Control structure selection of increased-pressure extractive distillation process for DMC-MeOH azeotropic mixture

Producing dimethyl carbonate (DMC) as a green chemical with the desired purity is important in the industry. Although studies on the steady-state design of energy-efficient extractive distillation processes are important for the purification of DMC-methanol (DMC-MeOH) azeotropic mixtures, the dynamic controllability of these processes is also critical in the case of feed condition changes, and it should be investigated carefully. Results of the limited studies in the literature show that changing the operating pressures in extractive distillation processes might have different effects on the dynamic controllability of different systems. Thus, in this study, alternative control strategies are developed for a recently proposed increased-pressure extractive distillation process to separate DMC-MeOH mixture. All control structures are designed using inferential temperature controllers, which have a general acceptance in industrial applications. Effects of different ratio controllers are investigated by evaluating the dynamic responses of control structures for disturbances in feed flowrate and composition. Two metrics including integral absolute error and steady-state deviation of purities are used in the evaluation of alternatives. Results of dynamic simulations show that a control structure including reflux ratio controller is not a suitable strategy for this process. It is demonstrated that a control structure including reflux to feed ratio controller for both distillation columns is necessary for the robust and efficient control of a pressure-increased extractive distillation process. These efficient dynamic results support the economic advantage of increased-pressure extractive distillation process separating DMC-MeOH azeotropic mixtures.     

Preparation and characterization of phosphine oxide containing organosilica hybrid coatings by photopolymerization and sol–gel process

A series of UV-cured organic–inorganic hybrid coating materials containing up to 20 wt.% silica were prepared by sol–gel method from tetraethoxy silane (TEOS) which is used as the primary inorganic precursor, and diallylphenylphosphine oxide monomer (DAPPO), aliphatic urethane diacrylate resin (Ebecryl 210) are employed as the source of the organic components. In addition, methacryloxypropyltrimethoxy silane (MAPTMS) was used as both a secondary inorganic source and a silane-coupling agent to improve the compatibility of the organic and inorganic phases. The DAPPO content in all the coating formulations were from 0 to 20 wt.%. The physical and mechanical properties such as gel content, hardness, adhesion, gloss, contact angle as well as tensile strength were measured. These measurements revealed that all the properties of the hybrid coatings improved effectively, in case of adding the sol–gel precursor and DAPPO monomer content in the hybrid systems. The photo-calorimetric-DSC studies showed that the double bond conversion of the hybrid coatings was faster than the coating materials without silica. The thermal stabilities of the UV-cured hybrid materials were investigated by thermogravimetric analysis. The results showed that the addition of sol–gel precursor and DAPPO into the organic network also improves the thermal-oxidative stability of the hybrid coating materials. The surface morphology was also characterized by scanning electron microscopy (SEM). SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Synthesis of fluorinated/methacrylated epoxy based oligomers and investigation of its performance in the UV curable hybrid coatings

Organic–inorganic hybrid coatings based on fluorinated/methacrylated soybean oil and bisphenol A/F epoxy methacrylate were obtained by combining photopolymerization and sol–gel process. Hard and transparent hybrid coatings were prepared on polycarbonate panels and their physical and mechanical properties such as gel content, hardness, adhesion, gloss, contact angle as well as tensile strength were measured. Results from the mechanical measurements showed that the properties of hybrid coatings improved with the increase in fluorine and sol–gel precursor contents. Thermo gravimetric analysis results demonstrated that fluorine and silica incorporations significantly enhanced the thermal oxidative stability of the hybrid coating materials. The surface morphology was also characterized by scanning electron microscopy (SEM). SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Backstepping approach for design of PID controller with guaranteed performance for micro-air UAV

Flight controllers for micro-air UAVs are generally designed using proportional-integral-derivative (PID) methods, where the tuning of gains is difficult and time-consuming, and performance is not guaranteed. In this paper, we develop a rigorous method based on the sliding mode analysis and nonlinear backstepping to design a PID controller with guaranteed performance. This technique provides the structure and gains for the PID controller, such that a robust and fast response of the UAV (unmanned aerial vehicle) for trajectory tracking is achieved. First, the second-order sliding variable errors are used in a rigorous nonlinear backstepping design to obtain guaranteed performance for the nonlinear UAV dynamics. Then, using a small angle approximation and rigorous geometric manipulations, this nonlinear design is converted into a PID controller whose structure is naturally determined through the backstepping procedure. PID gains that guarantee robust UAV performance are finally computed from the sliding mode gains and from stabilizing gains for tracking error dynamics. We prove that the desired Euler angles of the inner attitude controller loop are related to the dynamics of the outer backstepping tracker loop by inverse kinematics, which provides a seamless connection with existing built-in UAV attitude controllers. We implement the proposed method on actual UAV, and experimental flight tests prove the validity of these algorithms. It is seen that our PID design procedure yields tighter UAV performance than an existing popular PID control technique.     

Electrochemical and optical properties of dicyclohexylmethyl substituted poly(3,4‐propylenedioxythiophene) analogue

An analogue of disubstituted 3,4‐propylenedioxythiophenes, namely 3,3‐bis(cyclohexylmethyl)‐3,4‐dihydro‐2H‐thieno[3,4‐b][1,4]dioxepin (ProDOT‐CycHex₂), was synthesized and its electrochemical polymerization was carried out successfully in an electrolyte solution of 0.1 M tetrabutylammonium hexafluorophosphate dissolved in a mixture of acetonitrile and dichloromethane (3/1: v/v). The corresponding polymer called PProDOT‐CycHex₂ has a reduced band gap of 1.85 eV and an electrochromic property: blue/violet when neutralized and highly transparent when oxidized. Also, PProDOT‐CycHex₂ film exhibited faster response time (0.7 s) and higher coloration efficiency (769 cm²/C) during oxidation when compared to its benzyl substituted analogue. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46214.     

A figure of merit for optimization of nanocrystal flash memory design

Nanocrystals can be used as storage media for carriers in flash memories. The performance of a nanocrystal flash memory depends critically on the choice of nanocrystal size and density as well as on the choice of tunnel dielectric properties. The performance of a nanocrystal memory device can be expressed in terms of write/erase speed, carrier retention time and cycling durability. We present a model that describes the charge/discharge dynamics of nanocrystal flash memories and calculate the effect of nanocrystal, gate, tunnel dielectric and substrate properties on device performance. The model assumes charge storage in quantized energy levels of nanocrystals. Effect of temperature is included implicitly in the model through perturbation of the substrate minority carrier concentration and Fermi level. Because a large number of variables affect these performance measures, in order to compare various designs, a figure of merit that measures the device performance in terms of design parameters is defined as a function of write/erase/discharge times which are calculated using the theoretical model. The effects of nanocrystal size and density, gate work function, substrate doping, control and tunnel dielectric properties and device geometry on the device performance are evaluated through the figure of merit. Experimental data showing agreement of the theoretical model with the measurement results are presented for devices that has PECVD grown germanium nanocrystals as the storage media.