Increase In Reaction Pressure Research Articles

Numerical investigations on hydrothermal flame characteristics of water-cooled hydrothermal burner

Abstract Supercritical hydrothermal combustion, as a quick homogeneous oxidizing process, offers a promising treatment option for industrial wastewater. This paper established a computational fluid dynamics model of a water-cooled hydrothermal combustion burner to investigate the thermal flame characteristics. The effects of the fuel mass flow rate, fuel concentration, initial reactor temperature, reaction pressure, and oxidant temperature on the thermal combustion ignition were revealed. The results indicate that the fuel concentration (from 10 wt% to 60 wt%) and initial reactor temperature (from 623 to 773 K) had less effect on the ignition temperature. In contrast, the ignition temperature increases by 398 K with increasing fuel mass flow rate (from 24 kg h−1 to 1080 kg h−1). As the oxygen temperature increases (from 273 to 673 K), the ignition temperature gradually decreases to 573 K and then increases. An increase in reaction pressure can facilitate a decrease in ignition temperature to a certain extent, and the optimal reaction pressure is 25 MPa. This study provides a vital reference for a hydrothermal burner’s scale-up design and ignition operation.

Study on the coupling properties of hydrogen PEMFC and air source heat pump

Abstract A steady-state model for the coupling of a proton exchange membrane fuel cell and an air source heat pump (PEMFC–ASHP) is established in this paper. The influence of reaction pressure and relative humidity on the polarization curve and operating characteristics of PEMFC, as well as the influence of ambient temperature and compressor speed on the system performance are investigated. The results show that the increase of reaction pressure and relative humidity is conducive to the improvement of fuel cell output voltage and efficiency, and the influence of reactant gas relative humidity is more obvious. As the increase of ambient temperature and compressor speed, the heat pump efficiency and system efficiency decrease. The research results can provide theoretical guidance for the design and operation of the PEMFC–ASHP system.

Experimental investigation on gasification characteristics of polyethylene terephthalate (PET) microplastics in supercritical water

In this work, the gasification experiment of PET microplastics in supercritical water was carried out in a quartz tube reactor. The effect of operating conditions on gasification was investigated. Inspired by marine microplastics, the artificial seawater was provided to gasification. A detailed gasification model of PET microplastics was established to reveal the gasification path. The results showed that the increase in gasification temperature and time improved gasification efficiency, but the increase in reaction pressure had little effect on the characteristics of the supercritical water so that gasification efficiency did not change significantly. The carbon conversion of 98.00 wt% was obtained at 800 °C for 10 min. The metal salts contained in seawater promoted the gasification of plastics, which meant that seawater was an efficient utilization route to the plastic gasification. The gasification model demonstrated that PET plastics were prone to form biphenyl, which was not conducive to PET gasification at low temperatures.

Selective CO Hydrogenation Over Bimetallic Co-Fe Catalysts for the Production of Light Paraffin Hydrocarbons (C2–C4): Effect of Space Velocity, Reaction Pressure and Temperature

Synthetic natural gas (SNG) using syngas from coal and biomass has attracted much attention as a potential substitute for fossil fuels because of environmental advantages. However, heating value of SNG is below the standard heating value for power generation (especially in South Korea and Japan). In this study, bimetallic Co-Fe catalyst was developed for the production of light paraffin hydrocarbons (C2–C4 as well as CH4) for usage as mixing gases to improve the heating value of SNG. The catalytic performance was monitored by varying space velocity, reaction pressure and temperature. The CO conversion increases with decrease in space velocities, and with an increase in reaction pressure and temperature. CH4 yield increases and C2+ yield decreases with increasing reaction temperature at all reaction pressure and space velocities. In addition, improved CH4 yield at higher reaction pressure (20 bar) implies that higher reaction pressure is a favorable condition for secondary CO2 methanation reaction. The bimetallic Co-Fe catalyst showed the best results with 99.7% CO conversion, 36.1% C2–C4 yield and 0.90 paraffin ratio at H2/CO of 3.0, space velocity of 4000 mL/g/h, reaction pressure of 20 bar, and temperature of 350 °C.

Investigation on composition and structure of asphaltenes during low-temperature coal tar hydrotreatment under various reaction pressures

Hydrotreatment (HDT) of low-temperature coal tar (LCT) were carried out in a fixed-bed hydrogenation equipment under various reaction pressures. Asphaltenes were characterized by elemental analysis (EA), gel permeation chromatography (GPC), and proton nuclear magnetic resonance (1H-NMR). As the reaction pressure increased from 6 to 12 MPa, the content of toluene insoluble compounds and asphaltenes as well as the polydispersity of asphaltenes decreased gradually, indicating that the increase of pressure inhibited the condensation reaction of macromolecular radicals to produce toluene insoluble substance. What’s more, the removal rate of sulfur and nitrogen increased about 20% and 3%, respectively. This phenomenon revealed that sulfides were gradually removed as reaction pressure increased, owing to different removal degree of alkylates, thioethers, sulfoxides and sulfones in sulfides of LCT asphaltenes. By contrast, the increase of reaction pressure had negligible effect on removal rate of nitrogen because aromaticity (fA) of LCT asphaltenes is high and nitrogen mainly exist in the form of heterocyclic nitrides (more than 85%), which are difficult to be removed. By analyzing the structure, fA of LCT asphaltenes tended to decrease and the condensation degree parameter of the aromatic ring system (HAU/CA) increased gradually, indicating that the aromatic of the asphaltenes’ unit layers lessened and the condensation degree of aromatic rings decreased. In addition, the naphthenic ring number (Rn) remains almost unchanged, while the aromatic ring number (RA) reduced with the increase of pressure, demonstrating that the ring-opening rate of naphthenic ring is slightly larger than the hydrogenation saturation rate of aromatic ring during the HDT process of LCT.

Effect of Reaction Pressures on Structure–Performance of Co2C-Based Catalyst for Syngas Conversion

The effect of reaction pressures on structure–performance of Co2C-based catalyst for syngas conversion was studied in detail. Co2C nanoprisms with exposed facets of (101) and (020) used for the dissociation adsorption of CO molecules were stable at low reaction pressure, and promising FTO (Fischer–Tropsch to olefins) performance with low CH4 selectivity and high C2–4= selectivity simultaneously was achieved. With the increase of reaction pressure, the oxygenates selectivity significantly increased at the expense of decreasing C2–4= selectivity. The characterization results indicated that the morphology of Co2C nanostructures changed from nanoprisms to nanospheres and that the metallic Co0 was observed with the increase of reaction pressures. The appearance of Co2C(111) benefited CO insertion, and the formation of Co/Co2C(111) as dual active sites contributed to the enhancement of oxygenates selectivity at elevated pressure. This study suggested that reaction pressures had a strong effect on structure–perf...

Prediction of by-Products from Wet Air Oxidation Module for Sludge Treatment of Produced Water

This study presents and verifies the deep-well wet air oxidation (WAO) reaction model for treating organic sludge (among the various by-products discharged from produced water treatment facilities) for recycling, and predicts the reaction characteristics. The deep-well WAO reaction model is established theoretically and a simulation model is developed. The validity of the simulation model is examined by comparing the modeled pressure change inside the reactor with that given by a model developed in a previous study. In terms of the pressure profile inside the reactor, the developed simulation model shows a 2.3% difference from the previously proposed model. It is confirmed that the increase in reaction pressure and residence time inside the deep-well WAO reactor improves organic decomposition by increasing the oxygen mass transfer rate in water containing such organics.

Hyperbranched bisphosphinoamine ligands: synthesis, characterization and application in ethylene oligomerization

Two hyperbranched bisphosphinoamine (PNP) ligands and chromium complexes were synthesized in good yield with 1.0 generation (1.0 G) hyperbranched macromolecules, chlorodiphenylphosphine (Ph2PCl) and CrCl3(THF)3 as raw materials. The hyperbranched PNP ligands and chromium complexes were characterized by FT-IR, 1H NMR, 31P NMR, UV and ESI-MS. Comparing with the chromium complexes, the hyperbranched PNP ligands, in combination with Cr(III), and activation by methylaluminoxane (MAO) in situ generated species with better catalytic performance for ethylene oligomerization. The effect of solvent, chromium source, ligand/Cr molar ratio, reaction temperature, Al/Cr molar ratio and reaction pressure on the catalytic activity and product selectivity were studied. The results showed that with increase of ligand/Cr molar ratio, reaction temperature and Al/Cr molar ratio, the catalytic activity increased at first and then decreased. However, the catalytic activity continuously increased with increase of reaction pressure. Under the optimized conditions, the catalytic system of hyperbranched PNP/Cr(III)/MAO led to catalytic activity of 2.68 × 105 g/(mol Cr·h) and 37.71% selectivity for C6 and C8.

Bimetallic Cu-Ni catalysts supported on MCM-41 and Ti-MCM-41 porous materials for hydrodeoxygenation of lignin model compound into transportation fuels

The design of novel, efficient supported bimetallic catalysts for the transformation of renewable lignin model compounds into valuable products is currently an emerging research topic. This study investigates the synthesis, characterization and the catalytic application of bimetallic Cu-Ni catalysts supported on pure MCM-41 and Ti incorporated MCM-41 porous materials for the valorization of a lignin model compound (i.e. guaiacol) into the transportation fuels via hydrodeoxygenation route (HDO). The investigated characterization results revealed that the Ti species are well-dispersed within the MCM-41 framework by a tetrahedral coordination. NH3-TPD studies show that the incorporation of Ti into the MCM-41 framework generates large amounts of acidic sites. It was also found that, the coordinated Ti species enhance the dispersion of CuO and NiO species on the surface of Ti-MCM-41 support. The CuNi/Ti-MCM-41 catalyst shows excellent reducible properties due to the co-operative effects of CuO and NiO with the Ti-MCM-41 support. The catalytic experiments revealed that the CuNi/Ti-MCM-41 catalyst exhibits a higher guaiacol conversion (~90.49%) and superior selectivity to cyclohexane (~50.09%) than the CuNi/MCM-41 catalyst which exhibits only ~10.57% cyclohexane selectivity with a guaiacol conversion of ~37.03%. The guaiacol conversion and cyclohexane selectivity were found to increase with the increase of reaction pressure from 40 to 100bar for CuNi/Ti-MCM-41 catalyst. It has been demonstrated that the HDO of guaiacol proceeds via demethoxylation (CAR-OCH3 cleavage) over the CuNi/Ti-MCM-41 catalyst and both demethylation (CARO-CH3 cleavage) and demethoxylation (CAR-OCH3 cleavage) pathways are possible over the CuNi/MCM-41 catalyst in HDO of guaiacol.

A comparative thermodynamic study on the CO2 conversion in the synthesis of methanol and of DME

A thermodynamic approach of the synthesis processes of methanol and of DME from H2 + CO + CO2 has been conducted, in order to compare the feasibility of incorporating CO2 in the feed of both processes. The effects of reaction temperature (200–400 °C), pressure (10–100 bar) and CO2/(CO + CO2) ratio in the feed on the CO2 conversion, yield and selectivity of oxygenates (methanol + DME), and heat released in each process have been studied. CO2 conversion is strongly dependent on the CO2 content in the feed and is higher in the DME synthesis for high CO2 concentration values in the feed (CO2/(CO + CO2) > 0.75). The increase of reaction temperature and the increase of the CO2 content in the feed have an unfavorable effect on the oxygenate yield and selectivity, while the increase of reaction pressure has a favorable effect. Comparing both processes, higher oxygenate yield and selectivity values are obtained in the synthesis of DME, which is more relevant for CO2 rich feeds. Moreover, feeding CO2 lessens the exothermic nature of both processes which is a positive effect for protecting the metallic function of the catalyst, as the formation of hot spots is avoided.

Hydrogenation of CO2 to methanol over In2O3 catalyst

The superior catalytic activity of In2O3 for CO2 hydrogenation to methanol is demonstrated here. The experimental results demonstrate that the reaction temperature and pressure have a significant influence on methanol yield. The conversion of CO2 over In2O3 increases with the increase of reaction temperature and pressure. The yield and formation rate of methanol also increase with the increase of reaction pressure. However, they increase firstly with the increase of reaction temperature but start to decrease when the temperature rises above 330°C. At 330°C and 4MPa, the yield of methanol reaches 2.82%, while the methanol production rate reaches 3.69molh−1kgcat−1, higher than many other reported catalysts, which normally show very low selectivity of methanol at such high temperature. This confirms the previous theoretical study that In2O3 inhibits the reverse water gas shift, a competitive endothermic reaction for methanol synthesis from CO2 hydrogenation. The mechanism for CO2 hydrogenation to methanol over In2O3 catalyst has been discussed.

Effect of carriers on physico-chemical properties and activity of Pd nano-catalyst in n-hexane isomerization

In this work zeolites HY, HZSM-5 and mixes of zeolites with γ-Al2O3 in different ratios were taken as carriers for 0.8 wt% Pd catalysts. Physico-chemical characteristics of the catalysts were determined by methods of Brunauer–Emmett–Teller (BET)–N2 adsorption, x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), hydrogen pulse chemisorption (HPC) and NH3 adsorption–desorption. The activity of catalysts was studied at 225–450 °C, at 0.1 and 0.7 MPa with molar ratio of H2:n-C6H14 = 5.92 and n-hexane concentration 9.2 mol%. Mixing of γ-Al2O3 with zeolite made acidity of catalyst weaken and led to a decrease of Pd cluster size, to an increase of Pd dispersity and a reduction of the extent of Pd in the case of catalyst Pd/HY; but for the catalyst Pd/HZSM-5 such mixing led to the reverse effect. That is why the increase of activity in the first case and the decrease of activity in the second case have been observed. It has been found that the optimal ratio of mixed carrier is γ-Al2O3:HY = 2.5:1 and the optimal calcined temperature of NH4ZSM-5 to obtain HZSM-5 is 500–550 °C. An increase of reaction pressure from 0.1 to 0.7 MPa remarkably increased the activity, selectivity and stability of Pd-based catalysts.

H2 rich gas production via pressurized fluidized bed gasification of sawdust with in situ CO2 capture

The continuous increase in energy demand and the growing attention on global warming worldwide have aroused great research interest in a novel near zero emission energy utilization system which is based on CaO sorption enhanced gasification. This paper presents the experimental results of pressurized CaO sorption enhanced sawdust gasification in a self-design pressurized fluidized bed gasifier, aiming to survey the effects of reaction pressure, CaO to carbon mole ratio (CaO/C), steam to carbon mole ratio (H2O/C) and reaction temperature (T) on hydrogen (H2) production under pressurized gasification conditions. Results showed that the pressurized operation not only promoted gasification reactions, but also apparently enhanced CaO carbonation. Within the experimental ranges investigated in this work, H2 fraction and H2 yield were both elevated with the increase in reaction pressure, CaO/C, H2O/C and T. Comparing with previous atmospheric fluidized bed gasification results, pressurized gasification was capable of producing syngas with higher H2 fraction and lower CO2 fraction even at lower CaO/C, H2O/C and T. It was also verified that pressurized operation increased the carbon conversion and cold gas efficiency for CaO sorption enhanced sawdust gasification.

Biocarbon production from Hungarian sunflower shells

The production of biodiesel and bioethanol fuels is often accompanied by the co-production of lignocellulosic “waste” byproducts. For example, the oil from sunflower seeds (that can be used to manufacture biodiesel fuel) has as “waste” co-products the sunflower shell and its stem. In this paper we examine the production of biocarbon (charcoal) from sunflower shells produced in Hungary. The conversion of these shells to biocarbon via the University of Hawaii's Flash Carbonization TM process is efficient and very quick. An increase in reaction pressure from 1.27 to 2.17 MPa causes a reduction in reaction time that results in a significant increase in charcoal production and profitability. These findings justify further study of the benefits of charcoal production at pressures above 2 MPa.

Char Gasification with O2, CO2, and H2O: Effects of Pressure on Intrinsic Reaction Kinetics

Measurements of the intrinsic reaction rates of two Australian coal chars (made under laboratory conditions) with O2, CO2, and H2O at increased pressures (up to 30 atm) have been made using a pressurized thermogravimetric analyzer (TGA). It was found that the reaction order in CO2 and H2O was not constant over the pressure range investigatedvarying from 0.5 to 0.8 at atmospheric pressure and decreasing at pressures above approximately 10 atm. The apparent reaction order in oxygen was less affected by pressure over the range 1 to 16 atm. Char surface area after reaction at higher pressures was generally greater than that after reaction at lower pressures. This resulted in a reduced effect of pressure on the intrinsic rates at 10% conversion. Activation energies for all three reactions were not significantly affected by an increase in reaction pressure. The intrinsic rate data obtained in this work were used to estimate the high-temperature reactivity of the chars using a basic knowledge of the pore structure of the samples. This provided a framework within which coal behavior under high-temperature gasification conditions can be predicted using intrinsic rate data and a knowledge of the structure of the char.

Slurry-phase CO2 hydrogenation to hydrocarbons over a precipitated Fe-Cu-Al/K catalyst: Investigation of reaction conditions

The hydrogenation of CO2 to hydrocarbons over a precipitated Fe-Cu-Al/K catalyst was studied in a slurry reactor for the first time. Reducibility of the catalyst and effect of reaction variables (temperature, pressure and H2/CO2 ratio of the feed gas) on the catalytic reaction performance were investigated. The reaction results indicated that the Fe-Cu-Al/K catalyst showed a good CO2 hydrogenation performance at a relatively low temperature (533 K). With the increase of reaction temperature CO2 conversion and olefin to paraffin (O/P) ratio in C2-C4 hydrocarbons as well as the selectivity to C2-C4 fraction increased, while CO and CH4 selectivity showed a reverse trend. With the increase in reaction pressure, CO2 conversion and the selectivity to hydrocarbons increased, while the CO selectivity and O/P ratio of C2-C4 hydrocarbons decreased. The investigation of H2/CO2 ratio revealed that CO2 conversion and CH4 selectivity increased while CO selectivity and O/P ratio of C2-C4 decreased with increasing H2/CO2 ratio.

超臨界域のアルカリ水溶液による加硫ゴム廃棄物の再資源化（第２報） 加硫ＥＰＤＭゴムの油化における超臨界域のアルカリ水熱反応の特徴と生成油状物の工学的利用

The application of hydrothermal solution containing NaOH under supercritical conditions to convertsion of the scrap vulcanized ethylene-propylene-diene terpolymer (EPDM) rubber into reusable oily materials as softeners for the rubber synthesis was verified through batch process experiments using a microautoclave.In this paper, the properties of resultant oily materials from a rubber by the hydrothermal treatment under supercritical conditions were compared with those by pyrolysis.In addition, effects of reaction pressure on the desulfurization, and liquefaction in hydrothermal solution and pyrolysis were investigated. These results lead to the followings:(1) Remarkable desulfurization takes place with cracking in hydrothermal solution, (2) Desulfurization and depression of liquefaction in hydrothermal solution are not caused by the increase of reaction pressure but are attributed to the characteristic reactivity of hydrothermal solution, (3) All resultant oily materials were composed of paraffinic hydrocarbons, (4) Resultant oily materials by hydrothermal treatment are more homogeneous than those by pyrolysis. The rubber compound mixed with the resultant oily material by hydrothermal treatment showed the same properties as one mixed with a paraffinic softener commercially available.Since the resultant oily materials by hydrothermal treatment can be used as a softener in a cyclic manner, a closed rubber manufacturing process can be established. These findings and those previously reported motivate us to develop a new recycle process by hydrothermal treatment; the process can simplify hitherto known complex purification steps and facilitate the control of reactions without damaging to the present earth environment.

Activity and Selectivity Regulation of Synthesis Gas Reaction over Supported Ruthenium Catalysts

Abstract The catalytic activities of supported ruthenium for synthesis-gas conversion to hydrocarbons was found to be in the following order: TiO2>Nb2O3>ZrO2>SiO2>Ta2O5>Al2O3>V2O5>Mo3>WO3>MnO2>ZnO Turnover frequencies of the supported ruthenium increased with decrease in dispersion of the metal particles for every carrier material. Even the activities per unit weight of metals were higher for low-dispersion ruthenium on Al2O3, TiO2, and ZrO2. The chain-growth probability of a hydrocarbon product, which is characterized by the Schulz-Flory distribution, increased markedly with decrease in the metal dispersion irrespective of the carrier material. The catalytic activity of ruthenium particles with a dispersion level of 0.7 or higher reached a ceiling level at about 0.5 MPa, whereas that of low dispersed ruthenium increased almost linearly with an increase in reaction pressure (up to at least 2.0 MPa).