Maximum Carbon Yield Research Articles

Turbostratic carbon nanofibers produced from C2HCl3 over self-dispersing Ni-catalyst doped with W and Mo

In this research, a self-dispersing 92Ni-4Mo-4W catalyst showing high productivity towards the H2-assisted synthesis of turbostratic carbon nanofibers was proposed. The effect of reaction temperature on the efficiency of 92Ni-4Mo-4W alloy in the decomposition of trichloroethylene was studied. It was found that in the temperature range of 580–620 °C, the most rapid destruction of the initial alloy followed by the growth of carbon material is realized. This is confirmed by the minimum induction period (9–11 min) and the maximum carbon yield (95–107 g/gcat). As revealed, the catalytically active particles of submicron size contain uniformly distributed Ni, Mo, and W. It is demonstrated that the decomposition of trichloroethylene over the 92Ni-4Mo-4W catalyst results in the formation of a turbostratic carbon material with a segmented structure, containing a minimum quantity of amorphous carbon and possessing high textural characteristics (specific surface area of 330–410 m2/g; pore volume of 0.48–0.58 cm3/g).

Development of biochar/HDPE composites and characterization of the effects of carbon loadings on the electromagnetic shielding properties

The aim of this research is to develop high carbon-yielding biochar from pinewood, coffee husk, sugarcane bagasse, and maize cob and to characterize the biochar/HDPE composites for electromagnetic (EM) shielding application. During the biochar/HDPE composites fabrication, slow pyrolysis and compression molding manufacturing were used. The enhanced properties characterizations were conducted by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), differential thermal analysis (DTA), Fourier transform spectrometry (FTIR), Brunauer-Emmet-Teller (BET) analysis, digital multi-meter, and proximity analysis. The results of biochar pyrolysis showed the maximum carbon yield of 74.6 %, 68.9 %, 68.4 %, and 40 % for pine wood, maize cob, sugarcane bagasse, and coffee husk respectively. The BET analysis showed the maximum specific surface area (734.5 m2/g), pore volume (0.2364 cm3/g), and pore radius (9.897 Å) from the pine wood biochar. The biochar loading analysis results showed that the 30 % and 40 % pine wood biochar significantly enhanced the electrical conductivity, thermal conductivity, thermal stability, crystallinity, and EM shielding effectiveness (SE) of the biochar/HDPE composites. In particular, the biochar/HDPE composite with 30 wt% pine wood biochar showed the highest thermal conductivity of 2.219 W/mK, and the 40 wt% pine wood biochar/HDPE composite achieved the highest electrical conductivity of 4.67 × 10−7 S/cm and EM SE of 44.03 dB at 2.1 GHz.

A novel strategy for l-arginine production in engineered Escherichia coli

Backgroundl-arginine is an important amino acid with applications in diverse industrial and pharmaceutical fields. n-acetylglutamate, synthesized from l-glutamate and acetyl-CoA, is a precursor of the l-arginine biosynthetic branch in microorganisms. The enzyme that produces n-acetylglutamate, n-acetylglutamate synthase, is allosterically inhibited by l-arginine. l-glutamate, as a central metabolite, provides carbon backbone for diverse biological compounds besides l-arginine. When glucose is the sole carbon source, the theoretical maximum carbon yield towards l-arginine is 96.7%, but the experimental highest yield was 51%. The gap of l-arginine yield indicates the regulation complexity of carbon flux and energy during the l-arginine biosynthesis. Besides endogenous biosynthesis, n-acetylglutamate, the key precursor of l-arginine, can be obtained by chemical acylation of l-glutamate with a high yield of 98%. To achieve high-yield production of l-arginine, we demonstrated a novel approach by directly feeding precursor n-acetylglutamate to engineered Escherichia coli.ResultsWe reported a new approach for the high yield of l-arginine production in E. coli. Gene argA encoding n-acetylglutamate synthase was deleted to disable endogenous biosynthesis of n-acetylglutamate. The feasibility of external n-acetylglutamate towards l-arginine was verified via growth assay in argA− strain. To improve l-arginine production, astA encoding arginine n-succinyltransferase, speF encoding ornithine decarboxylase, speB encoding agmatinase, and argR encoding an arginine responsive repressor protein were disrupted. Based on overexpression of argDGI, argCBH operons, encoding enzymes of the l-arginine biosynthetic pathway, ~ 4 g/L l-arginine was produced in shake flask fermentation, resulting in a yield of 0.99 mol l-arginine/mol n-acetylglutamate. This strain was further engineered for the co-production of l-arginine and pyruvate by removing genes adhE, ldhA, poxB, pflB, and aceE, encoding enzymes involved in the conversion and degradation of pyruvate. The resulting strain was shown to produce 4 g/L l-arginine and 11.3 g/L pyruvate in shake flask fermentation.ConclusionsHere, we developed a novel approach to avoid the strict regulation of l-arginine on ArgA and overcome the metabolism complexity in the l-arginine biosynthesis pathway. We achieve a high yield of l-arginine production from n-acetylglutamate in E. coli. Co-production pyruvate and l-arginine was used as an example to increase the utilization of input carbon sources.

Coupling hydropyrolysis and vapor-phase catalytic hydrotreatment to produce biomethane from pine sawdust

This study investigated hydropyrolysis and subsequent vapor-phase hydrotreatment over a NiAl2O4 catalyst to produce biomethane (CH4) from pine sawdust. The non-catalytic pressurized hydropyrolysis generated tar, CO2, and CO as the primary products. However, using a NiAl2O4 catalyst in the second-stage reactor significantly increased the formation of CH4 and reduced CO and CO2 in gas products. The catalyst also fully converted tar intermediates to produce CH4, resulting in a maximum carbon yield of 77.7% with 97.8% selectivity. The temperature plays a crucial role in CH4 generation, with both its yield and selectivity showing a positive correlation with the reaction temperature. Increasing the reaction pressure from 0.2 to 1.2 MPa notably inhibited the production of CH4, leading to a shift towards cycloalkanes due to a competitive reaction. This tandem approach shows great potential as an innovative technique for producing alternative fuels from biomass wastes.

Carbon nanofiber growth from methane over carbon-supported NiCu catalysts: Two temperature regimes

An alternative route towards COx-free production of hydrogen is the thermal catalytic decomposition of methane. In addition to hydrogen, valuable carbon nanomaterials can be formed. Carbon nanofiber formation from methane decomposition over carbon supported NiCu catalysts was studied in-situ using a Thermogravimetric analyzer. We especially investigated how the carbon yield is influenced by reaction parameters. Based on experiments with varying temperature (450–600 °C), two distinct temperature regimes were identified. Different kinetic parameters were derived for the two regimes. Activation energies of 86 and 45 kJ/mol, and reaction orders in methane of close to 1 and 1.5, were found in the low and high temperature regimes, respectively. We postulate that at lower temperature the methane dissociation is rate limiting, while at higher temperature the carbon formation plays a more critical role. At low temperatures mostly full fishbone fibers are formed, whereas at higher temperatures mainly hollow fibers are formed. The maximum carbon yield is obtained at the transition between the two regimes, when the carbon supply and carbon nanostructure formation are balanced.

A numerical study on turquoise hydrogen production by catalytic decomposition of methane

Catalytic decomposition of methane (CDM) is a novel technology for turquoise hydrogen production with solid carbon as the by-product instead of CO2. A computational fluid dynamics model was developed to simulate the CDM process in a 3D fixed bed reactor, accounting for the impact of carbon deposition on catalytic activity. The model was validated with experimental data and demonstrated its capability to predict hydrogen concentration and catalyst deactivation time under varying operating temperatures and methane flow rates. The catalyst lifespan was characterized by the maximum carbon yield (i.e., gC/gcat), which is a crucial indicator for determining the cost of hydrogen generation. Parametric studies were performed to analyse the effect of inlet gas composition and operating pressure on CDM performance. Various CH4/H2 ratios were simulated to improve the methane conversion efficiency, generating a higher amount of hydrogen while increasing the maximum carbon yield up to 49.5 gC/gcat. Additionally, higher operating pressure resulted in higher methane decomposition rates, which reflects the nature of the chemical kinetics.

Catalytic upgradation of crude glycerol to produce bio-based aromatics over hierarchical MFI zeolite: Effect of bimodal hierarchical porosity enhancement and porosity-acidity interaction

The transformation of renewable biomass derived crude glycerol into value-added BTX aromatics is an attractive approach to facilitate carbon neutrality and recycling economy. Herein, two kinds of hierarchical HZSM-5 with distinct hierarchical porosity and acidity distribution were synthesized based on a seed-induced method by utilizing CTAB and TPOAC as soft mesoporogens, respectively. And the effects of bimodal hierarchical porosity and porosity-acidity interaction on the upgradation efficiency during the conversion of crude glycerol over hierarchical HZSM-5 were investigated. The abundant intra-mesopores and promoted porosity-acidity interaction in hierarchical HZSM-5 facilitated the transformation of macromolecules in crude glycerol into small oxygenated chemicals and olefins, resulting in higher BTX yield and longer catalyst lifetime. Among all catalysts, the hierarchical HZSM-5 sample templated with TPOAC exhibited the maximum carbon yields of BTX (38.5%) and longest lifetime (23 h) due to the better interconnectivity of shape-selective micropores and high mass transfer intra-mesopores. The reaction route and product distribution of upgradation of crude glycerol was strongly dependent on the morphology, bimodal hierarchical porosity and acidity variation resulting from the generation of intra-mesopores in HZSM-5 catalysts by the usage of different soft mesoporogens. The liquid route and side alkylation reaction was accelerated over HZSM-5/TPOAC catalyst while the gas route and secondary coking reaction was promoted over HZSM-5/CTAB sample.

Experimental and Simulation Study on Coproduction of Hydrogen and Carbon Nanomaterials by Catalytic Decomposition of Methane-Hydrogen Mixtures

Among all hydrocarbons, the methane molecule contains the highest amount of hydrogen with respect to carbon. Therefore, the catalytic decomposition of methane is considered as an efficient approach to produce hydrogen along with nanostructured carbon product. On the other hand, the presence of hydrogen in the composition of the initial gas mixture is required for the stable operation of the catalyst. In present work, the experiments on the catalytic decomposition of methane–hydrogen mixture were performed in a flow-through quartz reactor equipped with McBain balances under atmospheric pressure. The catalyst NiO-CuO/Al2O3 was prepared by the mechanochemical activation technique. The maximum carbon yield of 34.9 g/gcat was obtained after 2 h of experiment at 610 °C. An excess of hydrogen in the reaction mixture provided the long-term activity of the nickel–copper catalyst. The durability tests ongoing for 6 h within a temperature range of 525–600 °C showed no noticeable deactivation of the catalyst. Two kinetic models, D1a and M1a, were proposed for the studied decomposition of the methane–hydrogen mixture over the nickel–copper catalyst. The kinetic constants for these models were determined by means of mathematical modelling.

Kinetic study of thermocatalytic decomposition of methane over nickel supported catalyst in a fluidized bed reactor

ThermoCatalytic Decomposition of methane (TCD) offers an interesting route to convert natural gas into hydrogen and functional carbon. In this study the reaction kinetics of TCD is studied for a nickel supported catalyst using a special fluidized bed reactor. The effect of operating conditions such as temperature, concentrations of methane and hydrogen and space velocity (SV) was studied on a commercial nickel catalyst on a silica support. The performance of the catalyst was evaluated in terms of three parameters: maximum reaction rate, lifetime and carbon yield. Values up to and in excess of 70gC/gcat and 12h (at 550 °C and 70vol.% CH4-5vol.% H2) have been achieved for carbon yield and lifetime, respectively. The carbon product has fish bone structure. Our study has revealed that at lower temperatures and in the presence of small amounts of hydrogen (≤10%) a higher carbon yield is obtained. Lower concentration of methane (higher concentration of the inert) lowers the reaction rate, the lifetime and therefore the carbon yield. A dual kinetic approach has been adopted to determine maximum reaction rate and the associated deactivation factor. The kinetic parameters were estimated for the temperature range of 550-600 °C.

Effect of reduction conditions of Mo-Fe/MgO on the formation of carbon nanotube in catalytic methane decomposition

The effects of temperature, hydrogen partial pressure, and time in catalytic reduction step on carbon nanotube growth in a catalytic methane decomposition have been investigated for Mo-Fe/MgO catalysts. The results show that the reduction conditions of the catalyst affect the crystal structure of the metal formed on the catalyst surface and the growth mechanism of the generated carbon nanotubes. Both diameter distribution and crystallinity of the CNTs increased with the increase of reduction temperature in the range of 400 to 800 °C. The optimal reduction temperature with the maximum carbon yield was found to be 500 °C. The increase of hydrogen partial pressure and reduction time increased the CNT diameter distribution, and the optimal hydrogen partial pressure and reduction time with maximum carbon yield were found to be 0.1 atm, 60 min and 0.3 atm, 5 min, respectively. In the different combination of hydrogen partial pressure and reduction time for maximizing carbon yield, the CNT average diameter did not have a significant change, while the CNT crystallinity showed opposite trends depending on the methane decomposition reaction time. Ultimately, it was confirmed that the Mo-Fe/MgO catalyst can change the properties of CNTs produced through control of reduction conditions.

Fast pyrolysis of torrefied holocellulose for producing long-chain ether precursors in a fluidized bed

Combining torrefaction with fast pyrolysis is an achievable route for producing long-chain ether precursors. The results of structural characterization for native and torrefied holocellulose indicated that with increasing torrefaction temperature, the crystallinity index (CrI) decreased slightly and then sharply increased; hydroxyls, O-acetyl branches, ether bond and β-1,4-glycosidic bond were eliminated but carbonyls increased. Maximum mass loss rate and apparent activation energy increased after torrefaction. With an increase in torrefaction temperature, gaseous yield continuously dropped, and liquid product yield climbed to the highest point of 49.04% for holocellulose torrefied at 240 °C (240CS). Torrefaction was unfavorable for the production of small-molecule gases. The bio-oil analysis demonstrated that the yield of acetic acid decreased from 6.35% to 1.43% with torrefaction temperature increasing from 105 °C to 260 °C. Significantly, yields of targeted compounds were dramatically improved after torrefaction, and 240CS afforded the maximum carbon yield of 14.79%.

Metal-carbon compositions as thermolysis products of complex compounds [Co(А)6]х[Fe(CN)6]у•nH2O (А = NH3, en/2)

The formation conditions of residual carbon have been studied for thermolysis in an inert atmosphere of double complex compounds of two groups of analogs: [Co(А)6][Fe(CN)6] and [Co(А)6]4[Fe(CN)6]3∙nH2O, where A = NH3, en/2. Isothermal experiments were carried out for extreme points of thermograms to obtain and analyze thermolysis products. Carbon was extracted from thermolysis products by leaching with hydrochloric acid, and its composition, thermal stability in air, specific surface area, and crystalline modification were investigated. The maximum carbon yield was for the compound [Co(NH3)6][Fe(CN)6], the largest specific surface area of carbon was 380 m2/g for [Co(en)3][Fe(CN)6]∙2H2O. The extracted carbon contains the admixtures of Co and Fe. The extracted carbon is stable when heated in air up to 450-500°С and burns completely up to 700°С. The carbon samples are largely graphitized.

Coupling hydrothermal carbonization of digestate and supercritical water gasification of liquid products

This work investigates the coupling of hydrothermal carbonization (HTC) and supercritical water gasification (SCWG) as a combined process to fully valorise digestate from anaerobic digestion. Firstly, HTC was performed at three different temperatures (180, 220 and 250 °C) to convert digestate to hydrochar (HC) and aqueous HTC liquids (AHLs) and then, SCWG was performed on AHLs to produce a H2-rich gas. Different SCWG temperatures (500, 550 and 600 °C), residence times (15, 30, 60 and 90 s) and AHLs concentrations (6.7, 13.6 and 20.0%) were tested. Increasing SCWG temperature resulted in an increase of the carbon yield and H2 content in the gas phase, for increasing residence time the carbon yield in the gas phase decreased, while increasing the feedstock concentration led to a higher gas generation rate without affecting the carbon yield of the gas. The maximum carbon yield in the gas phase (51%) was reached for tests run at 600 °C, 15 s, and 6.7% of AHLs, the maximum hydrogen content in the gas phase (79%) was reached at 600 °C, 30 s, 6.7% of AHLs, the maximum gas generation rate (9.33 mL min−1) was reached at 600 °C, 30 s, 20.0% of AHLs.

Regulating light olefins or aromatics production in ex-situ catalytic pyrolysis of biomass by engineering the structure of tin modified ZSM-5 catalyst

Valorization of biomass to olefin or aromatics harbours tremendous practical value due to growing concerns about sustainable production of chemicals. Herein, the olefin or aromatics yields of ex-situ catalytic pyrolysis of pine can be regulated by impregnating Sn on hollow-structured ZSM-5 (M-ZSM-5) and microporous ZSM-5 catalysts in fixed-bed reactor, respectively. Results showed that Sn/ZSM-5 catalyst simultaneously increased medium acidic sites and maintained strong acidic sites, which obtained the maximum carbon yield of aromatics (33.77%) due to enhanced cracking and deoxygenation reactions. In addition, Sn boosted alkylation between olefin and aromatics, generating more alkylbenzene. In contrast, Sn/M-ZSM-5 catalyst produced the highest olefins carbon yield (12.39%) because the reduction of strong acidic sites and microporous volume inhibited the olefin aromatization. Moreover, olefins were easier to desorb from Sn/M-ZSM-5 due to the enhanced mass transfer ability, which weakened the alkylation reactions. The synergistic effect harbours great significance to manipulate the distribution of products.

Microbial Upgrading of Acetate into Value-Added Products-Examining Microbial Diversity, Bioenergetic Constraints and Metabolic Engineering Approaches.

Ecological concerns have recently led to the increasing trend to upgrade carbon contained in waste streams into valuable chemicals. One of these components is acetate. Its microbial upgrading is possible in various species, with Escherichia coli being the best-studied. Several chemicals derived from acetate have already been successfully produced in E. coli on a laboratory scale, including acetone, itaconic acid, mevalonate, and tyrosine. As acetate is a carbon source with a low energy content compared to glucose or glycerol, energy- and redox-balancing plays an important role in acetate-based growth and production. In addition to the energetic challenges, acetate has an inhibitory effect on microorganisms, reducing growth rates, and limiting product concentrations. Moreover, extensive metabolic engineering is necessary to obtain a broad range of acetate-based products. In this review, we illustrate some of the necessary energetic considerations to establish robust production processes by presenting calculations of maximum theoretical product and carbon yields. Moreover, different strategies to deal with energetic and metabolic challenges are presented. Finally, we summarize ways to alleviate acetate toxicity and give an overview of process engineering measures that enable sustainable acetate-based production of value-added chemicals.

Sustainable Production of Acetonitrile from Microalgae via Catalytic Fast Pyrolysis with Ammonia over Ga/HZSM-5 Catalysts

We report on catalytic fast pyrolysis microalgae under ammonia atmosphere into acetonitrile over Ga/HZSM-5, which provides a long-term sustainable option for acetonitrile production and microalgae valorization. The effect of various catalysts, reaction conditions and species of microalgae on acetonitrile production was explored systematically. Under the optimized conditions, the maximum carbon yield of acetonitrile from Chlorella vulgaris was 23.4%, and the selectivity of acetonitrile in bio-oil was up to 77.2%. The possible reaction pathways were proposed according to the comprehensive experimental investigation on the conversion of model compounds and intermediates (proteins, carbohydrates, lipids, amino acids, carboxylic acids, furans, and amines). High-resolution transmission electron microscopy (TEM) analysis showed that Ga was present mainly at the outer surface of zeolite crystals, and a small amount of Ga was doped into the zeolite crystals.

Features of the Carbon Nanofibers Growth over Ni-Pd Catalyst Depending on the Reaction Conditions

Ni-Pd alloy was prepared by a co-precipitation technique. Catalytic decomposition of a model chlorinated hydrocarbon (1,2-dichloroethane) was performed in a quartz flow-through reactor system. Both the temperature regime and the composition of the reaction mixture were varied during the experiments. Concentration of 1,2-dichloroethane was found to affect significantly the kinetics of the process, the yield of the nanostructured carbon product and its textural and morphological characteristics. In terms of optimal temperature, the maximum carbon yield was obtained within a range of 650-670 °C.

Conversion of lignin into light olefins and aromatics over Fe/ZSM-5 catalytic fast pyrolysis: Significance of Fe contents and temperature

The conversion of lignin into light olefins and aromatic compounds via catalytic fast pyrolysis was performed in a fixed bed reactor over a range of Fe-modified ZSM-5 catalysts at different temperatures. More specifically, catalysts containing 0, 1, 3, 6, and 9 wt.% Fe were prepared by an impregnation method, and the resulting catalysts were characterized by XRD, NH3-TPD, H2-TPR and BET analysis. The catalyst structure remained intact upon increasing the Fe loading, although the surface area, pore volume, and number of acidic sites of the catalysts varied, and the total acidity increased upon increasing the Fe loading. The maximum carbon yield of light olefins plus aromatic compounds was 12.8%, and this was obtained with a 3 wt.% Fe loading at 600 °C. This yield decreased upon further increasing the Fe loading and upon increasing the temperature to 700 °C. Moreover, the selectivity of C2H4 was more than 80%, and it was decreased with the Fe loading and increased with temperature increasing. The total acidity had a direct relationship with aromatic production, while light olefins were mainly affected by medium acid sites.

Improvements in the carbonisation of viscose fibres

The maximum theoretical carbon yield for the carbonisation of viscose fibres, which consist of the renewable resource cellulose, is 44%. In reality the carbon yield is just in the range of 20%. By chemical activation of viscose fibres, carbon yields of more than 30% were achieved along with a reduction of undesired tar formation by 75%. A further increase in carbon yield was realised by supplemental incorporation of carbon black into the cellulose matrix of the viscose fibres. The chemical activation did not change the state of chemical bonding of the carbon atoms and the supramolecular structure within the carbonised fibres. Also the fibre morphology remained unchanged in terms of shape of cross section and surface structure. However, activated viscose fibres delivered carbon fibres with a much higher specific surface area. Carbon fibres from activated viscose fibres provide a similar or even improved application potential as carbon fibres from standard viscose fibres.

Augmenting the Calvin\u2013Benson\u2013Bassham cycle by a synthetic malyl-CoA-glycerate carbon fixation pathway

The Calvin–Benson–Bassham (CBB) cycle is presumably evolved for optimal synthesis of C3 sugars, but not for the production of C2 metabolite acetyl-CoA. The carbon loss in producing acetyl-CoA from decarboxylation of C3 sugar limits the maximum carbon yield of photosynthesis. Here we design a synthetic malyl-CoA-glycerate (MCG) pathway to augment the CBB cycle for efficient acetyl-CoA synthesis. This pathway converts a C3 metabolite to two acetyl-CoA by fixation of one additional CO2 equivalent, or assimilates glyoxylate, a photorespiration intermediate, to produce acetyl-CoA without net carbon loss. We first functionally demonstrate the design of the MCG pathway in vitro and in Escherichia coli. We then implement the pathway in a photosynthetic organism Synechococcus elongates PCC7942, and show that it increases the intracellular acetyl-CoA pool and enhances bicarbonate assimilation by roughly 2-fold. This work provides a strategy to improve carbon fixation efficiency in photosynthetic organisms.