Hydrocarbons coke production

The hydrocarbon feed rate to the reactor also affects the burning kinetics in the regenerator. Increasing the reactor feed rate increases the coke production rate, which in turn requires that the air rate to the regenerator increase. Because the regenerator bed level is generally held constant, the air residence time in the dense phase decreases. This decrease increases the O2 content in the dilute phase and increases afterbum (Fig. 5). 

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). 

The presence of polycyclic aromatic hydrocarbons in the environment is of obvious concern and, apart from specific occupational environments, human exposure to these compounds derives from combustion products released into the atmosphere. Estimates of the total annual benzo[aJpyrene emissions in the United States range from 900 tons (19) to about 1300 tons (20). These totals are derived from heat and power generation (37-38%), open-refuse burning (42-46%), coke production (15-19%) and motor vehicle emissions (1-1.5%) (19,20). Since the vast majority of these emissions are from stationary sources, local levels of air pollution obviously vary. Benzo[aJpyrene levels of less than 1 pg/1,000 m correspond to clean air (20). At this level, it can be estimated that the average person would inhale about 0.02 pg of benzo[aJpyrene per day, and this could increase to 1.5 pg/day in polluted air (21). 

Although there are few chimney sweeps in business today, people are still exposed to considerable amounts of polycyclic aromatic hydrocarbons. Cigarette smoking, for example, is a major source of PAH ( ) coke production also has high PAH emissions (O. 

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. 

The activity and selectivity of catalyst HZSM5-1 was constant over 1 hour on stream although the formation of a linear hydrocarbon species at the catalyst was noticed. The IR spectra suggest that this species is a linear aliphatic hydrocarbon (coke precursor) increasing in concentration with time on stream [13], It is concluded that this species is adsorbed at the (catalytically inactive) Si-OH groups of the catalyst. During our measurements, the catalytically active Si-OH-AI groups were not blocked by this surface species and the product selectivity was not altered... 

When petroleum coke is utilized for anode and electrode production and some specialty applications, it is necessary to calcine it to remove moisture and hydrocarbon VCM. Product qualities, along with production rate, are based on feedstock composition, kiln temperature profile, kiln residence time and cooling procedures. The two methods available for calcining coke commercially are the rotary kiln (5 ) shown in Figure 8 and the rotary hearth (6J shown in Figure 9. 

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%). 

Catalysts tend to be deactivated in the process of plastics pyrolysis because of coke deposition on their surface. The deactivation of HZSM-5, HY, H-zeolite and silica-alumina was compared by Uemichi et al. [86]. In the case of PE pyrolysis and HZSM-5 added as catalyst, no deactivation occurred due to the low coke deposit, and high yields of light hydrocarbons (mainly branched hydrocarbons and aromatics) were achieved. In the case of PS, however, coke production increased dramatically, so HZSM-5 was deactivated very quickly. Silica-alumina catalyst was deactivated gradually and slowly with the increase of cracking gas, while HY- and H-zeolite molecule sieve catalysts were deactivated very quickly. Walendziewski et al. [87] studied the catalytic cracking of waste... 

Thermal reactions of acetylene, butadiene, and benzene result in the production of coke, liquid products, and various gaseous products at temperatures varying from 4500 to 800°C. The relative ratios of these products and the conversions of the feed hydrocarbon were significantly affected in many cases by the materials of construction and by the past history of the tubular reactor used. Higher conversions of acetylene and benzene occurred in the Incoloy 800 reactor than in either the aluminized Incoloy 800 or the Vycor glass reactor. Butadiene conversions were similar in all reactors. The coke that formed on Incoloy 800 from acetylene catalyzed additional coke formation. Methods are suggested for decreasing the rates of coke production in commercial pyrolysis furnaces. 

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. 

Sampling analysis during this project identified more than 1000 tons/year of soil entering the refinery s underground drainage system. Once there, the solid tends to become oil coated, deposit as sludge in the oil/water separator, and must be handled as listed hazardous waste. At Yorktown, most hazardous waste sludges are recycled to the refinery s coker where hydrocarbons are converted into usable liquid and solid products. A small amount of soil components remains in the coke product. 

Aromatic compounds have not only been of academic interest ever since organic chemistry became a scientific discipline in the first half of the nineteenth century but they are also important products in numerous hydrocarbon technologies, e.g. the catalytic hydrocracking of petroleum to produce gasoline, pyrolytic processes used in the formation of lower olefins and soot or the carbonization of coal in coke production [1]. The structures of benzene and polycyclic aromatic hydrocarbons (PAHs) can be found in many industrial products such as polymers [2], specialized dyes and luminescence materials [3], liquid crystals and other mesogenic materials [4]. Furthermore, the intrinsic (electronic) properties of aromatic compounds promoted their use in the design of organic conductors [5], solar cells [6],photo- and electroluminescent devices [3,7], optically active polymers [8], non-linear optical (NLO) materials [9], and in many other fields of research. 

This work deals with the study of the coke formation on H-mordenite during the benzene transalkylation with C9 aromatics, under several reaction conditions, in order to evaluate the condition which results in the lowest catalyst deactivation for industrial purposes. It was found that coke was produced in all samples but it was maintained around 4% (weight) without damage to activity and selectivity to toluene and xylenes. The coke was hydrogenated and could be easily removed. The soluble coke was mostly constituted by aliphatic hydrocarbons, while the insoluble coke was amorphous. These results were explained by the mordenite structure as well as by the presence of hydrogen. The best condition to perform the reaction depends much more on the selectivity to toluene and xylenes rather than on coke production. 

Polycyclic aromatic hydrocarbons (PAH) are introduced into the environment by a number of combustion processes, including heat and power generation, coke production, open refuse burning and motor vehicle emissions (, 2). Individuals can be exposed to PAHs from these environmental sources or from their occupation, diet or smoking habits. 

Benzene, is an aromatie hydrocarbon and historically has been produced during the process of coal tar distillation and coke production, while today benzene is produced mainly by the petrochemical industry. Based on the National Institute of Occupational Safety and Health (NIOSH), in the United States, it has been estimated that in 1976 two million Americans were exposed occupationally to benzene. Worldwide production of benzene is approximately 15 million tons and the production in the United States is estimated to be increasing at least 3% annually, approaching 6 million tons of benzene produced in the United States in 1990 and 6.36 million tons produced in 1993. Benzene has been described as a clear, colorless, non-corrosive, and flammable liquid with a strong odor. 

Petroleum coke is a carbonization product of high-boiling hydrocarbon fractions obtained in petroleum processing (heavy residues). It is the general term for all special petroleum coke products such as green, calcined and needle petroleum coke. 

Polycyclic aromatic hydrocarbons are the most notorious and widely distributed carcinogens. These compounds are produced in many burning processes in nature and human life. Many chemical industrial processes, especially coke production, are also the sources of polycyclic aromatic hydrocarbons. The chemical behaviors of polycyclic aromatic hydrocarbons are relatively inert, so they are relatively stable and decompose rather slowly. Therefore the accumulation of these compounds in environment has been one of the most serious problems to human health. 

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