Reduction of acetone to isopropanol using producer gas fermenting microbes.

Gasification-fermentation is an emerging technology for the conversion of lignocellulosic materials into biofuels and specialty chemicals. For effective utilization of producer gas by fermenting bacteria, tar compounds produced in the gasification process are often removed by wet scrubbing techniques using acetone. In a preliminary study using biomass generated producer gas scrubbed with acetone, an accumulation of acetone and subsequent isopropanol production was observed. The effect of 2 g/L acetone concentrations in the fermentation media on growth and product distributions was studied with "Clostridium ragsdalei," also known as Clostridium strain P11 or P11, and Clostridium carboxidivorans P7 or P7. The reduction of acetone to isopropanol was possible with "C. ragsdalei," but not with P7. In P11 this reaction occurred rapidly when acetone was added in the acidogenic phase, but was 2.5 times slower when added in the solventogenic phase. Acetone at concentrations of 2 g/L did not affect the growth of P7, but ethanol increased by 41% and acetic acid concentrations decreased by 79%. In the fermentations using P11, growth was unaffected and ethanol concentrations increased by 55% when acetone was added in the acidogenic phase. Acetic acid concentrations increased by 19% in both the treatments where acetone was added. Our observations indicate that P11 has a secondary alcohol dehydrogenase that enables it to reduce acetone to isopropanol, while P7 lacks this enzyme. P11 offers an opportunity for biological production of isopropanol from acetone reduction in the presence of gaseous substrates (CO, CO2, and H2).

Effect of nutrient limitation and two-stage continuous fermentor design on productivities during "Clostridium ragsdalei" syngas fermentation.

The effect of three limiting nutrients, calcium pantothenate, vitamin B(12) and cobalt chloride (CoCl(2)), on syngas fermentation using "Clostridium ragsdalei" was determined using serum bottle fermentation studies. Significant results from the bottle studies were translated into single- and two-stage continuous fermentor designs. Studies indicated that three-way interactions between the three limiting nutrients, and two-way interactions between vitamin B(12) and CoCl(2) had a significant positive effect on ethanol and acetic acid formation. In general, ethanol and acetic acid production ceased at the end of 9 days corresponding to the production of 2.01 and 1.95 gL(-1) for the above interactions. Reactor studies indicated the three-way nutrient limitation in two-stage fermentor showed improved acetic acid (17.51 gg(-1) cells) and ethanol (14.74 gg(-1) cells) yield compared to treatments in single-stage fermentors. These results further support the hypothesis that it is possible to modulate the product formation by limiting key nutrients during C. ragsdalei syngas fermentation.

Effect of temperature, pH and buffer presence on ethanol production from synthesis gas by "Clostridium ragsdalei".

Fermentation pH, incubation temperature, and presence or absence of media buffer can alter the activity of microorganisms. For instance, carbon monoxide and hydrogen components of syngas show decreased solubility with increasing temperature, Clostridium species preferentially switch from acetogenesis to solventogenesis phase at pH below 5.0, and morpholinoethanesulfonic acid (MES) added as media buffer has been shown to increase lag time for ethanol production. The objective of the present study was to determine the effects of temperature, pH and MES buffer on ethanol production by "Clostridium ragsdalei". This study showed syngas fermentation using "Clostridium ragsdalei" at 32°C with media without buffer was associated with higher ethanol concentration and reduced lag time in switching to solventogenesis. Temperature above 40°C and pH below 5.0 were outside the optimal range for growth and metabolism of the bacteria.

Syngas fermentation in a 100-L pilot scale fermentor: design and process considerations.

Fermentation of syngas offers several advantages compared to chemical catalysts such as higher specificity of biocatalysts, lower energy costs, and higher carbon efficiency. Scale-up of syngas fermentation from a bench scale to a pilot scale fermentor is a critical step leading to commercialization. The primary objective of this research was to install and commission a pilot scale fermentor, and subsequently scale-up the Clostridium strain P11 fermentation from a 7.5-L fermentor to a pilot scale 100-L fermentor. Initial preparation and fermentations were conducted in strictly anaerobic conditions. The fermentation system was maintained in a batch mode with continuous syngas supply. The effect of anaerobic fermentation in a pilot scale fermentor was evaluated. In addition, the impact of improving the syngas mass transfer coefficient on the utilization and product formation was studied. Results indicate a six fold improvement in ethanol concentration compared to serum bottle fermentation, and formation of other compounds such as isopropyl alcohol, acetic acid and butanol, which are of commercial importance.

Feasibility of incorporating cotton seed extract in Clostridium strain P11 fermentation medium during synthesis gas fermentation.

Biomass gasification followed by fermentation of syngas to ethanol is a potential process to produce bioenergy. To make this process more economical, the complexity of media should be reduced while using less costly components. In this study, the feasibility of incorporating cotton seed extract (CSE) as a media component for syngas fermentation to produce ethanol using Clostridium strain P11 was evaluated. A factorial experiment was conducted to screen and evaluate the effect of different media components, in relation to CSE, on ethanol production. Also, different CSE concentrations as well as the presence of MES buffer were tested to determine their effect on ethanol production. Bottle fermentations with media containing only 1.0 gL(-1) CSE produced more ethanol after 15 d (1.17 gL(-1)) than fermentation using any other media. Further bottle experiments showed that media containing only 0.5 gL(-1) CSE produced more ethanol after 15 days (2.67 gL(-1)) than a control media (0.6 gL(-1)) and media containing only 1.0 gL(-1) CSE (2.16 gL(-1)). Fermentations in 5- and 7.5-L stirred fermentors with 0.5 gL(-1) CSE media achieved ethanol concentrations similar to those observed in bottle studies. These results indicate that CSE can replace all the vitamin and mineral media components generally used for fermentation of syngas to ethanol by Clostridium strain P11, thereby improving the process economics.