STATISTICAL ANALYSIS OF REACTION RATE DATA OF LIQUID PHASE SYNTHESIS OF DIMETHYL ETHER FROM METHANOL

The liquid phase catalytic dehydration of methanol to dimethyl ether (DME) is a key reaction step in the single-step synthesis of DME from CO-rich syngas in a slurry reactor. The effect of process variables including temperature, pressure, impeller speed, and feed methanol flow rate on DME synthesis rate has been studied by a systematic 24 full factorial experimental design with single replicate. The significant effects and interactions have been quantified by F-tests. The estimates of significant effects have been obtained by Yates' algorithm. Residual probability and normal probability dots have been obtained to test model adequacy. Finally, a computational model has been developed to predict the DME synthesis rate alt various values of process variables. The model has excellent interpolational predictive capability as evidenced by parity plots.     

THERMAL STABILITY ANALYSIS OF THE LIQUID PHASE METHANOL SYNTHESIS REACTOR

The effect of addition of an inert liquid phase on the rate of heat generation in the catalytic synthesis of methanol from syngas has been studied. Gas compositions typical of product gases from Lurgi and Koppers-Totzek gasifiers, represented by H₂-rich and CO-rich syngas respectively, were used to experimentally verify the “slope” and “dynamic” critria in a three-phase fixed bed recycle reactor. The liquid medium, witco-40 oil, has been effective in controlling the rate of heat generation and in preventing catalyst overheating, signifying that the liquid phase synthesis is thermally far more stable than the vapor phase synthesis. The experimental thermal stability study provides crucial and valuable information in commercializing the liquid phase methanol synthesis process. The current approach of thermal stability analysis does not require any a priori assumption or predetermined reaction kinetics.     

KINETICS OF LIQUID PHASE CATALYTIC DEHYDRATION OF METHANOL TO DIMETHYL ETHER

The kinetics of the liquid phase catalytic dehydration of methanol to dimethyl ether were investigated. The experiments were carried out under low concentrations of feed in a 1-L stirred autoclave, according to a statistical experimental design. The inert liquid phase used for this investigation was a 78:22 blend of paraffinic and naphthenic mineral oils. A complete thermodynamic analysis was carried out in order to determine the liquid phase concentrations of the dissolved species. A global kinetic model was developed for the rate of dimethyl ether synthesis in terms of the liquid phase concentration of methanol. The activation energy of the reaction was found to be 18,830 cal/gmol. Based on a step-wise linear regression analysis of the kinetic data, the order of the reaction which gave the best fit was 0.28 with respect to methanol. Effects of the solid to liquid and the gas to liquid mass transfer resistances on the kinetic rate have also been investigated.     

Removal of p-nitrophenol using hydrodynamic cavitation and Fenton chemistry at pilot scale operation

In the current work removal of p-nitrophenol has been investigated using hydrodynamic cavitation, either operated individually or in combination with H₂O₂ and conventional Fenton process. In hydrodynamic cavitation, two different cavitating devices viz. orifice plate and venturi have been used. Effect of different operating parameters such as initial concentration (5 g/l and 10 g/l), inlet pressure (over a range 5.7–42.6 psi) and pH (over a range 2–8) on the extent of removal has been investigated. In conventional Fenton process two loadings of FeSO₄, 0.5 g/l and 1 g/l were investigated and three ratios of FeSO₄:H₂O₂ viz. 1:5, 1:7.5 and 1:10 were used. Removal observed with venturi was higher than with orifice plate in combination with Fenton chemistry. For 5 g/l initial concentration of p-nitrophenol, maximum removal of 63.2% was observed whereas for 10 g/l solution it was 56.2%.     

Optimization of a hydrodynamic cavitation reactor using salicylic acid dosimetry

In the present work, optimization of a hydrodynamic cavitation reactor, for maximizing the extent of hydroxyl radical generation, has been investigated using salicylic acid as a dosimeter. The effect of different operating parameters such as inlet pressure into the reactor, shape of the orifice, and concentration of salicylic acid employed was investigated where the extent of hydroxyl radical generation was quantified in terms of concentration of the hydroxylated products 2,5- and 2,3-dihydroxybenzoic acid. With an upstream pressure of <100 psi no hydroxyl radicals were produced but excellent results were obtained with a small circular nozzle at 4000 psi and a salicylate concentration of 750 ppm. The use of a combination of ultrasound along with hydrodynamic cavitation is also reported for the first time and results in a 15% improvement in the hydroxyl radical generation when the distance between the orifice and transducer is 5–10 mm.     

Corneal ulcer caused by Nocardia asteroides in a patient with leprosy

Nocardia asteroides is a rare cause of keratitis usually associated with trauma. We report a case of corneal ulceration caused by N. asteroides in a patient with leprosy. This is the first case report of nocardial keratitis from Southeast Asia. The diminished corneal sensation in a patient with leprosy could be a predisposing factor for development or exacerbation of corneal ulceration.     

Catalysis by nanoscale gold (Au/MOx): B. Reaction mechanisms of low temperature CO oxidation reactions

Here, in Part B of this Series, we take a critical look at the reaction mechanisms of low temperature CO oxidation reactions over nanoscale gold, including adsorption, surface reaction, and desorption of key substrates, viz., CO and O₂. Based on a concerted analysis of reactivity data of Au nanoparticles, physicochemical surface characterization, and theoretical first principles calculations, we conclusively prove that out of the 2 most commonly invoked reaction mechanisms, gold-only vs. gold-assisted, the latter is the only mechanism operative for supported gold particles in the quantum size range of 2–5?nm. The Au-MO_x support perimeter interface is a structural motif that is very rich in small metallic particles, and extremely low-coordinated Au sites (with N ～4–5), and some in presence of atomic bonding with Zn atoms. There is both charge and species transfer at this perimeter interface, which also provides highly active sites for adsorption of CO and O₂.     

The direct,one-step process for synthesis of dimethyl ether from syngas. III. DME as a chemical feedstock

In Parts I & II of this Series, we illustrated the process research studies on a new, trendsetting indirect syngas conversion process, the direct, one-step LPDME^tm process, which is now a shining example of “dual catalysis” or “cooperative/adaptive” catalysis and also of thermodynamic/kinetic coupling in series-parallel reactions.

In this part III, we take a look at several processes on the research and pilot scale that employ methanol and DME as chemical feedstocks for further conversion to value-added chemicals. A most rational and cogent argument for the use of DME as a feedstock is that the unit production cost of DME from the direct, one-step DME processes, most notably the LPDME^tm process, can be lower than methanol (from LPMeOH^tm), on a methanol-equivalent basis. DME also has inherently more benign physical and chemical properties, contains 1 less mole of water, and results in a substantially similar product distribution, as methanol, for the methanol-to-gasoline (MTG) and methanol-to-olefins (MTO) process. DME can also be converted to several other important chemicals; some of these include dimethoxymethane, dimethoxyethane, methylal, formaldehyde, acetic acid, methyl acetate, and polyoxymethylene ethers. In this report, we offer a critical assessment of the current status of these processes and a projected path to commercialization. Considering the trendsetting and impactful nature of DME as a chemical entity and as a chemical feedstock, along with its “free” cost, we are of the opinion that the future of DME, and of its chemical conversions, as so-called “DME economy”, is very bright.     

Degradation of polypropylene using ultrasound-induced acoustic cavitation

Cavitation results in generation of hot spots as well as turbulence associated with liquid circulation which can result in degradation of polymeric compounds. In the present work cavitation generated using ultrasound has been utilized for degradation of polypropylene and effect of different operating parameters on the extent of degradation has been investigated. Different concentrations (0.5%, 1% and 1.5%, w/v) and different volumes (50, 75 and 125 ml) were subjected to ultrasonic irradiation using a horn-type reactor. Two different solvents (p-xylene and decalin) have also been used to investigate the dependency of the intensity of cavitation on the type of the solvent. It was found that extent of degradation increases with a decrease in reaction volume and concentration. Use of p-xylene as a solvent resulted in higher extent of degradation. It was also observed that a constant solution viscosity is reached beyond which ultrasonic irradiation could not further degrade polypropylene. The limiting viscosity was also observed to depend on the volume and concentration of polypropylene.