The downcomer is the key component of a multi-stage fluidized bed.A pneumatically controlleddowncomer has been devised,consisting of a fully fluidized dipleg followed by a conical spout for upwarddischarge in dense phase.Such a design has been found to insure against bridging of solids in descent andagainst spouting of solids from a lower layer caused by gas by-passing.In experimental investigations,flow characteristics are measured including the pressure drops of thedifferent fluidized beds and of the downcomers for various gas and solids flow rates as well as the solidsresidence time distribution,operating either with a multiplicity of gas sources for the various downcomersor with only two gas sources.In a particular design,a multi-stage ftuidized bed with dual gas supply,inwhich one half is incorporated centrally in the other,has been tested on pilot scale for recovering solventfrom low concentration ethylene dichloride streams of a plant waste gas.Main test results obtained wereas follows:adsorption rate>97%concentration of waste gas<25 mg/m~3active carbon loss<0.1%This kind of conical downcomer in which the solids arc either transported from a high- to a low-pressure region,or from a low- to a high-pressure region,is also used to control the solids discharge ofcyclone diplcgs or the feeding and discharging in other solids circulation systems.

The four coefficients A,B,C and D of the correlation of ideal gas heat capacity,C_p~0=A+BT+CT~2+DT~3,have been determined for 435 substances by the method of least squares with a digital computer onthe basis of the recently published C_p~O data during the period of 1968 to 1978.The average percent devia-tion of the calculated values of C_p~O from the experimental values is 0.160.The substances have been selec-ted according to their relative importance in fundamental chemical industries.For part of the substancesselected,there are so far still no heat-capacity correlations,and for the others,the already existing cor-relations are not based on recently published experimental C_P~O,data.

One of the important characteristics of a close-boiling fractionating column is the requirement ofmuch longer start-up time,and consequently the search for ways to minimize such time have been receivedmuch concern and attention.The conventional method of starting up a column is under the conditionof constant vapor velocity,while in this paper,the authors propose another way of operation,i.e.start-up with stepwise lowering of vapor velocity.The mathematical models of these two methods of start-upare developed and solved to obtain the analytical solutions of exponential type to represent the unsteadyconcentration profiles.The derived equations are in agreement with the experimental data.Both theoreti-cal study and experimental work show that,when the same final concentration is reached,the start-uptime for the proposed operation is shorter than that for the conventional.

It has been well-known that the optimum reflux ratio and the optimum packing size are importantcharacteristics of a packed column,especially for close-boiling fractionation.A correlation is proposed toestimate the NTU at finite reflux and from which a relationship to find the optimum reflux ratio is de-rived based on minimum cost.It is found that the maximum value of optimum reflux ratio is about 1.4R_M.For the study of optimum packing size,experimental work is undertaken with n-heptane-methylcyclohex-ane system in four laboratory columns ranging from 20 to 44 mm in diameter and being packed with 2.5×2.5mm angular helices.The optimum ratio of column diameter to packing size is found to be 13-14which is in rough agreement with that for ordinary or industrial size of packing.

Following the work on gas lift reactor (Pachuca tank) for gas-liquid-suspended solid 3-phase reaction,multideck gas lift reactors have been developed.This type of reactor has many unique advantages suchas realization of counter-current operation between gas and slurry,reduction of gas consumption and lower-ing of the amount of volatile components of the liquid which has to be recovered from the exit gas.The stability of the overflow tube of the reactor was studied.A semiempirical equation was derived tocalculate the flooding point of the reactor.The operating range of the overflow tube was also deter-mined.This multideck reactor has been operated successfully in a pilot plant of ammonia leaching of copperore.Results agree reasonably well with those predicted from small scale batch experiments.The extractionof vanadium from soda roasted steel slag in a 5-deck reactor with carbon dioxide in the gas phase wasalso satisfactory.Experimental results obtained from the continuous flow 5-deck reactor and those calcu-lated from batch experimental data with CSTR model were in agreement.

In the range of 76°to 1200C,Dalin and others studied the kinetics on molybdenum-catalyzed epoxi-dation of propylene with ethylbenzene hydroperoxide,proposed a mechanism model of this reaction andsuggested that effective concentration of catalyst is constant during the process of epoxidation.In thispaper the reaction has been studied experimentally based on Dalin’s investigation.After analyzing thedata obtained in our experiment and those of Dalin,it is shown that the effective concentration of thecatalyst is not a constant but a variable,and its rate of consumption behaves in accordance with the firstorder reaction.Thus,the authors have modified the mechanism model in literature [3] and pointed outthat the deactivation mechanism of the catalyst is different from the inhibition mechanism described byFarberof.

The process of producing propylene oxide by epoxidation of propylene with ethylbenzene hydroper-oxide is one of the most promising methods in recent years.In order to select an optimum reaction equip-ment technologically,the mathematical models of epoxidation reactor for plug flow,single-stage andmultistage perfect mixing have been founded in this paper by means of the kinetic model on epoxidationand the effects of various flow patterns on the reaction are also discussed.The analyses show that themultistage reactor is a more ideal one for industrial equipment,and its optimum operating conditions aresuggested.

Starting from isothermal excess enthalpy data (two or more than two sets) and isothermal vapo pressuredata (one set),and based on the principle of corresponding states of solutions,a complete computationprocedure of vapor-liquid equilibrium data is proposed:(1)Calculation of excess enthalpy ~E,based on the principle of corresponding states of solutions;(2) Calculation of Gibbs free energy ~E or its Q function;(3)Calculation of bubble point;(4)Calculation of vapor-liquid equilibrium data.The computation results for benzene-cyclohexane,benzene-n-hexane,benzene-n-heptane,benzene-n-octane,carbon tetrachloride-benzene,carbon tetrachloride-cyclohexane and carbon tetrachloride-n-heptane,compared with the corresponding vapor-liquid equilibrium experimental data are quite satisfactory.Theproposed computation procedure is appropriate to non-polar and slightly polar binary systems under rela-tively low pressures.

The characteristics of a staged bubble column can be described by a multi-stage backmixing model,provided: (1) Each stage can be considered as a perfect mixing reactor,and (2) The backmixing coeffi-cients do not vary with time and reactant concentrations.Experimental results indicate that the first conditionis approached under certain conditions,while the second assumption is correct.Studies were made using steady state chemical tracer method to determine the backmixing coefficientsof each plate between stages.The fluid flow through the holes of perforatcd plates is a stochastic process.From the statistical point,the experimental data could be correlated by semicmpirical equation developed.This equation can also be used to correlate the data reported by Nishiwaki for bubble column with plateshaving high percentage of opening area and large size holes between stages.Continuous oxidation of unsaturated sulfur compounds (mainly in the form of thiosulfatc and also somein polythionate form) in nickel ammonium carbonate solution were carried out in bubble columns with heightof 3400mm and diameters of 36 mm and 100mm respectively.The oxidation has to be taken in a multistagebubble column for high degree of oxidation.The axial concentration of unsaturated sulfur compoundsalong a multi-stage bubble column can be calculated from the backmixing model and the kinetic equationof oxidation.Results of calculation agree with the data taken along the column height.Equation was alsodeveloped to calculate the optimum temperatures of oxidation which agree favorably with the experimentalresults.

For a determined mathematical model,it is not only necessary to obtain the estimates of parameters,but also their reliabilites.The present work deals with a sequential statistical design strategy for anexperimental program to obtain precise parameter estimetes for a nonlinear kinetic model.It aims at de-creasing the indeterminatness of the parameter estimates,in reducing the correlation between parameterestimates,and in inceasing the adequacy and accuracy of the model.The paper discusses the experimental design criterion for precise parameter estimates-the minimun vol-ume design criterion and the spherical shape design criterion,and the practical value of a sequential statis-tical design strategy.At last,an example was performed to precise estimate the parameters in the kinetic model of ammoniasynthesis reaction which was selected as being adequate in the previous work.Comparison of the results from the industrial unit and the corresponding values calculated with themodel using the estimates of parameters reveals the reasonable reliability of the model.