Gregory S. Patience

Scaling considerations for circulating fluidized bed risers

Abstract The ratio between actual gas velocity to particle velocity in the hydrodynamically fully developed region of Circulating Fluidized Bed risers (CFB) may be approximated by ϕ=1+5.6/Fr+0.47Fr0.41t=Ug/ϵVp. This ratio, termed the slip factor, is about 2 at operating conditions characteristic of industrial risers several meters in diameter and agrees with observations of J. M. Matsen (in D. L. Keairns (ed.), Fluidization Technology, Vol. 2, Hemisphere, 1976, p. 135). The proposed relationship between the gas and solids velocity is an adequate first approximation to estimate gas and solids residence times, blower capacity and standpipe length.

Gas phase hydrodynamics in the riser of a circulating fluidized bed

Abstract The hydrodynamics of a circulating fluidized bed (CFB) were studied using radioactive argon as a tracer. The impulse experiments show that gas passes through the riser at velocities significantly greater than superficial gas velocities. A core-annular flow model was used to describe the hydrodynamics. Axial dispersion in the core zone is negligible and mass transfer to the denser, stagnant annulus is characterized by a cross-flow coefficient, k . The Gilliland-Sherwood equation for wetted wall towers, modified to account for the increase in mass transfer rate introduced by the solids, correlates the data reasonably well: The ratio of the cross-sectional area of the lean core to riser cross-sectional area, Φ g , decreases with solids mass flux but increases with gas velocity. Based on a number of experimental investigations, the effects of riser diameter and particle characteristics on Φ g were qualified and the data were fit with a simple two parameter model: This relationship adequately predicts gas bypassing in risers from 0.05 to 0.94 m in diameter.

A New Commercial Scale Process for n-Butane Oxidation to Maleic Anhydride Using a Circulating Fluidized Bed Reactor

Abstract DuPont has developed a new process for n-butane oxidation to maleic anhydride using a circulating fluidized bed (CFB) reactor. An extensive effort spanning a period of ten years has resulted in a successful demonstration of the process on a large demonstration plant. A novel approach to imparting attrition resistance to the catalyst for the process has been demonstrated on a commercial scale. The demonstration plant was used to activate the catalyst, optimize hydrodynamics of the CFB, confirm catalytic performance and attrition resistance, and generate data for the design of a very large commercial plant. Construction of the first commercial plant using this technology is scheduled to be completed in 1995.

Butane partial oxidation in an externally fluidized bed-membrane reactor

An externally fluidized bed-membrane reactor (EFBMR) for partial oxidation reactions is described. This novel reactor concept combines the advantages of fixed bed and fluid bed reactors. Catalyst is loaded inside a porous membrane tube into which the hydrocarbon is fed. An oxygen rich gas fluidizes a powder on the shell side. Oxygen crosses the membrane wall and reacts. Butane partial oxidation to maleic anhydride was adopted as the model reaction and the kinetic parameters were derived based on a full scale commercial pilot plant. A detailed reaction engineering model of the EFBMR showed that hot spots are minimized and the reactor is inherently safer because the flammability potential is lower. Maleic yields are potentially 50% higher in an EFBMR compared to a conventional fixed bed reactor and the reactant concentration operating range is much wider.

Fines effects on collapsing fluidized beds

Abstract When the gas flow to a fluidized bed is suddenly interrupted, the pressure drop variation with time follows a logistic dose response function. The time it takes the bed to deaerate, or collapse, is a function of system geometry, particle characteristics and the fluid properties. For certain Geldart Group A powders, the collapse time may double by increasing the fines (dp

Modelling of propylene oxidation in a circulating fluidized-bed reactor

The performance of a circulating solids fluidized-bed riser reactor for the partial oxidation of propylene t o acrolein has been analyzed using a detailed reaction engineering model. The model accounts for the complex interaction between gas-solid hydrodynamics, heat and mass transfer, and intrinsic kinetics using a core-annular model as the basis for the gas and solid phase flow patterns. Key hydrodynamic model parameters are obtained by interpretation of gas and solid tracer experiments under cold-flow conditions in a pilot-scale reactor. The model predictions give insight into the factors that affect the riser performance, and demonstrate that it has potential as an alternate reactor type for the commercial scale production of acrolein.

Ultrasonic free fatty acids esterification in tobacco and canola oil

Ultrasound accelerates the free fatty acids esterification rate by reducing the mass transfer resistance between methanol in the liquid phase and absorbed organic species on Amberlyst®46 catalyst. The reaction rates of canola oil is three times greater than for tobacco seed oil but half the reaction rate of pure oleic acid as measured in a batch reactor. The beneficial effects of ultrasound vs. the conventional approach are more pronounced at lower temperatures (20°C and 40°C vs. 63°C): at 20°C, the free fatty acids conversion reaches 68% vs. 23% with conventional mechanical stirring. The increased conversion is attributed to acoustic cavitation that increases mass transfer in the vicinity of the active sites. The Eley-Rideal kinetic model in which the concentration of the reacting species is expressed taking into account the mass transfer between the phases is in excellent agreement with the experimental data. Ultrasound increases the mass transfer coefficient in the tobacco oil 6 and 4.1 fold at 20°C and 40°C, respectively.

Catalytic glycerol hydrogenolysis to 1,3-propanediol in a gas–solid fluidized bed

Glycerol is a potential feedstock to produce 1,3-propanediol (1,3-PDO), which is a valuable commercial polyester monomer. Here, we report the gas-phase glycerol hydrogenolysis to 1,3-propanediol over Pt/WO3/Al2O3 in a fluidized bed operating above 240 °C and at ambient pressure. Fluidized beds are ideal contactors for this reaction because the heat transfer rates are sufficiently high to vaporize glycerol thereby minimizing its combustion and thermal degradation. The yield of 1,3-PDO approached 14% after 2 h at 260 °C. The major co-products were 1,2-PDO (18%), 1-propanol (28%) and 2-propanol (15%). In the first step, glycerol may dehydrate to acrolein, followed by rehydration to 3-hydroxypropanal and then hydrogenation to 1,3-PDO. The concentrations of the by-products including acrolein, ethylene glycol, propane, and acetone increased with increasing temperature.

Partial oxidation of 2-methyl-1,3-propanediol to methacrylic acid: experimental and neural network modeling

Methacrylic acid (MAA) is a specialty intermediate to produce methyl methacrylate (MMA), which is a monomer for poly methyl methacrylate. Current processes to MMA and MAA rely on expensive feedstocks and multi-step processes. Here we investigate the gas-phase oxidation of 2-methyl-1,3-propanediol (2MPDO) to MAA over heteropolycompounds as effective catalysts, finding that the maximum selectivity to MAA was 41% with 63% conversion of reactant at 250 °C over Cs(NH4)2PMo12O40(VO)Cu0.5. Cesium (Cs) stabilized the catalyst structure at 250 °C, and vanadium(V) and copper (Cu) played a positive role as an oxidant and promoter, respectively. A 0.3 mm nozzle atomized the liquid reactant over the catalyst surface into a μ-fluidized bed reactor. The proposed Artificial Neural Network (ANN) model predicts MAA selectivity based on 2MPDO and oxygen compositions and catalyst components (Cs, V, Cu) as independent factors. The model accounts for 97% of the variance in the data (R2 = 0.97). Vanadium as a catalyst component and oxygen concentration are the two most significant factors. Genetic algorithms (GA) coupled with ANN modeling optimized the input parameters to improve the selectivity. The selectivity to MAA over the optimized catalyst (Cs(NH4)2PMo12O40(VO)Cu0.15) and optimum feed compositions (2MPDO/O2/Ar = 13%/10%/77%) was 43% at 250 °C.

Gas phase oxidation of 2-methyl-1,3-propanediol to methacrylic acid over heteropolyacid catalysts

The acetone cyanohydrin process (ACH) to produce methyl methacrylate (MMA) relies on expensive and toxic feedstock and suffers from low yield. Methacrylic acid (MAA) esterification to MMA is an alternative to ACH. However, current processes to produce MAA require multiple steps and catalyst lifetimes are short. Here, we report an alternative chemistry based on 2-methyl-1,3-propanediol (2MPDO) which is a co-product of the hydroformylation of allyl alcohol to 1-4 butanediol. The cesium salt of a Keggin-type heteropoly acid (HPA) partially oxidized 2MPDO to MAA. Inserting vanadium into the HPA reduced the Mo6+ to Mo5+, and promoting it with copper increases the selectivity to MAA but decreases the conversion by 11%. The HPA catalyst operated in a gas-phase fluidized bed in which a 0.3 mm nozzle atomized the 2MPDO liquid feed into the bed at 250 °C. The maximum selectivity to MAA and methacrolein (MAC) was 41% and 33%, respectively, at 63% conversion. In the first step, oxygen reacts with 2MPDO to form 3-hydroxy-2-methylpropanal. This intermediate dehydrates to methacrolein (MAC) in the second step, and finally in the third step, oxygen reacts with MAC to form MAA. The main by-products were methane (gas phase) due to decomposition of the reactant and 2-methylpropanal (liquid phase) because of hydrogen transfer of MAC.