No description available.

No description available.

The efficiency of a broad class of continuous processes operated under unsteady conditions must often be expressed as a ratio of two integrals: in chemical reactor problems this may represent the selectivity of a desired product in a complex reaction scheme. Objective functions taking this form are included in the optimal control formulation of unsteady state-operation of lumped parameter continuous processes; the resultant additional necessary condition of optimality appears in a convenient form so that the complexity of the problem is only marginally increased. The difference between the dynamic and the steady performance of continuous chemical processes is only meaningful under strictly comparable conditions. A computationally efficient procedure is developed which, without any assumptions about the form of the inputs, enables the determination of optimal continuous periodic modes of operation under comparable conditions. The proposed procedure can also be effectively used to test the optimality of a given periodic operation. The application of the proposed procedure to chemical reactor problems under inlet control conditions indicated that in many cases the optimal steady performance can be improved by on-off periodic inputs. In particular, simultaneous increases in both the yield and selectivity of a desired product in a complex reaction scheme are attainable while using the same sources and equal*average amounts of the raw materials.

A fundamental study of liquid phase and gas-liquid precipitation of calcium carbonate in narrow channel reactors is presented. Precipitation is strongly dependent on transport rates, as the final product properties are determined by local values of the concentrations during the reaction. The high transport rates available in narrow channels provided the intensification of a precipitation process in this type of equipment. Liquid phase precipitation of calcium carbonate was studied in two square cross section reactors with diagonal lines of I and 2 mm. Flow rates ranging between 0.15 and I CM3/S were used. Mixing efficiency in the narrow channels was characterized with the iodide-iodate reaction scheme. The results showed that mixing efficiency increased with Reynolds number. The mean particle size of calcium carbonate precipitate was found to range between 3 um and 8 um approximately. The narrow channels allowed production of particles similar or smaller in size than in a well stirred batch reactor. Liquid phase precipitation was ftirther characterized by monitoring the change in electrical conductivity, during precipitation, in a narrow channel reactor with embedded electrodes. This system allowed a preliminary study of precipitation rate and limited data on scaling by solid deposits were also obtained. Gas-liquid precipitation of calcium carbonate was studied in a square cross section 2 mm diagonal line narrow channel reactor. The carbonation reaction between a calcium hydroxide solution or suspension andC02 gas was considered. Liquid flow rates between 0.35 and 1.48 CM3/s and carbon dioxide flow rates between I and 8.22 CM3/S were used. Flow patterns for the water-carbon dioxide system were visually characterized. The experimental volumetric mass transfer coefficients for precipitation from a calcium hydroxide solution were found to vary between 0.33 and 0.8 s-1. Particle size and morphology were characterized on selected calcium carbonate samples obtained in both cases from a calcium hydroxide solution and suspension.

The synthesis of hydrazine from ammonia at a pressure of 10 torr has been studied in two types of glow discharge reactors, viz., a crossed discharge reactor and a beam scanning reactor. These reactors were developed in an attempt to eliminate the problems associated with beam constriction phenomena. A limited amount of work was carried out with the first reactor and when it became apparent that it had no real advantages, it was abandoned in favour of the beam scanning reactor. The latter has now been studied in depth using both continuous and pulsed DC power supplies. It has been found that both hydrasine formation and ammonia conversion are improved by beam scanning. Under certain conditions, the effects of operating variables may be described through two parameters; the product of the discharge current and mean residence time in the continuous discharge and the pulse number in the pulsed discharge. Decreasing values of these parameters are associated with an increasing efficiency of hydrazine production.

Over recent years, the spinning disc reactor (SDR) has been developed as a chemical processing device whereby rapid mass and heat transfer rates can be obtained from the thin film of liquid produced by the act of rotation. In exploiting these characteristics, the SDR is considered a tool of process intensification; compact, flexible, intrinsically safe, continuous and capable of delivering better product quality. An SDR and spinning cone reactor were previously investigated in the precipitation of barium sulphate crystals. It was seen that incredibly rapid mixing coupled with high levels of supersaturation lead to very small crystals with a tighter size distribution being produced. This was seen to produce better quality than conventional process techniques. The present study investigates the potential of the spinning disc as a reactor for the precipitation of calcium carbonate. Three different process routes were identified for the study. The first route is the carbonation of calcium hydroxide solution; the second is the carbonation of calcium hydroxide slurry. The third was the precipitation from mixing sodium carbonate and calcium chloride solutions. For each study, the process parameters and crystal size distributions of the product are evaluated for the spinning disc and complimentary batch reactions. As calcium carbonate is capable of forming three polymorphs, the size, size distribution and shape of the crystals are studied using particle size analysis and electron microscopy. The gas-liquid reaction study showed the SDR to have a higher mass transfer rate than a 1-litre batch with a smaller crystal size distribution. The calcium hydroxide slurry carbonation showed that the SDR could process the slurry faster than the batch with comparable size distribution. Mixing two solutions together yielded different sizes and shapes at different supersaturations but by adding glutamic acid to the process, some degree of shape control was achieved.

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The aim of this project consists of detennining the feasibility of a new tandem reaction comprising isomerization and telomerization steps starting from internal diolefins. This type of reactions achieves not only a minimization 9fthe number of steps but also potentially reduces waste fonnation and process capital costs, thus fulfilling the main objectives of Green Chemistry towards the design of sustainable processes. Telomerization is a 100% atom efficient route to the fonnation of functionalized long chain molecules. However, only telomerization of tenninal . conjugated dienes has been reported which limits its applications due to the thennodynamically unfavourable presence of tenninal dienes in natural feedstocks. If proved feasible, the proposed tandem reaction would open opportunities for the utilization ofnew feedstocks and a potentially significant industrial impact. Titanate nanotubes was found to be a good support for metal catalysts (Pd, Rh, Ru), showing high activity in the isomerization of diolefins and very high selectivity for the reaction with allylbenzene. A novel Ru-PPh3-resin catalyst was also highly active in diolefins isomerization (including linoleic acid) with similar catalytic activity than homogeneous catalysts and the possibility of being reused without loss of activity. Screening of homogeneous catalysts based on phosphorus and carbene ligands was carried out for the telomerization reaction and the influence of different operation conditions such as temperature, initial concentration and the nature of nucleophiles was investigated. Heterogeneous catalysts based on DVBresins were also studied, revealing an unusual selectivity to tail-to-head products by Pd-(dvds)-PPh3-resin in the reaction of isoprene with methanol. The telomerization reaction was extended to 1,3-hexadiene when long-chain alcohols are used as nucleophiles and Pd(Imes)(dvds) as catalyst, opening opportunities for long-chain reactants. Finally, the feasibility of tandem reactions was successfully demonstrated with the best results obtained with homogeneous isomerization and telomerization catalysts in the presence of free carbene ligands in the reaction medium.

No description available.

A continuous stirred tank reactor operating under direct digital control has been constructed, commissioned and used for the practical evaluation of estimation and control techniques of interest to chemical engineers. Several increasingly complex algorithms, based on the Kalman filter, were applied to estimate process states and/or unmeasurable parameters under a variety of simulated and practical conditions. A number of multivariable suboptimal control algorithms were also investigated and, by combination with the Kalman-type estimators, on-line adaptive control was realised. The simulation studies showed that for single input- single output systems, a most useful technique for process identification was the summed sine wave method; however, for multivariable systems, it was necessary to use estimators based on state-space models. Increasing estimator complexity progressively enhanced estimates and, in the case of the most sophisticated, eliminated biases: unfortunately, the unavoidable increase in computational burden sometimes precluded on-line use. A reduced, order filter, which operated on exact measurements, gave satisfactory (but slightly biased) parameter estimates. Simulation studies confirmed that all the suboptimal control schemes considered were feasible and, when coupled with an estimator, capable of controlling the process adaptively in stochastic environment. Practical results verified the simulation work; for example, close agreement was obtained between experimental estimates of a highly nonlinear parameter and the value quoted in the literature. Real process sensors were designed to be essentially noise-free and under these conditions proportional plus integral control gave good results, illustrating the power of feedback. Multivariable control, operating under more adverse conditions, gave less satisfactory results because of modelling errors, which produced state biases. However, the more sophisticated adaptive algorithms were effective in correcting parameter errors, (and therefore state biases), and gave enhanced control.