化工双输入输出时滞过程解耦PID控制器解析设计

基于常规单位反馈控制结构,针对具有时滞特性的化工双输入输出过程提出一种解耦PID控制器的解析设计新方法.该解耦PID控制器的突出优点是控制器设计过程简单直观;控制器可以实现标称系统输出间的显著解耦;系统输出分别使用相应控制器对角元素中的调节参数进行单参数整定.同时,对于实际生产过程中常见的被控过程乘性不确定性,分析了系统保持鲁棒稳定的充要条件.仿真实例验证了该方法优于其它方法.     

Phase‐Transfer‐Catalyzed Enantioselective Mannich Reaction of Malonates with α‐Amido Sulfones

The highly enantioselective reaction between in situ generated, Cbz‐protected azomethines and malonates in the presence of 150 mol % of potassium carbonate (50 % w/w) and 1 mol % of quinine‐derived quaternary ammonium bromides as phase‐transfer organocatalysts has been developed. This study reports a novel approach for the asymmetric Mannich‐type reaction and a wide range of azomethines, including those derived from enolizable aldehydes, is tolerated by the present system. The adducts, obtained in excellent yields with ee up to 98 %, are suitable precursors of optically pure β‐amino acids.     

Bioinspired,Base‐ and Metal‐Free,Mild Decarboxylative Aldol Activation of Malonic Acid Half Thioesters Under Phase‐Transfer Reaction Conditions

Utilizing ‘off the shelf’ commercially available, cheap, small synthetic molecules that mimic the efficient mediation of important bioreactions utilized by Nature is not only highly sought after but also currently highly topical. This paper details our preliminary efforts at developing a unique base‐ and metal‐free phase‐transfer‐mediated malonic acid thioester (MAHT) ‘activation protocol’ that efficiently generates (±)‐β‐thioesters. Our bioinspired aldol process is exceptionally mild, conducted under near neutral pH reaction conditions, does not require an inert, oxygen‐free atmosphere or anhydrous reaction conditions and is highly atom‐economic. Exemplifying the utility of our protocol, the synthesis of an array of structurally and functionally diverse (±)‐β‐hydroxy thioesters equipped with highly prized functionality, i.e., chlorine, bromine, fluorine, nitrile and nitro groups, is reported, as is the diastereoselective potential of this important reaction.

     

Enantioselective Phase‐Transfer Catalytic α‐Benzylation and α‐Allylation of α‐tert‐Butoxycarbonyllactones

A new enantioselective α‐benzylation and α‐allylation of α‐tert‐butoxycarbonyllactones was devloped. α‐Benzylation and α‐allylation of α‐tert‐butoxycarbonylbutyrolactone and α‐tert‐butoxycarbonylvalerolactone under phase‐transfer catalytic conditions (50% cesium hydroxide, toluene, −60 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐NAS bromide (1 mol%) afforded the corresponding α‐substituted α‐tert‐butoxycarbonyllactones in very high chemical yields (up to 99%) and optical yields (up to 99% ee). The synthetic potential of this method has been successfully demonstrated by the asymmetric synthesis of unnatural α‐quaternary homoserines, 3‐alkyl‐3‐carboxypyrrolidine and 3‐alkyl‐3‐carboxypiperidine.     

Preparation,characterization, and prominent thermal stability of phase‐change microcapsules with phenolic resin shell and n‐hexadecane core

Microcapsules with phenolic resin (PFR) shell and n‐hexadecane (HD) core were prepared by controlled precipitation of the polymer from droplets of oil‐in‐water emulsion, followed by a heat‐curing process. The droplets of the oil phase are composed of a polymer (PFR), a good solvent (ethyl acetate), and a poor solvent (HD) for the polymer. Removal of the good solvent from the droplets leads to the formation of microcapsules with the poor solvent encapsulated by the polymer. The microstructure, morphology, and phase‐change property as well as thermal stability of the microcapsules were systematically characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimety (DSC), and thermogravimetric analysis (TGA). The phase‐change microcapsules exhibit smooth and perfect structure, and the shell thickness is a constant fraction of the capsule radius. The initial weight loss temperature of the microcapsules was determined to be 330°C in N₂ and 255°C in air, respectively, while that of the bulk HD is only about 120°C both in air and N₂ atmospheres. The weight loss mechanism of the microcapsules in different atmosphere is not the same, changing from the pyrolysis temperature of the core material in N₂ to the evaporation of core material caused by the fracture of shell material in air. The melting point of HD in microcapsules is slightly lower than that of bulk HD, and a supercooling was observed upon crystallization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Low‐order optimal regulation of parabolic PDEs with time‐dependent domain

Observer and optimal boundary control design for the objective of output tracking of a linear distributed parameter system given by a two‐dimensional (2‐D) parabolic partial differential equation with time‐varying domain is realized in this work. The transformation of boundary actuation to distributed control setting allows to represent the system's model in a standard evolutionary form. By exploring dynamical model evolution and generating data, a set of time‐varying empirical eigenfunctions that capture the dominant dynamics of the distributed system is found. This basis is used in Galerkin's method to accurately represent the distributed system as a finite‐dimensional plant in terms of a linear time‐varying system. This reduced‐order model enables synthesis of a linear optimal output tracking controller, as well as design of a state observer. Finally, numerical results are prepared for the optimal output tracking of a 2‐D model of the temperature distribution in Czochralski crystal growth process which has nontrivial geometry. © 2014 American Institute of Chemical Engineers AIChE J, 61: 494–502, 2015     

Phase‐separation prevention and performance improvement of poly(vinyl acetate)/TEOS hybrid using modified sol‐gel process

The formation of covalent bonds between silanols in copolymer and those in silica prevents organic–inorganic phase separation. Two series of hybrid composite materials, poly(vinyl acetate‐co‐vinyl trimethoxysilane)/TEOS and poly[vinyl acetate‐co‐3‐(trimethoxysilyl)propyl methacrylate]/TEOS, were fabricated using a modified sol‐gel process. The hybrids were transparent. Two kinds of silane coupling agents, vinyl trimethoxysilane (VTS) and 3‐(trimethoxysilyl)propyl methacrylate (γ‐MPS), were used to prevent macrophase separation through formation of covalent bonds. Thermal analysis showed that γ‐MPS was more effective than VTS for the formation of covalent bonds. Enhancement of thermal stability of the hybrids was investigated by thermogravimetric analysis. Photomicrographs of scanning electron microscopy and images of atomic force microscopy indicated that inorganic silica particles were homogeneously dispersed in less than 50 nm in organic matrix. The morphological properties of hybrids were strongly dependent on the organic–inorganic composition. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2310–2318, 2001     

Improvement of state profile accuracy in nonlinear dynamic optimization with the quasi‐sequential approach

Quasi‐sequential methods are efficient and flexible strategies for the solution of dynamic optimization problems. At the heart of these strategies lies the time discretization and approximation of dynamic systems for nonlinear optimization problems. To address this question, we employ a time derivative analysis within the quasi‐sequential approach and derive a finite element placement strategy. In addition, methods for direct error prediction are applied to this approach and extended with a proposed time derivative analysis. According to the information for current time derivatives, subintervals are introduced that improve accuracy of state profiles. Since this is only done in the simulation layer, the nonlinear programing solver need not be restarted. An efficient gradient computation is also derived for these subintervals; the resulting enhanced accuracy accelerates convergence performance and increases the robustness of the solution to initialization. A beer fermentation process case study is presented to demonstrate the effectiveness of the proposed approach. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Time dependences of conduction and self‐heating in acetylene carbon black‐filled high‐density polyethylene composites

The time dependences of electrical conduction and self‐heating behaviors in high‐density polyethylene filled with acetylene carbon black of 0.082 in volume fraction are studied in relation to voltage and ambient temperature. The characteristic decay current constant τ_i, and the exponential growth time constant for self‐heating τ_g are determined for the samples under voltages U above the critical value U_c for the onset of self‐heating. The influences of voltage and ambient temperature on τ_i and τ_g as well as the amplitude of the low‐resistance to high‐resistance switching are discussed on the basis of the random resistor network (RRN) model and the relationship between U_c and the intrinsic resistivity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1124–1131, 2006     

Diastereoselective and Enantioselective Epoxidation of Acyclic β‐Trifluoromethyl‐β,β‐Disubstituted Enones by Hydrogen Peroxide with a Pentafluorinated Quinidine‐Derived Phase‐Transfer Catalyst

An efficient catalytic asymmetric epoxidation of β‐trifluoromethyl‐β,β‐disubstituted unsaturated ketones has been achieved by a pentafluorine‐substituted phase‐transfer catalyst with hydrogen peroxide (30%). Thus, the β‐trifluoromethyl‐α,β‐epoxy ketones with a quaternary carbon centre were obtained in excellent diastereoselectivities (up to 100:1 dr) and excellent enantioselectivities (up to 99.7% ee). Low catalyst loading, recycle of catalyst, environmentally benign oxidant and easy transformation of the epoxides into medicinally important trifluoromethylated intermediate make our protocol much more practical.     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

A Wavelet Characterization of Continuous‐Time Periodically Correlated Processes with Application to Simulation

We introduce a wavelet characterization of continuous‐time periodically correlated processes based on a linear combination of infinite‐dimensional stationary processes. The finite version of this linear combination converges to the main process. The first‐order and second‐order estimators based on the wavelets are presented. Under a simple and easy algorithm, the periodically correlated process is simulated for a given autocovariance function. The proposed algorithm has two main advantages: first, it is fast, and second, it is distribution free. We indicate through four examples that the simulated data are periodically correlated with the desired period.     

Optimal geometry design of the coat‐hanger die with uniform outlet velocity and minimal residence time

In this article a method combining the orthogonal array design and the numerical simulation is used to optimize the geometry parameters of the coat‐hanger die with uniform outlet velocity and minimal residence time. The outlet velocity and the residence time are obtained by simulating the three‐dimensional nonisothermal polymer flow in the coat‐hanger die, while the optimal geometry design is accomplished via the orthogonal array method. The effects of the manifold angle, the land height and the slot gap on the outlet velocity and the residence time are investigated. The results show that the effects of all the three parameters are significant for the outlet velocity. For the residence time, the manifold angle and the slot gap are the significant factors, while the effect of the land height is insignificant. The optimal geometry parameters of the coat‐hanger die achieved in this study are that the manifold angle is 5°, the height land is 70 mm, and the slot gap is 3 mm. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Assessment of Physico‐Thermal Properties,Combustion Performance,and Ignition Delay Time of Dimethyl Amino Ethanol as a Novel Liquid Fuel

Dimethyl amino ethanol (DMAE) contains both hydroxyl and amino functional groups, which may be introduced as a new liquid fuel with high safety and less toxicity with respect to common high performance liquid fuels. Physico‐thermal properties, combustion performance and ignition delay time of DMAE are compared with the usual high performance liquid fuels as well as ethanol and dimethylamine. Combustion performances of DMAE (specific impulse at sea level) with common liquid oxidizers including white fuming nitric acid (WFNA), inhibited red fuming nitric acid (IRFNA), nitrogen tetroxide (N₂O₄), hydrogen peroxide (H₂O₂), liquid oxygen (LOX), and the mixed oxides of nitrogen (MON) are also evaluated. Maximum and minimum specific impulses of DMAE are obtained with LOX (299.6 s) and WFNA (262.4 s), respectively. Maximum density‐specific impulse is obtained with DMAE‐N₂O₄ bipropellant. The ignition delay time of DMAE with several liquid oxidizers are measured with open cup test method. DMAE‐WFNA and DMAE‐IRFNA bipropellants are hypergolic where their ignition delay times are 26 and 42 milliseconds, respectively.     

Synthesis and spectral characterization of surface‐enriched polymer‐supported phase transfer catalysts and their effects on alkylation of phenylacetone

Polymer‐supported phase transfer catalysts with active sites mostly on the surface were prepared by suspension copolymerization of styrene (St), divinylbenzene (DVB), and vinylbenzyl chloride (VBC) with AIBN, followed by the quaternization of the resulting copolymer beads with triethylamine. Active sites on the surface were achieved by the delayed addition of functional monomer (VBC) to the partially copolymerized St/DVB. Polymer beads enriched with active sites were characterized by SEM, EDAX, FTIR, and ESCA. The electron micrographs showed that the exterior surface of delayed‐addition functional monomer catalysts (type 1) has a large number of nodules attached to the surface compared to the smooth surface exhibited by the conventional type 2 catalyst upon the simultaneous addition of all three monomers. In the EDAX analysis up to a depth of 100 Å, the surface chloride of type 1 peak intensity is greater (compared with type 2), indicating the  CH₂Cl enrichment on the surface. In FTIR, the peak intensities of the C N stretching (quaternary onium group) in type 1 are greater than those of type 2, confirming the evidence of more quaternization on the surface than in the bulk. From ESCA analysis to a depth of about 30 Å, it was found that type 1 (beads) contains 26% and type 2 contains 14% of covalent chloride on the surface, which strongly supports the grafting of VBC on St/DVB. In the estimation found by the Volhard method, type 1 has 4.73 m eq g⁻¹ and type 2 has 2.29 m eq g⁻¹ of ionic chloride, thus supporting the surface grafting of VBC. The catalytic activity of these two different catalysts was tested by studying the reaction, that is, the C‐alkylation of phenylacetone. The rate constants of this reaction for type 1 are almost twofold greater than those of type 2, a finding that could uphold the preceding experimental observations. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 408–418, 2000     

Economic model predictive control of nonlinear time‐delay systems: Closed‐loop stability and delay compensation

Closed‐loop stability of nonlinear time‐delay systems under Lyapunov‐based economic model predictive control (LEMPC) is considered. LEMPC is initially formulated with an ordinary differential equation model and is designed on the basis of an explicit stabilizing control law. To address closed‐loop stability under LEMPC, first, we consider the stability properties of the sampled‐data system resulting from the nonlinear continuous‐time delay system with state and input delay under a sample‐and‐hold implementation of the explicit controller. The steady‐state of this sampled‐data closed‐loop system is shown to be practically stable. Second, conditions such that closed‐loop stability, in the sense of boundedness of the closed‐loop state, under LEMPC are derived. A chemical process example is used to demonstrate that indeed closed‐loop stability is maintained under LEMPC for sufficiently small time‐delays. To cope with performance degradation owing to the effect of input delay, a predictor feedback LEMPC methodology is also proposed. The predictor feedback LEMPC design employs a predictor to compute a prediction of the state after the input delay period and an LEMPC scheme that is formulated with a differential difference equation (DDE) model, which describes the time‐delay system, initialized with the predicted state. The predictor feedback LEMPC is also applied to the chemical process example and yields improved closed‐loop stability and economic performance properties. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4152–4165, 2015     

Chemorheology and ultimate behavior of epoxy‐amine mixtures modified with a liquid oligomer

Rubber toughening of epoxy resins has been actively studied since the 1960s with clear progress in understanding of the ultimate properties: microstructure relationships. The morphology, obtained after curing of the modified thermosetting matrix, is a function of the process conditions as well as of the materials used because both influence the thermodynamics and the kinetics of phase separation. In this work several amounts of poly(oxypropylentriamine) (POPTA), have been added as modifier to a diglycidyl ether of bisphenol‐A (DGEBA)‐based epoxy matrix cured with a cycloaliphatic amine. Molecular weight of the neat resin and amine/epoxy stoichiometric ratio have also been used as variables. This investigation has focused upon the importance of cure chemorheology for microstructure formation by using both physicochemical (isothermal and dynamic calorimetry) and rheological techniques. In the second part of this study, the influence of the molecular weight of the epoxy resin in the ultimate properties of 15 wt % POPTA‐modified epoxy matrices is also analyzed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1269–1279, 2000     

Poly‐2‐oxazolidones with tailored physical properties synthesized by catalyzed polyaddition of 2,4‐toluene diisocyanate and different bisphenol‐based diepoxides

In the current study, we investigated poly‐2‐oxazolidones containing one of four different diglycidyl ethers carrying different bulky bisphenol centers. With increasing steric hindrance of the bisphenol‐based diepoxide from bisphenol F to bisphenol A, Z and TMC, the glass transition temperature (T_g) increased markedly from 156 to 211 °C, whereas the plateau modulus of the polymer, i.e. the chain flexibility as determined from rheological characterization, remained almost unchanged. This study demonstrates the general feasibility of the chemical design of poly‐2‐oxazolidones as an amorphous high‐performance thermoplastic. © 2016 Society of Chemical Industry     

Enhancing separation of titanium and iron by three‐liquid‐phase extraction with 1,10‐phenanthroline as additive

BACKGROUND: A three‐liquid‐phase system (TLPS) composed of an organic solvent‐rich top phase, a polymer‐rich middle phase and a salt‐rich bottom phase is a newly emerging separation medium. Due to low affinity of the polymer‐rich phase for metals it is necessary and important to search for a suitable complexing agent that has a definite affinity for the polymer‐rich middle phase and a high selectivity for the metal ion of interest. RESULTS: Addition of 1,10‐phenanthroline (phen) is effective in enhancing the separation of titanium and iron from magnesium in the TLPS consisting of trialkylphosphine oxide (TRPO)‐PEG 2000‐(NH₄)₂SO₄. Hydrogen‐bonding interactions between PEG 2000 and phen molecules are the driving force for anchoring tri(phen)‐iron(II) sulfate complexes in the middle phase. Under the conditions (pH = 1.5, molar ratio of phen to iron(II) = 3.4:1), nearly 86% of titanium was extracted into the top phase while 100% of iron(II) was distributed in the middle phase, without any interference between the metal species. The separation factor of titanium and iron in the upper two phases was greater than 20 000. CONCLUSIONS: A single step of extraction and separation of titanium and iron from magnesium was realized in the TRPO‐PEG 2000‐(NH₄)₂SO₄ TLPS with phen as additive. It highlights the effectiveness of TLPS in dealing with multi‐metal solutions and suggests a potential use of TLPS in the separation of iron and other target metals. As iron is ubiquitous the separation of iron is often needed in both analytical processes and the hydrometallurgical industry. Copyright © 2012 Society of Chemical Industry