Fuels Technical Information

Catalyst fines are small particles of spent catalyst that remain in the by products from the catalytic cracking process in the refinery. If not reduced by suitable fuel treatment the abrasive nature of these fines causes increased wear in the engine. The areas usually affected are fuel pumps, injectors, piston rings and liners.

The purpose of the catalytic cracker in refinery processing is to increase the quantity of gasoline from the crude processed. Fluid bed catalytic cracking (FCC) was pioneered in the early 1940s and today there are numerous grades and manufacturers of catalyst.

The commonality of all these grades is that they all contain aluminium silicate, but are complex crystalline particles bound in a framework of interconnected voids.

In a catalytic cracker the particles of catalyst are in constant motion at relatively high velocities and they collide with each other and the containment vessels. As a result of these collisions, break-up of the catalyst particles leads to the production of smaller catalyst fines.

The catalyst is expensive and refiners have various systems to minimise catalyst loss, which although usually extremely effective are not 100% efficient. Some of the catalyst in the form of catalyst fines remains in the cycle oil streams which are a by product of the catalytic cracker.

These streams form a useful component in the blending of residual fuel because their high aromaticity increases the available solvency of a fuel and reduces the likelihood of incompatibility problems.

Catalyst fines are variable in size, with a range from sub micronic to approximately 30 microns and occasionally larger. Whilst catalyst fines are frequently considered as spherical particles this is not necessarily the case.

Because of the interconnecting voids of the catalyst one gram can have a surface area of several hundred square meters. Catalyst fines are hard and hence can cause abrasive wear. The hardness of a particular catalyst is not directly related to the relative hardness of either aluminium or silicon.