Terdthai Vatanatham

Kinetics of limestone neutralization of acid waters

The rate of neutralization of sulfuric acid by limestone particles is shown to be controlled by hydrogen diffusion in the pH range of 2 to 6. The first-order rate constant is 10 to 4l./(cm)2(S) at 298 K for a limestone containing 87 wt % carbonates, using as a driving force the hydrogen concentration in the bulk phase minus that at equilibrium at the end of the neutralization. A shrinking particle model physically described dissolution of the limestone. Particle sizes investigated vary from 0.037 to 0.044 mm to 0.500 to 0.595 MM. Effects of temperature (274-348 K), stoichiometry, turbulence, and carbon dioxide pressure are analyzed.

Mathematical modeling and simulation for gas-liquid reactors

Abstract Gas–liquid reactors are widely used in many industrial processes such as oxidation, hydroformylation, chlorination, etc. The paper develops comprehensive model for reactors using the mixing cell approach. It incorporates heat and mass transfer effects in the film and uses a boundary element method to solve the film model equations. The fluxes obtained at the interface are then directly used as the link to the reactor model. Simple isothermal and non-isothermal reactions were numerically tested. Application to two industrially important case studies, chlorination of butanoic acid and oxidation of cyclohexane are briefly illustrated. For the autocatalytic chlorination of butanoic acid, the yield of desired product, monochlorobutanoic acid, is favored by the high degree of mixing in the liquid phase. Therefore, this reaction should be carried out in a CSTR. A series of five bubble tanks with parallel gas reactant feed for cyclohexane oxidation was also simulated. It was found that the cyclohexane conversion is low while the oxygen conversion is relatively high and almost constant in each tank. Due to the complex multistep nature of this reaction scheme, oxygen is consumed in many steps of oxidation and selectivity of main products (which are intermediate products in the reaction scheme) depends on the critical control of over-oxidation in the kinetic mechanism.

Kinetics and modeling of methyl methacrylate graft copolymerization in the presence of natural rubber latex

A graft copolymerization model for using cumene hydroperoxide/tetraethylenepentamine (CHPO/TEPA) as a redox initiator was developed to describe the grafting of methyl methacrylate onto natural rubber latex as a core-shell particle. The model allows estimating the effects of the initiator concentration, monomer-rubber weight ratio, and temperature on the properties of graft product, e.g., % grafting efficiency and the % monomer composition in the graft copolymer and free polymer. The rate expressions of polymer chain formation are developed by taking into account a reduction of CHPO by TEPA and a population event of radicals between core/shell phases. The parameter estimation is performed to find the kinetic parameters. Validation with experimental results demonstrates a good applicability of the proposed model. The model results reveal that the formation of grafted polymer chains rather form by the chain transfer reaction to rubber chains from homopolymer radicals and the initiation reaction of cumyloxy radicals to rubber chains.

DEM MODELING AND SIMULATION OF A DOWN-FLOW CIRCULATING FLUIDIZED BED

A mathematical model based on the distinct element method (DEM) was developed to investigate the hydrodynamics in a gas-solid down-flow circulating fluidized bed reactor (downer). The models consist of the equations of particle motion and fluid motion. The contact force is calculated by using the analogy of a spring, dashpot, and friction slider. Simulation results show that the radial solids holdup and particle velocity profiles are uniform in the core region. Near the wall, the solids holdup is higher with lower particle velocity. An increase in the particle size decreases the solids holdup and increases the particle velocity. The solids holdup decreases with superficial gas velocity but increases with solids circulation rate. Particle velocity increases with gas velocity and solids circulation rate. The solids holdup and particle velocity are almost uniform along the height of the downer except near the distributor. The hydrodynamic behavior from this simulation showed trends similar to those of the experimental results. The results obtained from this model fit better with the experimental results than Kimms and Bolkans models do.

Heat transfer effect in scaling-up a fluidized bed reactor for propylene polymerization

The effects of operating conditions and scaling-up on reactor temperature control and performance in propylene polymerization fluidized bed reactors were studied by phenomenological and CFD models. A phenomenological model with CFD hydrodynamics parameters predicts average information, while a CFD-based reactor model provides local information. Results suggest improved productivity and reactor temperature control by cautiously increasing catalyst feed rate, operating temperature, reactor size and superficial velocity, with consideration of hot spots and catalyst deactivation. High catalyst loading increases productivity but involves risk with regards to the control of oscillating temperature and hot spots. The model identifies an operating window to improve productivity and temperature control and to study operation details. Mixing effect is important to heat transfer but not to propylene conversion. Scaling-up cannot provide similarity of heat transfer. Keeping the same temperature when scaling up from 0.2 to 4 m in diameter requires heat transfer area multiplying factors of 2.43 to 5.26 or lowering the wall temperature by 7 to 18 K. Hot spots are detected with a temperature variation of 10 to 14 K. The results are useful for analyses of laboratory and industrial scale reactors and provide information on scale up.

The Effect of Process Factors to the Kinetic Studies of Emulsion Copolymerization of Natural Rubber and Styrene

Graft copolymer of styrene on natural rubber was prepared in laboratory by emulsion polymerization using potassium persulfate and sodium laurysulfate as an initiator and an emulsifier, respectively. The concentrations of initiator and emulsifier were varied in the range of 0.7 to 2.0 parts and 5.0 to 11.0 part per 100 parts of organic compositions, respectively. The gross polymers were purified by soxhlet extraction to remove ungrafted polystyrene and ungrafted natural rubber to obtain the graft copolymer (NR-g-PS). Characterization of graft copolymer was confirmed by FTIR spectroscopy. The results of the conversion, the kinetic rate of polymerization and grafting efficiency as a function of initiator and emulsifier concentration were studied. It was found that the conversion and the rate of polymerization increased with initiator and emulsifier concentration. At 1.0 parts of initiator and 5.0 parts of emulsifier were the optimum values. Therefore, the conversion and grafting efficiency can be used to predict the reaction conditions as a guideline for the graft copolymer production in pre-scale up reactor.