Cellulosic ethanol: status and innovation

Abstract

Although the purchase price of cellulosic feedstocks is competitive with petroleum on an energy basis, the cost of lignocellulose conversion to ethanol using today's technology is high. Cost reductions can be pursued via either in-paradigm or new-paradigm innovation. As an example of new-paradigm innovation, consolidated bioprocessing using thermophilic bacteria combined with milling during fermentation (cotreatment) is analyzed. Acknowledging the nascent state of this approach, our analysis indicates potential for radically improved cost competitiveness and feasibility at smaller scale compared to current technology, arising from (a) R&D-driven advances (consolidated bioprocessing with cotreatment in lieu of thermochemical pretreatment and added fungal cellulase), and (b) configurational changes (fuel pellet coproduction instead of electricity, gas boiler(s) in lieu of a solid fuel boiler).

Rational strain engineering interventions to enhance cellulase secretion by Saccharomyces cerevisiae

“…The potential of second‐generation cellulosic biofuels has been slow to become a reality at industrial level . While more biorefineries are coming online to deliver on the decades old promise of cellulosic ethanol and other green chemicals, the recalcitrance of feedstocks, development of appropriate pre‐treatments, production of appropriate hydrolytic enzymes, and the development of ethanologens able to thrive in the hostile fermentation environment remain significant challenges to the growth and sustainability of this industry. The challenges of various feedstocks, the status quo of pre‐treatment methodologies, and the development of organisms for first‐ and second‐generation biofuels production have been reviewed recently …”

Bioethanol from Lignocellulosic Biomass

“…However, costs are much higher for the first plants now beginning operations for which capital costs are about 2.6-4.0 US$/liter of ethanol produced vs. the much lower capital cost estimate of 1.01 US$/annual liter [58]. In addition, the lower ethanol production capacities of between 38 and 114 million liters/year for these first-of-a-kind projects will incur somewhat larger annualized capital costs due to not taking advantage of the economies of scale that the presented design would enjoy with production rates that are 1.8-5.5 times larger.…”

“…Although significant advances in enzyme activity and pretreatment could lower costs for biological conversion of cellulosic biomass to be competitive, many years of enzyme research, development, and production have not yet succeeded in lowering biological deconstruction costs to be competitive when petroleum prices are low [58]. Thus, it is important to consider paradigm shifts that could dramatically alter the costs of biological ethanol production.…”

“…Wastewater treatment to remove soluble components left in the water so it can be recycled or released to the environment 9. Product storage for sale [13,58,178] Details can be found from various sources on the many possible choices and configurations for these operations and associated costs. The following briefly summarizes a process design developed to estimate ethanol production costs [179] (for more details see [179]).…”

“…The primary components making up cellulosic/ lignocellulosic biomass are cellulose, hemicellulose, and lignin, typically in that order of prevalence, plus generally lesser amounts of various other ingredients such as proteins, pectin, minerals, and sugars [3,18,58].…”