Michael F. Zarochak

Hydrodynamic study in a slurry-bubble-column reactor

Abstract Local gas holdup, bubble diameter and bubble rise velocity in the nitrogen/Drakeol-10 oil system were measured at both laboratory (ambient temperature and pressure) and industrially relevant (high temperature and pressure) conditions using a dual conductivity probe in a slurry-bubble-column reactor. It was found that a constant superficial velocity, the Sauter mean bubble diameter decreases with increasing pressure and temperature. The bubble rise velocity significantly decreases as the pressure increases. Large bubbles rise faster than smaller bubbles. Akita and Yoshidas correlation [1] was utilized to compute the bubble size. Predicted values agree with the experimental data at high temperature.

Effects of pretreatment on the surface properties of iron Fischer-Tropsch catalysts

Abstract A potassium- and copper-promoted iron Fischer-Tropsch (F-T) catalyst was studied by X-ray photoelectron spectroscopy, Auger spectroscopy and ion scattering spectrometry to determine the changes in surface speciation of iron and carbon, and the distribution of potassium and copper on exposure to various pretreatment conditions. A transformation in surface composition from Fe2O3 to Fe3O4 to iron carbide was enhanced by pretreating catalysts with hydrogen-carbon monoxide compared with carbon monoxide and retarded by the addition of water vapor to the gases. A lower initial F-T activity observed for hydrogen-carbon monoxide-compared with carbon monoxide-pretreated catalysts, may be explained by greater coverage of the “active” carbide species by surface carbonaceous material formed during pretreatment.

Effect of initial was medium on the Fischer-Tropsch slurry reaction

Abstract This investigation measured the impact of the liquid starting medium on syngas (H 2 +CO) conversion via the Fischer-Tropsch (F-T) synthesis in a 11 continuous stirred tank reactor (CSTR). The experiments were conducted with a low-wax producing iron catalyst, so that the liquid medium composition was unaltered by accumulation of product wax throughout the experiment. Our results show a greater deactivation rate for the F-T reaction in heavier starting media (Polywax-655, Allied AC-1702, and Mobil F-T product wax) versus the lighter medium ( n -octacosane). The syngas (H 2 +CO) conversions were approximately equal and steady for the first five days in both light and heavy, commercially available wax media. However, the conversions dropped more rapidly in the heavier wax media (from 85% to 60% in 12–13 days), but only modestly in the light wax media (from 90% to 85% in 15 days). An even sharper deactivation rate occurred with the heavy Mobil F-T wax (from 85% to 60% in six days). For all experiments, the water gas shift (WGS) ratio in the outlet gases dropped concurrently. One proposed explanation for this increased deactivation in the heavier waxes is that heavier products are being formed by secondary reactions. These products could build up over time and restrict the diffusion of hydrocarbon products and water vapor out of the pores. The presence of higher partial pressures of water vapor could irreversibly oxidize the catalyst.

Slurry phase Fischer-Tropsch synthesis with iron-manganese catalysts

Abstract Synthesis gas was reacted over different compositions of iron-manganese Fischer-Tropsch catalysts in a slurry reactor. The reactor operates in a back-mixed mode with a continuous flow of feed gas through the catalyst suspended in the liquid medium. Four catalysts with iron-manganese ratios of 57/43, 44/56, 22/78, and 10/90 were investigated at identical process conditions after a standard activation procedure. With time on stream for each catalyst system, hydrogenation of olefins occurred, along with olefin isomerization reactions. Activity, selectivity, and stability are discussed in general. Analyses of used catalyst samples are also reported.

Iron/manganese oxide catalysts: surface specification and slurry -phase fischertropsch activity

Abstract Coprecipitated iron-manganese catalysts, prepared with 20 wt% Fe and 80 wt% Mn and having K concentrations from 0 to 1.3 wt%, were analyzed for surface speciation by X-ray photoelectron spectroscopy in H 2 -, CO- and (CO + H 2 )- exposed states. These data show that the degree of carburization of the surface iron depends on the amount of K present in the catalysts. In addition, the type of surface carbon that is present after CO or (CO + H 2 ) exposure, and the interaction of MnO with surface iron are dependent upon the concentration of K. The concentrations of MnO and oxidized iron species at the surface were investigated with respect to the slurry phase activity observed for the conversion of 1:1 H 2 /CO to hydrocarbons. Specific to this analysis is the dependence of the K concentration on the double-bond isomerization activity of these Fe/Mn catalysts.

ULTRASONIC CHARACTERIZATION OF THREE-PHASE SLURRIES

An ultrasonic technique is under development for measuring solids concentration in a three-phase slurry reactor. Preliminary measurements have been made on slurries consisting of water, glass beads, and air bubbles. The data show that both the sound speed and attenuation are well-defined functions of both the solid and gas concentrations in the slurries. A simple model is proposed to correlate the solids concentration with the measured ultrasonic signals.

Effects of pressure on the oxyhydrochlorination of methane

Abstract Methane was oxyhydrochlorinated over a promoted copper catalyst at total pressures of up to 930kPa. The catalyst yield increased three-fold as pressure increased from 130 to 930 kPa for relative inlet concentrations of CH 4 :HCl:O 2 of 5:2:1. Selectivity to CH 3 Cl decreased as temperature and pressure increased; a higher percentage of polychlorinated methanes and carbon oxides were produced at higher temperature and pressure. The pressure effect on CH 3 Cl selectivity remained even when corrected for the higher CH 4 conversions at higher pressures. Decreasing O 2 concentration in the inlet stream had no major effect on CH 3 Cl yield, although less CO and CO 2 were produced at higher temperatures. Decreasing HCl concentration increased CO 2 selectivity at the expense of chloromethane products.

ULTRASONIC CHARACTERIZATIONS OF GAS HOLDUP IN A BUBBLE COLUMN REACTOR

An indirect method of measuring gas holdup in gas-liquid bubble column reactors has been developed. This technique is based on the analysis of the ultrasonic wave transmitted through the two-phase flow. Gas holdup measurements have been made on water-nitrogen bubble system at ambient conditions. The data clearly show that the attenuation of the sound is a well-defined function of the gas holdup in the bubble column for homogeneous flow regime only (i.e., the superficial gas velocity is 4 cm/sec or less).

Measurements of solids concentration in a three-phase reactor by an ultrasonic technique

An ultrasonic technique was developed to measure the concentration of solids in a three-phase slurry reactor. Preliminary measurements were taken on slurries consisting of water, glass beads, and nitrogen bubbles. The data show that the speed and attenuation of the sound are well defined functions of the solid and gas concentrations in the slurries. A simple model is proposed to correlate the concentration of solids with the measured characteristics of the ultrasonic signals.

Ultrasonic measurement of solids concentration in an autoclave reactor at high temperature

Abstract An ultrasonic technique was developed to measure the slurry concentration in an autoclave reactor. Preliminary measurements were conducted on slurries consisting of molten FT-200 wax, glass beads, and nitrogen bubbles at a typical Fischer–Tropsch (FT) synthesis temperature of 265 °C. The data show that the velocity and attenuation of the sound are well-defined functions of the solid and gas concentrations in the molten FT-200 wax. The results suggest possibilities for directly measuring solids concentration during operation of a three-phase slurry reactor under the reaction temperature and with molten FT-200 wax.