Dehydrogenation and Reforming

The beneficial effects of sulphur (a few p.p.m. in the feed) on Pt reforming catalysts (lower initial activity but enhanced lifetime and stability, less coking) were reviewed in the earlier Report and further examples have appeared. A selectively sulphided Pt(0.25)-Re(0.25)-Q(1.0)/Al2O3 catalyst with S/Re atomic ratio 0.93 was more active and longer-lived in the reforming 

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When considering membrane reactors for dehydrogenation and reforming reactions, three types of membrane are of most interest dense palladium or palladium composite membranes,... 

Coke deposits. A special type of poisoning in many hydrocarbon reactions (e.g., catalytic cracking, dehydrogenations and reforming) is the formation of coke or carbonaceous deposits as a result of reaction on catalyst particles or membranes or both, depending on the reactor configuration. Carbonaceous or coke deposits block active sites of a catalyst or catalytic membrane and ultimately leads to deactivation of the catalyst or the membrane. 

In Fig. 6 carbon dioxide reactions are categorized by industrially important products. Hydrogenation reactions produce alcohols, hydrocarbon synthesis reactions produce paraffins and olefins, and amine synthesis produces methyl and higher-order amines. Hydrolysis reactions can produce alcohols and organic acids. Carbon dioxide serves as an oxygen source in the ethyl benzene to styrene reaction. It can be used in dehydrogenation and reforming reactions. 

The composition of a reforming catalyst is dictated by the composition of the feedstock and the desired reformate. The catalysts used are principally platinum or platinum—rhenium on an alumina base. The purpose of platinum on the catalyst is to promote dehydrogenation and hydrogenation reactions. Nonplatinum catalysts are used in regenerative processes for feedstocks containing sulfur, although pretreatment (hydrodesulfurization) may permit platinum catalysts to be employed. 

In the alkylcyclohexane (ACH) to aromatic equihbrium, ACH Ar, aromatics are favored by high temperatures and low pressures. Normal reforming conditions promote rapid ACH dehydrogenation and a high conversion to aromatics. 

Fig. 5 Free energy changes in the steam reforming, decomposition, dehydrogenation and dehydration of ethanol. The data for water-gas-shift reaction also is included.

Hydroprocessing and special absorption techniques are utilized to remove sulfur and nitrogen from the reformer. If not removed through hydroprocessing, feedstock sulfur will be converted to H2S in the reformer. The H2S will then serve as a poison to the platinum reformer catalyst and diminish the dehydrogenation and dehydrocyclization reactions. When present, H2S can neutralize the acid sites on the catalyst diminishing the ability of the catalyst to promote isomerization, dehydrocyclization, and hydrocracking reactions. 

In the catalytic reforming process, the feed is pumped to operating pressure and mixed with a hydrogen-rich gas before heating to reaction temperatures. The net hydrogen produced is a by-product of the dehydrogenation and cyclization reactions. Several reactions occur ... 

Ethylbenzene (EB) is the precursor molecule for production of styrene monomer. It may be synthesized via alkylation of benzene and is also produced as a component of the C8 aromatics fractions obtained from catalytic crackers and reforming units (4). EB is converted to styrene via dehydrogenative or oxidative routes. As much as... 

The ensemble control plays a role also in catalytic reforming on platinum or bimetallic catalysv. A good catalyst should have low activity for hydrogenolysis resulting in production of lower alkanes, and it should have a slow build-up of carbon overlayers to maintain stable activity for isomerization, dehydrogenation and dehydrocyciiration ... 

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