Product property and production rate control of styrene polymerization

A multivariable multi-rate nonlinear model predictive control (NMPC) strategy is applied to styrene polymerization. The NMPC algorithm incorporates a multi-rate Extended Kalman Filter (EKF) to handle state variable and parameter estimation. A fundamental model is developed for the styrene polymerization CSTR, and control of polymer properties such as number average molecular weight (NAMW) and polydispersity is considered. These properties characterize the final polymer distribution and are strong indicators of the polymer qualities of interest. Production rate control is also demonstrated. Temperature measurements are available frequently while laboratory measurements of concentration and molecular weight distribution are available infrequently with substantial time delays between sampling and analysis. Observability analysis of the augmented system provides guidelines for the design of the augmented disturbance model for use in estimation using the multi-rate EKF. The observability analysis links measurement sets and corresponding observable disturbance models, and shows that measurements of moments of the polymer distribution are essential for good estimation and control. The CSTR is operated at an open-loop unstable steady state. Control simulations are performed under conditions of plant-model structural mismatch and in the presence of parameter uncertainty and disturbances, and the proposed multi-rate NMPC algorithm is shown to provide superior performance compared to linear multi-rate and nonlinear single-rate MPC algorithms. The major contributions of this work are the development of the multi-rate estimator and the measurement design study based on the observability analysis.     

Effect of a Hydrophilic PEO–PPO–PEO Copolymer on Cetyltrimethyl Ammonium Tosylate Solutions in Water

Cetyltrimethyl ammonium tosylate (CTAT) in water forms long flexible wormlike micelles at concentrations above 10 mM, leading to highly viscous solutions and viscoelastic stiff gels above 100 mM. In the presence of a nonmicellar hydrophilic PEO–PPO–PEO triblock copolymer F87 (TBC-F87, Total mol.wt. = 7,700, EO = 70%) these wormlike micelles RE transformed into smaller structures, as evident from a sharp decrease in viscosity and increase in specific conductance. These results are quantified by small angle neutron scattering (SANS) measurements. The PPO middle block of TBC-F87 gets inserted in the CTAT micelle, the size and total aggregation number of CTAT/TBC-F87 mixed micelles decreased but the number of TBC-F87 molecules in the mixed micelles increased with an increase in [TBC-F87]. Two break points in the typical specific conductance versus CTAT concentration plot at various [TBC-F87] amounts represent interactions between CTAT and TBC-F87. The penetration of PPO of TBC-F87 inside CTAT micelles decreases hydrophobicity of the core while the presence of PEO end blocks enhances hydrophilicity each favoring smaller micelles.     

Potential of Sr4Al14O25: Eu2+,Dy3+ inorganic oxide-based nanophosphor in Latent fingermark detection

In this paper, the potential of the Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺ fluorescent nanophosphor is explored to visualize the latent fingermarks. The nanophosphor has been synthesized using self-propagating high temperature synthesis and shows intense luminescence and strong long after glow properties. These nano particles have been characterized for their particle size, crystalline phase, and photoluminescent properties. The calculated PL CIE co-ordinates (0.138, 0.359) correspond to the blue–green shade. Different porous, non-porous, as well as slightly non-smooth surfaces are taken and successfully tested for latent fingerprints development with the prepared Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺ fluorescent nanophosphor powder. Present nano powder is advantageous to use on luminescent or multicolored surfaces as it gives greater contrast and also eliminates the problem of background interferences with the friction ridges due to its strong long after glow property. The results are very good when latent fingerprints were developed on the currency notes with optical variable ink and highly fluorescent pattern areas.     

INNOVATIVE TESTS TO PREDICT THE STRENGTH AND TYPE OF ASPHALT-AGGREGATE BONDS

ABSTRACT

This paper discusses two techniques to characterize the type and measure the strength of asphalt-aggregate bonds. The Modified Lottman Test is commonly used to measure the physical strength of asphalt-aggregate bonds. Under certain conditions bonds may become weak due to chemical factors that are not accounted for in the Modified Lottman Test. In order to measure the chemical strength of the bond, a chemical preconditioning stage was introduced prior to performing the Modified Lottman Test. During this stage a compacted mix pill was exposed to an environment that was rich in either OH^?- or H^plus; ions. Such high or low pH conditions affect bonding reactions that are reversible in nature, and thereby expose the chemical weakness of the bond. Results show that different antistrip agents react differently to such conditions. The paper also discusses the effect of mix curing on bond strength under these limiting pH conditions. The other technique discussed in this paper, U a test that characterizes different aggregates in terms of their reactivity with aspnaltic components, which subsequently helps identify those aggregates that would form strong bonds with asphalt. It was observed that even within limestones aggregates, different types reacted to a different extent, and thereby, could be easily characterized     

Achievable PID performance using sums of squares programming

In addition to process elements like time delay, the PID structure of the controller can pose fundamental limitations on the achievable control performance. A key difficulty in characterizing the limitations due to controller structure is the non-convexity of the resulting optimization problem. In this paper, we present a global lower bound on the achievable PID performance, defined in terms of output variance, by solving a series of convex programs using sums of squares programming. This result is also extended to minimize the weighted sum of the variances of input rate and output. The tightness of the proposed bounds is demonstrated using several benchmark examples drawn from literature.     

X-ray diffraction study of epitaxial zinc and cadmium films prepared by hot-wall technique

Hot-wall technique greatly improves the quality of zinc and cadmium films deposited on glass substrate. At substrate temperature the growth of such films is well ordered, showing highly preferred orientation along c-axis. However, if the substrate temperature is increased beyond certain limit, we get polycrystalline growth of the films. This shows that the growth of zinc and cadmium films on glass substrate strongly depends on the substrate temperature.     

Recovery of oleate‐inhibited anaerobic digestion by addition of simple substrates

Four laboratory‐scale anaerobic digesters were deliberately and completely inhibited by feeding sodium oleate to such an extent that no methane was produced from the digesters. Three of them were then respectively fed glucose, cysteine or glucose and cysteine along with sodium oleate, while the remaining digester was operated as control reactor and continued to be fed with only sodium oleate. Oligonucleotide probes ARC915, EUB338, MB310, MC1109, MSMX860 and MG1200 were used to target and quantify specific groups of microbes, Archaea, Bacteria, Methanobacteriales, Methanococcales, Methanosarcinaceae, and Methanomicrobiaceae, Methanocorpusculaceae and Methanoplanaceae respectively throughout the operation of reactors. Addition of glucose and/or cysteine assisted with the recovery of methane production from oleate inhibition. The addition of glucose was more effective than cysteine, while the combination of glucose and cysteine was most effective on this recovery. The addition of these substrates also stimulated the degradation of oleate in the reactor. Daily methane production from the digesters correlated negatively with residual oleate concentration and positively with Archaea counts. Addition of glucose was more effective than cysteine on increasing the number of Archaea cells, while cysteine was more effective in increasing the number of Bacteria cells. All microbial populations recovered to pre‐inhibition levels within 40 days when glucose together with cysteine was fed. Copyright © 2006 Society of Chemical Industry