Solid hydrocarbon activation

As a further illustration of the compensation effect, we use solid-acid-catalyzed hydrocarbon activation by microporous zeolites. A classical issue in zeolite catalysis is the relationship between overall rate of a catalytic reaction and the match of shape and size between adsorbate and zeolite micropore. 

The C-H activation chemistry can also be conducted on solid hydrocarbons, such as adamantane (Equation (13)).78 A suitably inert solvent for such a reaction is 2,2-dimethylbutane. Rh2( -DOSP)4-catalyzed decomposition of methyl phenyldiazoacetate in the presence of 2 equiv. of adamantane generated the C-H insertion product in 90% ee. 

The second time-temperature indicator is based on the use of horseradish peroxidase in liquid and solid paraffin (126). The enzyme is deposited onto non-porous glass beads md mixed with melted paraffin containing the substrate. The suspension is mixed well and quickly cooled in a dry ice/acetone bath. When the enzyme is stored in solid paraffin, the activity is extremely slow. But when the temperature increases, the paraffin may melt and thereby make the enzyme reaction a millionfold faster than in the solid hydrocarbon phase. This time-temperature integrator is based on the same concept as the I-point, but here the... 

Background on Primary Petroleum Products. Petroleum is a natural resource found in many types of sedimentary rock formations. Naturally occurring petroleum is a complex mixture of gaseous, liquid, and solid hydrocarbons. Entire industries have grown up around the activities required to produce the crude oil, transport it to refineries, and convert the natural petroleum into a variety of end... 

Wet compounding is another way to hasten the formation of a solid solution. In this method, a homogenous solution or a colloidal solution containing active components of the catalyst is mixed with other components of the catalyst in solid form. The reaction between solution and solid is activated by vigorous mixing and subsequent calcination. Solid phosphoric acid catalyst for hydrocarbon polymerization is prepared by this method. ... 

Soluble metallocene catalysts can be prepared by using hydrocarbon-soluble methylaluminoxane or organoborate activators, or their insoluble counterparts can be made by deposition of the metallocene onto silica or alumina solid acid activators [496]. In our experience, the differences in activity, and in the polymer, between soluble nonsupported and insoluble supported catalysts, are not great, which is another indication that under normal conditions the mass transport is not a major issue. 

The slower decrease in activity of the catalyst at medium pressures was shown also by the smaller temperature increase necessary to obtain the maximum yield of liquid and solid hydrocarbons. Increasing time of operation was associated with gradual lowering of the activity of the catalyst. This reduction could be partly compensated by raising the reaction temperature. In the experiments at 6-16 atmospheres the initial temperatures of 175-180° C. were not raised to 195° C. even after 6 months of operation. At 1 atmosphere the initial temperature of 180° had to be increased to 195° C. after only 5 weeks of operation. 

Because sites that are active for adsorption also tend to be active catalytic sites, compounds in the streams that would not normally cause deactivation may react to form nondesorbables. Olefins, diolefins, and other unsaturated hydrocarbons are especially difficult since they easily polymerize to long-chain species in the presence of high-surface-atea solids. Hydrocarbons in the presence of oxygen can form oxygenated species such as aldehydes and ketones, which can further react by aldol condensation to finrn heavier components. The presence of oxygen with sulfur compounds can create elemental sulfur. 

The possibility of solid-state NMR spectroscopy to perform the analysis of hydrocarbons in the adsorbed states on zeolites at room and higher temperatures and directly in the course of the reaction is the basis for application of this method for reaction characterization occurring on zeolites and other solid catalysts. Solid-state NMR provides in situ monitoring of the reaction proceeding identification of the reaction intermediates, analysis of the reaction kinetics. This allows establishing the mechanisms of the reaction as well as the pathways of hydrocarbon activation. Here we provide some examples to demonstrate the approaches that are used in NMR studies to identify the nature of the intermediate on zeolite surface, to follow the kinetics of the reaction and establishing the reaction mechanisms. 

To explain how solid acids such as Nafion-H or HZSM-5 can show remarkable catalytic activity in hydrocarbon transformations, the nature of activation at the acidie sites of such solid acids must be eon-sidered. Nafion-H contains acidic -SO3H groups in clustered pockets. In the acidic zeolite H-ZSM-5 the active Bronsted and Tewis acid sites are in close proximity (—2.5 A). 

Certain highly porous solid materials selectively adsorb certain molecules. Examples are silica gel for separation of aromatics from other hydrocarbons, and activated charcoal for removing liquid components from gases. Adsorption is analogous to absorption, but the principles are different. Layers of adsorbed material, only a few molecules thick, are formed on the extensive interior area of the adsorbent - possibly as large as 50,000 sq. ft./lb of material. 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

Zeolites are used in various applications such as household detergents, desiccants and as catalysts. In the mid-1960s, Rabo and coworkers at Union Carbide and Plank and coworkers at Mobil demonstrated that faujasitic zeolites were very interesting solid acid catalysts. Since then, a wealth of zeolite-catalyzed reactions of hydrocarbons has been discovered. Eor fundamental catalysis they offer the advantage that the crystal structure is known, and that the catalytically active sites are thus well defined. The fact that zeolites posses well-defined pore systems in which the catalytically active sites are embedded in a defined way gives them some similarity to enzymes. 

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