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The conversion of biomass, specifically lignocellulosic biomass, into fuels and chemicals has recently gained national attention as an alternative to the use of fossil fuels. Increasing the concentration of the biomass solids during biochemical conversion has a large potential to reduce production costs. These concentrated biomass slurries have highly viscous, non-Newtonian behavior that poses several technical challenges to the conversion process. A collaborative effort to measure the rheology of a biomass slurry at four separate laboratories has been undertaken. A comprehensive set of rheological properties were measured using several different rheometers, flow geometries, and experimental methods. The tendency for settling, water evaporation, and wall slip required special care when performing the experiments. The rheological properties were measured at different concentrations up to 30% insoluble solids by mass. The slurry was found to be strongly shear-thinning, to be viscoelastic, and to have a significant concentration-dependent yield stress. The elastic modulus was found to be almost an order of magnitude larger than the loss modulus and weakly dependent on frequency. The techniques and results of this work will be useful to characterize other biomass slurries and in the design of biochemical conversion processing steps that operate at high solids concentrations.

Electrochemical synthesis can provide more sustainable routes to industrial chemicals 1 – 3 . Electrosynthetic oxidations may often be performed ‘reagent-free’, generating hydrogen (H 2 ) derived from the substrate as the sole by-product at the counter electrode. Electrosynthetic reductions, however, require an external source of electrons. Sacrificial metal anodes are commonly used for small-scale applications 4 , but more sustainable options are needed at larger scale. Anodic water oxidation is an especially appealing option 1 , 5 , 6 , but many reductions require anhydrous, air-free reaction conditions. In such cases, H 2 represents an ideal alternative, motivating the growing interest in the electrochemical hydrogen oxidation reaction (HOR) under non-aqueous conditions 7 – 12 . Here we report a mediated H 2 anode that achieves indirect electrochemical oxidation of H 2 by pairing thermal catalytic hydrogenation of an anthraquinone mediator with electrochemical oxidation of the anthrahydroquinone. This quinone-mediated H 2 anode is used to support nickel-catalysed cross-electrophile coupling (XEC), a reaction class gaining widespread adoption in the pharmaceutical industry 13 – 15 . Initial validation of this method in small-scale batch reactions is followed by adaptation to a recirculating flow reactor that enables hectogram-scale synthesis of a pharmaceutical intermediate. The mediated H 2 anode technology disclosed here offers a general strategy to support H 2 -driven electrosynthetic reductions. A quinone-mediated hydrogen anode design shows that hydrogen can be used as the electron source in non-aqueous reductive electrosynthesis, for a more sustainable way to make molecules at larger scale.

CHARLES G. HILL, JR., SC.D, is Professor Emeritus at the University of Wisconsin-Madison with over 200 peer-reviewed publications to his credit. In addition to his academic work, he has served as a consultant to government agencies and private corporations. Dr. Hill's research has been highly interdisciplinary, including experience as a Fulbright Senior Scholar collaborating on studies of enzymatic reactions at the Institute for Catalysis and Petrochemistry (Spain). THATCHER W. ROOT, PHD, is Professor of Chemical Engineering at the University of Wisconsin-Madison. Dr. Root was awarded an NSF Presidential Young Investigator Award and recently received the Benjamin Smith Reynolds Award for Excellence in Teaching Engineers.

Additives that alter the rheology of lignocellulosic biomass suspensions were tested under conditions of variable pH, temperature, and solid concentration. The effects of certain ions, biomass type, and time after the addition of rheological modifier were also examined. Torque and vane rheometry were used to measure the yield stress of samples. It was found that the effectiveness of rheological modifiers depends on pH over a range of 1.5 to 6, biomass type, concentration of certain ions, and time after addition. The time-dependent properties of rheologically modified biomass are sensitive to the type of rheological modifier, and also to mixtures of these additives, which can result in unexpected behavior. We show that time-dependent rheology is not correlated with time-dependent changes of the water-soluble polymer (WSP) in the aqueous environment, such as slow polymer hydration, suggesting that time-dependent changes in the polymer-fiber interaction may play a more significant role.

A large field of research has developed for the study of cyanobacteria for photosynthetic chemical production. Understanding the bioenergetics of growth and product secretion of cyanobacteria requires experiments in controlled environments with volumes large enough to allow sampling over time without removing most of the culture medium. The cost of commercial laboratory photobioreactors makes these experiments inaccessible to many researchers and limits experimental throughput. In this work, we designed and constructed a system of 12 independent, sterilizable cyanobacterial photobioreactors for cultures up to 1 L in volume for a cost less than a single commercial photobioreactor. This system allows gas mixing to a desired CO2 concentration for transfer to the culture medium, discrete modulation of light intensity through addition/removal of fluorescent tubes, temperature control in the range of ambient temperature to 45 C, and simple sterile sampling for monitoring throughout long-term growth experiments. In the following sections, we will describe the assembly and operation of this photobioreactor system.

NOx reduction product speciation during regeneration of a fully formulated lean NOx trap catalyst has been investigated using a bench-scale flow reactor. NH³ and N₂O were both observed during the regeneration phase of fast lean/rich cycles that simulated engine operation. Formation of both products increased with higher reductant concentrations and lower temperatures. Steady flow experiments were used to decouple the regeneration reactions from the NOx storage and release processes. This approach enabled a detailed investigation into the reactions that cause both formation and destruction of non-N₂ reduction products. Pseudosteady state experiments with simultaneous flow of NOx and reductant indicated that high concentrations of CO or H₂ drive the reduction reactions toward NH₃ formation, while mixtures that are stoichiometric for N₂ formation favor N₂. These experiments also showed that NH₃ is readily oxidized by both NO and O2 over the LNT catalyst. These observations were incorporated into a schematic of the regeneration process that takes into account the spatial and temporal variations occurring within the catalyst.