The demand for fossil derivate fuels and chemicals has increased, augmenting concerns on climate change, global economic stability, and sustainability on fossil resources. Therefore, the production of fuels and chemicals from alternative and renewable resources has attracted considerable and growing attention. Ethanol is a promising biofuel that can reduce the consumption of gasoline in the transportation sector and related greenhouse gas (GHG) emissions. Lignocellulosic biomass is a promising feedstock to produce bioethanol (cellulosic ethanol) because of its abundance and low cost. Since the conversion of lignocellulose to ethanol is complex and expensive, the cellulosic ethanol price cannot compete with those of the fossil derivate fuels. A promising strategy to lower the production cost of cellulosic ethanol is developing a biorefinery which produces ethanol and other high-value chemicals from lignocellulose. The selection of such chemicals is difficult because there are hundreds of products that can be produced from lignocellulose. Multiple reviews and reports have described a small group of lignocellulose derivate compounds that have the potential to be commercialized. Some of these products are in the bench scale and require extensive research and time before they can be industrially produced. This review examines chemicals and materials with a Technology Readiness Level (TRL) of at least 8, which have reached a commercial scale and could be shortly or immediately integrated into a cellulosic ethanol process.

The cost of enzymes makes enzymatic hydrolysis one of the most expensive steps in the production of lignocellulosic ethanol. Diverse studies have used commercial enzyme cocktails assuming that change in total protein concentration during hydrolysis was solely due to adsorption of endo- and exoglucanases onto the substrate. Given the sensitivity of enzymes and proteins to media conditions this assumption was tested by evaluating and modeling the protein concentration of commercial cocktails at hydrolysis conditions. In the absence of solid substrate, the total protein concentration of a mixture of Celluclast 1.5 L and Novozyme 188 decreased by as much as 45% at 50 °C after 4 days. The individual cocktails as well as a mixture of both were stable at 20 °C. At 50 °C, the protein concentration of Celluclast 1.5 was relatively constant but Novozyme 188 decreased by as much as 77%. It was hypothesized that Novozyme 188 proteins suffer a structural change at 50 °C which leads to protein aggregation and precipitation. Lyophilized β-glucosidase (P-β-glucosidase) at 50 °C exhibited an aggregation rate which was successfully modeled using first order kinetics (R2 = 0.97). By incorporating the possible presence of chaperone proteins in Novozyme 188, the protein aggregation observed for this cocktail was successfully modeled (R2 = 0.96). To accurately model the increasing protein stability observed at high cocktail loadings, the model was modified to include the presence of additives in the cocktail (R2 = 0.98). By combining the measurement of total protein concentration with the proposed Novozyme 188 protein aggregation model, the endo- and exoglucanases concentration in the solid and liquid phases during hydrolysis can be more accurately determined. This methodology can be applied to various systems leading to optimization of enzyme loading by minimizing the excess of endo- and exoglucanases. In addition, the monitoring of endo- and exoglucanases concentrations can be used to build mass balances of enzyme recycling processes and to techno-economically evaluate the viability of enzyme recycling.

Enzyme recycling by adsorption from supernatant to fresh substrate is a promising strategy to reduce enzyme expenses and the production cost of lignocellulosic ethanol. The study was performed using oxygen-delignified wheat straw, and the effect of lignin content, enzyme loading, and hydrolysis time on recycling was determined. The percent of recycled cellulases, 0–35% of initial cellulase loading, increased with increasing enzyme loading and hydrolysis time but decreased with increasing lignin content. Cellulose conversions of 10–71% were achieved during the second hydrolysis round using only recycled cellulases indicating the existence of a highly active subset of enzymes. To achieve constant production of sugars during enzyme recycling, fresh cellulases were loaded before the second hydrolysis round to match the cellulase loading used in the first round. Subsequently, similar glucose, xylose, and protein concentrations were obtained at the end of the first and second rounds for all conditions. Recycling mass balances were developed to support future techno-economic analyses to determine the impact of enzyme recycling on the cost of ethanol.

Cellulose nanocrystals (CNCs) have become valued bionanomaterials with enormous potential to bring fundamental changes and benefits to society. We evaluated the techno‐economic viability of using sulfuric acid and enzymatic hydrolysis technologies to produce CNCs from bleached eucalyptus Kraft pulp (BEKP) in stand‐alone facilities. Experiments were performed on the enzymatic and acid hydrolysis of BEKP and the separation and isolation of the generated CNCs. The results obtained were used to determine reaction yields and compositions through the process stages and to build mass balances for the production of CNCs via acid and enzymatic hydrolysis. We used the process data that were generated to simulate and scale up process models of the production of CNCs using Aspen Plus. Techno‐economic analyses of the simulated processes were performed using Aspen Process Economic Analyzer to generate capital and operating cost estimates. At an estimated minimum selling price (MSP) of $10 031/dry tonne of CNCs, the production of CNCs via acid hydrolysis can be technically and economically competitive. Further research and process optimization efforts should focus on low‐cost technologies that minimize water use and on sulfuric acid recovery technologies that lead to lower production costs. The production of CNCs via enzymatic hydrolysis requires a low capital investment. However, due to its low reaction yield, a reflection of the still early stage of process development, the production cost of the enzymatic CNCs, with an MSP of $65 740 dry tonne of CNCs t–1, is too high to be commercially attractive. Nonetheless, the low capital cost of producing CNCs by using enzymatic hydrolysis indicates that the process may be profitable if the enzymatic hydrolysis yield is drastically improved. Research efforts towards developing an enzyme cocktail designed and optimized specifically for CNCs production and the introduction of an efficient and low‐cost pretreatment stage prior to enzymatic hydrolysis to increase the accessibility of enzymes to cellulose may improve the hydrolysis yield. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd