Abstract
A downstream process for the purification and concentration of formic acid (FA) from FA/gluconic acid (GA) mixtures, obtainable by a coupled biocatalytic reaction of CO2 reduction and glucose oxidation, has been developed. The process involved two technologies: (i) a first nanofiltration (NF) step to separate FA and GA, and (ii) a second reactive liquid-liquid extraction (RLLE) step to concentrate FA. The NF process, using a Synder NFX membrane, consisted of three NF steps separated into two divergent lines, named permeate and retentate pathways. The first NF was common for both pathways, resulting in a permeate strongly enriched in FA and depleted in GA, and a retentate with opposite characteristics. In the permeate pathway, this first permeate was subjected to a second NF to obtain a 99.6% pure FA permeate. In the retentate pathway, an additional NF step on the first retentate resulted in a concentrated 99.4% pure GA retentate. The final diluted FA permeate was concentrated by RLLE using tri-N-octylamine as extractant in n-octanol, and a final back-extraction with NaOH. The optimized RLLE process involved a 100-fold volume decrease and resulted in a final FA solution (as sodium formate) of 174.5 g/L, 78 times more concentrated than the feed.
Highlights
The use of CO2 as a feedstock for producing chemicals through car bon capture and utilization (CCU) strategies is currently receiving a great deal of attention as a way to move towards a low carbon and circular economy [1]
Biotechnolog ical processes for the conversion of CO2 into formic acid (FA) involve a redox reaction catalysed by the enzyme formate dehydrogenase (FDH), a reversible reaction that in nature occurs in the opposite way, that is the oxidation of FA to CO2 [6]
A case study dealing with the development of a downstream process for the separation, purification and concentration of FA from FA/gluconic acid (GA) mixtures obtainable by a coupled biocatalytic reac tion is presented
Summary
The use of CO2 as a feedstock for producing chemicals through car bon capture and utilization (CCU) strategies is currently receiving a great deal of attention as a way to move towards a low carbon and circular economy [1]. An interesting alternative to the chemical methods is based on biotechnology and involves the use of microorganisms or enzymes to catalyse that conversion. It is generally accepted that biotechnological methods show some advantageous properties when compared with chemical ones, such as ambient tem perature and pressure operation, which reduces energy costs, and a high selectivity and specificity, which avoids by-product generation. The industrial implementation of a biotechnological process for the conversion of CO2 into FA is currently a great challenge, mainly due to the high NADH requirements, which need the introduction of a mechanism for its in situ continuous regeneration for repeated use throughout the process, and, most importantly, because the low productivity and yield of the reaction, as a direct result of the low solubility of gases, specially hydrogen, in water and, of the gas–liquid mass transfer lim itations [7]
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