Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “conversion”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Method for separation of coal conversion products from oxygen carriers

Complete fuel conversion represents an important, but unresolved, aspect in Chemical Looping Combustion (CLC). Different system design approaches are currently being investigated to maximize carbon conversion in the fuel reactor. To achieve greater than ninety percent conversion of the fuel in “fluid-bed” type reducers will require that CLC systems be equipped with additional process equipment to ensure that unburnt fuel leaving the reducer is minimized. This paper presents results obtained from a laboratory test system simulating a char stripper design comprising two components; one for separating large char particles, based on material density differentials, and another for removing small char particles from the oxygen carrier (OC) leaving the reducer, based on elutriation. A test unit was designed, built and operated to identify optimum conditions for separating OC material from unburnt solid fuel – char. The results obtained are necessary for designing a high temperature unit operated at temperatures expected within a CLC system.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2022

The role of lignin in the conversion of wheat straw to cellobionic acid by Neurospora crassa HL10

An engineered Neurospora crassa strain (HL10) naturally produces cellulases, cellobiose dehydrogenase (CDH), and heterologously expresses laccase. It can convert Avicel (cellulose) to cellobionic acid (cellobionate) without any enzyme addition at high yields. However, the addition of a catalytic amount of artificial redox mediators was required to achieve a high yield conversion. When a lignocellulosic substrate like wheat straw was used as the carbon source, it was found that adding exogenous artificial redox mediators did not improve cellobionate yield. We hypothesized that lignin and lignin degradation products were able to serve as redox mediators for the CDH-laccase conversion system. Experiments were designed to prove the hypothesis. When N. crassa HL10 was grown on Avicel, the addition of enzyme hydrolyzed lignin (EHL) can achieve a similar level of cellobionate production as with ABTS addition. The addition of EHL can increase the cellobionate production rate in the CDH-laccase bi-enzyme system using cellobiose as the substrate. The formation of lignin radicals, and the quenching of lignin radicals by reduced CDH, were verified by an electron paramagnetic resonance (EPR) experiment, providing further evidence that lignin radicals can serve as the electron acceptor of reduced CDH. Hence, lignocellulosic biomass is a self-sufficient substrate for the production of cellobionate. The conversion of the lignocellulosic substrate to cellobionate using N. crassa HL10 can be achieved without any exogenous enzyme addition or redox mediator addition.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Green synthesis of cellulose formate and its efficient conversion into 5-hydroxymethylfurfural

5-hydroxymethylfurfural (HMF) production from cellulose is a hot topic, while the rigidity of cellulose limits its efficient conversion into HMF. Cellulose formate has exhibited the great potential for HMF production but it’s synthesis via direct formylation of cellulose in formic acid is difficult. We reported a green synthetic route of cellulose formate and its efficient conversion into HMF. Ball milled cellulose formate (BCF) was synthesized via ball milling followed by formylation in formic acid at 80 °C for 0.5 h. The structure of BCF was thoroughly characterized and BCF was subsequently converted to HMF catalyzed by AlCl3 and HCl in dimethyl sulfoxide (DMSO)-H 2 O media. Results showed that ball milling of cellulose for 1–1.5 h efficiently deconstructed its crystallinity and degree of polymerization, boosting its further formylation and catalytic conversion. An overall 66.9% HMF yield from cellulose was achieved at 150 °C for 20 min using BCF derived from cellulose ball milled for 1.5 h as the substrate. BCF exhibits high reactivity toward HMF due to its excellent solubility and accessibility in DMSO-H 2 O media, and the release of formic acid in reaction further facilitates HMF production. BCF synthesized with different ball milling times shows different degrees of substitution of formyl groups, which could serve as an indicator and regulate the HMF production. The green synthesis of cellulose formate creates an efficient pathway for HMF production.

5-hydroxymethylfurfural↗
DOE OSTI2024

Pairing Ga/Al-Zeolites with tailored acidity as tandem catalysts for the conversion of alcohols to olefins

Zeolites are versatile catalysts owing to their tunable acidity where the active site(s) can be placed within the crystal framework or as extra-framework species in confined pores. A common approach to tailor Brønsted acidity is heteroatom exchange involving the replacement of framework aluminum with alternative elements. Introduction of heteroatoms often results in less acidic catalysts that can be used in tandem reactions for targeted reactive intermediates. Here, in this study, we prepare a series of three different zeolites with MWW, CHA, and MFI frameworks as aluminosilicates and gallosilicates to demonstrate their performance in alcohol dehydration reactions. The two reactions examined in this study are methanol conversion to dimethyl ether and ethanol conversion to ethylene. Our findings reveal that Ga-zeolites exhibit superior performance with Ga-MCM-22 (MWW) achieving nearly 100% alcohol conversion and selectivity to desired products at contact times that are significantly less than most dehydration catalysts reported in literature. The unique properties of Ga-zeolites are attributed to their reduced acid site strength via a direct (one-pot) synthesis that avoids conventional time-intensive, multi-step post-synthesis modifications of Al-zeolites. Here we demonstrate the use of Ga-zeolites as tandem catalysts when paired with a downstream Al-zeolite in a dual-bed reactor configuration to convert cheaper reagents (alcohols) upstream to more desired intermediates as feeds for downstream catalysts to produce light olefins. We demonstrate that dual beds using Ga-zeolite – Al-ZSM-5 (upstream–downstream) pairings outperform single bed configurations with Al-ZSM-5 or a physical mixture (Ga-/Al-zeolite) for methanol to hydrocarbons reactions, with notable improvements in catalyst lifetime and increased light olefins selectivity. Similarly, dual beds using Ga-zeolite – Al-SSZ-13 (upstream–downstream) pairings result in improved performance for ethanol to propylene reactions with significant increases in propylene selectivity (>20 %) compared to a conventional single bed configuration of Al-SSZ-13. Overall, this study offers a new perspective on the use of heteroatom-exchanged zeolite catalysts in tandem reactions as a means of capitalizing on their reduced acid site strength and suggests differences in the intrinsic acidity of zeolite crystal structures.

42 ENGINEERING↗
DOE OSTI2023

Meta-analysis of biogas upgrading to renewable natural gas through biological CO 2 conversion

Biogas upgrading through CO 2 conversion by hydrogenotrophic methanogenesis is receiving an increasing attention worldwide because of the demand for renewable natural gas. Herein, a holistic and statistical study of the operation conditions, driving forces, performances, and potential implementation of biogas upgrading via biological CO 2 conversion was conducted. Based on a systematic review and meta-analysis of 46 existing publications that were selected from 1475 papers, we have compiled a global dataset of CO 2 bioconversion biogas upgrading, encompassing 308 study cases. Subsequently, we employed a rigorous analytical framework incorporating data processing and mixed effects linear regression analysis to examine the dataset. This analysis revealed a significant positive relationship between the H 2 :CO 2 ratio and the methane percentage in the upgraded biogas when using the study as a random effect. Furthermore, we performed meta-analysis on observations taken when the ratio was close to 4:1 and found that ex situ reactors (91.93% [88.11%, 95.75%]) can perform better than in situ reactors (84.74% [80.69%, 88.80%]). No evidence of differential performance was found based on the present dataset between different temperature regimes or operation modes. Furthermore, those findings establish a database that will contribute to a deeper understanding of the biogas upgrading via biological CO 2 conversion.

Biogas upgrading↗
DOE OSTI2022

Conversion kinetics during melting of simulated nuclear waste glass feeds measured by dissolution of silica

In this work, we experimentally investigated the batch-to-glass conversion kinetics of two low-activity and two high-level nuclear waste melter feeds that represent widely different behavior during melting; tests comprised thermogravimetric analysis, the feed expansion test, evolved gas analysis, and x-ray diffraction. Our study indicates that the conversion processes, which include gas-evolving reactions, dissolution of crystalline phases, and primary foam expansion and collapse, are interconnected and influenced by the feed’s thermal history. The fraction of dissolved silica was adopted as a measure of the extent of conversion inside the cold cap—the floating layer of feed material on the top surface of the melt in an electric melter. The interface between the cold cap and the free-flowing melt below was associated with a constant fraction of dissolved silica. The estimated viscosity of glass-forming melt at this interface lies within a narrow range for the feeds studied.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

The Feasibility of Direct CO2 Conversion Technologies on Impacting Mid-Century Climate Goals

Recent IPCC modeling suggests that to limit global warming below 2 degrees C, "unprecedented" reductions in CO2 emissions will be required during the 2030-2050 time frame. The direct conversion of CO2 to fuels and chemicals using renewable electricity has garnered interest as one route to draw down emissions with the ability to synthesize products at a significantly lower carbon footprint than conventional methods. However, most direct CO2 conversion pathways are only in the early stages of development and face technical and market hurdles prior to scale-up, bringing into question what role they may play in influencing global CO2 emissions within this critical two-decade window. In this perspective, we highlight low-temperature electrolysis as a promising technology for direct CO2 conversion, including discussion on the products that could most impact global emission levels, and importantly, offer insight into the timeline, required advancements, and specific technical targets needed to successfully scale and deploy these technologies at the commercial level.

chemicals↗
DOE OSTI2016

Additives and solvents-induced phase and morphology modification of NaYF{sub 4} for improving up-conversion emission

Both cubic and hexagonal NaYF{sub 4} were synthesized in different reaction systems via hydro/solvo-thermal route. The effects of reaction temperature, solvents, and additives on the synthesis of NaYF{sub 4} have been studied in detail. It has been shown that phase transformation from cubic NaYF{sub 4} to hexagonal NaYF{sub 4} always occurred. The sequence of the ability for inducing the phase transformation was ethanol>H{sub 2}O>acetic acid. It is found that ethanol can not only facilitate the formation of hexagonal NaYF{sub 4} but also control the growth of the crystal. This is quite unusual for the growth of H-NaYF{sub 4}. The up-conversion emission properties of Yb/Er co-doped NaYF{sub 4} have also been investigated and the results demonstrated some general principles for improving up-conversion emission. - Graphical abstract: Additives and solvents can induce the phase transformation of NaYF{sub 4}, typically the use of organic sodium salt and ethanol. - Highlights: • The effect of additives and solvents on the synthesis of NaYF{sub 4} was studied in detail. • Ethanol can facilitate the formation of H-NaYF{sub 4} while acetic acid restrain it. • Three general principles for improving up-conversion emission were summarized.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Photon up-conversion production in Tb{sup 3+}–Yb{sup 3+} co-doped CaF{sub 2} phosphors prepared by combustion synthesis

Graphical abstract: Up-conversion luminescence from Tb{sup 3+} obtained by energy transfer from Yb{sup 3+} pairs in CaF{sub 2} powder prepared by combustion synthesis. - Highlights: • Calcium fluoride (CaF{sub 2}) powders were prepared by combustion synthesis. • Rare-earth ions doped in this material were found in interstitial sites. • Cooperative up-conversion was observed in Tb{sup 3+}:Yb{sup 3+}:CaF{sub 2} powder. • Energy transfer between Tb{sup 3+} and pairs of Yb{sup 3+} was analyzed using rate equations. - Abstract: Calcium fluoride (CaF{sub 2}) crystalline powders were successfully prepared by the combustion synthesis method. The powder material containing luminescent rare-earth ions, more specifically terbium (Tb{sup 3+}) and ytterbium (Yb{sup 3+}), was studied by X-ray diffraction, scanning electronic microscopy and optical spectroscopy. These ions are allocated in charge compensated interstitial positions of tetragonal (C{sub 4v}) and trigonal (C{sub 3v}) symmetry sites of the cubic (O{sub h}) CaF{sub 2} lattice. Up-conversion (UC) luminescence in Tb{sup 3+} was achieved using a low power diode laser operating at 975 nm. Tb{sup 3+} is insensitive to near-infrared radiation but UC can be achieved via energy transfer from pairs of Yb{sup 3+} ions to Tb{sup 3+} ions. The UC luminescence dynamics of Tb{sup 3+} was used to study the energy transfer mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Preparation and up-conversion luminescence of Tb3+/Yb3+ co-doped BaO-WO3-SiO2 glass ceramic

Highlights: • The Tb{sup 3+}/Yb{sup 3+} co-doped glass ceramics containing BaWO{sub 4} is prepared. • The optimum heat treatment schedules is obtained. • The up conversion luminescence mechanism is investigated. - Abstract: The Tb{sup 3+}/Yb{sup 3+} co-doped BaO-WO{sub 3}-SiO{sub 2} glass ceramic is prepared by melt crystallization method. The optimum heat treatment schedule is determined on basis of differential scanning calorimetry. The crystal phase is BaWO{sub 4} by X-ray diffraction analysis. The crystal grain sizes are examined by scanning electron microscope and crystal grain sizes increase with the increasing of heat treatment time. In the visible region, the transmittance of glass ceramic is 79%. The up-conversion fluorescence intensity increase with the increasing of heat treatment time up to 90 min and with the increasing of Yb{sup 3+} concentration up to 0.3 mol%. The possible mechanism of up-conversion in Tb{sup 3+}/Yb{sup 3+} co-doped BaWO{sub 4} glass ceramic is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Oxidative coupling of methane (OCM) conversion into C 2 products through a CO 2 /O 2 co-transport membrane reactor

Oxidative coupling of methane (OCM), which transforms CH 4 into C 2 products (C 2 H 6 and C 2 H 4 ) with molecular O 2 as the oxidant, is one of the most studied direct methane conversions (DMCs). However, a major technical hurdle to the OCM process is to achieve high CH 4 conversion at high C 2 (C 2 H 6 and C 2 H 4 ) selectivity. One rudimentary cause for this “tradeoff” behavior is the high chemical reactivity of the products (C 2 H 6 or C 2 H 4 ), which can be re-oxidized by O 2 . To overcome this thermodynamic challenge, minimizing the oxidizing power of the oxidant and lowering the local oxygen partial pressure are keys. Here, In this work, we demonstrate a new membrane reactor that capture CO 2 /O 2 from a flue gas and uses it for OCM conversion. The results show that the co-captured CO 2 /O 2 mixture converts CH 4 into C 2 H 6 in the presence of a 2%Mn–5%Na 2 WO 4 /SiO 2 catalyst, followed by thermal cracking of C 2 H 6 into C 2 H 4 and H 2 . The presence of CO 2 decreases the local partial pressure of O 2 , thus reducing the propensity of C 2 -products re-oxidation and leading to a higher C 2 selectivity. We show that a small button-type membrane reactor can achieve 12% C 2 yield with ~57% C 2 -selectivity using a diluted CH 4 -Ar mixture as the feedstock. We expect higher C 2 yield with tubular plug-flow membrane reactors in the future. We also highlight the unique advantage of the membrane reactor in intensifying CO 2 capture from both flue gas and OCM purification process into one single step.

42 ENGINEERING↗
DOE OSTI2026

Deep Learning enabled spectral energy conversion for in situ exposure measurements

A detector-specific deep learning (DL) approach is presented for spectra-to-exposure conversion using large-format sodium iodide (NaI(Tl)) detectors deployed for in situ environmental radiation measurements in emergency response scenarios. Accurate determination of exposure from NaI spectra is challenging due to poor energy resolution, partial energy absorption, and the strong sensitivity of traditionally deployed analytical conversion methods to calibrated source geometry and pre-deployment assumptions. Here, to address these limitations, a multi-layer perceptron model was trained on a hybrid in situ /Monte Carlo dataset constructed to span a broad range of photon energies, spatial extents, and realistic deployment variability, representative of general in situ emergency response conditions. The DL model was evaluated against commonly fielded analytical approaches under matched simulation conditions, including a single-factor method, a G-function method, and a modeled pressurized ion chamber (PIC) baseline. This study was intentionally computational in scope to enable controlled, like-for-like comparisons between conversion techniques while minimizing confounding real-world variability. Comparison to the modeled PIC provides contextual benchmarking and is not intended as a field inter-comparison with deployed instruments. Across the evaluated 20 keV to 3 MeV energy range, the DL approach consistently exhibited higher accuracy and reduced variance relative to the analytical methods against a deterministically calculated exposure. This may indicate improved robustness to spectral complexity without reliance on source-, geometric-, or spectral region-specific optimization. While results do not represent real-world validation, the presented work demonstrates that deep learning may effectively learn the nonlinear detector response-to-exposure relationship for asymmetric NaI(Tl) detectors and offers a promising pathway for improving in situ exposure estimation using spectroscopic systems already integrated into initial real-time emergency response operations.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2022

Significant improvement of conversion efficiency by passivation of low-angle grain boundaries in flexible low-cost single-crystal-like GaAs thin-film solar cells directly deposited on metal tape

We develop an easily implementable yet effective process to achieve high power conversion efficiency in newly-developed flexible single-crystal-like GaAs thin-film photovoltaic solar cells on cheap metal tape. We study various techniques on the fabricated devices to passivate the defect states associated with dangling bonds at low-angle grain boundaries (LA-GBs) existing in the single-crystal-like GaAs material. We report that sulfur by trioctylphosphine sulfide (TOP:S) solution treatment can partially but effectively passivate the defect states at the LA-GBs to increase all the solar cell performance parameters of open-circuit voltage VOC (33.2%), short-circuit current JSC (19.5%), and fill factor FF (25.8%), resulting in the improvement of the power conversion efficiency more than double. The material and device characterizations and numerical modeling are performed to propose a mechanism, also suggesting that the power conversion efficiency higher than 20%, which is an important target milestone in emerging solar cell technologies, can be achieved. This work presents the first effective passivation of the bulk defects in GaAs at the device level and can also offer a solution for other photonic and electronic devices using non-single-crystalline GaAs films for flexible electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Catalytic conversion of biomass-derived ethanol to liquid hydrocarbon blend-stock: Effect of light gas recirculation

Here, we describe a light gas recirculation (LGR) method to increase the liquid hydrocarbon yield with reduced aromatic content from catalytic conversion of ethanol to hydrocarbons. The previous liquid hydrocarbon yield is ~40% from one-pass ethanol conversion over V-ZSM-5 at 350 C and atmospheric pressure where the remaining ~60% yield is light gas hydrocarbons. In comparison, the liquid hydrocarbon yield increases to 80% when a simulated light gas hydrocarbon stream is co-fed at a rate of 0.053 mol g-1 h-1 with ethanol due to the conversion of most of the light olefins. The LGR also significantly improves the quality of the liquid hydrocarbon blend-stock by reducing aromatic content and overall benzene concentration. For 0.027 mol g-1 h-1 light gas mixture co-feeding, the average aromatic content in liquid hydrocarbons is 51.5% compared with 62.5% aromatic content in ethanol only experiment. Average benzene concentration decreases from 3.75% to 1.5% which is highly desirable since EPA limits benzene concentration in gasoline to 0.62%. As a result of low benzene concentration, the blend-wall for ethanol derived liquid hydrocarbons changes from ~18% to 43%. The remaining light paraffins and olefins can be further converted to valuable BTX products (94% BTX in the liquid) over Ga-ZSM-5 at 500 C. Thus, the LGR is an effective approach to convert ethanol to liquid hydrocarbons with higher liquid yield and low aromatic content, especially low benzene concentration, which could be blended with gasoline in a much higher ratio than ethanol or ethanol derived hydrocarbon blend-stock.

09 BIOMASS FUELS↗
DOE OSTI2018

Atomic Structure of 2 nm Size Metallic Cobalt Prepared by Electrochemical Conversion: An in Situ Pair Distribution Function Study

Conversion reactions, offering high capacity in batteries, imply a restructuration of the pristine atomic structure down to the nanoscale. The associated large broadening in the Bragg peaks of the restructured electrode renders the description of atomic structure, almost impossible using conventional X-ray diffraction. On the other hand, atomic pair distribution function (PDF) is well suited to probe the structure of few nanometer-sized particles. We investigated the formation mechanism and structure of 2 nm particle size of metallic Co obtained by electrochemical conversion of CoF 2 . We found that the conversion process stabilized a disordered structure consisting of a hexagonal-close-pack–face-centered-pack intergrowth. The reaction was followed by in situ PDF, providing unique insight into the growth of highly defective Co nanoparticles.

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

Theoretical Perspective of Promoting Direct Methane-to-Methanol Conversion at Complex Metal Oxide–Metal Interfaces

Direct methane conversion to methanol has been considered as an effective and economic way to release greenhouse effects and current high demand on methanol in industry. However, the process has long been challenging due to lack of viable catalysts to compromise the activation of methane that typically occurs high temperatures and retaining of produced methanol that requires mild conditions. Here, this perspective demonstrates an effective strategy to promote direct methane to methanol conversion by engineering the active sites and chemical environments at complex metal oxide - copper oxide - copper interfaces. Such effort strongly depends on the extensive theoretical studies by combining density functional theory (DFT) calculations and kinetic Monte Carlo (KMC) simulations to provide in-depth understanding of reaction mechanism and active sites, which built the strong basis to enable the identification of design principles and advance the catalyst optimization for selective CH 4 -to-CH 3 OH conversion.

03 NATURAL GAS↗
DOE OSTI2017

Fine Tuning of Open-Circuit Voltage by Chlorination in Thieno[3,4- b ]thiophene–Benzodithiophene Terpolymers toward Enhanced Solar Energy Conversion

A new family of thieno[3,4-b]thiophene benzodithiophene terpolymers (PBTClx) have been designed and synthesized, in which the chlorine/fluorine content has been adjusted and optimized. As the content of chlorine is increased in polymers, the twist angle between the donor and acceptor is increased, which leads to a diminishment in the planarity and conjugation. As a result, the UV vis absorption is continuous blue-shifted, and the band gap increases from 1.57 to 2.04 eV when the chlorinated moieties increased from 0 to 100%. The highest occupied molecular orbital (HOMO) levels of those polymers are decreased by increasing the content of chlorinated moiety, which opens a window to constantly modify the V-oc values and eventually meets a balance point for optimized solar energy conversion. The highest power conversion efficiency of 8.31% is obtained by using PBTCl25 as the donor and PC71BM as the acceptor in polymer solar cells (PSCs), in which the Voc increased from 0.79 to 0.82 V after 25% chlorinated monomer involved in copolymerization. Herein, the chlorine replacement could be a good method to further pump the solar conversion by increasing the open circuit voltage without reducing other factors of the polymer solar cells.

Qu, Shiwei↗
DOE OSTI2025

Photoreactive Capture and Conversion of Dilute Carbon Dioxide into Synthetic Natural Gas

This study introduces a photoreactive system that integrates the capture of dilute CO 2 streams with their catalytic conversion to synthetic natural gas (CH 4 ), utilizing a Ru nanoparticle (NP)-doped TiO 2 composite loaded with linear polyethylenimine (L-PEI) and enhanced with plasmonic titanium nitride (TiN). This light-driven approach mitigates challenges that have plagued traditional thermal reactive carbon capture (RCC) methods, such as CO 2 slip and amine degradation. We demonstrate that L-PEI enables stable CO 2 capture and conversion, achieving ~70% conversion of captured CO 2 to CH 4 across multiple reaction cycles using nonflammable forming gas (~5% H 2 ) as the reductant. In contrast, branched PEI (B-PEI)-loaded composites exhibited significant catalyst deactivation after several RCC cycles. Scanning transmission electron microscopy (STEM) imaging confirms that significant sintering of the Ru NPs occur in the B-PEI sample under RCC conditions, whereas their size remains stable in more rigid L-PEI composites. Technoeconomic analysis (TEA) estimates that CH 4 production using this system could cost less than $\$$5/kg based on current electrocatalytic H 2 prices. These results represent one of the most promising demonstrations of amine-based RCC employing dilute CO 2 sources to date.

36 MATERIALS SCIENCE↗