M.D. Ackerson

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.

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 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.

Bioreactor design for synthesis gas fermentations

Abstract Bacterial cultures have been isolated for the conversion of synthesis gas (CO, H2 and CO2) into ethanol or methane. These heterogeneous reactions require the transport of substrate through the gas phase, across the interface into the liquid phase, and to the solid micro-organisms. The reactions are generally mass transfer limited due to very low gas solubilities. Bioreactors must maximize mass transport, while achieving high cell densities to promote fast reaction. This paper examines the performance of both dispersed gas phase systems (continuous stirred-tank reactor) and dispersed liquid phase systems (immobilized cell reactor) under mass transfer controlled and non-mass transfer controlled conditions. Mass transfer coefficients are determined and models are developed to predict bioreactor behaviour. Retention times of a few minutes are achieved for these gaseous substrate fermentations.

Mass-transfer and kinetic aspects in continuous bioreactors usingRhodospirillum rubrum

In designing bioreactors for the conversion of sparingly soluble gases, both mass transfer and kinetic effects must be considered.Rhodospirillum rubrum, an anaerobic photosynthetic bacterium capable of carrying out the water gas shift reaction, is an ideal organism for studying the relative importance of mass-transfer and kinetics since the cell concentration in continuous reactors employingR. rubrum may be regulated by the quantity of light supplied to the bacterium. This article addresses the performance ofR. rubrum in continuous stirred-tank and trickle-bed reactors, with particular attention given to the importance of mass-transfer and reaction kinetics in modeling reactor performance. Estimates of mass-transfer coefficients are made for a trickle-bed reactor system based upon reactor performance equations and experimental observations.

Biological conversion of poultry processing waste to single cell protein

Abstract In the processing of poultry for the production of prepared foods such as soups and frozen dinners, waste-water is generated containing significant quantities of fats, protein and starchy materials. These materials must be removed from the wastewater before it is discharged. Typical recovery consists of removing the solids through a combination of dissolved air flotation and filtration. The solids can then be rendered and utilized as poultry feed. This paper investigates an alternative to traditional processing in biologically producing valuable single cell protein from poultry processing waste. The results of fermentation experiments to produce single cell protein by both direct and indirect routes are presented.

Bioreactors for synthesis gas fermentations

Abstract Bacterial cultures have been isolated for the conversion of synthesis gas (CO, H2 and CO2) into ethanol or methane. These heterogeneous reactions require the transport of substrate through the gas phase, across the interface into the liquid phase, and to the solid microorganisms. The reactions are generally mass transfer limited due to very low gas solubilities. Bioreactors must maximize mass transport, while achieving high cell densities to promote fast reaction. This paper examines the performance of both dispersed gas phase systems (CSTR) and dispersed liquid phase systems (immobilized cell reactors) under mass transfer controlled and non-mass transfer controlled conditions. Mass transfer coefficients are determined and models are developed to predict bioreactor behavior. Retention times of a few minutes are achieved for these gaseous substrate fermentations.

Biosolubilization and liquid fuel production from coal

Recently, several microorganisms have been shown to be capable of directly solubilizing low-rank coals. This bioextract has a high molecular weight and is water soluble, but is not useful as a liquid fuel. This paper presents the results of studies to biologically solubilize coal and convert the solubilized coal into more useful compounds. Preliminary experiments have been conducted to isolate cultures for the serial biological conversion of coal into liquid fuels. Coal particles have been solubilized employing an isolate from the surface of Arkansas lignite. Natural inocula, such as sheep rumen and sewage sludge, are then employed in developing cultures for converting the bioextract into fuels. This paper presents preliminary results of experiments in coal solubilization and bioextract conversion.

Lysine production in continuous culture

Lysine is an essential amino acid that is widely used as a feed additive. Many animal feeds are deficient in lysine, so the lysine, as well as other amino acids, are added to these feeds to supply an adequate diet. Lysine is also used in pharmaceuticals as a diet supplement.Lysine is produced commercially in batch culture. Owing to the economic importance and the relatively high annual production of lysine, however, improvements in the process could be made by producing lysine in continuous culture. This paper presents the results obtained from the continuous production of extracellular lysine by direct fermentation by a strain ofBrevibacterium lactofermentum. These results are compared to batch fermentation results by the same organism.

Modeling lysine and citric acid production in terms of initial limiting nutrient concentrations

Abstract As an alternative to the traditional Monod equation, bioprocess models may be written in terms of initial nutrient concentrations for those cases where the limiting nutrient concentration cannot be easily measured. This paper presents batch bioprocess results for growth and production of lysine by Brevibacterium lactofermentum and growth and production of citric acid by Saccharomycopsis lipolytica . A linear cell growth model was developed based only on initial cell and nutrients (ammonia/soytone) concentrations. Luedeking-Piret equations were used as mathematical models for substrate utilization and product formation. The parameters specific for each bioprocess were then determined and used in computer simulations. The models were found to predict growth and substrate utilization fairly well for both bioprocesses. The model used for citric acid production predicted the onset of acid formation with good accuracy, as well as the separation of growth and product formation. The model for lysine production accurately predicted simultaneous growth and product formation for the bioprocess conducted with B. lactofermentum .