New support layer material for the reactive extraction of lignosulfonates

In the sulfite process lignosulfonates (LS) are liberated in the digestion step into the spent liquor. Water solubility over the entire pH range and the complex matrix of the process stream makes lignosulfonate isolation challenging. A possible approach for the selective isolation of lignosulfonates is the extraction using amines as reactive agent. The main drawback of the extraction having such complex process streams is the emulsion and crud formation [1]. Supported liquid membrane permeation equipment effectively prevented emulsion formation, and this approach was tested for lignosulfonate extraction.
In this study the isolation of lignosulfonates from both, technical solution (calcium lignosulfonates) and a real process stream with semipermeable flat sheet cellulose membranes (thickness 53.1-69.6 μm) was investigated. Beside untreated membranes, cellulose films treated with HMDS and TFFA+Ac2O to influence the wettability were tested. The experiments were carried out in the two-phase contact, the aqueous feed and the organic extractant phase were separated by the cellulose films.
The results show that the extraction of lignosulfonates from technical solutions as well as real process streams through the cellulose membrane is possible. In addition, crud formation was successfully prevented. Particle size distribution measurements of the feed and the stripping phase using dynamic light scattering (DLS) revealed that only the smaller fraction of lignosulfonates was isolated, a fractionation process was hence realized at the same time as selective separation of lignosulfonates especially from hemicellulose was observed. This result is of high interest since applications of lignosulfonates often require a constant product quality regarding particle size and without hemicellulose as accompanying product.