Steam conversion

The process which was developed hy DOW involves cyclodimerization of hutadiene over a proprietary copper-loaded zeolite catalyst at moderate temperature and pressure (100°C and 250 psig). To increase the yield, the cyclodimerization step takes place in a liquid phase process over the catalyst. Selectivity for vinylcyclohexene (VCH) was over 99%. In the second step VCH is oxidized with oxygen over a proprietary oxide catalyst in presence of steam. Conversion over 90% and selectivity to styrene of 92% could he achieved. ... 

In most cases, fuel cells are operated with air oxygen as the oxidizer. Pure oxygen can be used when no air is available, as in submarines or spaceships. The reducer most often is hydrogen, either pure or technical grade, that is produced by steam conversion or gasification reactions of natural gas, petroleum products, and/or other liquid organic compounds. 

In the model cell shown in Figure 4.1, steam of molar flow rate, fc and pressure, Pc, is reduced to hydrogen gas of flow rate,/D — f, and partial pressure, P0(f0 — f)/f0, in the cathode compartment (fa /)//D is a conversion ratio from steam (F420) to F42 (steam conversion ratio). The partial pressure of 02, is assumed to be unity. Using the steam conversion ratio, X = (fa f )/f0, Equation 4.4 can be written as follows ... 

The value of E - y is called the open-circuit voltage of the cell, which is related to the composition of the product. Note that the steam conversion ratio, X, depends on the open-circuit voltage, and is not affected by the pressure or flow rate of the reactant. Also, the open-circuit voltage decreases with increasing temperature because of the endothermic nature of the reaction. However, due to the temperature dependence of the logarithmic term in Equation 4.5, this effect decreases with the value of X. 

Barbier, Jr., J., and Duprez, D. 1993. Reactivity of steam in exhaust gas catalysis. I. Steam and oxygen/steam conversions of carbon monoxide and of propane over PtRh catalysts. Appl. Catal. B Environ. 3 61-83. 

Several important chemical reactions for the conversion of coal to methane are shown in Table 2. Steam conversion involves the reaction of coal with steam to produce hydrogen and carbon monoxide. Hydrogen conversion is a reaction in which coal and hydrogen react to form methane. Oxygen conversion produces hydrogen and carbon monoxide by partial oxidation of coal. Methan-ation involves a reaction in which methane and water are produced from carbon monoxide and hydrogen. The water gas shift reaction between carbon monoxide and steam produces carbon dioxide and hydrogen. 

Coal Conversion Chemical Reaction Steam Conversion... 

Steam conversion/methanation has a theoretical heat recovery efficiency of 1005L Hydrogen conversion has a theoretical efficiency of about 90%, if the production of hydrogen by steam conversion is taken into account, however, the theoretical efficiency drops to 81%. Oxygen conversion/methanation has a theoretical efficiency of only 61 which is the lowest of the conversion systems. 

Z.-H. Yu, Hydrocarbon-steam Conversion Engineering, Hydrocarbon Processing Press, Beijing, 1989 (in Chinese). 

Removal of sulfanilic acid from wastewater Lactic acid purification and concentration Enrichment of bisphenol A Phenol recovery from aqueous solutions Zinc(ll) recovery from HCI solution Hydrogen separation from methane steam conversion products... 

Graphs of the two-step one-route mechanisms (the Temkin-Boudart mechanisms) for the steam conversion of CO and liquid-phase hydrogenation are illustrated in Fig. 3(b) and (c)... 

Integration of Eq. (8) yields the kfa rate of steam conversion for a given contact time tc. 

The rate of steam consumption is equal to the steam flow rate times the steam conversion, and the rate of HBr formation is twice the rate of steam consumption. The formation of HBr at a given reaction time tR depends upon the melt composition. A second-order reaction of CaBr2 was found to match the experimentally measured reaction rates far better than a first-order reaction. The reaction constant is then derived from the rate of HBr formation, which is experimentally measured. The observed kinetic constant was 2.17 10-12 kmol s-1 m-2 MPa-1 (1.30 1CH g-mol min-1 cm-2 bar-1) for the hydrolysis reaction, which is 24 times greater than the constant reported for solid CaBr2 reaction. This higher rate promises to significantly reduce the size and design complexity of the hydrolysis reactor. 

The second may be considered as the resultant of conversion (1.1) and of the reverse reaction of CO steam conversion... 

At 800°C with excess carbon, Kshift is approximately 1.0. Invariably the oxygen exchange reactions never reached equilibrium. The apparent or pseudo values for K8hift were generally less than 0.2. Ergun and Menster found similar low values when steam conversion was low. 

Heat pipe capacity (GJ/h) Area of permeation (m ) Methane conversion Steam conversion Product gas temperature ( K) Hydrogen yield... 

Operations. Steam is added to the reactor feed as a diluent. Molten salt is circulated through each reactor and cooled externally, usually by generating low-pressure steam. Conversion of ethylene and acrolein is nearly coiiq)lete and 85 to 90 percent is converted to acrylic acid with the remainder being mostly acetic acid, a valuable byproduct. Dq)ending on the conversions, recycle of off gases may or may not be necessary. 

Reactions 4, 5 and 6 are expressed in terms of steam conversion. The sum of these conversions gives the total conversion of steam. 

The apparent increase in rate may arise from the increase in surface as carbon was removed from the original particle. Although the conventional experimental rate equation for the carbon-steam reaction (6) states that steam is a part of the rate equation, it further states that steam also inhibits the rate. The test procedure used here maintains inlet steam at a fixed velocity and in large excess thus any effect of the level of steam conversion should be negligible on the integral rates calculated here. In the runs shown in Figure 2, the maximum use of steam by carbon in a 5-min. period varied from 3.6 to 8.5% of the total steam available. Of... 

Table II compares non-, single-, and multiple-catalyzed coal-steam conversions in the previously described single-stage reactor. In spite of the difficulty in obtaining reproducible results and satisfactory mass balances on this small scale, the results are believed to represent conversions under the indicated conditions. Thus, there are several noticeable differences between the non-, single-, and multiple-catalyzed runs. They include coal conversion, product composition, total gas produced, product heating value, and gasification rates.

Steam can be considered a cor-eactant of oxidation during rich-phases (lean in O2) [3-5], In oxy-steam conversion of propane, we showed (fig.l) that propane oxidation was catalyzed by platinum (between 200 and 350°C) while rhodium was the key-component in the catalysis of steam reforming (between 350 and 600°C). Ceria was an excellent promotor of steam reactions [3, 6], particularly when this reaction was carried out in the presence of oxygen. Therefore, the steam reforming activity is an excellent indicator of the rhodium surface state since the activity systematically decreases when the metallic rhodium area decreases [7]. On the other hand, oxidation activity is a more complex indicator of platinum surface state because there exists an optimum dispersion [8,9]. 

Consider the production of inorganic oxides by steam conversion of halides in plasma. Conversion of gaseous UFg into UO2, which is an important step in the nuclear fuel cycle, can be done in arc discharges by injection of UFg in water vapor plasma (Tumanov, 1989 Ivanov, 2000) ... 

Figure 10-14. Plasma (electric) energy cost of syngas production during plasma conversion of kerosene as function of specific energy input in the system (1) partial oxidation (2) steam-oxygen conversion with preheating of air (3) steam-oxygen conversion with excess water, (4) steam-conversion in low-temperature regime (5) steam conversion in high temperature regime.

Plasma-Catalytic Steam Conversion and Partial Oxidation of Kerosene for Syngas Production... 

Figure 10-15. Illustration of the plasma catalysis in the steam conversion of kerosene. Additional plasma energy input Aft = 0.2 J/cm (pathway 0-3) leads not to an increase, but to a decrease of temperature in the system. Additional thermal energy input of the equivalent value (pathway 1 -A) results in lower conversion degree and increase of temperature in the system. Curve 2 represents experiments with the plasma-catalytic microwave discharge.

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