31 Search Results

The advantage of a membrane/catalyst system in oxidative coupling of methane (OCM) compared to conventional reactive systems is that by introducing oxygen to the OCM catalytic sites through a membrane, parasitic gas phase reactions of O₂(g), responsible for lowering product selectivity, can be avoided. The design and fabrication of membrane/catalyst systems has, however, been hampered by low volumetric chemical conversion rates, high capital cost, and difficulties in codesigning membrane and catalyst properties to optimize the performance. We solve these issues by developing a dual-layer additive manufacturing process, based on phase inversion, to design, fabricate and optimize a hollow fiber membrane/catalyst system for OCM. We demonstrate the approach though a case study using BaCe_0.8Gd_0.2O_3-δ (BCG) as the basis of both the catalyst and separation layers. We show that by using the manufacturing approach we can codesign the membrane thickness and catalyst surface area so that the flux of oxygen transport through the membrane and methane activation rates in the catalyst layer match each other. Here, we demonstrate that this “rate matching” is critical for maximizing the performance, with the membrane/catalyst system significantly overperforming conventional reactor designs under identical conditions.

A method to produce 5-hydroxymethylfurfural (HMF) from C6 carbohydrates. The method includes the steps of reacting a reactant comprising at least one C6 carbohydrate, in a reaction mixture comprising at least about 5% (v/v) water, a polar, aprotic solvent, and an acid, for a time, at a temperature, and at a hydrogen ion concentration wherein at least a portion of the C6 carbohydrate present in the reactant is converted to 5-hydroxymethyl furfural (“HMF”).

The design of heterogeneous catalysts relies on understanding the fundamental surface kinetics that controls catalyst performance, and microkinetic modeling is a tool that can help the researcher in streamlining the process of catalyst design. Microkinetic modeling is used to identify critical reaction intermediates and rate-determining elementary reactions, thereby providing vital information for designing an improved catalyst. In this review, we summarize general procedures for developing microkinetic models using reaction kinetics parameters obtained from experimental data, theoretical correlations, and quantum chemical calculations. We examine the methods required to ensure the thermodynamic consistency of the microkinetic model. We describe procedures required for parameter adjustments to account for the heterogeneity of the catalyst and the inherent errors in parameter estimation. We discuss the analysis of microkinetic models to determine the rate determining reactions using the degree of rate control and reversibility of each elementary reaction. We introduce incorporation of Brønsted–Evans–Polanyi relations and scaling relations in microkinetic models and the effects of these relations on catalytic performance and formation of volcano curves. We review the analysis of reaction schemes in terms of the maximum rate of elementary reactions, and we outline a procedure to identify kinetically significant transition states and adsorbed intermediates. Here, we explore the application of generalized rate expressions for the prediction of optimal binding energies of important surface intermediates and to estimate the extent of potential rate improvement. We also explore the application of microkinetic modeling in homogeneous catalysis, electro-catalysis, and transient reaction kinetics. We conclude by highlighting the challenges and opportunities in the application of microkinetic modeling for catalyst design.

5-Hydroxymethyl furfural (HMF) is a platform chemical, which can be derived from lignocellulosic biomass, and used for production of liquid fuels and polymers. We demonstrate a process for production of HMF using sequential enzymatic and catalytic reactions of glucose to synthesize HMF, and simulated-moving-bed (SMB) separation to purify HMF. The adsorption thermodynamic parameters of glucose, fructose, and HMF on a commercial chromatography resin are experimentally determined for modeling the SMB-based HMF production process. The experimental data are used to develop a rigorous process model and then estimate the cost of production. Chromatographic separation of HMF has 16% lower operating costs compared to an extraction-based process and has a minimum selling price of approximately $1478 per ton. We demonstrate that the HMF process can be integrated with the high fructose corn syrup (HFCS) process, and we performed analyses considering two systems including construction of a new integrated facility and retrofitting an existing HFCS facility to produce HMF. Our analyses suggest that the latter approach is a promising short-term low-risk strategy to advance the HMF production technology to commercial scale.

Hitting the limits on propene synthesis The greater abundance of propane from shale gas has spurred efforts to use it as a propylene feedstock. Direct dehydrogenation catalysts consisting of platinum–tin alloy nanoparticles supported on alumina often must run with hydrogen dilution to avoid carbon buildup and excess tin to avoid alloy segregation. Motagamwalaet al.report that platinum–tin nanoparticles interact more weakly with a silica support and the metals thus do not segregate. The use of undiluted reactants allowed the reaction to run near the thermodynamically limit of about 67% conversion with a selectivity to propylene of more than 99%. This catalyst also does not build up carbon and could run up to 30 hours without deactivation. Science, abg7894, this issue p.217

Intentional (“on-purpose”) propylene production through nonoxidative propane dehydrogenation (PDH) holds great promise for meeting the increasing global demand for propylene. For stable performance, traditional alumina-supported platinum-based catalysts require excess tin and feed dilution with hydrogen; however, this reduces per-pass propylene conversion and thus lowers catalyst productivity. We report that silica-supported platinum-tin (Pt ₁ Sn ₁ ) nanoparticles (<2 nanometers in diameter) can operate as a PDH catalyst at thermodynamically limited conversion levels, with excellent stability and selectivity to propylene (>99%). Atomic mixing of Pt and Sn in the precursor is preserved upon reduction and during catalytic operation. The benign interaction of these nanoparticles with the silicon dioxide support does not lead to Pt-Sn segregation and formation of a tin oxide phase that can occur over traditional catalyst supports.

Following biomass fractionation of corn stover using γ-valerolactone (GVL) pretreatment, the resulting lignin stream was subjected to base hydrolysis reactions to achieve the isolation of pcoumaric acid (pCA) from p-coumarate esters present as pendent groups on the lignin. pCA was produced from 5-g-scale experiments in crude yields of 8.3 wt % with 95% purity and, following a straightforward purification using liquid–liquid extraction and crystallization from water, yielded crystalline pCA in 4.8 wt % yield with 97% purity; a methodology to realize 99.5% purity is demonstrated. Because of the mild saponification, the remaining lignin residue retains its value as a feedstock for oxidative or hydrogenolytic deconstruction or as a fuel for energy production in the biorefinery.

We show that 5-(hydroxymethyl) furfural (HMF) and acetone can be selectively converted into a range of biomass-derived high molecular weight chemicals in high yield (>90%). HMF was condensed with acetone and purified to produce HMF-Acetone-HMF dimer (HAH). We then selectively synthesized various compounds from HAH by the sequential catalytic reaction pathway of hydrogenation, ring-opening, and hydrodeoxygenation. These synthesized HMF-derived chemicals were characterized by 1D and 2D NMR spectra and high resolution mass spectrometry (HRMS). The HMF-derived molecules described in this paper can be feedstocks for the polymer, pigment, and petroleum industries.

A method to produce an aqueous solution of carbohydrates containing C5- and/or C6-sugar-containing oligomers and/or C5- and/or C6-sugar monomers in which biomass or a biomass-derived reactant is reacted with a solvent system having an organic solvent, and organic co-solvent, and water, in the presence of an acid. The method produces the desired product, while a substantial portion of any lignin present in the reactant appears as a precipitate in the product mixture.

During the past ten years, there has been significant interest and investment in the study of catalytic conversion of biomass-derived feedstocks into renewable fuels and chemicals. In the United States, an estimated $25 billion has been spent by venture capitalists, industry, and government agencies during this period of time to commercialize “renewable technologies” including solar energy, wind power, batteries, and biofuels (e.g., cellulosic ethanol). Four societal factors are driving these investments including: (1) the increased price of crude oil; (2) concerns about global warming; (3) the desire to improve rural economies where biomass is produced, and; (4) national goals to become energy self-sufficient. Furthermore, underlying these efforts is the realization that lignocellulosic biomass is the only realistic, near-term and non-food-competitive source of renewable organic carbon. To this end, legislative efforts, such as the US Renewable Fuel Standards, have been implemented to create subsidies, tax credits, mandates, and loan guarantees to help bring renewable fuel technologies to market. However, the representative body of industrial efforts to this end has faced significant challenges, with several startup companies having commercialized biomass conversion technologies but having struggled to reach commercial scale; in fact, many of these companies have filed for bankruptcy. This situation is likely due to the challenges associated with scaling up unproven pioneer processes, as well as neophyte investors not understanding the decade-long time frames and the sheer amount of funding that is often required to bring chemical process technologies to market. Nevertheless, several emerging catalytic technologies have either entered the market place, or are currently demonstrating their technologies in fully integrated pilot plants. Commercial and near commercial technologies for second generation biomass conversion technologies to-date include, among others: biomass-derived jet and diesel fuel from both waste vegetable oils and ethanol; small scale production of renewable jet and diesel from landfill gases via Fischer-Tropsch synthesis; catalytic conversion of carbohydrates into gasoline and aromatics; hydropyrolysis of biomass into gasoline and diesel, and; catalytic conversion of wood into aromatics. To be successful, biomass conversion technologies must ultimately be able to compete economically with petroleum technologies, which are already operating at large commercial scales and have been practiced for decades. To this end, various factors must be considered when evaluating the potential for new processes to compete with incumbent technologies; factors such as regional variations in feedstock quality and availability, government policy, subsidies and tax rates, and the proprietary positions of the ancillary technologies that might support the process. By any measure, however, a critical metric of the economic potential of a process is its efficiency with respect to the yield of products from raw materials, and this metric of performance is directly related to atom efficiency of the underlying chemical reactions. Therefore, while promising biomass conversion technologies continue to demonstrate progress towards commercialization, there remains an important need for the catalysis community to aid in this effort by: (1) designing more active, selective and stable catalysts, and (2) elucidating a more detailed understanding of the catalytic chemistries underlying these processes. Indeed, the study of catalytic biomass conversion has grown tremendously during the past decade; and new or emerging technologies that are in the laboratory stage have allowed for biomass to be converted into a wider variety of commodity chemicals and the full range of liquid fuels that are produced from petroleum. The objective of this perspective is to highlight some of the ongoing, fundamental challenges with respect to the catalytic conversion of biomass into renewable products, and to provide insight as to how the catalysis community can overcome several of these challenges. It is our belief that, as an international academic community of catalysis researchers, we can (and must) work together to address these challenges, and to drive progress toward the production of next-generation renewable chemicals and fuels from biomass.