactions by removing one of the products. By removing water from esterification or acetalisation reactions the productivity can be improved significantly.
Acetals are considered as an important biobased diesel additive but the production from an alcohol and an aldehyde suffers from a low conversion. A critical evaluation on the HybSi membrane performance, catalyst activity, optimal configuration, and feed composition leads to the conclusion that a combined reaction and separation (membrane reactor) is, however, not preferred for this process.
The membrane selectivity was sufficiently high. The water permeance was somewhat too low in relation with the catalyst activity, the reactor volume and selected membrane area. These results were published together with the Engineering School of Bilbao in J of Membrane Science.