James L. Gaddy

The Biological production of ethanol from synthesis gas

There has been considerable interest recently in the production of liquid fuels from coal through direct or indirect liquefaction. A culture has been isolated from animal waste that is capable of producing ethanol and acetate from carbon monoxide and from hydrogen and carbon dioxide, the major components of synthesis gas. This paper presents results of batch and continuous laboratory studies with this culture. Special efforts are directed toward maximizing the ratio of ethanol to acetate.

Bioconversion of synthesis gas into liquid or gaseous fuels

Abstract CSTR and packed-column models are presented for the biological production of liquid and gaseous fuels from coal synthesis gas.

Synthesis gas as substrate for the biological production of fuels and chemicals

Synthesis gas provides a simple substrate for the production of fuels and chemicals. Synthesis gas can be produced via established technologies from a variety of feedstocks including coal, wood, and agricultural and municipal wastes. The gasification is thermally efficient and results in complete conversion of the feedstock to fermentable substrate.Clostridium ljungdahlii grows on the synthesis gas components, carbon monoxide, hydrogen, and carbon dioxide. Production of acetic acid and ethanol accompanies growth with synthesis gas as sole source of energy and carbon. Rate and yield parameters are compared forC. ljungdahlii grown on carbon monoxide, or hydrogen with carbon dioxide.

Biological conversion of coal and coal-derived synthesis gas

Recent research has resulted in a number of promising biological pathways to produce clean fuels from coal. These processes all involve two or more steps: either the biosolubilization of coal, followed by bioconversion to ethanol or methane; or conversion of coal to synthesis gas, followed by bioconversion into alcohols or methane. Sulfur may also be removed from the solubilized coal or synthesis gas in a separate, or concurrent, biological step. This paper presents research results from both the direct and indirect conversion of coal to liquid fuels using biological processes. A review of direct conversion techniques in producing liquid fuels from coal in a serial conversion process is presented. In addition, bioreactor design data for the conversion of CO, CO2 and H2 in synthesis gas by Clostridium ljungdahlii in both batch and continuous culture are reviewed and discussed.

Biological production of ethanol from coal synthesis gas: Medium development studies

The anaerobic bacteriaClostridium ljungdahlii produces ethanol and acetate from CO, CO2, and H2 in synthesis gas. Early studies with the bacterium showed that relatively high concentrations of ethanol could be produced by lowering the fermentation pH and eliminating yeast extract from the medium in favor of a defined medium. This article presents the results from a medium development study based on the aerobic bacteriumEscherichia coli. The results of continuous-reactor studies in a continuously stirred tank reactor (CSTR) with and without cell recycle are shown to demonstrate the utility of this improved medium.

The effects of furfural on ethanol production by saccharomyces cereyisiae in batch culture

Browning reaction products such as furfural and 5-hydroxy-methyl-furfural (HMF) have been shown to inhibit microbial growth and metabolism in ethanol fermentations using Saccharomyces cerevisiae. This paper quantifies the extent of furfural inhibition on yeast growth, glucose utilization, and ethanol production as a function of inoculum size (0.1–9 gl−1. Batch culture experiments were conducted using furfural concentrations in the range of 0 to 2.0 gl−1. and mathematical correlations were proposed and tested. The results indicate that the specific growth rate decreased with increasing furfural concentration and inoculum size, while the maintenance coefficients were unaffected. The apparent and true cell yield coefficients on glucose were depressed with the addition of furfural. Specific production rates were unaffected at the furfural levels used but ethanol inhibition was apparent. The specific production rate was less inhibited by ethanol at higher inoculum sizes. Global specific productivities were not affected by the presence of furfural. At a 0.1 gl−1. inoculum size, furfural depletion was complete within 15–20 h, depending upon the furfural concentration employed. At higher inoculum levels (2–9 gl−1. all furfural was depleted in less than 5 h.

Biological production of alcohols from coal through indirect liquefaction

ConclusionsA bacterial culture has been isolated from animal waste that is capable of converting CO in synthesis gas to ethanol and acetate. The culture requires a yeast extract level of approximately.01 g/L, and the conversion is enhanced by agitation. The culture produces a higher yield of ethanol and ratio of ethanol to acetate when BESA and excess yeast extract are removed from the media. An ethanol concentration of 4.3 g/L has been obtained in batch screening experiments.The culture has been purified by successive dilution and tentatively identified as a member of theClostridium species. Further experimentation is required for positive identification.

Design of bioreactors for coal synthesis gas fermentations.

Abstract Anaerobic bacteria may be utilized in the conversion of CO, CO 2 and H 2 in synthesis gas to products such as methane, acetate, ethanol and butanol. Bioreactors for these fermentations are mass transfer limited due to very low gas solubilities. Several reactor designs have been examined for these conversions including batch, continuous stirred tank and bubble column reactors. This paper presents laboratory results for these reactor systems using the strict anaerobe Peptostreptococcus productus as a model organism. Results comparing the performance of these reactors and showing the effects of increased mass transfer and total pressure on system performance are presented are discussed.

Biological production of liquid and gaseous fuels from synthesis gas

Liquid and gaseous fuels may be produced biologically from coal by the indirect conversion of coal synthesis gas. Methane has been produced from synthesis gas using acetate and CO2/H2 as intermediates, utilizing a number of CO-utilizing and methanogenic bacteria. Also, a bacterium that is capable of producing ethanol from synthesis gas through indirect liquefaction has been isolated fron natural inocula. This paper summarizes research to optimize the performance of some of these cultures. These conversions, involving H2 and CO, which are only slightly soluble in the liquid media, may be mass transfer limited, and methods to enhance mass transport are examined. Experimental results and models for several reactor designs, including CSTR and packed columns, are presented and discussed.

Continuous fermentation for the production of citric acid from glucose

Citric acid is finding new areas of use each year and the demand for the acid is constantly increasing. Being a bulk chemical, the continuous production of citric acid would be advantageous. The paper presents the results from ammonia limited batch and continuous fermentations using the yeast strainSaccharomycopsis (Candida) lipolytica (NRRL Y-7576). Mathematical models were developed for growth and glucose utilization in batch and continuous culture. Cell and acid yields appeared to be almost the same in batch and continuous culture. The specific production rates were found to be constant, equal to 0.053 g/g h, in the batch fermentations but varied in the continuous experiments from 0 to 0.11 g/g h depending on the fermentation conditions. Continuous production in a single stage CSTR was studied for over 1,000 hours without shutdown.