Wen-De Xiao

A reactive distillation process for a cascade and azeotropic reaction system : Carbonylation of ethanol with dimethyl carbonate

Modelling and simulation of the reactive distillation column have been carried out for the carbonylation process of ethanol with dimethyl carbonate (DMC) producing diethyl carbonate (DEC). As it includes three azeotropes and two cascade reversible reactions with an undesired intermediate, methyl-and-ethyl carbonate (MEC), the reactive distillation is ideally appropriate. Calculations via a robust transient method reveal that a complete DMC conversion, a sound DEC selectivity over 99.5%, a perfect overcoming of azeotropic limitation, as well as a thorough separation of the alcohols from carbonates can be accomplished in the studied column. The model reliability is analyzed by assuming several values of Murphree tray efficiency, showing no considerable difference between the equilibrium and non-equilibrium models for this system. Moreover, effects of the feed locations of the two reactants and the reflux ratio on the performance of the column are discussed, too.

Kinetics of heterogeneous oxidation of concentrated ammonium sulfite

Abstract The heterogeneous oxidation of ammonium sulfite solution was investigated in stirred cell and packing column. The concentration range of sulfite is 0.05–4.7gmol/l and that of oxygen in the gas phase is 21–100%, temperature range is 30–75°C. The results indicated that there is a critical sulfite concentration, below which the reaction order with respect to sulfite is 0.2, while above which the order turns to −1.0. The reaction order with respect to oxygen is 1. Apparently, the ionic strength was found to inhibit the oxidation. The apparent energy of activation determined is 32.7kJ/mol.

Preparation and catalytic activity of nanometer gold ultrafines supported on Co3O4

Abstract In this article a new method with urea as precipitant is adopted in the preparation of ultra-fine supported gold catalyst with satisfactory results. The gold particles thus obtained have an average particle diameter of about 4 nm. Au/Co3O4 (5 wt.%) catalyst is applied in the selective catalytic oxidation (SCO) of NO in simulated flue gases with satisfactory sulfur resistance, water resistance and low-temperature activity.

Theoretical Analysis of Fluidized-Bed Reactor for Dimethyl Ether Synthesis from Syngas

Dimethyl ether (DME) is regarded as an environmentally benign fuel for vehicles. Two kinds of reactor technologies for DME synthesis have been proposed by previous researchers: the fixed-bed and the slurry reactor. As the reactions are highly exothermic and the temperature window of the catalyst is very narrow, the fixed-bed reactor provides a limited heat removal capability and a low conversion of the syngas. The slurry reactor can provide an effective temperature control but a very high inter-phase mass transfer resistance is added by the liquid medium. The Fluidized bed reactor can be an ideal reactor for DME synthesis as it possesses both high heat and mass transfer efficiencies. In this paper, a two-phase model is used to theoretically analyze the DME synthesis in a fluidized bed reactor, with both phases assumed to be in plug flow and taking into account the changes in bubble diameter resulting from the reaction. Three reactions take place simultaneously when DME is manufactured from the syngas (H2 + CO): a) CO+2H2 = CH3OH; b) 2CH3OH = DME+H2O; and c) CO+H2O = CO2+H2. The simulation shows that, at the reactor outlet, the equilibrium approaches of the three reactions are 0.32, 0.1, and 0.61, respectively. When H2/CO=1.0, the CO conversion and DME selectivity in a fluidized bed reactor are 62% and 95%, while those in a fixed-bed reactor are 9% and 86%. In a slurry reactor, the CO conversion and DME selectivity are 17% and 70%, respectively. Therefore, the fluidized-bed is the most promising candidate reactor for conducting the DME synthesis from syngas. Effects of the operating conditions on the performance of DME synthesis in the fluidized-bed reactor are discussed in details. The optimal H2/CO ratio is between 1.0-1.5, and increasing the pressure is shown to improve the reactor performance.

Modelling and simulation for adiabatic fixed-bed reactor with flow reversal

Abstract In this paper, an efficient and robust algorithm has been developed for simulation of unsteady-state fixed-bed reactors with flow reversal. This algorithm is based upon a rigorous dynamic heterogeneous model, which is solved by a hybrid procedure of discretization and integration. A modified nonequidistance finite-difference method, based on that of Eigenberger and Butt (1976, Chem. Engng Sci. 31 , 681–691), is presented for discre tizing the temperature profiles. The resulting ODEs defining solid-phase temperature are solved by an explicit integrator proposed by Ashour and Hanna (1990, Comput. Chem. Engng 14 , 267–272). SO 2 oxidation over vanadium catalysts is presented as an example. The “wrong-way” behavior of the reactor has been discussed, with a critical feed temperature defined for its occurrence.

An SO2 converter with flow reversal and interstage heat removal : From laboratory to industry

Abstract This paper gives a brief report on the research and development work in commercialization of an SO 2 converter with flow reversal and interstage heat removal. It starts with modelling of the converter, and experimental verification of the model with a laboratory reactor and a pilot scale converter. To deal with strongly fluctuating SO 2 concentrations from 1% to higher than 4%, an appropriate converter configuration is suggested based on simulation. The converter consists of three catalyst packed stages, and two interstage heat exchangers, with two temperature buffers mounted at both ends. A dual position control strategy to open or shut the interstage heat exchanger is developed, which has been proven to be effective.

Experimental determination of equilibrium constant for the complexing reaction of nitric oxide with hexamminecobalt(II) in aqueous solution.

Ammonia solution can be used to scrub NO from the flue gases by adding soluble cobalt(II) salts into the aqueous ammonia solutions. The hexamminecobalt(II), Co(NH3)6(2+), formed by ammonia binding with Co2+ is the active constituent of eliminating NO from the flue gas streams. The hexamminecobalt(II) can combine with NO to form a complex. For the development of this process, the data of the equilibrium constants for the coordination between NO and Co(NH3)6(2+)over a range of temperature is very important. Therefore, a series of experiments were performed in a bubble column to investigate the chemical equilibrium. The equilibrium constant was determined in the temperature range of 30.0-80.0 degrees C under atmospheric pressure at pH 9.14. All experimental data fit the following equation well: [see text] where the enthalpy and entropy are DeltaH degrees = - (44.559 +/- 2.329)kJ mol(-1) and DeltaS degrees = - (109.50 +/- 7.126) J K(-1)mol(-1), respectively.

Unsteady-state SO2 converters with inter-stage heat removal

Abstract In this paper, modeling and simulation of the unsteady-state SO 2 converters with one or two inter-stage heat exchangers have been done. Effects of the input SO 2 concentration, the superficial velocity, the cycle duration of the flow reversal, and the heat removal capacity of the inter-stage heat exchangers, and even the inert packing sections sandwiching the catalyst bed, have been discussed. The results obtained show considerable performance improvements by using the inter-stage heat removal over the adiabatic unsteady-state converters for the relatively concentrated gases involving SO 2 .

Practical studies of the commercial flow-reversed SO2 converter

Abstract A commercial-scale flow-reversed SO 2 converter with two inter-stage heat exchangers has been studied based on the author’s practices in a lead smelter. A control strategy with two control loops of cooling and cycling durations, and an special device ensuring the outlet temperature stability have been proposed and operated smoothly. Normally, the SO 2 final conversion is higher then 92%, and the maximum temperature is between 530 and 560°C as the SO 2 composition fluctuates within 1.0 and 4.5%(vol). Problems related to the commercialization of unsteady-state SO 2 converter are also discussed.