Comparative technoeconomic analysis of a softwood ethanol process featuring posthydrolysis sugars concentration operations and continuous fermentation with cell recycle

Abstract

Economical production of second generation ethanol from Ponderosa pine is of interest due to widespread mountain pine beetle infestation in the western United States and Canada. The conversion process is limited by low glucose and high inhibitor concentrations resulting from conventional low-solids dilute acid pretreatment and enzymatic hydrolysis. Inhibited fermentations require larger fermentors (due to reduced volumetric productivity) and low sugars lead to low ethanol titers, increasing distillation costs. In this work, multiple effect evaporation (MEE) and nanofiltration (NF) were evaluated to concentrate the hydrolysate from 30 g/l to 100, 150, or 200 g/l glucose. To ferment this high gravity, inhibitor containing stream, traditional batch fermentation was compared with continuous stirred tank fermentation (CSTF) and continuous fermentation with cell recycle (CSTF-CR). Equivalent annual operating cost (EAOC = amortized capital + yearly operating expenses) was used to compare these potential improvements for a local-scale 5 MGY ethanol production facility. Hydrolysate concentration via evaporation increased EAOC over the base process due to the capital and energy intensive nature of evaporating a very dilute sugar stream; however, concentration via NF decreased EAOC for several of the cases (by 2 to 15%). NF concentration to 100 g/l glucose with a CSTF-CR was the most economical option, reducing EAOC by $0.15 per gallon ethanol produced. Sensitivity analyses on NF options showed that EAOC improvement over the base case could still be realized for even higher solids removal requirements (up to two times higher centrifuge requirement for the best case) or decreased NF performance.

Hyper-Cross-Linked Additives that Impede Aging and Enhance Permeability in Thin Polyacetylene Films for Organic Solvent Nanofiltration

“…A green alternative for these energy-intensive purification techniques is membrane separation techniques (including pervaporation, membrane distillation) where energy consumption and investment costs are significantly lower. 3 In applications where alcohols are isolated from solid molecules, organic solvent nanofiltration (OSN) membranes are preferred. 1,4 Such membranes are characterized by their ability to prevent certain molecular weight compounds from permeating and their solvent-resistance.…”

“…Depending on the end application, alcohol purification can also be designed to maximize product recovery. , Batch solvent purification techniques, such as distillation and molecular sieving, are fundamental processes for the production of alcohols despite their high energy and spatial requirements. A green alternative for these energy-intensive purification techniques is membrane separation techniques (including pervaporation, membrane distillation) where energy consumption and investment costs are significantly lower . In applications where alcohols are isolated from solid molecules, organic solvent nanofiltration (OSN) membranes are preferred. , Such membranes are characterized by their ability to prevent certain molecular weight compounds from permeating and their solvent-resistance.…”

Ionic liquid pretreatment of yellow pine followed by enzymatic hydrolysis and fermentation

“…The progressive depletion of fossil fuel reserves due to the increase in energy consumption and the environmental concerns (such as CO 2 emissions) of fossil fuel consumption have entailed the search for alternative sustainable sources of energy . In this context, cellulosic ethanol has been considered as a promising alternative biofuel to conventional fossil fuels since it can be produced from inexpensive, abundant, renewable, and environmentally friendly lignocellulosic feedstocks . Ethanol production from lignocellulosics consists of four main steps: pretreatment, hydrolysis, fermentation, and product separation/distillation .…”