Research at SDSU has shown that the use of biochar (BC) or biochar based activated carbon (BAC) can adsorb individual chemicals or mixtures of chemicals from either liquid or gaseous streams. Biochar is a readily available byproduct of biofuel production.
Various biochemical and thermochemical technologies result in solutions that contain different levels of several types of products, typically in a solvent such as water. These chemicals may include long chain alcohols, alkenes, alkanes, aromatics and other organic chemical products. Following adsorption, the specific chemical(s) can be de-adsorbed by various mechanisms, such as temperatures or pressure swing, resulting in a liquid solution containing higher concentrations of the target chemicals. If the concentration of these chemicals is greater than their solubility, they can be separated from residual water by low cost phase separation.
For many types of biochemical or thermochemical technologies, the chemical product of interest is present in the bulk process liquid, which is often water. This aqueous solution could itself be passed through the BC or BAC to adsorb the chemical. Alternatively, the aqueous solution could be volatilized by heating, with the gas phase passing through the BC or BAC. Another option would be the use of gas or steam stripping to volatilize the chemicals, while minimizing the amount of water vapor generated. In biochemical technologies such as microalgae or cyanobacteria cultures, CO2 enriched air is passed through the culture vessel to supply CO2 and this gas can volatilize certain chemical products, so that the exhaust gas would pass through the BC or BAC.
The majority of biochemical and thermochemical processes to produce biofuels result in dilute mixtures of many compounds. Efficient and low cost recovery is crucially needed to achieve economic feasibility. In many cases the various chemicals present in these mixtures are difficult to economically separate. For example, butanol production processes typically also generate low levels of acetone and ethanol. The proposed BC or BAC process would separate these chemicals into individual columns based on adsorption and temperature. The cyanofactory process being developed to produce third generation biofuels from CO2 results in volatilization of water and the specific chemical in the gas phase that passes through the photobioreactor. The BC or BAC columns would adsorb the water and chemical from the gas phase, and following desorption and condensation, the concentration of the chemical should be sufficient to allow low cost phase separation.