Nitrile hydratase (NHase) is the biocatalyst which has been used in industrial bioconversion of acrylonitrile to acrylamide using microorganisms.Recent advances in the studies on structure,mechanism,photoreactivity,thermostability,etc.about NHases are reviewed.NHases contain metallic ions,which act as accessory factors in the active sites.The metal-binding sites play a crucial role in the enzymatic reaction.The photoactivation mechanism of Fe-type NHases is clarified.An endogenous NO is bound to the non-heme iron in the inactive NHase and its photodissociation activates the enzyme.From a practical point of view, the Nhases previously reported are still unsatisfactory catalysts because of their relatively low thermostability and the availability of some thermostable Nhases will help to reduce the inactivation of the enzyme.It is also clarified that amide compounds are essential for subunit assembly to yield active NHases.Some other factors are also discussed in this paper.Some perspectives on future research of NHase are presented.

Ethylbenzene can be produced very efficiently from ethylene and benzene over catalyst in catalytic distillation column.The non-equilibrium stage model is introduced for its simulation in this paper.Thermal balance is assumed among vapor,liquid and solid phases.Some equations are simplified in the simulation,and the values of variables are limited to a certain area.It permits a wider range of the initial value for the Newton- type method.The SRK mode is used to calculate the equilibrium of the phases.The temperature and concentration profiles in the column are presented.The results of the simulation fit in well with the experimental data obtained from the laboratory scale catalytic distillation column.

The large axialradial reactor for ethylbenzene dehydrogenation is a new type of radial flow reactor with catalysts self-sealing structure at the top of the bed,complex two-dimensional fluid flow in the catalyst bed.The continuity equation and the Ergen equation on the representative volume element are used to describe fluid flow in the axial-radial reactor in this paper,and the results are verified in a large cold model of size Φ 3000×10000.Flow fields are obtained by computer simulation with the finite difference method,and the effects of catalyst sealing length and flow direction on fluid field are discussed.The result shows that the fluid flow is mainly radial-flow at the radial section and mainly axial-radial flow at the catalyst sealing zone; Q _a/ Q is approximately equal to Q _r/ Q when δ equals 0.7 for centripetal flow and 1.1 for centrifugal flow, when δ is less than the values the fluid flow in the catalyst sealing zone is mainly axial-flow,when δ is bigger than the values the fluid flow is mainly radial-flow.Compared with centrifugal axial- radial reactor,centripetal axial- radial reactorcan limit the flux which flows through the catalyst sealing zone.

A two-dimensional quasi-homogenous mathematical model has been developed on the basis of the two-dimensional flow model to simulate the axial-radial flow reactor for dehydrogenation of ethylbenzene to styrene under reduced pressure in this paper.The mathematical model is solved by using the finite difference method.The results show that the conversion of the axial-radial flow reactor is higher by 0.1%～0.6% than the radial flow reactor whereas the selectivity is approximately same and there is a low temperature and high styrene concentration area in the catalyst sealing zone.The model is verified by the data of a commercial axial-radial flow reactor for ethylbenzene dehydrogenation and can be used to guide its design.

The radial distribution functions and chemical potentials of supercritical NaCl-H ₂O system at 723.15K and 823.15K were studied by NVT ensemble MC molecular simulation.The chemical potentials were calculated by perturbation theory considering hard sphere, dispersion and dipole-dipole terms.The results show that the chemical potentials calculated from these two methods coincide with each other on the whole.

A novel two-phase model for the fluidized bed of polyethylene with condensed mode operation was proposed.The model considered heat and mass conservation in emulsion phase and bubble phase, heat and mass transfer between emulsion phase and bubble phase,polymerization as well as resident time distribution of particles in emulsion phase.The relations between operating variables and reactor performance were investigated by the model.Simulation results agreed well with the industrial data.Simulation results indicate the productivity of reactor as well as ash in polymer will increase greatly, and low the temperature region will expand when the condensed mode is operating with the conventional catalyst.A type of catalyst which suits condensed mode operation was proposed.

A heat and mass transfer model across the external boundary layer of polymer particles in emulsion phase with condensed mode operation was derived.The overheat possibility of particles was analyzed by using the model.Simulation results indicate that in the early lifetime,there exist multi-steady states of surface temperature of growing particles.Using the condensed mode operation will be helpful to reduce the temperature gradient for larger particles,but not for very small particles.The type of catalysts with a low startup,high activity and quick deactivation was suggested to be used in the condensed mode operations.

In this paper,the effects of temperature and liquid volume fraction on pressure rise in non-loss cryogenic vessels are analyzed. Graphs are provided for the relation between environmental temperature and the performance of non-loss storage for the different types of cryogenic vessel(multi-layer insulation, vacuum-powders insulation, high-vacuum insulation), as well as for the relationship between storage-pressure and heat flow received by the container per unit volume for various volume fractions.The conception of optimum liquid volume fraction is also presented .The results are useful for the design,use and choice of non-loss storage vessels for liquefied gases, precious gases,rare gases and poisonous gases.

The effect of the thermal conductivities of condenser materials on dropwise condensation heat transfer has not been resolved yet. Numerical simulation of dropwise condensation heat transfer of steam on copper, stainless steel, zinc, mild steel surfaces are performed in this paper by using a model of dropwise condensation heat transfer proposed by the present authors. The results indicate that dropwise condensation heat transfer coefficient is greatly dependent upon the surface thermal conductivity, and decreases with decreasing surface thermal conductivity.

Adiabatic laminar bubbly flow is a basic problem in the research on bubbly flow. Published two-fluid models previously used to describe the flow are restricted to the flows within a limited bubble size range because these models do not reasonably take the interaction between the two phases into consideration. The universal basic averaged equations for bubbly flow were developed by applying the time averaging operator to the local instantaneous flow equations. According to analysis of the motion of bubbles in the flow field, the constitutive relations for interfacial momentum exchanges caused by interface-averaged stress,and interfacial momentum exchanges caused by asymmetric stress distributions on interfaces which include drag, virtual mass force, lift and wall-force were determined. A new formulation was proposed for wall force,which was derived from theoretic research and corrected by experimental data. Influence of bubble deformation on the flow was also considered as a correcting coefficient C w in the formulation of wall-force.The analysis of the stress in the phases indicated that the stress in gas phase is negligible in comparison with interactions between the phases. The shear stress in liquid phase was derived as an averaged liquid viscous stress term and the relation for the fluctuating stress in laminar bubbly flow was given.A closed two-fluid model was established to describe the flow.Comparison of the experimental data published in literature with the present model prediction showed that the present model can be applied to flows in a wider bubble size range due to the reasonable consideration of the near-wall effect.

Characterization of oil-water two phase flow patterns in vertical upward flow pipes is studied based on fractal and chaotic time series analysis of conductance fluctuation signals. For 60.5%≤ K _w≤91% and 10 m ³· d ^-1 ≤ Q _t≤60 m ³·d ^-1 ,local fractal dimension and correlation dimension of chaotic attractors are in the range from 1.006 to 1.631 and from 4.30 to 6.77, respectively. For K _w=51% or K _w=51.5% and 20 m ³·d ^-1 ≤ Q _t≤60 m ³·d ^-1 ,fractal dimension and correlation dimension of chaotic attractors are in the range from 1.17 to 1.758 and from 5.46 to 7.05, respectively. Both dimensions show an irregular sudden change with variation of total flowrate Q _t,which corresponds to happenings of transitional flow pattern. The irregular sudden changes in dimensions are verified with complex power spectrum and flow pattern map proposed by our previous study. It is shown that fractal dimension and correlation dimension of chaotic attractors is sensitive to flow pattern variation as an "indicator".

The delignification of wheat straw by alkali-oxygen-anthraquinone cooking was studied.The results showed that when temperature was 140℃,anthraquinone was 0.6%, the concentration of NaOH was 6%,the pressure of oxygen was 0.8 MPa,the ratio of solid(wheat straw) to liquid was 0.13, the rate of delignification and lignin in cellulose were 88% and 2.2%, respectively.The structures of lignin analyzed by means of IR and GC-MS spectrum indicated that there were syringyl and guaiacyl in lignin and the macro-molecules of lignin were changed into micro-molecules of lignin after cooking.

The influence of inert particles on crystal sized distribution (CSD) in gas-liquid-solid three-phase fluidized crystallization process is studied with potassium chloride solution in a conical fluidized bed. The results show that nature of inert particles,volume concentration, size and shape affect crystal size distribution effectively, with the increase density, size and concentration of inert particles, CSD becomes worse. CSD also becomes worse with the increase of gas flow rate, however, when gas flow rate further increases, CSD will become better and then worse again. Increasing density, size,concentration of inert particles will make the effects of enhancing gas flow rate on CSD less effective, meanwhile the gas flow rate corresponding with the turning point of CSD from worse to better will increase. To inhibit the adverse effects of inert particles on CSD, light, small and low concentration particles should be used.

The training process of Back Propagation Neural Network (BPNN) is easily converged at a local minimum, which slows the training process sharply.In this paper, an analysis is given to the chief formative reason of local minimum, and an improved Genetic Algorithm (GA) is introduced to overcome local minimum.Most BPNNs use Sigmoid function as the transfer function of network nodes, this paper indicates that the flat characteristic of Sigmoid function results in the formation of local minimum.In the improved GA, pertinent modifications are made to the evaluation function and the mutation model.The evaluation of solution is associated with both values of error function and gradient model corresponding to the certain solution, so that solutions away from local minimum are highly evaluated.The sensitivity of error function to network parameter is imported to form a self-adapting mutation model, which is powerful to diminish error function.Both modifications help to drive solutions out of local minimum.A case study of a real industrial process shows the advantage of the improved GA to overcome local minimum and to accelerate the training process.

Theory and computing methods are described for the analysis of the drying behavior and the prediction of drying performance in a Z-path moving bed.The model is based on mass conservation and energy conservation.The theoretical treatment of the proposed mathematical model is numerical solution,by the method of R-K of the differential equations.And then a computer program is developed.Numerical simulation result is compared with the experimental data and they have very good agreement.It indicates that both the model and the program could be used to optimize the design and performance of the Z-path moving bed drier.

The reaction characteristic of catalytic oxidative dehydrogenation of ethane over a silica supported heteropoly acids is examined.It is observed that there exists a ignition temperature for ethane oxidative dehydrogenation.When the reaction is carried out over this temperature,the reaction is controlled by a free radical gas phase mechanism.The acidity of HPA controls the ethane adsorption on the surface.The stronger the acidity,the higher the ignition temperature of radical reaction.

The interfacial properties of extractants (or surfactants) such as primary amine N ₁₉₂₃ ,trioctylamine (TOA), Tri n octylphosphine Oxide (TOPO),tributyl phosphate(TBP) and sodium dodecyle sulphonate (SDS),were studied at (294±1)K.The interfacial adsorption parameters, c _min , A _I,were calculated respectively.The effect of additives on the interfacial tensions were discussed.These results could be used to explain and assume the extraction rate or mechanism.