(400d) Volatile Product Recovery From a Photobioreactor Using Modified Blue Green Algae Strains and Bio-Char Based Activated Carbon As Adsorbent

Cyanobacteria (blue green algae) strains have been genetically modified to produce valuable biorenewable chemicals, long chain hydrocarbons and alcohols, including farnesene, myrcene, limonene, and linalool.  This transformative concept is proposed to establish a continuous cyanobacterial platform to convert sunlight and CO₂ into energy dense fuels and organic chemicals which could be used for sustainable chemical production in the specialty fragrance industry.  Furthermore, this cyanobacteria platform could fit into the current ethanol industry that produces surplus CO₂ throughout the Midwest and Great Plains.

Photobioreactors (PBR’s) growing these algal strains require substantial CO₂/Air bubble flow for optimum growth, but at the same time, the air flow will generally volatilize the specialty chemicals and carry the bioproducts to the reactor’s exhaust.  In order to capture the volatized fraction of products, an adsorption column loaded with activated carbon was attached to the photobioreactor’s exhaust for gas stripping.  Prior to the adsorption column, the exhaust vapor proceeded through an ice water condenser to remove excess moisture.  This effectively enhanced the chemical product’s concentration before adsorption.  The activated carbon column was thermally regenerated and coupled with a condenser to capture the desorbed products.

Different activated carbon materials were developed and compared to optimize the adsorption dynamic and equilibrium for each individual chemical product.  The hydrophobicity and hydrophilicity of activated carbon were determined to be important factors for chemical product recovery.   The regeneration characteristics, desorption point and heat of desorption, were measured using a Differential Scanning Calorimeter (DSC).  Simultaneously, the lifetime of activated carbon adsorbents were quantified.

Developing an integrated, recirculating adsorption recovery system, which harvests volatile products by gas stripping the photobioreactor’s exhaust, will be critical for expanding novel algal technologies.  The CO₂ requirement for algae growth already limits its accessibility for widespread geographical applications, but a synergistic combination of PBR’s with commercial ethanol plants could further improve the carbon efficiency and economics of ethanol production.  This technology will allow us to exploit two under-utilized resources in the Midwest and Great Plains (sunlight and CO₂) by converting them into storable, transportable, energy-dense, biorenewable fuels and chemicals.