Marylin C. Huff

Partial oxidation of alkanes over noble metal coated monoliths

The production of olefins and synthesis gas (CO and H2) from CH4, C2H6 C3H8, and n-C4H10 in the presence of air or O2 at atmospheric pressure has been examined over monoliths coated with various metals at residence times between 10−3 and 10−2 s. Experiments are carried out by feeding gases at atmospheric pressure and 25°C into an autothermal monolith reactor operating between 800 and 1200°C. In CH4 oxidation, > 90% selectivity to syngas is achieved over Rh at > 90% CH4 conversion, while Pt forms more H2O, Ir sinters, and Ni volatilizes. In C2H6 oxidation, Pt forms up to 70% selectivity to C2H4, while Rh gives up to 70% selectivity to syngas, and Pd forms solid carbon. Carbon formation is suppressed under conditions where graphite formation is predicted on some metals, but forms readily on others. The C2H6 results can be interpreted quite simply in terms of hydrogen abstraction by adsorbed oxygen to form the alkyl, followed by β-hydrogen elimination to yield the olefin (Pt) or pyrolysis to yield syngas (Rh) or carbon (Pd). When C3H8 and n-C4H10 are used, considerable cracking to ethylene plus alkane is also observed.

Synthesis of ketenes from carboxylic acids on functionalized silica monoliths at short contact times

We have synthesized ketene and dimethylketene by dehydration of acetic acid and isobutyric acid, respectively, over functionalized silica monoliths at contact times of 10 to 100 ms. Molar yields of ketene and dimethylketene of 79 and 87% per pass, respectively, are routinely achieved. These results indicate that the control of contact time is a valid strategy for maximizing yield in catalytic ketene synthesis.

Partial Oxidation of CH4, C2H6, and C3H8 on Monoliths at Short Contact Times†

The autothermal production of partial oxidation products including synthesis gas (CO and H2) and C2H4 from CH4, C2H6, and C3H8 in the presence of air or O2 at atmospheric pressure has been examined over monoliths coated with various metals at residence times between 10-4 and 10-2 seconds. Experiments are carried out in an autothermal reactor operating between 800 and 1200°C Rh gives the highest selectivity to syngas; while Pt forms more H2O, Pd forms solid carbon, Ir sinters, and Ni volatilizes. Carbon formation is suppressed under conditions where graphite formation is predicted on some metals, but forms readily on others. Ethylene production is also observed under fuel rich conditions for reactions of C2H6 and C3H8. Pt gives the highest selectivity to C2H4; while Rh and Pd form solid carbon. Causes of selectivity variations and coke formation will be discussed.

Catalytic oxidative dehydrogenation of isobutane in a Pd membrane reactor

Publisher Summary The kinetics of oxidative dehydrogenation in a membrane reactor has been found to be more favorable than the kinetics of catalytic dehydrogenation in the absence of oxygen. The goal of the research discussed in this chapter is to balance the reaction rate and the rate of H 2 removal from the reactor by adjusting the residence time and availability of oxygen to create an extremely efficient membrane reactor for the production of isobutylene. Isobutylene is typically produced by catalytic dehydrogenation over a Cr 2 O 3 –Al 2 O 3 catalyst in the absence of free oxygen. On the other hand oxidative dehydrogenation is kinetically fast and may relieve the limitation of catalytic dehydrogenation. The chapter presents the coproduction of isobutylene and hydrogen in oxidative dehydrogenation that causes this system to be thermodynamically limited. By using a membrane reactor, the co-produced H 2 is continuously removed while still benefiting from the fast oxidation kinetics. It has been shown that, although the current reactor and membrane configuration is only allowed for a 10% hydrogen removal, the removal of hydrogen substantially increases both isobutane conversion and isobutylene selectivity.

Oxidative dehydrogenation over promoted chromia catalysts at short contact times

The oxidative dehydrogenation of ethane and propane at millisecond contact times was studied using Cr 2 O 3 and Pt coated ceramic foam monoliths. The supported Cr 2 O 3 catalyst was able to achieve a higher selectivity to C 2 H 4 at higher conversion of the hydrocarbon feed than the Pt coated monolith.

Rapid synthesis of ketenes from carboxylic acids on functionalized silica monoliths

The synthesis of ketene and dimethylketene have been investigated on functionalized silica monoliths from acetic acid and isobutyric acid respectively. With contact times of about 10 milliseconds, yields of ketene and dimethylketene of 70% per pass are routinely achieved. These results indicates that the control of contact time is a valid strategy for synthesis of ketenes.

Natural gas utilization through CO2 reforming in a membrane reactor

By removing H 2 through a 50 μm Pd membrane, the CO 2 reforming of CH 4 can be considerably enhanced. Both CH 4 conversion and H 2 selectivity can be significantly increased above their conventional equilibrium values, especially at low reactant space velocities. For example, when the dry reforming reaction is carried out over a bed of 0.5% Pt/γ-Al 2 O 3 pellets at 550°C with an equimolar reactant GHSV of 65 h −1 , the CH 4 conversion and H 2 selectivity are 50% and 99%, respectively. At equilibrium in a conventional reactor, the corresponding CH 4 conversion and H 2 selectivity are only 24% and 78%.