Hydrodealkylation processes

Abstract

Carburization and metal-dusting while hydrodealkylating a hydrodealkylatable hydrocarbon are reduced even in the substantial absence of added sulfur.

Description

BACKGROUND OF THE INVENTIONThe present invention rotates to an improved technique for the hydrodealkylation of a hydrodealkylatable hydrocarbon, particularly under conditions of low sulfur, which minimizes carburization thus preventing premature plant shut-downs.The hydrodealkylation of hydrodealkylatable hydrocarbons such as alkyl aromatics has been practiced for many years. The principal processes involve the conversion of toluene and like alkyl-substituted benzenes to benzene and various byproducts. Such processes are either catalytic or non-catalytic in nature. The catalytic processes employ one or more catalysis that promote the conversion of the alkyl aromatic compounds to benzene and the remaining alkyl. The non-catalytic processes typically employ heat and pressure to promote the conversion of the alkyl aromatic compounds to benzene and the remaining alkyl.Some conventional catalytic hydrodealkylation processes employ Group VIII metals such as Rh and Pt supported on an alumi...

AI Technical Summary

Benefits of technology

Additionally, it has been found that certain preferred coatings are sulfur-tolerant, for example, the tin-based protective layers can tolerate up to 200 ppm sulfur. The protective layers eliminate the need to presulfide the metallurgy, reduce sulfide corrosion and improve product values and waste disposal due to induced levels of sulfur. Chromium-, Sb- and Ge-based protective layers can tolerate even higher sulfur levels, up to 5 or more wt. %. Most preferably, the layers can tolerate the respective amounts of sulfur for a period of at least 200, preferably at least 400, and most preferably 600 hours without degrading to an extent that carburization will occur, resulting in shut-down of the system due to excessive coking.

Problems solved by technology

Somehow, the sulfur interferes with the carburization reaction.

But with low sulfur systems or with sulfur outages, this inherent protection no longer exists especially when the system is exposed to high temperatures such as in thermal hydrodealkylation.

The problems associated with carburization include coking, carburization of system metallurgy, and metal dusting.

The excessive "metal-dusting" adds active metal particulates to the system, which particulates provide additional sites for coke formation in the system.

Coking is generally not a problem which must be addressed in hydrodealkylation processes, but this significant source of calm formation due to the absence of sulfur in reactor feedstreams excessively aggravates the problem.

As a result, a premature coke-plugging of the reactor system occurs which can lead to a premature shut-down of the system.

However, the addition of sulfur increases production cost and process complexity.

Moreover, at high temperatures coking and carburization will still occur even when sulfur is added to the feed.

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