Guojie Zhang

Catalytic performance of activated carbon supported cobalt catalyst for CO2 reforming of CH4

Syngas production by CO2 reforming of CH4 in a fixed bed reactor was investigated over a series of activated carbon (AC) supported Co catalysts as a function of Co loading (between 15 and 30wt.%) and calcination temperature (Tc=300, 400 or 500°C). The catalytic performance was assessed through CH4 and CO2 conversions and long-term stability. XRD and SEM were used to characterize the catalysts. It was found that the stability of Co/AC catalysts was strongly dependent on the Co loading and calcination temperature. For the loadings (25wt.% for Tc=300°C), stable activities have been achieved. The loading of excess Co (>wt.% 25) causes negative effects not only on the performance of the catalysts but also on the support surface properties. In addition, the experiment showed that ultrasound can enhance and promote dispersion of the active metal on the carrier, thus improving the catalytic performance of the catalyst. The catalyst activity can be long-term stably maintained, and no obvious deactivation has been observed in the first 2700min. After analyzing the characteristics, a reaction mechanism for CO2 reforming of CH4 over Co/AC catalyst was proposed.

Pyrolysis characteristics and kinetics of two Chinese low-rank coals

The pyrolysis characteristics and kinetics of two Chinese low-rank coal samples have been studied through thermogravimetric technique and mathematical modeling. Applicability of three kinetic models, viz. the Doyle temperature integral model, Achar–Brindley–Sharp–Wendworth (ABSW) derivative model and Coats–Redfern integral model, is evaluated. The results showed that Doyle model and ABSW model cannot describe the pyrolysis process accurately, while Coats–Redfern integral model was appropriate to describe pyrolysis reaction of the two low-rank coals. From the Coats–Redfern integral model, the reaction order of low-rank coals was of nxa0=xa02, and the pyrolysis process can be divided into four stages; the activation energy decreased with increasing heating rate above 20xa0Kxa0min−1 and increased continuously with the coalification degree.

Thermogravimetric study of the kinetics and characteristics of the pyrolysis of lignite

For a better understanding of the devolatilization characteristics of lignite, a highly volatile lignite was devolatilized at four different heating rates in a thermogravimetric analyzer in this study. The results showed that the lignite pyrolysis process was strongly affected by the heating rate. As the heating rate increased, the differential thermogravimetry peak shifted toward higher temperature. Based on thermal analysis and kinetic equations, the effects of the heating rate on the pyrolysis characteristics has been studied and the information about the linkage between the activation energy (E), pre-exponential factor (A) and weight loss of each heating rate has been analyzed simultaneously. In the pyrolysis of lignite, the activation energies of the samples were found to increase with decreasing heating rate for each temperature stages.

Synthesis of ZrO2- Based Catalyst for Coke Oven Gas CO Shift via an Orthogonal Experiment Design

An orthogonal experiment design was adopted for synthesis and optimization of ZrO2-Based catalyst for coke oven gas CO shift. The influence of the operating parameters on catalytic properties was investigated, with a composition being similar to typical industrial heterogeneous catalysts for WGS process. The experimental CO conversion data was analyzed by marginal and variance analysis. The optimal operating parameters for ZrO2-Al2O3 based catalyst were suggested by CO conversion.

A review of oxygen removal from oxygen-bearing coal-mine methane

In this article, a comparison will be made concerning the advantages and disadvantages of five kinds of coal mine methane (CMM) deoxygenation method, including pressure swing adsorption, combustion, membrane separation, non-metallic reduction, and cryogenic distillation. Pressure swing adsorption has a wide range of application and strong production capacity. To achieve this goal, adsorbent must have high selectivity, adsorption capacity, and adequate adsorption/desorption kinetics, remain stable after several adsorption/desorption cycles, and possess good thermal and mechanical stabilities. Catalytic combustion deoxygenation is a high-temperature exothermic redox chemical reaction, which releases large amounts of thermal energy. So, the stable and accurate control of the temperature is not easy. Meanwhile partial methane is lost. The key of catalytic combustion deoxygenation lies in the development of high-efficiency catalyst. Membrane separation has advantages of high separation efficiency and low energy consumption. However, there are many obstacles, including higher costs. Membrane materials have the requirements of both high permeability and high selectivity. The development of new membrane materials is a key for membrane separation. Cryogenic distillation has many excellence advantages, such as high purity production and high recovery. However, the energy consumption increases with decreasing CH4 concentrations in feed gas. Moreover, there are many types of operational security problems. And that several kinds of deoxygenation techniques mentioned above have an economic value just for oxygen-bearing CMM with methane content above 30%. Moreover, all the above methods are not applicable to deoxygenation of low concentration CMM. Non-metallic reduction method cannot only realize cyclic utilization of deoxidizer but also have no impurity gases generation. It also has a relatively low cost and low loss rate of methane, and the oxygen is removed thoroughly. In particular, the non-metallic reduction method has good development prospects for low concentration oxygen-bearing CMM. This article also points out the direction of future development of coal mine methane deoxygenation.

A Novel Study of Methane-Rich Gas Reforming to Syngas and Its Kinetics over Semicoke Catalyst

A small-size gasification unit is improved through process optimization to simulate industrial United Gas Improvement Company gasification. It finds that the reaction temperature has important impacts on semicoke catalyzed methane gas mixture. The addition of water vapor can enhance the catalytic activity of reforming, which is due to the fact that addition of water vapor not only removes carbon deposit produced in the reforming and gasification reaction processes, but also participates in gasification reaction with semicoke to generate some active oxygen-containing functional groups. The active oxygen-containing functional groups provide active sites for carbon dioxide reforming of methane, promoting the reforming reaction. It also finds that the addition of different proportions of methane-rich gas can yield synthesis gas with different H2/CO ratio. The kinetics study shows that the semicoke can reduce the activation energy of the reforming reaction and promote the occurrence of the reforming reaction. The kinetics model of methane reforming under the conditions of steam gasification over semicoke is as follows: k-=5.02×103·pCH40.71·pH20.26·exp(−74200/RT).

The Pyrolysis Characteristics of Low Ash Lignite

The pyrolysis characteristics of lignite with low ash were investigated and the influences of heating rate on the weight loss process were also discussed. The results showed the lignite pyrolysis process can be divided into three stages, in which the second stage, the temperature range is about 300oC ~550oC, is the main process of the weight loss; with the heating rate is enhanced, the temperature of maximum rate of weight loss was increased while the maximum rate of coal weight loss is increased, and the temperature of maximum rate of coal weight loss is basically the same.

Fuel Oil Prepared by Blending Heavy Oil and Coal Tar

The effect of temperature, harmonic ration, surfactant and shearing to fuel oil prepared by blending heavy oil and coal tar were detailedly studied. The results show that the viscosity of the blended oil increases gradually with the increase of harmonic ration from 2:1 to 7:1. It shows that the viscosity decrease rate can be divided into two sections with temperature increasing: In the first section, increasing the temperature of reaction , the viscosity of blended oil decreased sharply, and the decrease rate reached about 160 mPa•s / ¿. In the second section, the viscosity of blended oil changed slightly, the average decrease rate about 24 mPa•s / ¿. It was caused by the change of intermolecular interaction energy and van der waals force. The further research shows that, adding nonionic surfactant or shearing decrease significantly bled oil viscosity. At 50 ¿, adding 3‰ nonionic surfactant, bled oil viscosity decreased 900 mPa•s, and bled oil viscosity decreased 1200 mPa•s by shear. Compared without using shear, the viscosity of the blend oil was decreased by 27% at 50¿. The mathematical model between viscosity and temperature has been derived by using mathematical method. In the first section (70¿¿, the mathematical model between viscosity and temperature can be described as lgvm=∑xi lgvi - K2 - 1.1 / {1 + exp [ ( T - 351.5 ) / 6.3 ] }

Structure Property-CO2 Capture Performance Relations of Amine-Functionalized Porous Silica Composite Adsorbents

In order to investigate the influence of support structure properties on CO2 capture performances of solid amine adsorbents, a novel three-dimensional disordered porous silica (3dd) with hierarchical pore networks was developed and then compared to other three materials as adsorbent support, namely, hierarchical porous silica (HPS), MCM-41, and SBA-15. They were all functionalized with tetraethylenepentaamine (TEPA) to prepare CO2 adsorbents. The adsorbents ability to capture CO2 was examined on a fixed-bed reactor. When these supports had 60 wt% TEPA loading, the amounts of CO2 captured followed the order 3dd > HPS > SBA-15 > MCM-41 at 75 °C; the adsorption capacities were 5.09, 4.9, 4.58, and 2.49 mmol/g, respectively. The results indicate that a larger pore volume can promote the dispersion of amine species to expose more active sites for CO2 capture. The larger pore size can decrease the CO2 diffusion resistance. High surface area is not an important factor in determining capture performance. In addition, compared with conventional single-size mesopores, the hierarchical pore networks can disperse the TEPA species in different levels of the channel to limit undesired loss/aggregation of impregnated TEPA species. Thus, the 3dd support exhibits the best stability and highest regeneration conversion compared to the other three supports. This work demonstrates that the rational design of adsorbent support systems can effectively relieve the trade-off between amine loading and diffusion resistance. One method to surmount this trade-off is to utilize an adsorbent platform with hierarchical pore networks. Thus, this work may provide a feasible strategy for the design of CO2 solid amine adsorbents with high capture amount and amine utilization efficiency.

Hydrogasification of Low-Oxygen Semi-Coke to Produce Methane by Consuming Less Hydrogen

The presented work aimed at investigating the hydrogasification of low-oxygen semi-coke. For comparison, the hydrogasification of lignite was conducted. Variation of gaseous products concentration and reaction rate of the semi-coke hydrogasification process were investigated. The results shown that the methane yield of low-oxygen semi-coke is 24.8% greater than the lignite, but also the hydrogen consumption reduced greatly; the hydrogasification process can be divided into three stages: hydro-pyrolysis stage, rapid hydrogasification stage and slow speed hydrogasification stage; the difference of the reactive is attributed to different carbon structure forms .