Syngas fermentation to ethanol: the effects of gas recycling on economics

Syngas fermentation is a biochemical pathway to produce ethanol and has been commercialized successfully. The economic viability of this process could be further improved to become more competitive in the existing ethanol market. Improving gas utilization is the key, and can be done by recycling the unreacted syngas. This work is an early...

Quantification and mitigation of byproduct formation by low-glycerol-producing Saccharomyces cerevisiae strains containing Calvin-cycle enzymes

Background: Anaerobic Saccharomyces cerevisiae cultures require glycerol formation to re-oxidize NADH formed in biosynthetic processes. Introduction of the Calvin-cycle enzymes phosphoribulokinase (PRK) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) has been shown to couple re-oxidation of biosynthetic NADH to ethanol...

Gas mass transfer in syngas fermentation broths is enhanced by ethanol

In gas fermentations (using O2, CO, H2, CH4 or CO2), gas-to-liquid mass transfer is often regarded as one of the limiting processes. However, it is widely known that components in fermentation broths (e.g., salts, biomass, proteins, antifoam, and organic products such as alcohols and acids) have tremendous impact on the volumetric mass transfer...

Alleviating mass transfer limitations in industrial external-loop syngas-to-ethanol fermentation

Mass transfer limitations in syngas fermentation processes are mostly attributed to poor solubility of CO and H₂ in water. Despite these assumed limitations, a syngas fermentation process has recently been commercialized. Using large-sale external-loop gas-lift reactors (EL-GLR), CO-rich off-gases are converted into ethanol, with...

An engineered non-oxidative glycolytic bypass based on Calvin-cycle enzymes enables anaerobic co-fermentation of glucose and sorbitol by Saccharomyces cerevisiae

Background: Saccharomyces cerevisiae is intensively used for industrial ethanol production. Its native fermentation pathway enables a maximum product yield of 2 mol of ethanol per mole of glucose. Based on conservation laws, supply of additional electrons could support even higher ethanol yields. However, this option is disallowed by the...

Decarbonizing ethanol production via gas fermentation: Impact of the CO/H₂/CO₂ mix source on greenhouse gas emissions and production costs

This study explores key success factors for ethanol production via fermentation of gas streams, by assessing the effects of eight process variables driving the fermentation performance on the production costs and greenhouse gas emissions. Three fermentation feedstocks are assessed: off-gases from the steel industry, lignocellulosic biomass...

Decarbonising Industry via BECCS: Promising Sectors, Challenges, and Techno-economic Limits of Negative Emissions

Purpose of Review: This paper reviews recent literature on the combined use of bioenergy with carbon capture and storage (BECCS) in the industries of steel, cement, paper, ethanol, and chemicals, focusing on estimates of potential costs and the possibility of achieving “negative emissions”. Recent Findings: Bioethanol is seen as a potential near...

Understanding the failures in developing domestic ethanol markets: Unpacking the ethanol paradox in Guatemala

Fostered by environmental and economic drivers, liquid biofuels are expanding in the global energy matrix. However, many countries with biofuel potential, such as Guatemala, have yet to develop domestic biofuels markets. During the last decade, ethanol production in Guatemala has increased significantly, yet a domestic market does not appear...

Modeling ethanol production through gas fermentation: A biothermodynamics and mass transfer-based hybrid model for microbial growth in a large-scale bubble column bioreactor

Background: Ethanol production through fermentation of gas mixtures containing CO, CO₂ and H₂ has just started operating at commercial scale. However, quantitative schemes for understanding and predicting productivities, yields, mass transfer rates, gas flow profiles and detailed energy requirements have been lacking in...

Unveiling the Structure Sensitivity for Direct Conversion of Syngas to C2-Oxygenates with a Multicomponent-Promoted Rh Catalyst

Abstract: Mn and Li promoted Rh catalysts supported on SiO₂ with a thin TiO₂ layer were synthesized by stepwise incipient wetness impregnation approach. The thin TiO₂ layer on the surface of SiO₂ was proved to stabilize those small Rh nanoparticles and hinder their agglomeration. The reducibility of...

Novel genetic parts and cultivation strategies for yeast-based conversion of lignocellulosic feedstocks

The recent start-up of several full-scale ‘second generation’ ethanol plants marks a major milestone in the development of Saccharomyces cerevisiae yeast strains for fermentation of lignocellulosic hydrolysates of agricultural residues and energy crops. In contrast to the fermentation of hexose sugar-rich substrates, such as corn syrup or sugar...

Numerical investigation towards HiTAC conditions in laboratory-scale ethanol spray combustion

In the past 25 years high temperature air combustion (HiTAC) technology has been proved and utilized in industry as a promising way to increase thermal efficiency, create a relatively uniform temperature distribution, and reduce emissions of harmful pollutants such as NO_X and CO. However, due to the complexity of fuel-oil...

Exploring policy options to spur the expansion of ethanol production and consumption in Brazil: An agent-based modeling approach

The Brazilian government aims to increase the share of biofuels in the energy mix to around 18% by 2030, which implies an increase of ethanol production from currently 27 bln liters to over 50 bln liters per year. Biofuel policies play an important role in ethanol production, consumption, and investment in processing capacity. Nevertheless, a...