Volume 21, Issue 7

It was widely known that crystallization kinetics are the basis for crystallization behavior and crystallizer scale-up design. Cooling crystallization of potassium chloride was an essential unit operation in recycling industry. Some researchers have proposed the strategy of adding seed crystals for the intermittent cooling crystallization process to control the particle size and distribution of the target product. This paper studied the complex function relation between particle size and growth rate of KCI in the crystallization process in a continuous mixed-suspension mixed-product-removal (MSMPR) crystallizer at a steady state. Using the crystallization kinetics data, the mathematical models of coupling crystallization were established based on the population balance equations and mass balance equations. Since population density distributions of products behave multiform under different conditions, based on diffusion theory. The growth rate was obtained by a least square method for the multivariate linear regression, and the reliability of the kinetics model was validated experimentally. Fitting results indicated that some classical models, including several size-independent growth models and size-dependent growth models, such as Bransom, C-R, MJ2, ASL, and MJ3, could not model the size-dependent growth accurately. Based on this situation, an exponential growth model was proposed and confirmed to describe the size-dependent growth behavior. It was found that the model parameters have definite meanings and were strongly related to particle size. Compared with the classical models, this model showed good pertinency and adaptability to experimental results when used to describe the population density distribution and the size-dependent growth rate of KCI. This research could provide a theoretical guide for optimizing the crystallization process and designing industrial crystallizers.

The exclusive properties of β- cyclodextrin ( β -CD) combined with its harmless characters making it as an interesting and potential carbon adsorbent for water pollutants removal via adsorption. This work was aimed at evaluating the kinetics and isotherm parameters of methylene blue dye adsorption onto β -CD polymers. The carbon polymers were prepared by citric acid cross-linking, followed by post-treatment with sodium p-toluenesulfinate. The adsorbents were characterized using TGA, BET and FTIR. The adsorption of methylene blue was studied at varying concentrations (5–300 mg/L) and contact times (10–2880 min), and the kinetics and isotherm models were employed to describe the adsorption data. The post-treated carbon polymer exhibits a greater specific surface of 16.6 m 2 /g. The maximum adsorption of methylene blue by cross-linked and post-treated β -CD adsorbents are 263 and 227 mg/g, respectively. The kinetics data fitted well into pseudo-first order model, indicating physical adsorption. The Boyd’s model showed that film diffusion may be the controlling mechanism. The equilibrium data of methylene blue adsorption for the two β -CD polymers obeyed Langmuir model. To conclude, β -CD is a promising adsorbent candidate for the treatment of dye wastewater.

The aim of this study was to develop a new rotating photocatalytic reactor operating in recirculation mode with light sources placed outside the photoreactor vessel. The photoreactor with cylindrical geometry was equipped with four artificial lamps used to simulate solar irradiation (2.4% UVB and 12% UVA; 300–700 nm). The photocatalyst was immobilized on abrasive material used as a support and placed on the central (inner) photoreactor tube, which was connected to a power-driven shaft that allowed rotation at a desired speed. A suitable modification of the commercial TiO 2 P25 photocatalyst was carried out to reduce its band gap energy and electron-hole recombination and to extend the visible light response range of TiO 2 . The main task of this research was to apply the basic principles of process intensification methodology, i.e. to explore the influence of rotational hydrodynamics, which allows good access of reactants to the photocatalyst surface, good irradiation of the photocatalytic surface and reduction of mass transfer resistance, leading to increased process efficiency. The homemade photoreactor was used for the photocatalytic degradation of one of the major types of neonicotinoid insecticides, acetamiprid. The influence of various working conditions, such as initial solution pH, rotation speed, recirculation flow rate and initial concentration of acetamiprid on the photocatalytic degradation process was investigated. The optimum degradation conditions were found at a recirculation flow rate of 200 cm 3  min −1 and a rotation speed of 200 rpm, indicating that the mass transfer process strongly contributes to the photocatalytic degradation rate at the conditions used in this study. The results obtained during the photocatalytic degradation of acetamiprid in a rotating photoreactor were compared with those obtained under similar operating conditions in a flat-plate photoreactor, and the corresponding conclusions were drawn based on the performed kinetic analysis.

In this work NiMn 2 O 4 , NiMn 2 O 4 /TiO 2 and NiMn 2 O 4 /CeO 2 nanocomposites were prepared by co-precipitation method and evaluated for the selective catalytic reduction of NO x with NH 3 . Various characterization methods such as X-ray diffraction, field emission scanning electron microscope, specific surface area, average pore diameter, temperature programmed desorption (NH 3 -TPD), temperature-programmed reduction (H 2 -TPR) and inductively coupled plasma optical emission spectrometer were conducted to probe the physical and chemical properties of these catalysts. The catalytic activity tests showed that in the temperature window of 200–400 °C and the space velocity of 10,000–40,000 h −1 , NiMn 2 O 4 /CeO 2 demonstrated the best performance among the synthesized catalysts.

In this work, a sliding mode controller (SLMC) design approach has been proposed based on second order plus dead time process (SOPDTP). The SOPDTP model of the industrial processes have been obtained by performing a simple closed-loop set-point experiment (CLSPE) having a proportional controller only. The operating procedure of SLMC comprises of continuous and discontinuous control law. The parameters of continuous control law are derived by considering SOPDTP parameters and using the root locus technique. The discontinuous control law parameters are obtained by minimizing a performance index with the help of grasshopper optimization technique. The proposed SLMC design method has been validated by considering several examples with higher order process having diverse dynamics. The performance improvement by the proposed method over the recently reported work has been observed under nominal, perturbed and noisy conditions.

Advance process control is a proven control and optimization technology delivering measurable and sustainable improvements in production yield, coupled with the added value of energy savings. In this work, an adaptive based model predictive control (aMPC) is developed and implemented to control the hydrogenation of dimethyl oxide to ethylene glycol (EG) in a plug flow reactor. The aMPC is compared with 3 other control schemes; proportional-integral (PI), decoupled PI (dPI) and linear model predictive control. The aim is to determine the reliability of aMPC in controlling the production rate and reactor temperature for an optimized hydrogenation reactor. The aspects compared include set point tracking, disturbance rejection and robustness test. The analysis concludes that the aMPC offers the best overall performance compared to the other control schemes.

Multi-fuel operation of the coal-fired boiler is considered as a promising option for boiler reformation to reduce carbon emissions while recycling solid waste. In this work, co-combustion characteristics of sugarcane bagasse, Nanning meager-lean coal and petroleum coke under different conditions were investigated in detail. And the interaction between raw materials was analyzed. Finally, the kinetic parameters were estimated by using the first-order response model. The results show that differences in petroleum coke content affect the appearance of weight loss peaks in the DTG curve. When the proportion of sugarcane bagasse is between 40 and 60%, the ignition and burnout characteristic indexes are particularly sensitive to variations in sugarcane bagasse content. Additionally, the interaction between the three raw materials is promoted as the proportion of petroleum coke is less than 40%. The kinetic analysis suggests that the increase of heating rate is conducive to the precipitation of volatiles, but there is an optimal heating rate for the fixed carbon combustion stage. The change of particle size combination has little effect on the activation energy of the volatile fraction combustion stage. This study provides a reference to ensure the stable and high-efficient operation of the coal-fired boilers during the multi-fuel combustion.

In this work, a new hydrometallurgical process was developed to treat zinc ash produced from the hot galvanizing industry. The theoretical analysis shows the feasibility of dissolving zinc ash in the NH 3 –NH 4 Cl–H 2 O system, and the dissolution products are predominantly composed of Zn (NH 3 ) 4 2+ . The impacts of different experimental conditions were examined, and the leaching ratio of zinc was as high as 96.4% under the conditions of NH 3 /NH 4 + ratio of 1:1, liquid/solid of 9:1, total ammonia concentration of 8 mol/L and the stirring speed of 250 rpm at 313 K for 120 min. The kinetics of the leaching process were investigated and the calculated apparent activation energy was approximately 4.69 kJ/mol, which indicated that the zinc ash leaching process was controlled by diffusion-controlled. As revealed by the determination of impurity ions, on one hand, there were fewer impurities in the leaching solution, and the concentrations of Fe 2+ and Pb 2+ in solution are less than 0.02 mg/L and 0.05 mg/L respectively; on the other hand, there was no need for further impurity removal in this process. The proposed process has a certain application value in treating zinc ash.

A dual-degree of freedom (dual-DOF) propor-tional-integral proportional-derivative (PI-PD) controller is developed for integrating-type chemical processes with delay. The interior-loop PD controller is designed based on user-defined gain and phase margin. For designing the external-loop PI controller, the moment-matching method is augmented with maximum sensitivity specifications. The suggested design is suitable for chemical processes like continuously stirred tank reactors, boiler steam drums, heat exchangers and distillation columns. Using benchmark models of the aforementioned processes, the closed-loop system outputs and control signals are compared to vindicate the primacy of the suggested dual-DOF PI-PD controller. To study the performance-robustness trade-off of this design, rigorous perturbation analysis is also carried out. The performance improvement achieved by the suggested dual-DOF PI-PD controller is also quantitatively compared with contemporary works.