On-line GC Research Articles

Silane Gas Production Through Hydrolysis of Magnesium Silicide by Hydrochloric Acid

Monosilane (SiH4) is a common precursor for the production of high-purity silicon for solar PV applications. As an alternative to carbothermic reduction of silica to produce metallurgical grade silicon with subsequent conversion to silane, an alternative route over magnesiothermic reduction of silica to Mg2Si has been explored in our earlier work. In the current work, silane gas production through hydrolysis of Mg2Si in HCl acid solution was studied. Two sources of Mg2Si were chosen: a commercial Mg2Si source and a Mg2Si source produced through magnesiothermic reduction of high-purity natural quartz. Effects of various parameters on the hydrolysis of Mg2Si, including different experimental setups, temperature of the acid solution, acid concentration, reaction time, and relative amounts of reactants were studied. The evolution of produced gases was determined by two different methods: firstly, by passing the produced gas through a KOH solution to capture Si with subsequent analysis of the Si content in the KOH solution by inductively coupled plasma mass spectrometry and secondly, on-line gas analysis by GC–MS. The silane distribution between different silane species with reaction time was evaluated and the activation energy of silane formation was calculated. The results indicated comparable silane yields obtained from the on-line GC–MS method and KOH solution analysis method, as well as for commercial Mg2Si and the Mg2Si–MgO mixture produced through magnesiothermic reduction. Furthermore, adding HCl acid to Mg2Si in water led to higher SiH4 formation yield than adding Mg2Si to acid. However, the total silane yield for the two methods was similar at approximately 32%.Graphical

Photoreforming of glycerol to produce hydrogen from natural water in a compound parabolic collector solar photoreactor

To improve TiO2 for H2 generation, one strategy for the separation of photogenerated charges is the formation of heterostructures with other materials. In particular, NiO is a photocatalyst known for its good stability and low cost. However, no studies at pilot scale using solar energy have been described. Consequently, an evaluation of a physical NiO:TiO2 mixture at pilot scale (25 L) with natural irradiation (2.10 m2 of sun-exposed surface) and with simultaneous glycerol photoreforming was explored. NiO:TiO2 50 mg·L−1 resulted in the highest hydrogen production, showing an STH = 1.44%, considering only the UV fraction of the solar irradiation. H2 and CO2 production were analysed by on-line GC; Glycerol, dissolved organic carbon, carboxylic acids and nickel leaching were also evaluated. The NiO:TiO2 mixtures rendered a systematically lower H2 production in natural water than in high-purity water. The increase of ionic strength increased the mean size of particle clusters, promoting rapid sedimentation. All this indicates the importance of testing under real field conditions for attaining reliable solar to hydrogen (STH) efficiency.

Monitoring Drug Substance Drying with Online GC

Monitoring Drug Substance Drying with Online GC

Towards a Fully-Quantitative Picture of SEI Chemical Composition and Its Native Li+ Exchange in Liquid Electrolytes

Energy density requirements for next-generation batteries make the lithium (Li) metal anode a key candidate to replace graphite in lithium-ion batteries due to Li’s improved capacity (3,860 mAh/g vs. 372 mAh/g). However, Li anodes display lower Coulombic efficiency (CE, <99.9%) than graphite (>99.95%),1 resulting in faster loss of reversible Li over cycling. This shortfall derives from parasitic Li-electrolyte reactions that lead to accumulation of inactive Li0 and electrolyte-derived byproducts, which result in the formation of a native solid electrolyte interphase (SEI) on Li. In addition to contributing to capacity loss, the SEI also has the important role of regulating Li+ exchange between Li and the electrolyte, which may affect Li plating morphology and reversibility.2 Despite significant advances, the framework on which the understanding of SEI composition and function was built has largely been qualitative, often due to experimental limitations and/or lack of self-consistent techniques.To bridge this gap, my thesis work focuses on advancing experimental techniques and methodologies to precisely quantify the chemical composition and rates of Li+ exchange in native SEIs. Using a combination of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), self-consistent rates of Li+ exchange are reported across a wide range of electrolytes.3 Notably, we found that native SEIs formed in high CE electrolytes displayed consistently higher rates of Li+exchange. The improved transport in high-CE electrolytes was found to emerge after an SEI formation cycle, and amplified over cycling, indicating that fast Li+ exchange is beneficial to Li reversibility.In order to identify which SEI phases grant high-CE electrolytes their beneficial functional properties, we also developed and expanded upon a series of titration experiments based on GC, ICP-AES and NMR that can track an extended array of key SEI phases: semicarbonates (ROCO2Li), lithium carbide (Li2C2), olefins (RLi), LiF, P-containing phases, and total Li loss.4 In the 1 M LiPF6 EC/DEC electrolyte, we demonstrate chemical resolution up to 71% of Li loss and 33% of SEI loss. Among the quantifiable SEI phases, ROCO2Li was consistently the major phase, but its proportions were invariant with CE. Instead, Li2C2, a minor phase, exhibited clear inverse correlation with CE. We also demonstrate further quantitative chemical resolution can be achieved with online GC, which can differentiate between the different types of semicarbonate (i.e., which “R” in ROCO2Li) and alkoxide phases that form on Li.5 Altogether, these results add further nuance to the current understanding of SEI composition and their function, which we hope will allow more quantitative electrolyte design. Hobold, G. M.; Lopez, J.; Guo, R.; Minafra, N.; Banerjee, A.; Shirley Meng, Y.; Shao-Horn, Y.; Gallant, B. M., Moving Beyond 99.9% Coulombic Efficiency for Lithium Anodes in Liquid Electrolytes. Nat. Energy 2021, 6 (10), 951-960. Zheng, J.; Kim, M. S.; Tu, Z.; Choudhury, S.; Tang, T.; Archer, L. A., Regulating Electrodeposition Morphology of Lithium: Towards Commercially Relevant Secondary Li Metal Batteries. Chem. Soc. Rev. 2020, 49 (9), 2701-2750. Hobold, G. M.; Kim, K.-H.; Gallant, B. M., Beneficial Vs. Inhibiting Passivation by the Native Lithium Solid Electrolyte Interphase Revealed by Electrochemical Li+ Exchange. 2022. Hobold, G. M.; Gallant, B. M., Quantifying Capacity Loss Mechanisms of Li Metal Anodes Beyond Inactive Li0. ACS Energy Lett. 2022, 7 (10), 3458-3466. Hobold, G. M.; Khurram, A.; Gallant, B. M., Operando Gas Monitoring of Solid Electrolyte Interphase Reactions on Lithium. Chem. Mater. 2020, 32 (6), 2341-2352.

Efficient process of VOC degradation from the high airflow in conical fluidized photocatalytic reactor by mesoporous C-N doped -ZnO powder under visible light

Mesoporous carbon–nitrogen, doped ZnO powders were synthesized from the zeolite imidazolate framework (ZIF-8) by a facile thermal decomposition in the atmosphere of nitrogen and air, respectively. The prepared material was used as the photocatalyst in a conical fluidized photocatalytic reactor under visible light irradiation for degradation of acetaldehyde (as a model molecule of indoor volatile organic compounds). The synthesized samples were characterized by DRS, BET, EDAX, FTIR, XRD, TGA, and FESEM analysis. DRS analysis revealed that the absorption edge of the prepared samples from ZIF-8 was significantly shifted to the visible range. The band gap and absorption edge of the bare ZIF-8 was changed from 5.1(eV) and 243(nm), respectively, to almost 3(eV) and 400 (nm) in the prepared C-N doped ZnO. FTIR analysis confirmed the existence of carbon and nitrogen in the surface of the prepared material. The N2 adsorption–desorption analysis revealed the IV-type isotherm confirming mesoporous structure with improved specific pore volume. The photocatalytic activity of the samples was evaluated from the airflow polluted with a trace amount of acetaldehyde, under an alkali metal halide lamp in the conical fluidized reactor, and the outlet flow was analyzed by the online GC versus the time. According to the results, all samples exhibited significant photocatalytic activity compared with the bare ZIF-8, and commercial ZnO powder. Almost 90% acetaldehyde removal occurred by the sample prepared by N2 thermal decomposition of ZIF-8 at 600 °C for 120 min, followed by air annealing at 450 °C for 90 min. Subsequently, the reaction rate was investigated and modeled on the base of Langmuir-Hinshelwood type equation as a function of acetaldehyde concentration and light intensity.

An experimental and modeling study on the oxidation of ammonia and n-heptane with JSR

The oxidation of neat ammonia, n-heptane, and ammonia/n-heptane blends was investigated both experimentally and numerically. Experiments were carried out in a fused silica jet-stirred reactor (JSR) under atmospheric pressure and lean conditions covering a temperature range of T=500–1200 K. Mole fraction profiles of 28 species were obtained with online SVUV-PIMS and GC techniques. A detailed analysis of reaction products and intermediates was performed, and the results were interpreted with an improved kinetic model, describing the oxidation of ammonia and n-heptane, as well as fuel interaction and NOx formation. The measurements indicate that ammonia reactivity is promoted by n-heptane addition at wide-ranging temperatures, while ammonia addition can also accelerate the oxidation process of n-heptane, especially at intermediate temperatures, manifesting mutual reinforcement in oxidation reactivity. Kinetic analysis shows that the low-temperature reaction of n-heptane generates reactive species that initiate and interact with the oxidation of ammonia along the pathway of NH2→H2NO/HNO→NO→NO2 at low temperatures. As the reaction pathway changes with increasing temperature, n-heptane oxidation likely provides the radical pool necessary to trigger ammonia oxidation through H2O2 decomposition at an intermediate temperature; while ammonia oxidation in turn accelerates the generation of hydroxyl radicals via NOx chemistry as a more direct pathway. As such, a self-reinforcing looping cycle could be formed, leading to the rapid oxidation of ammonia/n-heptane blends at intermediate temperatures. It is noted that despite the good overall performance, the kinetic model under-predicts NOx concentration and only qualitatively captures the rapid oxidation behavior. More kinetic modeling work is necessary in order to better understand the co-oxidation mechanism of ammonia and large hydrocarbons at wide-ranging operating conditions.

Genome access and other web-based IT solutions: Genetic counseling in the digital era.

Genetic counselors are healthcare professionals who are trained in both medical genetics and counseling to help guide individuals through what is known about genetic predispositions toward a variety of diseases, how they are inherited, and what impact this information can have on them and their partners and families. The range and scope of practice of GC has greatly expanded beyond where it started and now, it is employed in a variety of clinical and research settings. The traditional approach to GC involves meeting with a counselor in person. However, with the increasing availability of online resources, more people are seeking information about genetic disorders online. This shift has led to the development of online GC services. Indeed, genetic counselors are no strangers to improvements in terms of adopting digital solutions in their clinical routine, however, there are few studies assessing genetic counselors' attitudes regarding existing digital tools. Genome Access® is a digital platform that improves patient knowledge in the field of genetic diseases and supports specialists throughout different stages of counseling. This study aims to present Genome Access and discuss the importance of adopting digital technologies designed specifically for GC and what tools these solutions should include.

Experimental and kinetic modeling study of ethylene oxidation at elevated pressure

The oxidation of ethylene (C2H4) was performed in a jet-stirred reactor (JSR) at the equivalence ratios (Φ) of 0.5, 1.0, and 3.0, within the temperature range of 650–1000 K, at 12.0 atm. Six C1-C3 hydrocarbons and four oxygenated species were identified and quantified by using online GC and GC-MS. Among them, acrolein, propanal, and epoxypropane were newly detected compared to previous oxidation studies of C2H4. A detailed kinetic model involving 125 species and 671 reactions was developed, and its predictions were found to be in reasonable agreement with the measured data. Generally, the peak concentrations of hydrocarbons and oxygenated species tend to increase with the increase of Φ, while the inorganic substances exhibit contrary tendencies. Rate-of-production analysis indicates that C2H4 consumption is generally governed by the addition of H-atom and OH radicals, which mostly transform to C2H5 under rich conditions and to CH2CH2OH under lean condition. Sensitivity analysis reveals that the reactions H2O2(+M) <=> 2OH(+M) and CH2O + O2 <=> HCO + HO2 are the most promoting and inhibiting reactions for C2H4 consumption, respectively. By comparing the results of 1.0-59.2 atm, it can be found that the increase of pressure leads to the reduction of the initial reaction temperature. Under higher pressure, the reaction temperature interval of C2H4 shifts towards a lower temperature. The current mechanism could reproduce the literature-reported ignition delay times and laminar flame velocities under wide pressures. The results will enrich the understanding of the high-pressure oxidation of C2H4 and serve as a foundation for developing large hydrocarbon fuel models.

Realistic Operando‐DRIFTS Studies on Cu/ZnO Catalysts for CO2 Hydrogenation to Methanol – Direct Observation of Mono‐ionized Defect Sites and Implications for Reaction Intermediates

AbstractOur recent study in this journal highlighted misassignments of surface intermediates of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements of published Cu/ZnO (CZ) catalyst systems for methanol synthesis. Here we investigate a recent and very active CZ system, in part promoted by oxidative fluorination (i. e., a Cu/ZnO1–x/ZnF2 system), with realistic operando‐DRIFTS measurements of a 3H2/CO2 gas feed (30 bar, 513 K). This DRIFTS setup is linked to an online GC analysis system and the catalytic performance of the Cu/ZnO1–x catalyst showed a similar performance of the catalysis process in the DRIFTS cell as in the catalyst test station. In the DRIFTS measurements, a very broad absorption band with a maximum at about 1500 cm−1 (=I1500) is evident. This I1500 band is absent in nitrogen; its intensity increases in pure hydrogen and is particularly high during methanol synthesis. I1500 results from photoionization of an electron residing in a mono‐ionized oxygen vacancy VO+ in the ZnO1–x part of the Cu/ZnO1–x catalyst. Consequently, the I1500 band intensity provides information on the extent of the strong metal‐support interaction SMSI. Therefore, measurement of the I1500 band intensity could be a novel and efficient tool to characterize any CZ‐based catalyst systems online. Mechanistically, the maximum VO+ photoionization I1500 band intensity in a 3H2/CO2 gas stream is coupled to the reaction of CO2 giving the CO2−. radical anion intermediate that is rapidly trapped in the VO2+ site formed. This trapped intermediate may react by hydrogen migration to the well‐known surface formate (1603, 1371, and 1314 cm−1). However, the long‐lived formate with this spectroscopic signature is only a spectator. It is also visible by DRIFTS in catalyst samples that in the same setup do not produce methanol (GC). By contrast, the band intensities of the surface species at 1759, 1691, 1457 and 1398 cm−1 are directly connected to methanol production and the applied WHSV. Therefore, only these surface species are relevant for CO2 hydrogenation to methanol at higher pressure and likely represent true reaction adsorbates/intermediates.

An experimental and modeling study of oxidation of real RP-3 aviation kerosene

The major components of a real Chinese RP-3 aviation kerosene were measured as 64.15% alkanes, 18.48% cycloalkanes, 15.88% aromatics. The oxidation of real Chinese RP-3 aviation kerosene was investigated in a jet-stirred reactor (JSR) at atmospheric pressure, φ = 2.0, and temperatures ranging from 575 to 1100 K. Mole fraction profiles of 25 species were detected with online GC and GC/MS. Three components (3C) surrogate fuel was validated against the measured results, as well as a detailed kinetic reaction model involving 453 species and 2991 reactions, was validated against the oxidation data A negative temperature coefficient (NTC) behavior of intermediates except for methane (CH4) was observed, due to the low-temperature activity of alkanes. The bimodal curves were observed for light hydrocarbons (C2-C4) and aromatic species and oxygenate, in which the second one is generally larger than the first one for light hydrocarbons (C2-C4) and aromatic species, while oxygenates exhibit adverse tendencies. Rate-of-production (ROP) analysis reveals that 1,3,5-trimethyl cyclohexane (T135MCH) mostly generates XCH2D35MCH radicals by dehydrogenation reaction, isomerizes to CH3SXD35MCH radicals, and further convert to C3H6. N-propylbenzene (NPB) is mainly dehydrogenated to form A1CHCH2CH3 and A1CH2CHCH3 radicals, which further transform to styrene (C6H5C2H3). Sensitivity analysis demonstrates that the consumption of both T135MCH and NPB are promoted by H/OH/HO2 radicals at low temperatures. At a temperature higher than 900 K, an insufficient supply of H/OH/HO2 radicals may lead to a competing reaction between the three components. Within the temperature range of 600 to 800 K, n-dodecane is the most active component to produce H/OH/HO2 radicals to initiate the oxidation of NPB and T135MCH. These results could improve the understanding of the specific combustion process of RP-3 aviation kerosene, and help the establishment of RP-3 aviation kerosene surrogate fuel as well.

Primary Thermal Decomposition Pathways of Hydroxycinnamaldehydes

Hydroxycinnamaldehyde monomers are important intermediates in the lignin biosynthesis and can be incorporated into plants in large quantities via genetic modification. They are also important products formed during the pyrolysis or combustion of lignocellulose. In this work, the decomposition of three hydroxycinnamaldehyde model compounds, cinnamaldehyde, p-coumaraldehyde, and coniferaldehyde, was studied in a micropyrolysis reactor equipped with an online GC × GC-FID/TOF-MS coupled with a customized GC for the online analysis of all the pyrolysis vapors including permanent gases. The vaporization or sublimation process of these model compounds in the reactor was fitted well based on the experimental time-resolved data. The dominating initial decomposition pathways were elucidated from a first-principles based kinetic model and usage of a rate of production analysis. For cinnamaldehyde (at 773–1123 K) and p-coumaraldehyde (at 873–1123 K), the concerted decarbonylation reactions in the condensed phase determine the initial decomposition, with almost no contribution from radical chemistry. For coniferaldehyde (at 773–1023 K), the homolysis of the O-methyl (O–CH3) bond initiates a radical chain mechanism at temperatures above 773 K, and the H atom abstraction on the aldehyde group is the most dominant consumption pathway at high temperatures. The presence of methoxy groups on the aromatic rings accelerates the decomposition of hydroxycinnamaldehydes. Models that do not account for these important structural differences will have difficulties in the prediction of the decomposition of real lignocellulosic biomass.

Experimental and modeling studies of exo-tetrahydrobicyclopentadiene and tetrahydrotricyclopentadiene pyrolysis at 1 and 30 atm

To better understand the decomposition behaviors of exo-tetrahydrobicyclopentadiene (exo-TCD, a main component of JP-10) and tetrahydrotricyclopentadiene (THTCPD), the experiments were performed in a flow tube reactor at 1.0-30.0 atm over a temperature range of 773–1148 K with high helium dilution. The mole fraction profiles of pyrolysis products, involving C1-C5 small hydrocarbons, monocyclic and polycyclic aromatic hydrocarbons (MAHs and PAHs), were obtained using online GC–MS/FID. A universal kinetic model of exo-TCD and THTCPD pyrolysis was developed by coupling a common base mechanism and their respective sub-mechanisms. It was validated against a wide range of pyrolysis experimental data, newly measured in this work as well as taken from the literature covering the intermediate-to-high temperature range in different reactors. The rate of production analysis shows that for the decomposition of two fuels, the unimolecular C-C dissociations and H-abstractions by H and aC3H5 attacking play a dominant role at both 1.0 and 30.0 atm. Due to the lower C-C bond dissociation energy and more H-abstraction sites, THTCDP exhibits a faster pyrolysis curve and covers a lower temperature range than exo-TCD. The simultaneously formed fuel radicals in exo-TCD and THTCPD pyrolysis impact the formation pathways of C1–C5 small products and MAHs. Notably, an extra five-membered ring in THTCPD results in slightly high production of C5 cycloalkenes, involving 1,3-cyclopentadiene and cyclopentene. The formation of MAHs, such as benzene, toluene and ethylbenzene, is also affected by fuel-specific reaction channels, yielding different peak concentrations. Concerning the two- and four-ring PAHs, the speciation profiles show a large extent of similarity in the decomposition of two fuels, which is mainly attributed to the similar formation pathways, especially at high temperature. Their formation is dominated by the bi-molecular addition reactions of c-C5H5 with c-C5H5, c-C5H6, as well as a series of resonantly stabilized radicals, which are barely influenced by the specific fuel chemistry.

Rapid tool for evaluation of acido‐basic properties of solid catalysts at high reaction temperature conditions using 2-propanol and benzyl alcohol as probe molecules

We introduce a simple, fully automated and practical methodology to measure the relative activity of heterogeneous catalysts using probe molecules at operating temperature conditions employed in industrial processes. The applicability of this approach was demonstrated by studying the conversion and selectivity of model probe molecules, isopropanol and benzyl alcohol reactions at 250−450 °C, on γ-Al2O3, MM clay, ZnO and Fe2O3. Catalyst was packed into the bed of in-house fabricated bench-top unit, automated vapor generation unit was used to pass probe molecules through the bed, and the products were sampled by on-line GC. Amongst the probe molecules, benzyl alcohol was found to be more suitable for evaluation of surface acido‐basic properties, as it exhibited high conversion at all the studied temperatures, along with concomitant formation of toluene and benzaldehyde based on the relative presence of surface active sites, acidic sites yield toluene, and strong basic sites yield benzaldehyde.

On-line micro GC testing of protium analysis in DT fuels from TCAP products

To support Chinese Inertial Confined Fusion research, a thermal cycling absorption process (TCAP) system was previously developed for protium removal from D–T fuels. However, to monitor the product quality in each TCAP cycle (10 min), an on-line analysis method is required. At ITER, the Analytical System is an individual system used, which meets the static analysis requirement via interconnecting lines. In this study, to meet the dynamic analysis requirement, a new on-line micro gas chromatography system is installed in this system glovebox and is directly connected to the sampling point. For proximity to the sampling point, its sampling valve is connected with two 10-cm, 1/16-inch stainless steel tubings. Two six-port valves are combined to perform the sampling cycle of “vacuum-loading-injection.” A 30 m MnSO4 deactivated alumina metallic PLOT column is prepared for sufficient resolution of hydrogen isotopes at 77 K. The results show that the D2 retention time is 3.6 min, and that the resolutions between H2 and HD and between HD and D2 were 1.5 and 3.8, respectively. The estimated lower detection limit of HD was 20 ppm for a sampling volume of 1 cm3. The times of sample loading, sample injection, and vacuum were 1, 0.5, and 2.5 min, respectively. A D–T mixture testing is in progress.

Atmospheric and high pressures pyrolysis study of n-decane in a flow reactor with online GC-MS/FID analysis: Experiments and modeling

The atmospheric and high-pressure pyrolysis of n-decane was studied in a flow tube reactor combined with online GC–MS/FID at 723−1123 K, 0.1–3.0 MPa (highly diluted in helium). Compared with 0.1 MPa, the conversion of n-decane and mole fraction of alkenes clearly increased at 3.0 MPa at the fixed temperature, and more aromatics were observed including toluene, styrene, ethylbenzene, indene and naphthalene, suggesting that the secondary reactions are more intense under high pressure. To account for these differences, a detailed kinetic model with 191 species and 1117 reactions was constructed by incorporating the aromatics subset to a n-decane model developed in previous low-pressure work, and further validated against literature data covering a wide pressure range (0.004–7.2 MPa) with reasonable reproducibility. The current model was compared against three literature kinetic models (LLNL, JetSurf 2.0 and Rev1stGen) and showed a better accordant with the conversion of n-decane and the selectivity of major products. Based on the rate of production and sensitivity analysis using the current model, the results show that although the total consumption of n-decane is weakly pressure-dependent at fixed temperature and residence time under the investigated conditions, the formation and consumption pathways of primary products change significantly attributed to the enhanced bimolecular abstraction and combination reactions at higher pressures. For the formation of benzene, the combination of 1,3-butadien-2-yl with ethylene is the main pathway at both 0.1 and 3.0 MPa, while the additional combination reactions: propargyl with allyl and cyclopentadienyl (c-C5H5) with CH3 become dominant at 0.1 MPa and 3.0 MPa, respectively. For the formation of larger aromatic naphthalene, the self-recombination of c-C5H5 is the most important channel at all investigated pressures.

Experimental and modeling studies of quadricyclane and 2-ethylnorbornane pyrolysis from atmospheric to high pressure

To improve the understanding of cyclopentadiene-based high-density liquid hydrocarbon fuels combustion chemistry, the pyrolysis experiments of 1,3-cyclopentadiene (c-C5H6), quadricyclane (QC) and ethylnorbornane (EthNB, reported in our recent work: Wang et al.,2020), were performed in a flow reactor at atmospheric and high pressure over 348–1173 K. The mole fraction profiles of products in three fuels pyrolysis were obtained using online GC–MS/FID. Based on theoretical calculations and literature research, a universal kinetic model (397 species and 1522 reactions) of QC and EthNB, incorporating the sub-mechanisms of c-C5H6 and polycyclic aromatics, was constructed in this work. It was validated against the present data and pyrolysis data of c-C5H6 as well as norbornane in literature with reasonable reproducibility. The rate of production analysis shows that the retro-Diels-Alder reaction to c-C5H6 plus C2H2 is always the dominant path to 2,5-norbornadiene (NBD, the only isomer product of QC) consumption at atmospheric and high pressures, whereas the contribution of isomerization to 1,3,5-cycloheptatriene increases with the increasing pressure and is almost equal to that of the former at high pressure and low conversion. The aromatics formation channels in QC pyrolysis are affected by the presence of C2H2 and different from those of c-C5H6 pyrolysis, especially under high pressure. For EthNB decomposition, the open-ring and H-abstraction reactions play a dominant role. The C2-C6 alkene products are formed via the decomposition of ethylnorbornyl radicals and the further reactions of these alkenes are the precursors of aromatics in EthNB pyrolysis. Although QC and EthNB have a similar U-shaped carbon skeleton structure, the difference is that the former has an extra four-membered ring with more strain energy, which leads a lower initial decomposition temperature. Similarly, the extra CC double bonds, in NBD compared to EthNB, result in more c-C5H6 and C2H2 formation and further increase the growing tendency of initial PAH.

Conversion of volatile organic compounds in a twin surface dielectric barrier discharge

A voltage and power controlled surface dielectric barrier discharge for the removal of volatile organic compounds (VOCs) from gas streams is studied by means of current–voltage measurements, flame ionization detectors, and gas chromatography–mass spectrometry (GC–MS). The discharge is generated in a defined synthetic air gas stream at atmospheric pressure by application of a damped sinusoidal voltage waveform resulting from a resonant circuit. Multiple organic compounds, namely n-butane, butanol, isobutanol, ethyl acetate, diethyl ether, and butoxyethanol, are tested at concentrations of 50, 100, 200, and 400 ppm (parts per million), as well as peak-to-peak voltages of 8 to 13 kVpp and pulse repetition frequencies of 250 to 4000 Hz. The dissipated power within the system is calculated utilizing the measured voltage and current waveforms. The conversion and absolute degradation of the VOCs are determined by flame ionization detectors. An increasing concentration of VOCs is found to increase the dissipated power marginally, suggesting a higher conductivity and higher electron densities in the plasma. Of the applied VOCs, n-butane is found to be the most resistant to the plasma treatment, while higher concentrations consistently result in a lower conversion and a higher absolute degradation across all tested compounds. Corresponding amounts of converted molecules per expended joule are given as a comparable parameter by weighting the absolute degradation with the dissipated power. Finally, specific reaction products are determined by online GC–MS, further confirming carbon dioxide (CO2) as a major reaction product, alongside a variety of less prevalent side products, depending on the structure of the original compound. The findings of this study are intended to promote the development of energy efficient processes for the purification of gas streams in both, industry and consumer market. Potential applications of the presented technique could be found in car paint shops, chemical plants, hospital ventilation systems, or air purifiers for living space.

CO2 conversion to methane using Ni/SiO2 catalysts promoted by Fe, Co and Zn

Mitigation of CO2 emissions has become an important issue nowadays, as well as its reutilization as a carbon source to obtain chemicals and fuels. CO2 conversion to CH4 comes up as an interesting alternative, since it is a natural gas substitute and H2 storage source. In this study, Ni/SiO2 catalysts promoted by Fe, Co and Zn were prepared by simple wet impregnation and evaluated in the CO2 conversion to methane. The samples were characterized by TGA-DTA, XRD, N2 physisorption, H2-TPR and TPO-DTA. The reactions were carried out at 1 atm in a fixed bed reactor with H2/CO2 = 4 and online GC analysis. The addition of a second metal enhanced the surface area and lowered the Ni° crystallite size, indicating that metallic dispersion was improved. These characteristics had positive influence on the methanation performance of the Fe and Co promoted catalysts, which showed improved CO2 conversion and CH4 selectivity in comparison to unpromoted catalysts. Ni-Co/SiO2 presented the best results, attaining 73 % of CO2 conversion and 98.5 % of CH4 selectivity at 350 °C and high resistance to sintering. The catalyst promoted by Fe presented the higher resistance to carbon formation, whereas the promotion with Zn led to a strong decrease in selectivity for CH4 and a consequent increase in selectivity for CO. These results suggest the use of both Fe and Co as promoters of Ni/SiO2 catalysts has a high potential for the CO2 conversion to CH4.

Direct Gas-Phase Derivatization by Employing Tandem μ-Reactor-Gas Chromatography/Mass Spectrometry: Case Study of Trifluoroacetylation of 4,4'-Methylenedianiline.

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is a promising technique allowing the rapid characterization of the polymer structure and additives of microgram-scale plastics. However, the Py-GC/MS analysis of polymers with urethane bonds is challenging because they produce highly reactive pyrolyzates such as amines and isocyanates polymerizing in the GC column, which limits the efforts to elucidate the pyrolysis mechanism and plastic characterization by online GC analysis. Herein, a novel pyrolysis-gas-phase derivatization-GC/MS (Py-GPD-GC/MS) technique was developed, allowing the pyrolysis of polymers and the subsequent direct gas-phase derivatization of pyrolyzates, employing a modified tandem μ-reactor-GC/MS system. This work conducted the gas-phase trifluoroacetylation of 4,4'-methylenedianiline (MDA), which is one of the major polyurethane (PU) pyrolyzates, using N-methyl-bis-trifluoroacetamide (MBTFA) as a derivatization agent. The trifluoroacetylation gas-phase reaction was monitored by in situ GC/MS analysis and the effects of derivatization conditions were investigated. The highest MDA conversion observed was 65.6 area %. Furthermore, the sequential PU pyrolysis and direct trifluoroacetylation of PU pyrolyzates in the first μ-reactor and second μ-reactor, respectively, were successfully operated, achieving the inhibited polymerization and detection of trifluoroacetylated derivatives. Thus, the Py-GPD-GC/MS method has a significant potential to be applied for other combinations of pyrolyzates and derivatization reactions, enabling deeper characterization of plastics producing highly reactive pyrolyzates that cannot be accurately analyzed by conventional Py-GC/MS analysis.

Biogas dry reforming over Ni-M-Al (M = K, Na and Li) layered double hydroxide-derived catalysts

In this work, Ni-M-Al (M = K, Na, and Li) LDH-derived catalysts were evaluated for the biogas dry reforming. The catalysts were prepared by co-precipitation and characterized by SBET, XRD, TPR, NH3-TPD, CO2-TPD, SEM and TPO. Reactions were carried out in a fixed bed reactor with online GC analysis in step-wise mode in the range of 500–750 °C and the stability tests were performed at 700 °C. All prepared samples exhibited hydrotalcite-type structure. Differences in reducibility and in the acidity of oxides were observed. The acidity of the catalyst was in the order: NiLi > NiNa > NiK, which is in the opposite order of monovalent cation size. The NiLi catalyst showed the highest resistance to sintering during the reactions due to the higher reduction temperature of mixed oxides (Ni2AlO4 and NiAl2O4) which results in smaller Ni° crystallite size after reduction. The results at 700 °C showed that NiLi catalyst deactivation occurs mainly by carbon deposition, whereas the deactivation of NiK and NiNa catalyst occurs mainly by sintering. TPO results indicated different carbon species produced depending on how the reaction is performed. All the catalysts produced carbon nanotubes at 700 °C.