Using new packages for modelling, equation oriented simulation and optimization of a cogeneration plant

The development and testing of an equation-oriented (EO) mathematical model for the optimization of heat and power systems using a new state-of-the-art sequential quadratic programming (SQP) method called filterSQP has been reported in an earlier paper. The model has been extended to include combined cycle cogeneration plants (CCCPs), the economic optimization of which involves adding equipment investment, cost functions and operating cost models to the stream and unit operation models of the earlier paper. These systems are of substantial industrial interest and are substantially larger than those in Rodríguez-Toral et al., Computers and Chemical Engineering, August 2000. Their size and complexity required the use of a new flexible modelling system (FMS) recently created within our research group. FMS can be used to set up large systems of equations, create networks to be modelled and give starting guesses easily for problems of any size. Also, FMS is able to interact with solvers for EO simulation and optimization, which have been developed here and elsewhere. A number of EO simulation and optimization examples, from simple unit operations to a whole real cogeneration plant involving a commercial gas turbine with 1275 variables and equations, are used to demonstrate the applicability of the CCCP model and the modelling package.     

Modification of natural rubber latex. II. Natural rubber poly(methyl methacrylate) composite latexes synthesized using an amine-activated hydroperoxide

Composite latex particles based on natural rubber latex have been synthesized to yield materials which may be formally regarded as interpenetrating polymer networks and semiinterpenetrating polymer networks. Methyl methacrylate was added to a carefully stabilized natural rubber latex and polymerized in situ using an amine-activated initiator, tert-butyl hydroperoxide. The resulting materials were cast to yield solid sheets. The morphology of the materials was determined both by transmission electron microscopy and by dynamic mechanical analysis. In addition the stress–strain behavior was studied.     

The structure of crosslinked poly(glyceryl methacrylate) hydrogel networks

Poly(glyceryl methacrylate) hydrogels with different degrees of hydration (75–98% H) and cross-linking densities (X = 0.005–0.05 mol tetraethylene glycol dimethacrylate/mol glyceryl methacrylate) have been prepared by solution polymerization. Cross-linking densities of the fully swollen hydrogels were analyzed using a modified Flory equation. Poly(glyceryl methacrylate) gels polymerized with no added cross-linker were found to be highly cross-linked, the degree of cross-linking depending upon monomer dilution at polymerization. Modeling studies indicated that entanglement of polymer chains explained the highly cross-linked nature of these materials. Gels polymerized with tetraethylene glycol dimethacrylate exhibited higher cross-link densities than did gels polymerized with no added cross-linker. However, for gels polymerized with cross-linker, but at different initial dilutions, cross-linking densities varied depending upon initial concentration, indicating that entanglement contributed appreciably to cross-linking. These hydrogels may be regarded as highly swollen entangled networks, contrary to previous views. Correlation of these findings with those from earlier studies on the ultrafiltration behavior of the poly(glyceryl methacrylate) hydrogels suggested that the packing density of polymer fibers in the matrix may be more predictive of ultrafiltration behavior than is mesh size. © 1993 John Wiley & Sons, Inc.     

Composites formed by interstitial polymerization of vinyl monomers in polyurethane elastomers: 6. Low angle X-ray scattering and turbidity

Low angle X-ray scattering (LAXS) from an interstitially polymerized poly(methyl methacrylate)-polyurethane system has been analysed in terms of a model due to Debye to give the mean chord intercept lengths of the disperse phase (PMMA) and matrix (PU). The model was found to fit the scattering within the experimental errors and the results are in excellent agreement with the results of electron microscopy. A theoretical expression is derived relating the turbidity with (a) the difference in refractive indices between the polyvinyl and polyurethane phases, (b) the size of the two phase domain structure, and (c) the volume fraction of the phases. The expression has been tested experimentally. The domain sizes derived from the turbidity equation agree reasonably with those observed by LAXS and electron microscopy.     

The lamella size distribution in non-isothermally crystallized low density polyethylene

It has been observed that linear and high pressure polymerized low density polyethylenes crystallize with the branches excluded from the crystals, the extent and size of the crystallities which develop being limited by the number and distribution of branches within the molecules. Using a random distribution of branches as a model, the lamellar size distribution has been calculated and compared with those observed experimentally in slow cooled crystallized samples of PE with different degrees of branching. Nitric acid etching of the crystalline regions from the amorphous background followed by g.p.c. analysis of the product, as well as analysis of the melting range have been used to determine crystalline size distribution. Good agreement has been obtained between the observed and calculated values of the most abundant lamellar thicknesses, but problems due to molecular weight fractionation and un-etched amorphous material casts doubt on the experimentally determined size distribution at high and low stem lengths.     

Long-Term Stability of Glucose Responsive Dextran Methacrylate-Concanavalin A Methacrylamide Gels as Part of an Implantable Artificial Pancreas

A closed loop implantable insulin delivery device that delivers insulin to the peritoneum in an automated fashion linked to changing glucose levels has been developed and previously tested in diabetic rats and pigs. The device delivers insulin via a glucose-sensitive gel that comprises of photopolymerized acrylic derivatives of dextran and concanavalin A and acts as both a sensor and controller of the amount of insulin released. In this work the long-term stability of these acrylic polymerized gels and also dextran and concanavalin A mixtures has been shown at 20°C and 37°C by rheological characterization when stored with and without 0.1% w/w glucose. Acrylic gels were found to have a stable complex viscosity for over 730 days at these temperatures indicating that over time they do not undergo degradation. Mixtures and polymerized gels were also dialyzed in the presence of chymotrypsin, which is present in the peritoneum (device implant site) to assess gel integrity across a range of pore size dialysis membranes. Polymerized acrylic gels contained in dialysis membranes of 50 kDa were found to be resistant to degradation over a long time (>500 days). These results show that these gels would be ideal candidates as part of an implantable insulin delivery device.     

Simultaneous MINLP synthesis of heat exchanger networks comprising different exchanger types

This paper describes the simultaneous MINLP synthesis of heat integrated heat exchanger networks comprising different heat exchanger types. The stage-wise superstructure of heat exchanger networks (HEN) by Yee and Grossmann (Comput. Chem. Eng. 14 (1990) p. 1165) is extended to alternative exchanger types. The selection of the types is modeled by disjunctions based on operating limitations and the required heat transfer area. Since different types of heat exchangers involve different design geometries, which influences the inlet and outlet temperatures of heat exchangers, additional constraints are specified to provide a feasible temperature distribution in HEN. The consideration of different exchanger types drastically increases the combinatorics, size and computation effort needed to solve the problem. The integer-infeasible path MINLP approach has been applied to perform an efficient initialization scheme and to halve CPU times for solving MILP master problem of the modified OA/ER algorithm. A special multilevel MINLP procedure in reduced integer space has been proposed to solve medium size HEN problems (20 streams) comprising 10³ and more binary variables.     

Self-Compatibilization of poly(butyl methacrylate)/acrylonitrile-co-styrene blends via concentrated emulsion polymerization

Two concentrated emulsions in water were prepared: one from weakly polymerized butyl methacrylate (BMA) and the other one from a weakly polymerized mixture of acrylonitrile (AN) and styrene (St). Each of the concentrated emulsions also contained a small amount of a vinyl-terminated macromonomer (VTM). After the concentrated emulsions were partially polymerized, they were mixed and subjected to complete polymerization. This generated a blend of poly(butyl methacrylate) (PBMA), binary copolymer AN-co-ST (AN—St), and networks containing chains of VTM and those formed from different monomers. The networks constitute compatibilizers between the PBMA and AN—St. Such a preparation method, in which the components and compatibilizer are generated simultaneously, was called self-compatibilization. The blend possesses excellent tensile properties and toughness compared with the ternary copolymer AN—St—BMA and with the solution blends of PBMA/AN—St. The generation of the compatibilizers and the compatibilization mechanism were investigated via kinetic studies. The effects of the VTM, polymerization conditions, and the weight ratio of AN/St were also examined. © 1996 John Wiley & Sons, Inc.     

Exploring the Functional Consequences of Protein Backbone Alteration in Ubiquitin through Native Chemical Ligation

Ubiquitin (Ub) plays critical roles in myriad protein degradation and signaling networks in the cell. We report herein Ub mimetics based on backbones that blend natural and artificial amino acid units. The variants were prepared by a modular route based on native chemical ligation. Biological assays show that some are enzymatically polymerized onto protein substrates, and that the resulting Ub tags are recognized for downstream pathways. These results advance the size and complexity of folded proteins mimicked by artificial backbones and expand the functional scope of such agents.     

Partially crystalline epoxy networks with superior mechanical and adhesion properties

The mechanical and adhesion behavior of cationically polymerized, partially crystalline epoxy networks is presented. For this, a reactive and a nonreactive poly(?-caprolactone) (PCL) were used as the crystalline component for the formation of copolymers and polymer alloys, respectively. The trade-off between toughness on the one hand and glass transition temperature and mechanical strength on the other can be reduced by the presence of nanostructures in combination with small crystalline domains (相似文献   

Characterization of Miniemulsion Polymerization by Small-Angle Neutron Scattering

Summary Emulsion polymerization is one of the major techniques for the manufacture of adhesives, coatings, thermoplastics and elastomers. In miniemulsion polymerization, relatively stable oil droplets within a size range of 500 to 5000 ? are prepared by emulsifying a monomer in a medium, generally water, with the aid of a surfactant and a hydrophobic compound. Droplet size and size distribution are by far the most important parameters of miniemulsion because they affect directly both the miniemulsion stability and droplet nucleation. Therefore, the understanding of the mechanism ruling miniemulsion polymerization strongly depends on an accurate determination of the particle size. Small-angle neutron scattering has been used for the polymerization study of the 1,3,5-tris(trifluoropropylmethyl)cyclotrisiloxane (F₃). In particular, the shape and the size of the particles before and after the anionic polymerization were sought. Surprisingly, the sizes obtained are of the order of 250 ? which ranges this system rather into the microemulsion domain and the observed growth in the mean particle size (25%) implies that there is no full preservation of the particles during the polymerization reaction. On the other hand, the contribution to the scattering of a second population of smaller particles (38 ?) with a broad size distribution in the polymerized sample is attributed to secondary products leading to a 80% polymerization reaction yield.     

Two-component diacrylate networks from liquidcrystalline and non-liquid-crystalline monomers II. small- and wide-angle x-ray scattering

The structure of single- and two-component networks of diacrylate monomers which were synthesized by photoinduced polymerization in the isotropic phase has been investigated by small- and wide-angle X-ray scattering. In all systems one component was a liquid-crystalline diacrylate whereas the second component was non-liquid-crystalline. The chemical structure (size, geometry, and polarity) of the second component was varied. For the single-component networks the scattering profiles in the small-angle regime reveal inhomogeneities of the electron density of the order of some ten nanometers. For the two-component networks no additional scattering contribution due to composition inhomogeneities has been found. This is an evidence that no phase separation occurs during the photoinduced cross-linking of the thermosets. This picture of an amorphous single-phase structure is supported by the scattering profiles in the wide-angle regime. For the single-component networks a broad maximum is found, the corresponding characteristic length of which can be correlated with the structure of the monomers. For the two-component networks also only one characteristic length is found which shifts with composition between the length of the single-component thermosets. By both methods no indication for the development of a liquid-crystalline phase during network formation has been revealed.     

Determination of the porosity of fibrous cloth spun by a one-stage method from a polymer melt

Conclusions The effect of technological parameters in the aerodynamic spinning process on the integral mean size of pores in heat-bounded fibrous materials has been studied.A model has been obtained for determining the basic pores of a heat-bonded fibrous fabric for the case of dense networks of straightened-out fibres.Translated from Khimicheskie Volokna, No. 2, pp. 43–44, March–April, 1989.     

Carbon as a support for catalysts—III glassy carbon as a support for iron

As described in the Hucke patent, glassy carbons containing not only open pores of molecular size but also pores in the transitional or macropore range can be produced from appropriate formulations. The formulation always consists of a carbon-yielding monomer, an organic to yield larger pores upon its removal once the monomer has been partially polymerized, and a polymerization catalyst. It may contain a dispersing agent, depending upon the size of the larger pores which is desired. In this study, furfuryl alcohol was the monomer. Great flexibility is shown to exist in the total surface areas of the carbons which can be produced, degree of carbon molecular sieving in the super micropores, and pore volume and pore size in the larger pores following polymerization and carbonization steps. Different ways of adding iron into the mix are explored which also can have pronounced effects on the nature of the porosity in the final carbons. Further modification is shown upon addition of potassium or boron into the mix. Carbons produced are expected to have potential as catalyst supports.     

Gradient interpenetrating polymer networks. I. Poly(ether urethane) and polyacrylamide IPN

The swelling properties of poly(ether urethane)s and the preparation of interpenetrating polymer networks (IPNs) from a poly(ether urethane) thermoplastic elastomer and hydrogel forming polyacrylamide have been studied. The acrylamide monomer was polymerized with simultaneous crosslink formation, in the presence of the swollen thermoplastic elastomer. Upon removal of the swelling solvent, an IPN was obtained which absorbed water in the manner of a hydrogel but had mechanical properties superior to a hydrogel.     

Low-Temperature Synthesis of Cubic and Rhombohedral Y6WO12 by a Polymerized Complex Method

Cubic Y₆WO₁₂, which has a defect fluorite-type structure with disordered cation and anion sublattices, was synthesized for the first time at the low temperature of 600°C by a polymerized complex method. The crystallization process of Y₆WO₁₂ from an amorphous precursor has been investigated in detail using TG-DTA, XRD, and TEM. Above 400°C, the cubic phase began to crystallize upon decomposition of the organic materials in the precursor. The crystallite size of the cubic Y₆WO₁₂ increased from about 5 nm at 600°C up to about 35–40 nm at 1000°C. Above 1200°C, the cubic phase transformed to rhombohedral Y₆WO₁₂, which is a stable phase.     

Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template

Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m²/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials.     

FDT: A technique for direct study of water attack at the silane-filler interface

A technique is presented for the direct study of water attack at the silane-filler interface. This technique, Filler Desorption Test (FDT), involves observations of surface tension changes which occur when a silane-treated filler is floated on a water surface. If all the silane has been appropriately cured to form one integral polymerized siloxane network, then the rate and degree of surface tension lowering are a sensitive measure of the adhering tendency of the polymerized silane film. Data are presented which suggest that, all other things being equal, the strength of the coupling agent (C.A.)-filler bond under water attack can be assessed by observation of the ease with which the first small amount of polymerized silane leaves the filler and the relative degree of hydrophobicity of the resulting surface. FDT is a new tool for fundamental studies of the coupling agent-filler interface and interphase. The method also allows rapid screening and evaluation of a wide range of chemical and physical modifications designed to improve C.A. response on various filler systems.     

Modelling diffusion and reaction accompanied by capillary condensation using three-dimensional pore networks. Part 2. Dusty gas model and general reaction kinetics

A pore network model incorporating a rigorous model of diffusion/reaction and an analysis of pore filling by capillary condensation has been developed. This paper presents an extension of the algorithm described in part 1 to cover multicomponent diffusion and reaction represented by any type of kinetic expression. The novel aspects of the model reported here are that reactions of interest to industry can be simulated since realistic rate equations, such as Langmuir-Hinshelwood expressions, are represented and the possibility of capillary condensation in the pores is also accounted for. Bulk diffusion, Knudsen diffusion and convection of multicomponent vapours are analysed using the dusty gas model, representing a more comprehensive approach to modelling transport in a pore than the Fickian model applied in part 1. The model is used to simulate thiophene hydrogenation over a Co-Mo/Al₂O₃ catalyst. At temperatures and pressures close to the dew point, capillary condensation occurs in the network. For example at 553 K and 21.5 bar, 55% of the pores are liquid filled. Capillary condensation in the network leads to a decrease in thiophene conversion at the network centre. This effect is particularly pronounced when the percolation threshold of the network is approached. The reduction of thiophene conversion in networks containing condensate is thought to result from loss of surface area available for vapour phase reaction and an increased fraction of dead-end pores, which contribute less to the flux of reactants than open pores. The effect of the size of the network used in the simulations upon the range of pressures over which capillary condensation and percolation phenomena occur is considered.     

Self-compatibilization of polymer blends via concentrated emulsions

Summary A novel approach to the formation and compatibilization of polymeric blends is suggested, namely the self-compatibilization via concentrated emulsions. In this method, two concentrated emulsions are prepared from different monomers and subjected to partial polymerization; at least one concentrated emulsion contains also some di-vinyl-terminated macro-monomers. A blend is formed by mixing the partially polymerized latexes and subjecting the mixture to complete polymerization. Some AB networks, with the macro-monomers as chains A and the homo- and co-polymers generated from the other monomers as chains B, are formed, which ensure the self-compatibilization of the resulting blend. Blends of styrene-co-methyl methacrylate and poly (vinyl acetate) were prepared and investigated as a model system.