Producing concentrated sugars and minimizing water usage are key elements in the economics and environmental sustainability of advanced biofuels. Conventional pretreatment processes that require a water-wash step can result in losses of fermentable sugars and generate large volumes of wastewater or solid waste. To address these problems, we have developed high gravity biomass processing with a one-pot conversion technology that includes ionic liquid pretreatment, enzymatic saccharification, and yeast fermentation for the production of concentrated fermentable sugars and high-titer cellulosic ethanol. The use of dilute bio-derived ionic liquids (a.k.a. bionic liquids) enables one-pot, high-gravity bioethanol production due to their low toxicity to the hydrolytic enzyme mixtures and microbes used. We increased biomass digestibility at >30 wt% by understanding the relationship between ionic liquid and biomass loading, yielding 41.1 g L -1 of ethanol (equivalent to an overall yield of 74.8% on a glucose basis)using an integrated one-pot fed-batch system. Our technoeconomic analysis indicates that the optimized one-pot configuration provides significant economic and environmental benefits for cellulosic biorefineries by reducing the amount of ionic liquid required by ~90% and pretreatment-related water inputs and wastewater generation by ~85%. In turn, these improvements can reduce net electricity use, greenhouse gas-intensive chemical inputs for wastewater treatment, and waste generation. The result is an overall 40% reduction in the cost of cellulosic ethanol produced and a reduction in local burdens on water resources and waste management infrastructure.

This article reports the first prospective life-cycle net energy assessment of a gigawatt-scale photoelectrochemical (PEC) hydrogen production facility.

Successfully interfacing enzymes and biomachineries with polymers affords ondemand modification and/or programmable plastic degradation during manufacture, utilization, and disposal, but requires controlled biocatalysis in solid matrices with macromolecular substrates. [1][2][3][4][5][6][7] Embedded enzyme microparticles have sped up polyester degradation, but compromise host properties and unintentionally accelerate microplastics formation with partial polymer degradation. 6,8,9 Here, by nanoscopically dispersing enzymes with deep active sites, semi-crystalline polyesters can be degraded primarily via chain-end mediated processive depolymerization with programmable latency and material integrity, akin to polyadenylationinduced mRNA decay. 10 It is also feasible to realize the processivity with enzymes having surface-exposed active sites by engineering enzyme/protectant/polymer complexes.Polycaprolactone and poly(lactic acid) containing less than 2 wt.% enzymes are depolymerized in days with up to 98% polymer-to-small molecule conversion in standard soil composts or household tap water, completely eliminating current needs to separate and landfill their products in compost facilities. Furthermore, oxidases embedded in polyolefins retain activities. However, the hydrocarbon polymers do not closely associate with enzymes like their polyester counterparts and the reactive radicals generated cannot chemically modify the macromolecular host. The studies described here provide molecular guidance toward the enzyme/polymer pairing and enzyme protectants' selection to modulate substrate selectivity and optimize biocatalytic pathways. They also highlight the need for in-depth research in solid-state enzymology, especially in multi-step enzymatic cascades, to tackle chemically dormant substrates without creating secondary environmental contamination and/or biosafety concerns.

1,3-Butadiene (1,3-BD) is a high-value chemical intermediate used mainly as a monomer for the production of synthetic rubbers. The ability to source 1,3-BD from biomass is of considerable current interest because it offers the potential to reduce the life-cycle greenhouse gas (GHG) impact associated with 1,3-BD production from petroleum-derived naphtha. Herein, we report the development and investigation of a new catalyst and process for the one-step conversion of ethanol to 1,3-BD. The catalyst is prepared by the incipient impregnation of magnesium oxide onto a silica support followed by the deposition of Au nanoparticles by deposition-precipitation. The resulting Au/MgO-SiO2 catalyst exhibits a high activity and selectivity to 1,3-BD and low selectivities to diethyl ether, ethylene, and butenes. Detailed characterization of the catalyst shows that the desirable activity and selectivity of Au/MgO-SiO2 are a consequence of a critical balance between the acidic-basic sites associated with a magnesium silicate hydrate phase and the redox properties of the Au nanoparticles. A process for the conversion of ethanol to 1,3-BD, which uses our catalyst, is proposed and analyzed to determine the life-cycle GHG impact of the production of this product from biomass-derived ethanol. We show that 1,3-BD produced by our process can reduce GHG emissions by as much as 155 % relative to the conventional petroleum-based production of 1,3-BD.

Decarbonizing the air transportation sector remains one of the most challenging hurdles to mitigating climate change.

Biofuels are widely touted as viable, albeit not straightforward, alternatives to petroleum-derived fuels. To best determine their utilization, many practitioners turn to life-cycle assessment (LCA) to ascertain the “environmental footprint”. Although parameters such as resource and land use, along with infrastructure, can be incorporated into LCA algorithms, many have noted that the methodological approach still needs careful attention. In this Feature, McKone et al. outline seven grand challenges that need to be engaged and surmounted to provide the best way forward for biofuel use.

In the modern global economy, water and energy are fundamentally connected. Water already plays a major role in electricity generation and, with biofuels and electricity poised to gain a significant share of the transportation fuel market, water will become significantly more important for transportation energy as well. This research provides insight into the potential changes in water use resulting from increased biofuel or electricity production for transportation energy, as well as the greenhouse gas and freshwater implications. It is shown that when characterizing the water impact of transportation energy, incorporating indirect water use and defensible allocation techniques have a major impact on the final results, with anywhere between an 82% increase and a 250% decrease in the water footprint if evaporative losses from hydroelectric power are excluded. The greenhouse gas impact results indicate that placing cellulosic biorefineries in areas where water must be supplied using alternative means, such as desalination, wastewater recycling, or importation can increase the fuel's total greenhouse gas footprint by up to 47%. The results also show that the production of ethanol and petroleum fuels burden already overpumped aquifers, whereas electricity production is far less dependent on groundwater.

Decarbonizing the transportation sector is critical to achieving global climate change mitigation. Although biofuels will play an important role in conventional gasoline and diesel applications, bioderived solutions are particularly important in jet fuels and lubricants, for which no other viable renewable alternatives exist. Producing compounds for jet fuel and lubricant base oil applications often requires upgrading fermentation products, such as alcohols and ketones, to reach the appropriate molecular-weight range. Ketones possess both electrophilic and nucleophilic functionality, which allows them to be used as building blocks similar to alkenes and aromatics in a petroleum refining complex. Here, we develop a method for selectively upgrading biomass-derived alkyl methyl ketones with >95% yields into trimer condensates, which can then be hydrodeoxygenated in near-quantitative yields to give a new class of cycloalkane compounds. The basic chemistry developed here can be tailored for aviation fuels as well as lubricants by changing the production strategy. We also demonstrate that a sugarcane biorefinery could use natural synergies between various routes to produce a mixture of lubricant base oils and jet fuels that achieve net life-cycle greenhouse gas savings of up to 80%.