Steam cracker tar

Aromatic Pitch Production Using Steam-Cracker Tar... 

Steam cracker tar (SCT) is a by-product from the steam cracking of naphtha or gas oils to produce ethylene. The characteristics and yield of SCT is dependent on the feed characteristics, the plant design and severity of cracking,... 

Table I. Physical and Chemical Characteristics of Steam Cracker Tars from Naphtha and Gas Oil Cracking...

Coke formation will always be a potential problem in any high temperature process involving hydrocarbons. Coke and tars formed during reaction can deposit on reactor surfaces or in quench heat exchangers, and several effects have been observed in a steam cracker tube (4, 9 ). As the reaction proceeds the tube will accumulate coke towards the reactor exit, while the inlet zone remains relatively coke free, as a result of the induction time associated with the formation of tars and coke (J ). Gas phase reactants may adsorb and react on this bare metal, and the components of the gas phase in the reactor should and do reflect this interaction (4, 9, JO). Since carbon formation depends on the nature of the gas phase species, these interactions should also influence coke formation towards the exit of the ractor. Again, this is found to be the case (4, 9 - 11). 

Steam crackers for the production of ethylene are the primary source of CPD and DCPD, although a small amoimt is still recovered from coal tar distillation. The amoimt of CPD produced depends on the feedstock to the cracker. The yield from a naphtha cracker is 6-8 times of that from a gas cracker, which uses ethane and propane feed mixtin-e. 

Furnace carbon black is produced from the incomplete combustion of what is called carbon black oil feedstock, which consists of heavy aromatic residue oils. In the United States this oil is commonly the bottoms from catalytic cracker units. They are commonly referred to as cat cracker bottoms and contain relatively low hydrogen content (and conversely high carbon content). In Europe and other locations, the carbon black oil used is commonly a byproduct of high-temperature steam cracking of such products as naphtha, gas condensate, and gas oil to produce ethylene, propylene, and other olefins. Here, no catalysts are used in the cracking process. These types of carbon black oils are mainly unsaturated hydrocarbons. A third source of carbon black feedstock is coal tar, which is commonly used in China to manufacture carbon black. 

Feedstocks are usually either cat cracker bottoms from a petroleum cracking unit or tars from steam cracking for polyethylene production. Coal tars are commonly used as feedstocks to produce carbon black in China. 

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