Hydrogen coke production

Some hydrogen cyanide is formed whenever hydrocarbons (qv) are burned in an environment that is deficient in air. Small concentrations are also found in the stratosphere and atmosphere. It is not clear whether most of this hydrogen cyanide comes from biological sources or from high temperature, low oxygen processes such as coke production, but no accumulation has been shown (3). 

Aside from the above reforming reactions, a small amount of feed components are converted to polymeric hydrogen deficient products which deposit on the catalyst as "coke." A coke buildup results in activity and selectivity loss which ultimately requires catalyst regeneration. In semi-regenerative operation, the coking rate is maintained at a low level to provide cycles of at least three to six months. In cyclic units, coking conditions are inherently much more severe so that frequent regenerations are required. 

A number of indices relate metal activity to hydrogen and coke production. (These indices predate the use of metal passivation in the FCC process but are still reliable). The most commonly used index is 4 X Nickel + Vanadium. This indicates that nickel is four times as actiw as vanadium in producing hydrogen. Other indices [9] used are ... 

We have found that the activity of nickel towards dehydrogenation and dehydrocyclization is increased on particles which contain zeolites relative to non-zeolitic particles of the same matrix composition and surface area. However, the coke and hydrogen making capability of vanadium does not depend on the presence or absence of zeolite. The increase in hydrogen and coke production by nickel when the zeolite is present in the matrix suggests that the zeolite increases the metal activity in catalyzing secondary... 

Catalyst deactivation is primarily caused by the blockage of active sites due to the coke formed from these olefinic intermediates. Higher hydrogen pressures suppress the diolefin formation, making the selectivity between olefinic intermediates and liquid products (in contrast to coke products) more favorable. However, higher pressures reduce selectivity to aromatics in the desired liquid product. Thus, a rigorous model must accurately predict not only the rates of product formation, but also the formation of coke precursors... 

When alkanes are the sole products, Eqs. (3.46)-(3.49) represent the principal reactions with the formation of water, hydrogen, coke, and carbon oxides as byproducts eq. (3.49) describes the formation of aromatics ... 

In the gas black process (Fig. 55), the feed stock is partially vaporized. The residual oil is continuously withdrawn. The oil vapor is transported to the production apparatus by a combustible carrier gas (e.g., hydrogen, coke oven gas, or methane). Air may be added to the oil-gas mixture for the manufacture of very small particle size carbon black. Although this process is not as flexible as the furnace black process, various types of gas black can be made by varying the relative amounts of carrier gas, oil, and air. The carbon black properties are also dependent on the type of burners used. 

When antimony was injected, hydrogen production decreased to 58 SCF/BFF, and the load on the compressor was eased. Coke production decreased as evidenced by a decreased load on the air blower and the 17°F decrease in regenerator temperature. As the load on the compressor was eased, the compressor speed controller was effective, and this stabilized the refinery steam balance. Overall, the unit operated closer to steady state, and this helped... 

Thermal cracking investigations date back more than 100 years, and pyrolysis has been practiced commercially with coal (for coke production) even longer. Ethylene and propylene are obtained primarily by pyrolysis of ethane and heavier hydrocarbons. Significant amounts of butadiene and BTXs (benzene, toluene, and xylenes) are also produced in this manner. In addition, the following are produced and can be recovered if economic conditions permit acetylene, isoprene, styrene, and hydrogen. 

There, the depolymerizate is hydrogenated under high pressure (about 10 MPa) at some 400-450°C, using a liquid phase reactor without internals. Separation yields a synthetic crude oil, which may be processed in any oil refinery. Light cracking products end up in the off-gas and are sent to a treatment section, for removal of ammonia and hydrogen sulphide. A hydrogenated bituminous residue comprises heavy hydrocarbons, still contaminated with ashes, metals and salts. It is blended with coal for coke production (2 wt%). 

The results of this investigation and particularly of those with butadiene strongly suggest that at least portions of the inactive coke formed during pyrolyses involve the following sequence of events (a) production in the gas phase of unsaturated hydrocarbons, (b) chemical condensation or polymerization of unsaturated hydrocarbons to produce rather heavy hydrocarbons, (c) physical condensation of these heavy hydrocarbons as liquids on the reactor walls or in the transfer line exchangers, and (d) decomposition of the liquids to coke (or tars) and hydrogen. This sequence of events is essentially identical to the one proposed by Lahaye et al. (12) for coke production from cyclohexane, toluene, or n-hexane. 

In Fig. 1, as an example, the results of evolution of combustion products (CO, CO2 and H2O) at 500°C, for Samples 1 and 4, are shown. Sample 1 corresponds to the catalyst deactivated at 2 h time on stream, and Sample 4 corresponds to the same catalysts subjected to aging during 1 h. In Fig. la, it can be observed that for the most hydrogenated coke. Sample 1, with H/C = 2.0 5, the beginning of the combustion and the maximum peak of production of CO and CO2 correspond to lower values of temperature than those corresponding to the combustion of coke subjected to aging (Fig. lb). Sample 4, with H/C = 1.15. 

The crude black, viscous pyrolysis oil product requires an upgrading step to make it suitable as a refinery feedstock. This is accomplished by high-pressure hydrogenation in a manner very similar to the upgrading step used for the coking products in tar sands processing. The influence of overall process conditions on the polycyclic aromatic compounds found in the product has been examined [62], and the supercritical water extract of the pyrolytic product has been characterized [63]. 

The synthesis of light alkenes by modification of the Fischer-Tropsch process is recognised as an important route to high value fuel components (refs. 1,2). The essential requirement of the F-T catalyst is high selectivity towards alkenes, suppression of methane and resistance to coking under conditions which favour the formation of hydrogen deficient products. 

Tn synthesizing low sulfur fuels from coal the Stone Webster process A uses the step-by-step addition of hydrogen to coal under conditions which minimize coke production. The first step involves the conversion of solid coal to a liquid by mild hydrocracking in the presence of a recycle solvent. In the next step these liquids react further with hydrogen under more severe conditions to produce methane, ethane, and aromatics. 

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