Kechang Xie

Adsorption of Carbon Dioxide on Activated Carbon

The adsorption of CO2 on a raw activated carbon A and three modified activated carbon samples B, C, and D at temperatures ranging from 303 to 333 K and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus in order to obtain more information about the effect of CO2 on removal of organic sulfur-containing compounds in industrial gases. The active ingredients impregnated in the carbon samples show significant influence on the adsorption for C02 and its volumes adsorbed on modified carbon samples B, C, and D are all larger than that on the raw carbon sample A. On the other hand, the physical parameters such as surface area, pore volume, and micropore volume of carbon samples show no influence on the adsorbed amount of COa. The Dubinin-Radushkevich (D- R) equation was the best model for fitting the adsorption data on carbon samples A and B, while the Freundlich equation was the best fit for the adsorption on carbon samples C and D. The isosteric heats of adsorption on carbon samples A, B, C, and D derived from the adsorption isotherms using the Clapeyron equation decreased slightly increasing surface loading. The heat of adsorption lay between 10.5 and 28.4 kJ/mol, with the carbon sample D having the highest value at all surface coverages that were studied. The observed entropy change associated with the adsorption for the carbon samples A, B, and C (above the surface coverage of 7 ml/g) was lower than the theoretical value for mobile adsorption. However, it was higher than the theoretical value for mobile adsorption but lower than the theoretical value for localized adsorption for carbon sample D.

Comparison of reduction behavior of Fe2O3, ZnO and ZnFe2O4 by TPR technique

Abstract Advanced integrated gasification combined cycle (IGCC) power generation systems require the development of high-temperature, regenerable, desulfurization sorbents capable of removing hydrogen sulfide from coal gasifier gas to very low levels. As a sort of effective desufurizer, such as Fe2O3, ZnO and ZnFe2O4, it will endure strong reducing atmosphere in desulfurization process. The reduced degree of desufurizer can have an effect on its desulfurization reactivity. In this paper, Fe2O3, ZnO and ZnFe2O4 were synthesized by precipitation or co-precipitation at constant pH. After aging, washing and drying, the solids were calcined at 800 °C. The reduction behaviors of sample were characterized by temperature-programmed reduction (TPR). It is found that there are two reduction peaks for Fe2O3 in TPR, and whereas no reduction peaks for ZnO are found. The reduction process of ZnFe2O4 prepared by co-precipitation is different from that of Fe2O3. ZnFe2O4 is easier to be reduced than Fe2O3. The activation energy of reduction process for Fe2O3 and ZnFe2O4 is obtained at different reduction periods.

Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part IV. Pyrolysis of a set of Australian and Chinese coals

The formation of HCN and NH3 from the pyrolysis of a small set of Chinese and Australian coals were studied using a novel fluidised-bed/fixed-bed reactor and a fluidised-bed/tubular reactor. The fluidised-bed/fixed-bed reactor has some features of a fluidised-bed reactor and of a fixed-bed reactor, allowing the evaluation of the effects of coal properties on the formation of HCN and NH3 to be carried out on a similar basis for a wide range of coals. The thermal cracking of volatiles was investigated in a tubular reactor in tandem with the fluidised-bed/fixed-bed reactor where the nascent volatiles were generated in situ from the pyrolysis of coal. Our experimental results indicate that, in addition to coal rank, the petrographic composition and/or geographic origin of the coal are important factors influencing the formation of HCN and NH3 during pyrolysis. Among the few Chinese and Australian coals studied, the inertinite-rich Chinese coals tend to give more NH3 during pyrolysis than the Australian coals of similar carbon contents. It is believed that the structure of inertinites of less caking properties favours the formation of H radicals in the pyrolysing solid over a ‘correct’ temperature range to overlap with the activation and subsequent hydrogenation of the N-containing ring systems for the formation of NH3 in the solid. If the coal properties favour the release of coal-N as volatiles, the formation of HCN in the gas phase is more likely. Under the current experimental conditions, where volatiles may be deposited on the reactor wall, the formation and destruction of the sooty materials on the reactor wall play an important role in the formation of HCN from the cracking of volatiles.

Pyrolysis characteristics of macerals separated from a single coal and their artificial mixture

Abstract Sufficient quantities of the three major maceral groups (vitrinites, fusinites and liptinites) were separated from a single coal, Pingshuo bituminous coal. Nine model coals were prepared by mixing the individual macerals in different amounts. The behaviour and kinetics of these 12 samples during nitrogen pyrolysis have been investigated and the pyrolysis mechanism has been analysed in conjunction with the information obtained by Fourier transform infrared spectrometry and X-ray diffraction. The data presented indicate that there are three stages in the overall devolatilization process, and each stage is a first-order reaction. The pyrolysis conversion of the maceral mixtures (model coals) is equal to a calculated sum of the individual macerals, and the activation energy in each stage equals the sum of the activation energies of the individual macerals.

Studies of the release rule of NOx precursors during gasification of coal and its char

Abstract This investigation involved the formation and release of precursors of NO x , which were HCN and NH 3 , during gasification of coal and its char. Gasification was carried out in a fixed bed reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a pre-specified period of time at peak temperature. The influence of coal rank and coal particle size on the release of N-containing compounds during coal gasification with CO 2 is discussed. Gasification agents and coal gasification temperature were two key factors on the amount of nitrogenous compounds released. Results showed that with an increase of reaction temperature a great amount of NH 3 was formed during gasification with steam: The yield of NH 3 was highest at 800 °C during gasification with CO 2 . The volatiles in coal played the key role in the formation of HCN and NH 3 during coal gasification under steam atmosphere. Volatiles were the main source of the formation of HCN and NH 3 , mainly from the nascent char thermal cracking, whose procedure could be promoted by H 2 O(g): The yield of HCN during coal gasification had no strong relation with gasification agents and increased with an increase in gasification temperature. A reasonable mechanism for the formation of nitrogenous compounds during coal gasification was suggested in this study, which could explain some results in the literature on pyrolysis and gasification of coal.

Effect of Calcium Oxide Additive on the Performance of Iron Oxide Sorbent for High-Temperature Coal Gas Desulfurization

The effect of calcium oxide additive in iron oxide sorbent for hot gas desulfurization was investigated by XRD and TPR techniques. XRD characterization showed that CaO was highly dispersed after the calcination of sorbents. Calcium sulfate formed in the desulfurization was decomposed and regenerated to CaO by reacting with CO before the next sulfidation process. Calcium participated in every sulfidation/regeneration cycle and contributed to the enhancement of sulfur capacity. The TPR results showed that the reduction temperature of the sorbent increased with the increase of the content of calcium. Calcium played a role of retarding reduction. Therefore, the addition of calcium oxide additive will benefit the utilization of iron oxide sorbent in strongly reducing atmospheres.

Bench-Scale Testing of Zinc Ferrite Sorbent for Hot Gas Clean-up

Abstract Advanced integrated gasification combined cycle (IGCC) power generation systems require the development of high-temperature, regenerable desulfurization sorbents, which are capable of removing hydrogen sulfide from coal gasifier gas to very low levels. In this paper, zinc ferrites prepared by co-precipitation were identified as a novel coal gas desulfurization sorbent at high temperature. Preparation of zinc ferrite and effects of binders on pore volume, strength and desulfurization efficiency of zinc ferrite desulfurizer were studied. Moreover, the behavior of zinc ferrite sorbent during desulfurization and regeneration under the temperature range of 350-400 °C are investigated. Effects of binders on the pore volume, mechanical strength and desulfurization efficiency of zinc ferrite sorbents indicated that the addition of kaolinite to zinc ferrite desulfurizer seems to be superior to other binders under the experimental conditions.

Thermal Decomposition Behaviors of Lignite by Pyrolysis-FTIR

An in situ pyrolysis reactor combined with the Fourier transformation infrared spectrometer (PFTIR) technique is employed to study the coal structure and its thermal decomposition behaviors. The interface of pyroprobe with FTIR was designed delicately to ensure the path of the laser beam in FTIR was just 3 mm above the coal sample, so any detection information of products from coal pyrolysis would be acquired previous to the secondary reaction. The PFTIR technique can be adopted to determine the activation energy of coal pyrolysis. Lignite coal has been used to evaluate this new method. The thermal decomposition behaviors of functional groups from lignite pyrolysis coincide with the first-order reaction.

Investigation of the interaction between Cu(acac)2 and NH4Y in the preparation of chlorine-free CuY catalysts for the oxidative carbonylation of methanol to a fuel additive

The high temperature anhydrous interaction between copper(II) acetylacetonate Cu(acac)2 and NH4Y was investigated to prepare a chlorine-free CuY catalyst for the oxidative carbonylation of methanol to dimethyl carbonate. When a physical mixture of Cu(acac)2 and NH4Y is heated from ambient temperature to 230 °C, Cu(acac)2 firstly sublimates and then is adsorbed immediately onto the surface of the Y zeolite. Simultaneously the ion exchange between Cu(acac)2 and NH4Y occurs at about 174 °C. During the activation process from 230 to 500 °C, the exchanged Cu2+ is reduced to a Cu+ active center, and the adsorbed and unreacted Cu(acac)2 on the NH4Y surface decomposes to nano-CuO. For NaY zeolite, no solid state ion-exchange occurs between Cu(acac)2 and NaY during the heat treatment and only CuO exists on the Cu/NaY catalyst surface. While for HY zeolite, there is less ion-exchanged Cu+ in the supercages. The Cu/NaY catalyst has no catalytic activity and the Cu/HY catalyst exhibits lower activity than the Cu/NH4Y catalyst. Strong evidence is provided that during heat treatment, a solid state ion-exchange between Cu(acac)2 and NH4Y occurs and makes more of the Cu+ located in the supercages accessible to reactants.

Study on the structure and reactivity of swollen coal

A new method is presented to study the structure and reactivity of coal by solvent swelling technology. Four different rank coals are swollen by the use of N-methylpyrolidinone (NMP) under mild condition. Heat effect changes are demonstrated with differential scanning calorimetry (DSC) before and after the solvent swelling. Swollen coal volatile yields increase with the extent of coal swelling ratio (Q). During the swollen coal pyrolysis under the condition of 20°C/S to 1100°C, the activation energy of functional groups in coal structure is decreased. Furthermore, pyrolysis Fourier transform infrared spectroscopy (PY-FTIR) data show that the gasification reactivity of coal char has been improved. Thus, coal macromolecular structure becomes sufficiently flexible and will irreversibly be rearranged by good nucleophilic solvent pretreatment. Coal forms a lower energy conformation after the removal of solvent.