Scott Lynn

Novel applications of reaction coupling: use of carbon dioxide to shift the equilibrium of dehydrogenation reactions

In industrial systems, strict thermodynamic coupling (as it is formally defined) is unlikely, particularly where catalysis is used. Equilibrium shifts may still be possible due to coupling between sequential reactions, and recognition of this suggests a wider range of application of the technique than is traditionally considered. Guidelines for synthesis of coupled systems are given. Because of the complexity of coupled systems it is important to incorporate knowledge of kinetics at the earliest stages of process development. Experimental studies are usually necessary to assess catalyst and by-product behaviour. A promising application of reaction coupling is improving the equilibrium of high-temperature, gas-phase dehydrogenation reactions by coupling with CO2 via the water—gas-shift reaction. In the case of hydrogen sulphide this has led to the development of a process with considerable advantages over the existing technology. Dehydrogenation of ethylbenzene to styrene and cracking of light alkanes also have considerable potential, although further kinetic studies are necessary.

Micellar ultrafiltration in an unstirred batch cell at constant flux

An unsteady mass-transfer model is developed to describe the ultrafiltration of micellar surfactant solutions in an unstirred batch cell at constant flux. Excellent agreement between the model and new experiments for asymmetric polyethersulfone membranes [5000 and 50,000 molecular weight cutoff (MWCO)] with aqueous hexadecyl (=cetyl)pyridinium chloride (CPC) solutions in 0.01 M NaCl allows quantitative characterization of the intrinsic membrane rejection properties for both surfactant monomer and micelles, and supports the physics at the membrane surface presumed in the model. The 5000 MWCO membrane rejects all of the micelles (hydrodynamic radius ≈2.5 nm) and most of the singly dispersed surfactant molecules, or monomers (hydrodynamic radius ≈0.42 nm); the intrinsic rejection coefficient of this membrane for micelles is 1.0 and for monomers 0.80. For the 50,000 MWCO membrane, two pore types are necessary to explain the observations. The small-pore intrinsic rejection coefficients for monomers and micelles are 0.75 and 1.0, respectively, while the large-pore rejection coefficients are 0.4 and 0.85, respectively. At least 88% of the permeate flow for the 50,000 MWCO membrane is through pores that completely reject micelles. More of the monomers and micelles are sieved by the membranes than is expected from their advertised molecular weight cutoffs. Calculations of intrinsic rejection using estimates of pore and solute size indicate qualitatively that repulsive electrostatic interactions and surfactant adsorption significantly influence rejection.

Prediction of infinite dilution activity coefficients of sulfur dioxide in organic solvents

Infinite dilution activity coefficients of sulfur dioxide in various organic solvents were correlated with two basicity scales: the solvent Gutmann donor number and Arnett heat of hydrogen bonding. Linear correlations were observed for both basicity scales, and the accuracy of activity coefficient prediction is estimated to be ±20 to 25%. Infinite dilution activity coefficients of sulfur dioxide in over 80 organic solvents were estimated from the correlations.

SULFUR RECOVERY WITH REDUCED EMISSIONS, LOW CAPITAL INVESTMENT AND HYDROGEN CO-PRODUCTION

Abstract The main disadvantage of the Claus process is that by introducing air as oxidant a large volume of tail gas is produced. This must be treated to reduce atmospheric emissions of sulfur-containing gases. The costs of the tail-gas unit are a significant fraction of the total capital and operating costs for sulfur recovery. A new process uses thermal decomposition of hydrogen sulfide in the presence of carbon dioxide instead of air oxidation. The products of this reaction are hydrogen, carbon monoxide, elemental sulfur, water vapor and carbonyl sulfide. Carbonyl sulfide is easily converted to H2S and C02 by liquid- or vapor-phase hydrolysis. Unreacted H2S and C02 are recovered by absorption and recycled to the reactor. Since no air is introduced, there is no tail gas and the tail-gas unit is eliminated, giving a substantial reduction in capital investment. The concentrations of sulfur-containing gases in the product streams depend only on the operation of the absorber and stripper units and can be co...

Analysis and Design of a Viscous-Flow Cooler

A hot stream of a very viscous fluid, such as a polymer, may be cooled in a heal exchanger consisting of multiple parallel passages. However, if a quite uniform temperature distribution is desired in the exit stream, the fluid flowing through each of the passages must be cooled to very nearly the same temperature. An analytical treatment of heat transfer and pressure drop in viscous flow between parallel plates during cooling reveals the operating conditions and passage geometry required to achieve this goal. Solution of the equation obtained depends only on the physical properties of the fluid and the cooler geometry. Non-Newtonian behavior of the fluid is approximated by a power-law function. A unique type of heat exchanger was designed on the basis of this analysis.

Process Design and Evaluation of a Continuous Chemical Plant for the Singlet Oxygen-Iodine Laser

Process designs were evaluated for the continuous, large-scale generation of singlet delta oxygen for use in a chemical oxygen-iodine laser. The excited singlet oxygen is generated from the chemical reaction of chlorine gas with basic hydrogen peroxide. The chemical reaction also produces a large waste brine stream that can be controlled by recycling through a chlor-alkali cell, which regenerates the reactants Cl2 and NaOH. To prevent deactivation of this excited oxygen, a large excess of hydrogen peroxide is typically used to change the reaction mechanism. This use of excess hydrogen peroxide or nonstoichiometric generation leads to substantial increases in capital and operating costs when compared with theoretical stoichiometric (no excess) generation. For the generation of singlet oxygen at a 500-kW level of equivalent lasing power, a theoretical stoichiometric plant producing all reactants has an estimated capital cost of

Development of a feasible process for the simultaneous removal of nitrogen oxides and sulfur oxides from fossil fuel burning power plants

38 million. The capital cost for a nonstoichiometric plant is

Thermodynamic analysis of a fluidized-bed combustor

98 million. Oper...

Extractive crystallization of salts from concentrated aqueous solution

David T. Clay* and Scott Lynn A dry solids pro~ess has been developed for thesimultaneous removal of NO and so 2 from power plant stack gases. A· catalyst/ absorbent in a net reducing flue gas effects the removal of so2 by absorption as ferrous sulfide or sulfate and the removal of NO by reduction to nitrogen or ammonia. The solid is regenerable; reaction with air produces a.rich stream of so2 and ferric oxide. The so 2 may be converted to saleable H 2 so 4 and the solid is recycled to the ~rocess .. The process is capable of greater than 90% removal of so2 arid . NO. The emissions. of H 2 , CO, and 3 are well below acceptable emissions levels. The concentration o.f the solids in the effluent stream is not .significantly increased .over normal flyash levels. There i_s no significant increase in the quantity of solids which must be disposed of .. No flue gas cooling or reheating is required. There are no large storage vessels or slurry transport lines within the process. The regeneration process is thermally selfsufficient. · Experiments in a flow-through fixed-bed reactor between 370S40°C have confirmed that the process reactions are feasible. Known

Solubility of hydrogen sulfide, sulfur dioxide, carbon dioxide, propane, and n-butane in poly(glycol ethers)

Abstract A paper previously published in this journal (Thermochim. Acta, 75 (1984) 9) analyzed the thermodynamics of reactions involved in the capture of sulfur by calcium carbonate in fluidized-bed combustors. It is shown here that the earlier paper contained several fundamental errors, and consequently many of the results presented were incorrect. For this work a model of the system was developed that allowed for investigation of a wider range of temperatures and pressures and included the effect of vapor-phase non-ideality. Using this model a corrected thermodynamic analysis was performed and the scope of the previous study was extended to cover a range of operating conditions. The analysis shows that sulfur capture is primarily by reaction of SO2 with CaO formed from calcined limestone. For typical fluidized-bed combustor conditions of 850°C, 1 atm, sulfur is removed to a level of 0.003 ppm, while at pressures typical of pressurized fluidized-bed combustors (20 atm) the equilibrium sulfur concentration in the gas phase is 0.0003 ppm. There are pitfalls in applying the results of equilibrium predictions to actual performance.