Conversion of hydrocarbons for fuel cell applications. Part 1: Autothermal reforming of sulfur-free and sulfur-containing hydrocarbon liquids. Part 2: Steam reforming of n-hexane on pellet and monolithic catalyst beds

The autothermal reforming process for conversion of various hydrocarbons to hydrogen and the use of monolithic catalyst beds in the steam reforming of n-hexane are described

Voting Rights Federalism

It’s well-known that the federal Voting Rights Act is reeling. The Supreme Court nullified one of its two central provisions in 2013. The Court has also repeatedly weakened the bite of the statute’s other key section. Less familiar, though, is the recent rise of state voting rights acts (SVRAs): state-level enactments that provide more protection against racial discrimination in voting than does federal law. Eight states have passed SVRAs so far—five since 2018. Several more states are currently drafting SVRAs. Yet even though these measures are the most promising development in the voting rights field in decades, they have attracted little scholarly attention. They have been the subject of only a handful of political science studies and no sustained legal analysis at all. In this Article, then, we provide the first descriptive, constitutional, and policy assessment of SVRAs. We first taxonomize SVRAs. That is, we catalogue how they diverge from, and build on, federal protections against racial vote denial, racial vote dilution, and retrogression. Second, we show that SVRAs are constitutional in that they don’t violate any branch of equal protection doctrine. They don’t constitute (or compel) racial gerrymandering, nor do they classify individuals on the basis of race, nor are they motivated by invidious racial purposes. Finally, while existing SVRAs are quite potent, we present an array of proposals that would make them even sharper swords against racial discrimination in voting. One suggestion is for SVRAs simply to mandate that localities switch to less discriminatory electoral laws—not to rely on costly, time-consuming, piecemeal litigation. Another idea is for SVRAs to allow each plaintiff to specify the benchmark relative to which racial vote dilution should be measured—not to stay mute on the critical issue of baselines

Metabolomic and 13C-metabolic flux analysis of a xylose-consuming Saccharomyces cerevisiae strain expressing xylose isomerase

Over the past two decades, significant progress has been made in the engineering of xylose-consuming Saccharomyces cerevisiae strains for production of lignocellulosic biofuels. However, the ethanol productivities achieved on xylose are still significantly lower than those observed on glucose for reasons that are not well understood. We have undertaken an analysis of central carbon metabolite pool sizes and metabolic fluxes on glucose and on xylose under aerobic and anaerobic conditions in a strain capable of rapid xylose assimilation via xylose isomerase in order to investigate factors that may limit the rate of xylose fermentation. We find that during xylose utilization the flux through the non-oxidative Pentose Phosphate Pathway (PPP) is high but the flux through the oxidative PPP is low, highlighting an advantage of the strain employed in this study. Furthermore, xylose fails to elicit the full carbon catabolite repression response that is characteristic of glucose fermentation in S. cerevisiae. We present indirect evidence that the incomplete activation of the fermentation program on xylose results in a bottleneck in lower glycolysis, leading to inefficient re-oxidation of NADH produced in glycolysis.Shell Oil CompanyNational Institute of General Medical Sciences (U.S.) Biotechnology Training Progra

Modeling and Dynamic Characterization of the Czochralski Crystal Growth Process

A lumped parameter model of the Czochralski crystal growth process is proposed that captures the dominant nonlinear dynamics, internal coupling, and disturbance structure. Conventional and advanced actuators are modeled. The dynamic characteristics of the interface shape and input/outputs that limit the achievable controller performance are identified. Introduction In previous papers we reported a 7th order lumped model of the process with a flat interface A schematic of the Czochralski process is shown in The crystal is begun by bringing a small seed in contact with the melt. After some equilibration time, the seed is pulled away from the melt. The crystal acts as a "cooling fin" which drives the solidification process. The operator adjusts the pulling rate and heater power to first neck the crystal which is a long thin section used to grow out dislocations that might be propagated into the crystal during seeding. The crystal is then grown out to diameter, shouldered, and maintained at the desired diameter. As the crystal grows in length, the melt level decreases, and the operator or automatic control system adjusts the power and/or pull rate to maintain constant diameter. Towards the end of growth run, the crystal can be tapered into a tail or suddenly lifted up from the melt to end the growth run

Improving formaldehyde consumption drives methanol assimilation in engineered E. coli

Due to volatile sugar prices, the food vs fuel debate, and recent increases in the supply of natural gas, methanol has emerged as a promising feedstock for the bio-based economy. However, attempts to engineer Escherichia coli to metabolize methanol have achieved limited success. Here, we provide a rigorous systematic analysis of several potential pathway bottlenecks. We show that regeneration of ribulose 5-phosphate in E. coli is insufficient to sustain methanol assimilation, and overcome this by activating the sedoheptulose bisphosphatase variant of the ribulose monophosphate pathway. By leveraging the kinetic isotope effect associated with deuterated methanol as a chemical probe, we further demonstrate that under these conditions overall pathway flux is kinetically limited by methanol dehydrogenase. Finally, we identify NADH as a potent kinetic inhibitor of this enzyme. These results provide direction for future engineering strategies to improve methanol utilization, and underscore the value of chemical biology methodologies in metabolic engineering

Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts

The atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity

First-principles design of a single-atom–alloy propane dehydrogenation catalyst

The complexity of heterogeneous catalysts means that a priori design of new catalytic materials is difficult, but the well-defined nature of single-atom–alloy catalysts has made it feasible to perform unambiguous theoretical modeling and precise surface science experiments. Herein we report the theory-led discovery of a rhodium-copper (RhCu) single-atom–alloy catalyst for propane dehydrogenation to propene. Although Rh is not generally considered for alkane dehydrogenation, first-principles calculations revealed that Rh atoms disperse in Cu and exhibit low carbon-hydrogen bond activation barriers. Surface science experiments confirmed these predictions, and together these results informed the design of a highly active, selective, and coke-resistant RhCu nanoparticle catalyst that enables low-temperature nonoxidative propane dehydrogenation

Metabolic model integration of the bibliome, genome, metabolome and reactome of Aspergillus niger

The release of the genome sequences of two strains of Aspergillus niger has allowed systems-level investigations of this important microbial cell factory. To this end, tools for doing data integration of multi-ome data are necessary, and especially interesting in the context of metabolism. On the basis of an A. niger bibliome survey, we present the largest model reconstruction of a metabolic network reported for a fungal species. The reconstructed gapless metabolic network is based on the reportings of 371 articles and comprises 1190 biochemically unique reactions and 871 ORFs. Inclusion of isoenzymes increases the total number of reactions to 2240. A graphical map of the metabolic network is presented. All levels of the reconstruction process were based on manual curation. From the reconstructed metabolic network, a mathematical model was constructed and validated with data on yields, fluxes and transcription. The presented metabolic network and map are useful tools for examining systemwide data in a metabolic context. Results from the validated model show a great potential for expanding the use of A. niger as a high-yield production platform

Assessment of control techniques for the dynamic optimization of (semi-)batch reactors

YesThis work investigates how batch reactors can be optimized to increase the yield of a desired product coupling two appealing techniques for process control and optimization: the nonlinear model predictive control (NMPC) and the dynamic real-time optimization (D-RTO). The overall optimization problem is formulated and applied to calculate the optimal operating parameters of a selected case study and the numerical results are compared to the traditional control/optimization techniques. It has been demonstrated in our previous work (Pahija et al, Selecting the best control methodology to improve the efficiency of discontinuous reactors, Computer Aided Chemical Engineering, 32, 805-810, 2013) that the control strategy can significantly affect optimization results and that the appropriate selection of the control methodology is crucial to obtain the real operational optimum (with some percent of improved yield). In this context, coupling NMPC and D-RTO seems to be the ideal way to improve the process yield. The results presented in this work have been obtained by using gPROMS® and MS C++ with algorithms of BzzMath library