A new model in correlating and calculating the solid–liquid equilibrium of salt–water systems

In this work, a new activity coefficient model was deduced for the correlation of solid–liquid equilibrium(SLE) in electrolyte solutions. The new excess Gibbs energy equation for SLE contains two parts: the single electrolyte item and the mixed electrolyte item. Then a new hypothesis for the reference state of activity coefficients was proposed in the work. Literature data for single electrolyte solution and mixed electrolyte solution systems,with temperature spanning from 273.15 to 373.15 K, were successfully correlated using the developed model.

The green hydrolysis technology of hemicellulose in corncob by the repeated use of hydrolysate

To achieve green hydrolysis technology of hemicellulose through repeated using hydrolysate,the hydrolysis of hemicellulose in corncob was studied.The influence of repeated use of corncob hydrolysate on concentrations of D-xylose and L-arabinose was investigated.The loss rates of D-xylose in the prepared D-xylose solutions both with and without corncob,and repeated using corncob hydrolysate under identical acidity condition were discussed.The result shows that D-xylose concentration and L-arabinose concentration are all gradually increasing with the growing time of repeated use of corncob hydrolysate.After the fifth repetition,the concentrations of D-xylose and L-arabinose are 196.7 g·L^(-1)and 22.0 g·L^(-1),respectively.Substance inhibiting the degradation of D-xylose is generated during repeated use of corncob hydrolysate,and the production is further proved by the change of D-xylose concentration and the loss rate of D-xylose over heating time.

Experimental measurement and thermodynamic modeling of binary and ternary solid–liquid phase equilibrium for the systems formed by L-arabinose,D-xylose and water

Solid–liquid phase equilibrium data for binary(L-arabinose–water) and(D-xylose–water) systems at temperatures from(269.85–298.05) K and ternary(L-arabinose–D-xylose–water) system at temperatures of 273.85 K,278.85 K and 284.45 K were measured at atmospheric pressure.The ternary phase diagrams of the systems were constructed on the base of the measured solubility.Two pure solid phases were formed at given temperatures,including pure L-arabinose and pure D-xylose,which were con firmed and determined by the method of Schreinemakers' wet residue.At the same temperature,the crystallization region of L-arabinose was larger than D-xylose's.The acquired solubility data were then correlated using the NRTL model,Wilson model and Xu model.The calculated solubility with the three models agreed well with the experimental values.

Testing and validation of a self-diffusion coefficient model based on molecular dynamics simulations

In our previous work,we endowed a new physical meaning of self-diffusion coefficient in Fick’s law,which proposed that the diffusion coefficient can be described as the product of the characteristic length and the diffusion velocity.To testify this simple theory,in this work,we further investigated the underlying mechanism of the characteristic length and the diffusion velocity at the molecular level.After a complete dynamic run,the statistical average diffusion velocity and the characteristic length of molecules can be obtained by scripts,and subsequently the diffusion coefficient was determined by our proposed theory.The diffusion processes in 35 systems with a wide range of pressure and concentration variations were simulated using this model.From the simulated results,diffusion coefficients from our new model matched well with the experimental results from literatures.The total average relative deviation of predicted values with respect to the experimental results is 8.18%,indicating that the novel model is objective and rational.Compared with the traditional MSD-t model,this novel diffusion coefficient model provides more reliable results,and the theory is simple and straightforward in concept.Additionally,the effect of gas pressure and liquid concentration on the diffusion behavior were discussed,and the microscopic diffusion mechanism was elucidated through the distribution of diffusion velocity and the characteristic length analysis.Moreover,we suggested new distribution functions,providing more reliable data theoretical foundations for the future research about the diffusion coefficient.

A novel model for multi-plant mixed heavy crude oils refinery planning

In this paper, multi-refinery using the same heavy crude oils as raw materials is studied, while a new nonlinear model for mixed heavy crude distillation is proposed. In practical crude distillation operation, the distillate yield and product distribution of distillation units are different due to their various equipment and operating parameters, even the same ratio of raw materials is provided, so different process models for multi-refinery planning is therefore required. For process modeling, the relationships between total yields and mixing ratio of different refineries were determined, which is combined with process simulation using production data. Then,the yields and properties of crude distillation unit(CDU) fractions were calculated with the use of true boiling point(TBP) curves and property curves respectively when the initial cutting temperatures were given. Finally,in order to maximize the economic benefit of distillation, the optimal product distribution and the best mixing ratio of crude oil were calculated under the constraints of different properties of fractions. Comparing to previous models, the proposed model takes the influence of different refinery parameters on production process into account, while avoiding the complex process for determining the cutting points, which is considered more efficient and more accurate with respect to heavy crude refinery. Model was successfully verified by a case study,allowing a significant improvement of the refinery profit to be achieved.

Simulation of Countercurrent Multi-Effect Drying System

The paper bulids a countercurrent multi-effect drying process model which can be expressed as a linear programming(LP) problem with the minimum total energy consumption as target function. Based on the model it can be conventient to solve the heat load , degree of drying and other drying parameters of each effect. And it realizes the mathematical simulation an analysis of multi-effect drying process. Such process not only reuses the secondary steam but also utilizes the high energy grade. Drying silica sand using 1-effect drying to 5-effect drying is presented as an example. The energy consumption and energy saving rate are compared by using co-current multi-effect drying and countercurrent multi-effect drying. As a summary, the countercurrent multi-effect drying is better than co-current drying. Considered the equipment investment and energy conservation, the study also concluded that the countercurrent 4-effect drying is the optimum selection, and it can save 57.6% energy compared to countercurrent 1-effect drying.