Application of Membrane Processes for Concentration and Separation of Sugar Streams in Biofuel Production

The overall objective of this study was identification and development of a sugar concentration/separation membrane filtration unit to improve the bioconversion of lignocellulosic biomass into chemicals and fuels. This thesis is divided into three main parts. The first part is about our studies on the use of nanofiltration membranes for concentration of sugars in a lignocellulosic biomass hydrolysate. In addition, the feasibility of simultaneous removal of acetic acid, 5-(hydroxymethyl)furfural and furfural from the hydrolysate has also been investigated. The results obtained indicate that both concentration of sugars and removal of hydrolysis degradation products is feasible. However, careful selection of the membrane and operating conditions will be essential. Dead end filtration experiments have been used to test a number of commercially available nanofiltration membranes under a range of operating conditions. Model feed streams as well as real hydrolysates have been tested. The method developed here could be used to quickly screen membranes. Promising membranes and operating conditions could then be more rigorously tested in tangential flow operation. The second part of this work focuses on recycle of cellulase enzyme (biocatalyst) used to catalyze the biopolymers of cellulose to monomeric soluble sugars. The enzyme represents one of the main costs in bioconversion of lignocellulosic biomass into biofuel. But exploration and development of efficient ways to reuse and recycle the enzyme are of great interest. Here we explore the use of microfiltration and ultrafiltration membranes for enzyme recycle and reuse. Third part of this work is about modification of membranes using Layer-by-Layer (LbL) deposition of polyelectrolytes. Deposition of ultra-thin hyperbranched anionic and cationic polyelectrolytes on top of polysulfone ultrafiltration membranes results in a porous modified membrane showing nanofiltration characteristics. Deposition of polyelectrolytes on top of the polysulfone membrane substrate is confirmed by ATR-FTIR spectra, SEM images and filtration tests. We carried out several nanofiltration tests with 20 mM model feed streams containing sucrose, glucose and xylose. Results show that these membrane are capable of separating mono- and disaccharides

Optimizing Reaction-Absorption Process for Lower Pressure Ammonia Production

Ammonia separation using metal halide absorbents has been shown to be a viable path for ammonia production at lower pressure. This work reports on optimizing the operating parameters of the reaction–absorption process that can be adapted for large-scale processing. The experiments were executed in three different modes. First, the effect of reaction parameters on the production rate was studied. Then, the absorption conditions were investigated in a single-pass reaction-then-absorption mode to evaluate the effectiveness of the absorbent at different temperatures, pressures, and space velocities. Finally, fed-batch reaction-absorption tests were conducted in constant pressure to evaluate the process performance with optimized conditions and gain more in-depth understanding of the transient behavior of this process. Results suggest that the recycle flow rate and absorber temperature significantly influence the ammonia production rates. These findings were then used to optimize the performance of a continuous fed-batch ammonia production process at constant pressure. A production rate upward of 27 μmol gcat s–1 was obtained under the most optimized conditions, which is a factor of 14 greater than the best result reported earlier. The optimized conditions were then used to study the cyclic operation of the fed-batch reaction–absorption process in a cyclic process. A transient behavior was observed for the ammonia production, which could be attributed to the partial saturation of the absorber column. Stable performance of reaction-absorption process was demonstrated for more than nine cycles, with no decay in the performance of the absorber after relatively short regeneration cycles