William Kovarik
Radford University
and
Matthew E. Hermes
Kennesaw State University

Fuels and Society C: 6. Fuel Refinery Chemistry

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The purpose of this reforming process is to achieve high yields and high rates of production of aromatic hydrocarbons (BTX) since these materials have excellent anti-knock properties as components in motor fuels.   Petrochemical plants such as refineries cost hundreds of millions of dollars to build. The producers must gain a return on this investment on the sale of their products. A more efficient plant costs less in $/gallon of fuel than one with poor efficiency.

As TEL was removed from fuels, more and more of the BTX was needed. So if refiners could get more from the same plant, they could delay or eliminate the construction of costly, new facilities.

Reforming is perhaps the most important use of industrial catalysts. In the reforming process, at 770 degrees Kelvin and 10-35atm. pressure, catalsyts carry out two separate and distinct roles in reforming:

a. Dehydrogenation catalysis to break C-H bonds

b. Acid catalysis to break C-C bonds

Refiners need to rapidly break C-C bonds to reduce the chain lengths of the less volatile, higher molecular weight hydrocarbons to get them to the chain length for gasolines. (We gave thermodynamic reasons for this transformation in an earlier unit on fuels.) Then they need to cyclize these and dehydrogenate them to BTX components.

The catalysts consist of metals like platinum dispersed on finely sivided silica or alumina. Silica and alumina act as acids and speed the processes of bond breaking.

Simultaneously, the substances associate with the platinum metal and at the high temperatures of reaction, the entropy increase by the loss of gaseous hydrogen drives the reaction forward at a high rate in the presence of the catalyst to give dehdrogenated and cyclized BTX.

He found that the C-H bond breaking to form dehydrogenated components was much faster than the hydrogenolysis to break C-C bonds. This meant that in the presence of the two catalysts, much of the higher molecular weight material would be dehdrogenated before it was low enough molecular weight to be converted to BTX. The material would never be suitable for the gasoline fraction.

Dr. Sinfelt's studies of rates of reaction led to investigation of bimetallic catalysts - catalysts with two metals imbedded in the silica support. What he found in these fundamental studies was that the presence iof iridium metal, along with the platinum, gave an unexpected boost to the rate of hydrogenolysis. By speeding up the rate of C-C bond breaking, the amount of BTX components that could be produced in reforming was greatly increased.

Just by changing the catalyst, existing refineries would run much more efficiently.

In 1998 Dr. Sinfelt said of his work, "I started looking at the kinetics and I knew I could save a staggering amount of money by understanding the science of the reforming process."