(81b) In Situ biobutanol Recovery from Culture Media By Modified Activated Carbon: Equilibrium, Kinetics, and Reusability

In this research, a modified activated carbon was used to separate 1-butanol (2.35 g/L) produced by genetic modified SynechocystisPCC 6803 from culture media. Biobutanol produced from cyanobacteria was considered as a promising sustainable energy candidate for relieving the current energy crisis. The biobutanol can be separated by distillation, liquid extraction, sorption, pervaporation, and so on. The most widely used traditional method to separate the biobutanol from its culture media was distillation. However, with the consideration of the technical difficulties and energy consumption generated from other separation methods to recover this relatively low concentration biobutanol, the sorption that has been neglected on biobutanol recovery can be an alternative sustainable way to reduce the process energy consuming and corresponding minimize the operation cost comparing to the distillation process. To achieve such effective sorption on this low concentration biobutanol recovery without any previous research done before, the normal carbon was experienced a two-step modification to possess a super high hydrophobicity and lipophilicity.

The sorption step in this in situbiobutanol separation was simply applied after separating the culture media from the SynechnocystisPCC 6803 cells. Without breaking the cyanobacteria cell, the biobutanol, an extracellular product existed in the separated culture media, was directly sorbed by immersing the modified activated carbon into the media for 24 hours. The modified activated carbon after 24 hours sorption went through a rough filtration process by pouring the liquid media and modified activated carbon through a mesh. The resulted modified activated carbon was sent to the distillation for the desorption of the sorb liquid. Then, a layer separation was observed in the desorption liquid, with a top layer mainly consisting of butanol and a bottom layer mainly consisting of water according to the gravity. This layer separate approved an irreplaceable successful in both energy and cost saving of the sorption process compared to those of the distillation. Since in distilling the biobutanol with a low concentration of 2.35g/L, a layer separation can be found after distilling the biobutanol for the first time. Hence, for separating the same amount of biobutanol, the sorption cooperated with the distillation can significantly reduce the liquid amount that needed to be distilled. The liquid amount that needed to be distilled already concentrated on the biobutanol concentration by experiencing the sorption procedure. Meanwhile, the butanol concentration left in the culture media after sorption was as low as the butanol concentration after about 20 hours distillation, which also exhibited the energy saving aspect of the sorption procedure. Compared to other biobutanol recovery technology, such sorption technique that has been neglected was demonstrated highly effective in both energy consumption and cost expense. For the estimation of the operation cost and energy efficiency, the reusability of the modified activated carbon was also studied. The corresponding results of the reusability experiments strengthened the above conclusion by testifying the sorption capacity of the as-prepared hydrophobic activated carbon for 1 month reuse studies. To understand the sorption mechanisms better, both sorption kinetics and equilibrium was investigated on this biobutanol recovery procedure by comparing different mathematic models.