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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Process Intensification for Direct Conversion of Biomass-Based Syngas to High Octane Gasoline

The conversion of lignocellulosic-derived carbon sources via the creation of a CO2 rich syngas stream provides means to produce liquid hydrocarbon fuels, with advancements intended to create a cost-competitive method of sequential conversion via methanol and dimethyl ether intermediates. Previously developed methods with Cu/Beta zeolites enabled the conversion of dimethyl ether to linear and branched hydrocarbons, with high selectivities towards products with high-octane fuel properties. Through process intensification, use of a single reactor to convert syngas to methanol and DME, then further to hydrocarbons, allows for reduced capitol and operation cost for the same chemistries that typically use 3 reactors instead of one. Utilization of commercially available methanol synthesis catalyst (Megamax 800, Clariant, CZA) and methanol dehydration catalyst with the Cu/Beta catalyst allowed for conversion into hydrocarbon products in this single reactor set up. Reactor configuration with CZA and alumina catalysts mixed with or stacked in a bed physically above the Cu/Beta catalyst provided a system for the direct conversion of the syngas to hydrocarbons with improved yields and selectivities with higher net C1 conversions for stacked bed configurations. Through control of the process conditions, greater conversion of C1 oxygenate intermediates (i.e., methanol and dimethyl ether) was achieved with concomitant increase in selectivities towards gasoline and jet fuel range olefin and paraffin products. Lower hydrocarbon number products and less naphthenes were observed for the conversion of syngas compared to DME conversion on only the Cu/Beta system with prominent selectivities observed for C4, C5, and C7 hydrocarbons. The DME and methanol formation rates, with understanding of the equilibria for both processes, were determined as important factors to allow for improved performance of the Cu/Beta. Determination of the factors which allow for tuning of selectivities and yields created an intensified process which allows for a "market-responsive" biorefinery design, which can produce high octane gasoline or jet fuel range hydrocarbons to meet demands for a more sustainable route to liquid fuels.

BIOMASS FUELS↗
DOE OSTI2023

Polymers having stable cationic pendant groups for use as anion exchange membranes

Poly(aryl alkylene) polymers or poly(aryl-crown ether-alkylene) polymers with pendant cationic groups are provided which have an alkaline-stable cation, such as imidazolium, introduced into a rigid aromatic polymer backbone free of ether bonds. Hydroxide exchange membranes or hydroxide exchange ionomers formed from these polymers exhibit superior chemical stability, hydroxide conductivity, decreased water uptake, good solubility in selected solvents, and improved mechanical properties in an ambient dry state as compared to conventional hydroxide exchange membranes or ionomers. Hydroxide exchange membrane fuel cells and hydroxide exchange membrane electrolyzers comprising the poly(aryl alkylene) polymers or poly(aryl-crown ether-alkylene) polymers with pendant cationic groups exhibit enhanced performance and durability at relatively high temperatures.

Yan, Yushan↗
DOE OSTI2022

Catalyst design to direct high-octane gasoline fuel properties for improved engine efficiency

The paraffin-to-olefin (P/O) ratio in gasoline fuel is a critical metric affecting fuel properties and engine efficiency. In the conversion of dimethyl ether (DME) to high-octane hydrocarbons over BEA zeolite catalysts, the P/O ratio can be controlled through catalyst design. Here, we report bimetallic catalysts that balance the net hydrogenation and dehydrogenation activity during DME homologation. The Cu-Zn/BEA catalyst exhibited greater relative dehydrogenation activity attributed to higher ionic site density, resulting in a lower P/O ratio (6.6) versus the benchmark Cu/BEA (9.4). The Cu-Ni/BEA catalyst exhibited increased hydrogenation due to reduced Ni species, resulting in a higher P/O ratio (19). The product fuel properties were estimated with an efficiency merit function and compared against finished gasolines and a typical alkylate blendstock. Merit values for the hydrocarbon product from all three BEA catalysts exceeded those of the comparison fuels (0–5.3), with the product from Cu-Zn/BEA exhibiting the highest merit value (9.7).

Catalyst design↗
DOE OSTI2024

Experimental study of mechanistic factors influencing solvent-driven fractional crystallization of calcium sulfate

To advance dimethyl ether-driven fractional crystallization (DME-FC), a more sustainable method of water treatment and mineral recovery, a range of chemical equilibria were measured. These include varying concentrations of miscible organic solvents (MOS) used to experimentally measure the solvent-induced solid-liquid equilibrium (SLE) of calcium sulfate (CaSO 4 ) in water. Seven MOS, including dimethyl ether (DME), acetonitrile (MeCN), 1,4-dioxane, tetrahydrofuran (THF), acetone, ethanol, and diethylamine, were screened to establish trends associated with molecular volume, functional groups, and physical properties. The effect of MOS on CaSO 4 removal differed at concentrations <0.15 mol fraction MOS; MOS with greater molecular volume (THF, 1,4-dioxane, and diethylamine) induced greater CaSO 4 precipitation on a per mole basis. The solvent-induced SLE for all MOS converged between 0.15 and 0.2 mol fraction MOS, reaching a CaSO 4 concentration consistent with a water to MOS hydration ratio of 5:1 to 6:1, which may correspond to the solvent generating a solution-based pseudo-clathrate structure with continuity within the solution. Finally, solution pseudo-clathrate structures provide a mechanistic basis for DME-FC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Superior CO 2 /N 2 separation performance of highly branched Poly(1,3 dioxolane) plasticized by polyethylene glycol

With its high content of CO 2 -philic ether oxygen groups, poly(1,3-dioxolane) (PDXLA) has emerged as an attractive platform to achieve excellent CO 2 /N 2 separation properties for post-combustion carbon capture. Herein we demonstrate that the separation properties of PDXLA can be further enhanced by plasticizing with miscible polyethylene glycol (PEG)-based additives using an integrated experimentation and modeling approach. The effects of the chain end groups and loading level of the additives on the physical properties of the blends are thoroughly investigated, including glass transition temperature (T g ), fractional free volume, and gas transport properties, and the effects can be satisfactorily described using models available for homogeneous blends. Notably, a T g -integrated free volume model is adapted to successfully interpret the unified effect of the blend composition and temperature on gas diffusivity and permeability. A sample containing 45 mass% PEG dimethyl ether (PEGDME with a molecular mass of 240 g/mol) displays stable mixed-gas CO 2 permeability of 1540 Barrer and CO 2 /N 2 selectivity of 40 when challenged with a model flue gas at 60 °C, outperforming Robeson's 2008 upper bound. Elucidating how small plasticizers impact gas transport in homogeneous blends may unravel a facile way to design high-performance membranes for gas separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Demarcating the Impact of Electrolytes on High–Nickel Cathodes and Lithium–Metal Anode

The ever-growing demand for low-cost, high-energy-density lithium-ion batteries (LIBs) makes high-nickel layered oxide cathodes, especially LiNiO 2 (LNO), one of the most appealing candidates. However, poor structural and surface instability that leads to a short cycle life remains a formidable challenge. Herein, a systematic investigation of LNO performance in two different electrolytes (a conventional carbonate-based LP57 electrolyte and an ether-based localized high-concentration electrolyte (LHCE)) with different charge cut-off voltages is presented. These findings show that the cathode-electrolyte reactivity is the main factor dictating the performance degradation of LNO at high voltages rather than bulk integrity. While LHCE can provide good stability beyond 4.2 V with a robust, uniform solid–electrolyte interphase (SEI) layer on the Li-metal anode, there is no significant difference in cyclability at 4.15 V (96% capacity retention after 200 cycles) for both LP57 and LHCE. From LNO symmetric cells, carbonate-based electrolyte is found to be good for LNO stability while ether-based electrolyte is beneficial toward Li-metal anode. Furthermore, a suitable electrolyte or a low cut-off voltage is necessary to maintain a decent cycle life. Altogether, this work highlights the impact of electrolyte and cut-off voltage on LNO and Li-metal, which can help guide the development of cells based on LNO.

25 ENERGY STORAGE↗
DOE OSTI2020

A Comparative Study of Redox Mediators for Improved Performance of Li-Oxygen Batteries.

Redox meditators (RMs) are soluble catalysts located in an electrolyte that can improve the energy efficiency (reduced overpotential) and cyclability of Li-oxygen (Li-O-2) batteries. In this work, 20 RMs within a Li-O-2 system with dimethyl sulfoxide and tetraethylene glycol dimethyl ether electrolytes are studied and their electrochemical features such as redox potential, the separation of cathodic and anodic peaks, and their current intensities are measured using cyclic voltammetry (CV) experiments. Six RMs are selected as "primary" choices based on their electrochemical performance, and stability tests are then performed to examine their electrochemical responses after consecutive cycles. Moreover, galvanostatic cycling tests are performed within a Li-O-2 battery system assembled with selected six RMs for real case consistency investigations. It is found that results from CV to galvanostatic cycling tests are consistent for halides and organometallic RMs, where the former exhibit much higher stability. However, the organic RMs show high reversibility in CV but low in battery cycling results. Density functional theory calculations are carried out to gain more understanding of the stability and redox potentials of the RMs. This study provides comparative information to select the most reliable RMs for Li-O-2 batteries along with new fundamental understanding of their electrochemical activity and stability.

cyclic voltammetry↗
DOE OSTI2023

Vinyl Halide-Modified Unsaturated Cyclitols are Mechanism-Based Glycosidase Inhibitors

Suitably configured allyl ethers of unsaturated cyclitols act as substrates of β-glycosidases, reacting via allylic cation transition states. Incorporation of halogens at the vinylic position of these carbasugars, along with an activated leaving group, generates potent inactivators of β-glycosidases. Enzymatic turnover of these halogenated cyclitols (F, Cl, Br) displayed a counter-intuitive trend wherein the most electronegative substituents yielded the most labile pseudo-glycosidic linkages. Structures of complexes with the Sulfolobus β-glucosidase revealed similar enzyme-ligand interactions to those seen in complexes with a 2-fluorosugar inhibitor, the lone exception being displacement of tyrosine 322 from the active site by the halogen. Mutation of Y322 to Y322F largely abolished glycosidase activity, consistent with lost interactions at O5, but minimally affected (7-fold) rates of carbasugar hydrolysis, yielding a more selective enzyme for unsaturated cyclitol ether hydrolysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Reduced graphene oxide catalytically enhances the rate of cyanate ester curing under variable frequency microwave heating

Here, the curing of Lonza Primaset PT-30 novolac cyanate ester resin and EPON 826 bisphenol-A diglycidyl ether were investigated using convective thermal heating and variable frequency microwave (VFM) heating. The addition of 1 part per hundred reduced graphene oxide (r-GO) to PT-30 novolac cyanate ester increased the VFM cure rate compared to thermal heating. Curing it at 160°C for 240 min with VFM heating resulted in a 55% degree of cure compared to a 26% degree of cure with thermal heating. This observed VFM rate enhancement is due to selective microwave heating of the r-GO particles in the resin resulting in increased r-GO catalytic activity toward cyanate ester curing. It is both a thermal and catalytic effect, the latter of which is absent when r-GO is added to a bisphenol-A diglycidyl ether resin with o-phenylenediamine hardener. Impurities present in the PT-30 matrix do not appear to contribute to its overall cure kinetics, nor do they participate in the observed VFM rate enhancement.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Supramolecular Complexation-Enhanced CO 2 Chemisorption in Amine-Derived Sorbents

A supramolecular complexation approach is developed to improve the CO 2 chemisorption performance of solvent-lean amine sorbents. Operando spectroscopy techniques reveal the formation of carbamic acid in the presence of a crown ether. Here, the reaction pathway is confirmed by theoretical simulation, in which the crown ether acts as a proton acceptor and shuttle to drive the formation and stabilization of carbamic acid. Improved CO 2 capacity and diminished energy consumption in sorbent regeneration are achieved.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Nanofilm Composite Membranes of Bottlebrush Poly(1,3‐Dioxolane) Plasticized by Poly(Ethylene Glycol) for CO 2 /N 2 Separation

Abstract Poly(1,3‐dioxolane) has emerged as a leading membrane material for post‐combustion CO 2 capture due to its high ether oxygen content and strong affinity toward CO 2 . However, they are often cross‐linked to inhibit crystallization, which makes them impossible to fabricate into industrial thin‐film composite membranes. Herein, soluble and high molecular weight bottlebrush polymers ( b PDXLA) are synthesized using reversible addition‐fragmentation chain transfer polymerization and demonstrate the feasibility of fabricating nanofilm (≈100 nm) composite membranes (NCMs). Furthermore, b PDXLA can be plasticized using a miscible additive of poly(ethylene glycol) dimethyl ether (PEGDME) to improve CO 2 permeability while retaining good CO 2 /N 2 selectivity. For example, adding 20 mass% PEGDME improves CO 2 permeance from 930 to 1300 GPU and decreases CO 2 /N 2 selectivity from 74 to 53 at 25 °C; the membrane exhibits stable separation performance competitive with state‐of‐the‐art commercial membranes. This work unveils a practical approach to designing uncross‐linked, highly polar polymers for practical membrane gas separation and highlights a facile way to enhance performance by incorporating miscible plasticizers using industrial manufacturing processes.

Zhang, Gengyi [Department of Chemical and Biologic↗
DOE OSTI2024

Use of a Lignin-Based Admixture for Tailoring the Rheological Properties of Mortars for 3D Printing: Preprint

Efforts toward decarbonizing construction materials and industrial processes related to cement and concrete can be aided via multifaceted approaches that target alternative admixtures as well as precision control of fabrication. Chemical admixtures for water reduction have played a crucial role in the development of advanced concrete mixtures. Newer biomass processing techniques developed for aviation fuel production from corn stover biomass produce a more reactive lignin byproduct that is suitable for chemical modifications to mimic the properties of polycarboxylate ether admixtures with a smaller carbon footprint. The present study examines the use of lignin-based water-reducing admixture in cement pastes and mortar mixtures for 3D printing. The experimental program explores the use of different dosages of lignin-based admixture to produce 3D-printed samples with appropriate extrudability and buildability. The rheological characterization was performed to determine the flow curve of various mixtures. Finally, the heat of hydration of cement pastes was monitored via isothermal calorimetry to assess the impact of lignin-based admixtures on the hydration process of cement. The results of this study indicate that the use of biomass by-products, such as lignin-based admixtures have great potential to effectively control the fresh-state properties of cement-based materials.

bio-based admixtures↗
DOE OSTI2022

Olefin methylation over iron zeolites and the methanol to hydrocarbons reaction

The effect of olefin addition to a stream of dimethyl ether on the methanol homologation reaction is investigated using iron-substituted zeolites Fe-beta and Fe-ZSM-5. The reaction was investigated using plug-flow microreactors in the temperature range of 240–400 °C, at a total pressure of 0.239 MPa and a WHSV of 6.12 (g DME/ gcat -hr). For Fe-beta (Si/Fe= 9.2) catalysts, isobutene co-feeding almost doubles dimethyl ether (DME) consumption rate and shifts selectivity towards larger olefins with carbon numbers from 5 to 7. Addition of isobutene above 6.3%, however, resulted in a reduction of DME consumption rates, an effect assigned to the replacement of surface methoxy groups for adsorbed olefins in the zeolite pores. Below a temperature of 340 °C hydride-transfer rates are negligible; reaction rates are stable for over 5.5 h and the products consist almost exclusively of olefins and a small amount of methane. Above 360 °C the onset of catalytic hydride transfer processes is observed leading to fast catalyst deactivation rates and an increase in the concentration of aromatic species. Iron ZSM-5 (Si/Fe = 21.4) catalysts under similar reaction conditions consumes methanol faster than Fe-beta at approximately three times the TOF (on a per iron basis). The Fe-ZSM-5 catalyst was selective to a distribution of products (C5 to C8) as compared to Fe-beta which was selective to primarily C5 and C7. Co-feeding larger olefins (2-methyl-2-butene, 2,3-dimethyl-2-butene, 2,3,3-trimethyl-1-butene, and 2,4,4-trimethyl-2-pentene) at a 3.9% olefin concentration over Fe-beta changed selectivity towards cracking products (C4 compounds such as isobutene). As the size of the olefin increases, a reduction of DME consumption rate is also observed. Here these results show that co-feeding olefins with DME over Fe-zeolites is a promising route to increase methylation rates at relatively low temperatures producing larger branched olefins and that the product distribution is highly dependent on the zeolite pore size and structure of the olefin.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

O 2 -Dependence of reactions of 1,2-dimethoxyethanyl and 1,2-dimethoxyethanylperoxy isomers

Reaction mechanisms of Ṙ and ROȮ radicals derived from low-temperature oxidation of 1,2-dimethoxyethane (CH 3 O(CH 2 ) 2 OCH 3 ) were investigated using speciation from multiplexed photoionization mass spectrometry (MPIMS) measurements via Cl-initiated oxidation, in conjunction with electronic structure calculations. The experiments were conducted at 5 bar, from 450 K – 650 K, and O 2 concentrations from 1 · 10 14 cm –3 – 6 · 10 18 cm –3 to probe the effects on competing reaction channels of 1,2-dimethoxyethanyl (Ṙ) and 1,2-dimethoxyethanylperoxy (ROȮ) isomers. Several species were detected with photoionization spectral fitting – ethene, formaldehyde, methyl vinyl ether, and 2-methoxyacetaldehyde – and, as determined by electronic structure calculations, may form via unimolecular decomposition of 1,2-dimethoxyethanyl or 1,2-dimethoxyethanylperoxy. O 2 -dependent yield ratios show that the formation pathways for all species undergo a competition between O 2 -addition and unimolecular decomposition. Here, adiabatic ionization energies were also calculated and utilized along with exact mass determinations to infer contributions for other species derived exclusively from first- and second-O 2 -addition, including 1,2-dimethoxyethene, cyclic ethers, and dicarbonyls.

1,2-dimethoxyethane↗
DOE OSTI2020

Controllable depolymerization of lignin using carbocatalyst graphene oxide under mild conditions

Many efforts have been devoted to depolymerizing lignin to high-value aromatic monomers. However, a controllable and complete lignin inter-unit bond cleavage remains difficult because of the randomness in lignin structure and low selectivity in catalysis. Herein, we demonstrate that a sole carbocatalyst graphene oxide (GO) can selectively oxidize aryl- and alkyl-hydroxyl groups of lignin without the presence of any additional oxidizers, leading to lignin degradation under mild conditions. The results from lignin dimers, lignin oligomers, and organosolv lignin indicate that the depolymerization is catalyzed via an oxidative mechanism through an enol ether intermediate, a stable intermediate that has been chemically isolated here. Quantum chemistry calculations at the density functional theory level indicate that the phenolic –OH group in lignin facilitates the formation of radical cations and thus prohibits ring opening reactions, leading to the complete conversion of lignin dimers to guaiacol through the enol ether intermediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The quest for efficient oxygenated fuels: Examining interactions between lubricant components and oxygenates

This work empirically evaluated oxygenated blendstock-lubricant compatibility using a novel but simple method. The reactivity or compatibility was evaluated via gas chromatograph equipped with a flame ionization detector (GC-FID) before and after heating for 2h at 150 °C, which would roughly mimic conditions encountered in the combustion chamber of an Spark Ignition (SI) or Compression-Ignition (CI) engine. Five oxygenate blendstocks spanning several functional groups and chain lengths (prenol, isoprenol, butyl acetate, isohexanol, polyoxymethylene dimethyl ethers) were evaluated in a base fuel with nine variations of lubricant components of controlled concentrations, including fully formulated commercial lubricants. Baseline comparative examples were also generated, to decouple the effect of the oxygenate on the mixture, by heating only the base fuel with the lubricant component. Results demonstrate the relative compatibility between noted lubricants and oxygenates in base fuel upon heating. This was illustrated by minimal to no changes in the GC-FID traces. However, reactions of several of the chosen lubricants, especially Molybdenum di (2-ethylhexyl) phosphorodithioate (Molyvan L) and zinc dialkyldithiophosphate (ZDDP), with prenol and polyoxymethylene dimethyl ethers blendstocks showed substantial side reactions compared to corresponding baseline examples. Control experiments without oxygenates but comprising the same lubricant components showed no change in the mixture with heating. We concluded the incompatibility is due to the oxygenate and not the components of the base fuel. This preliminary work is valuable in establishing trends as well as provide useful information when a new component is introduced in the fuel.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Economic and Environmental Analysis to Evaluate the Potential Value of Co-Optima Diesel Bioblendstocks to Petroleum Refiners

The U.S. petroleum refining sector is undergoing a period of historic transformation, catalyzed by the decarbonization of the U.S. economy. Diesel-boiling-range bioblendstocks have gained traction, owing to their superior fuel properties and environmental performance as compared to traditional petroleum fuels. This work couples refinery linear programming models with life cycle assessment to quantify the potential economic and environmental benefits, and trade-offs, of blending diesel-boiling-range bioblendstocks at petroleum refineries. Linear programming models were developed in Aspen Process Industry Modeling Systems (PIMS) for three representative petroleum refinery configurations of differing complexity. Seven diesel-boiling-range bioblendstocks: 4-butoxyheptane, 5-ethyl-4-propylnonane, soy biodiesel, sludge hydrothermal liquefaction diesel, polyoxymethylene ethers, renewable diesel, and hexyl hexanoate, were investigated to identify key fuel properties that influence refineries' economics and to track the effect of adding bioblendstocks on refinery-wide cradle-to-gate greenhouse gases (GHG) emissions. These analyses considered blending levels from 10 to 30 vol% and fuel demand projections over the period 2040 to 2050. This analysis determines that bioblendstock sulfur content and cetane number are the primary fuel attributes with the potential to provide value to refiners. Life cycle assessment results indicate that the use of diesel-boiling-range bioblendstocks can reduce cradle-to-gate refinery GHG emissions by up to ~ 40 % relative to conventional refinery operations when considering carbon uptake in the supply chain of the bioblendstock. Refinery-wide marginal GHG abatement costs range from 120 to 3,600 USD2016/metric tons carbon dioxide equivalent avoided across the scenarios evaluated. Reducing the price of bioblendstocks is identified as a key to their adoption.

ADVANCED PROPULSION SYSTEMS,BIOMASS FUELS,ENERGY P↗