|M.Sc Student||Na'aman Yerucham|
|Subject||Forward Osmosis - Development of a Two Dimensional Model|
and Examination of a Process for Butanol
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Carlos Dosoretz|
|Full Thesis text - in Hebrew|
In Forward osmosis (FO) the solvent flows from a hypertonic to a hypotonic solution through a semi-permeable membrane. Two main factors preventing its application are: (i) Concentration polarization lowering the theoretical process potential; (ii) Large energy requirement for renewal of the hypertonic solution. The present research considered four aspects of FO related to these limitations.
The first one was aimed to develop the equations describing a two-component configuration with solute diffusion from the hypotonic solution in normal mode. The second aspect focused on understanding the impact of the geometrical structure of the support, i.e., tortuosity, porosity and permeability on the concentration-polarization (CP) phenomena. The third aspect of the research dealt with the development of a two-dimensional model for prediction of FO performance as a function of feed concentrations, cross-flow velocity and current flow (parallel or counter). The fourth aspect of the research was aimed to evaluate the potential of FO in the biofuel industry for pre-concentration of butanol produced by fermentation processes (toxic above 20 g/l). That is, exploding the osmotic potential in the concentrated sugar feed solution (20-40% glucose) generated for the fermentation process to draw out the water from the butanol solution. This hypertonic solution is always available and therefore there no regeneration is needed.
Unfortunately, the membranes (polyamides) that displayed considerable butanol rejection (80%) were not resistant to it at concentration of 20 g/L, and deteriorated after two hours run, whereas resistant membranes (CTA) displayed only 40% membranes. However, it was effective only when glucose concentration was above 1.5 molar (> 27%). Further research is needed on finding suitable FO membranes for butanol concentration, displaying high resistance & selectivity.
The basis for a two-dimensional model which allows the designing of an FO system according to its dimensions and flow regime was developed in the current study. This model allows the quantitative prediction of internal CP in a real process system as a function of the length of the membrane and of the product yield as a function of the solute concentration in both hypertonic and hypotonic solutions, in either parallel or counter-current flow. A calculation for a hypertonic solution of 1.5 M and an hypotonic solution of 0.5 M solved for a 1 meter membrane displayed an increase of 6% in the permeate flow in counter-current flow, highlighting the advantage of such system. A further enhancement in a full scale system (8-10 m length) is expected.