In a refinery, crude oil is first distilled, which separates it into light, medium and heavy fractions. After that, refiners start performing chemical reactions to change the oil’s molecules from their natural form into those needed in modern fuels. But the catalysts used in that process aren’t only expensive, they essentially end up as hazardous waste at the end of their productive life. That helps to explain why there’s been a lot of interest in catalyst recycling, which advocates see as a way for refiners to improve both their profitability and their environmental performance. In today’s RBN blog, we continue our look into catalyst recycling — the technology, economics and trade-offs — and detail some of the pushback against it.
As we noted in Part 1, catalysts are materials that accelerate chemical reactions during the refining process. This includes catalytic cracking, which “cracks” heavier molecules into lighter gasoline molecules, thereby increasing the volume of gasoline produced from a barrel of crude, and catalytic hydrogenation, which removes sulfur atoms embedded in the molecules, reducing air pollution from vehicle exhaust.
These reactions do not occur at measurable rates except in the presence of a catalyst. Catalysts consist of highly porous solid-base materials like alumina and silica, onto which expensive metals like cerium, cobalt, lanthanum, molybdenum, nickel, palladium, platinum, rhenium and tungsten have been carefully dispersed. Hydrogenation catalysts (see Figure 1 below) come as small particles in cylindrical, penne-pasta-like shapes while cracking catalysts are much finer solids. Their porosity, physical properties and the distribution of metals on them are carefully engineered for the specific reactions necessary to convert oil molecules from their natural state into the specific forms needed for 21st century fuels.
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