Engineering Issues in Synthesis-Gas Fermentations

Abstract

Biomass-derived synthesis gas can be readily converted into fuels and chemicals by anaerobic microorganisms. However, synthesis -gas fermentations typically exhibit low volumetric productivities due, in part, to low cell densities, production of unwanted by -products, and slow transfer of the synthesis gas into the liquid phase. Engineering approaches to improve bioreactor productivities are discussed, and recent advances in this area are summarized. Particular emphasis is placed on the use of bioreactor design to increase biocatalyst concentrations, development of metabolic models to study pathway regulation and the use of microbubble dispersions to enhance synthesis-gas mass transfer.Synthesis gas, which consists primarily of carbon monoxide (CO), and hydrogen (H 2 ), is produced by the partial oxidation of an organic feedstock at high temperature in the presence of steam. Although coal and petroleum have historically been the most commonly used feedstocks for synthesis-gas production, several new gasification plants have recently been based on biomass (7). Biomass offers several advantages over the traditional feedstocks. First, it has a much lower sulfur content than many coals. Synthesis gas produced from wood chips at the GE gasification plant in Schenectady, NY contained 28 ppm H 2 S (2), compared to 1-2% for coal-derived synthesis gases (3). Purification steps to remove sulfur from coal-derived synthesis gas are energy-intensive and add significantly to the product costs (4). Second, biomass materials are more reactive and thus require lower gasification temperatures and/or residence times. Fluidized-bed coal gasifiers are typically run at 1000°C using residence times of 0.5-3.0 h. By comparison, a temperature of 850°C was sufficient to gasify biomass using a residence time of 30 s to 5.0 min (5). Third, gasification of wood waste has the potential to solve a disposal problem while producing a valuable product. When wood waste is in

Enhancing CO−Water Mass Transfer by Functionalized MCM41 Nanoparticles

“…[1][2][3][4] Therefore, syngas fermentation is a potential pathway for converting biomass to a variety of fuels and chemicals because of its low cost and potentially high efficiency. The actual conversion efficiency depends on the microorganism and the desired product but can easily be 35% or higher.…”

Development of low cost medium for ethanol production from syngas by Clostridium ragsdalei

“…Syngas must be transferred from the gas phase to liquid phase so cells can convert it to products. Mass transfer is limited due to low solubility of CO and H 2 in the fermentation medium (Vega et al, 1990;Wilkins and Atiyeh, 2011;Worden et al, 1997).…”

Effect of Electrolytes on CO−Water Mass Transfer

“…Figure 2 shows the enhancement of CO-water volumetric mass transfer with various electrolytes as a function of electrolyte concentration. As shown in Figure 2a, the CO-water mass-transfer enhancement increased with electrolyte concentration when CuSO 4 2 O, the enhancement first increased, reached a maximum, and then decreased with increasing electrolyte concentration. For the sulfate salts, the maximum enhancement differed from 3.4 to 4.7 depending on the cation type.…”

“…Others have suggested that Gibbs elasticity, which is also proportional to (dγ/dc) 2 , provides an explanation for the influence of electrolytes on bubble coalescence. [30][31][32] Christenson and Yaminsky 31 suggested that the elastic response of the interface to changes in film thickness increases the coalescence time in electrolyte solutions compared to pure liquids (the Marangoni effect).…”

“…[30][31][32] Christenson and Yaminsky 31 suggested that the elastic response of the interface to changes in film thickness increases the coalescence time in electrolyte solutions compared to pure liquids (the Marangoni effect). The important quantity for this effect is the magnitude of dγ/dc or (dγ/dc) 2 . The electrolytes with low (dγ/dc) 2 values showed no inhibition in bubble coalescence.…”