Читать книгу Synthesis Gas - James Speight G., James G. Speight - Страница 34

Coke is the residue left by the destructive distillation (thermal cracking) of crude oil residua. That formed in catalytic cracking operations is usually non-recoverable, as it is often irreversibly adsorbed on to the catalyst and is employed as fuel for the process when it is burned from the catalyst. The composition of crude oil coke varies with the source of the crude oil, but in general, large amounts of high-molecular-weight complex hydrocarbon derivatives (rich in carbon but correspondingly poor in hydrogen) make up a high proportion. The solubility of crude oil coke in carbon disulfide has been reported to be as high as 50 to 80%, but this is in fact a misnomer, since the coke is the insoluble, honeycomb material that is the end product of thermal processes.

Crude oil coke is employed for a number of purposes, but its chief use is in the manufacture of carbon electrodes for aluminum refining, which requires a high-purity carbon – low in ash and sulfur free; the volatile matter must be removed by calcining. In addition to its use as a metallurgical reducing agent, crude oil coke is employed in the manufacture of carbon brushes, silicon carbide abrasives, and structural carbon (e.g., pipes and Rashig rings), as well as calcium carbide manufacture from which acetylene is produced:

However, with the progressive increase in the amount of coke produced from the heavier (more viscous) refinery feedstocks, there is a renewed interest in the utilization of coke as a feedstock for a gasification process. This is one of the attractive options and is gaining increasing attention to convert the petcoke to value‐added products. The process offers the refiners a variety of product slates mainly via the production of synthesis gas. The products include steam, hydrogen, electricity, chemicals (such as methanol, CH₃OH, and ammonia, NH₃), and liquid fuels by way of the Fischer-Tropsch synthesis (Murthy et al., 2013).