451921 Reaction Intensification in Coal Tar Refining
Reaction intensification in coal tar refining
SHASHATY A.1, GUILLOU L.2
1. McGill University, 845 Rue Sherbrooke O, QC H3A 0G4, Montréal, Canada
2. Fives Proabd, 20C rue de Chemnitz 68100 Mulhouse, France
Processing of coal tar oils has been a way of choice for the recovery of dozens of cyclic, aromatic or polyaromatic compounds: phenol, cresols, indane, coumarone, pyridine bases, thiophenols, carbazole,  The associated coal tar distillation industry has been the flag ship for the development of industrial chemistry up to the 50s. If this industrial area is nowadays considered as being mature the well established associated technology portfolio  is ready to evolve. Some opportunities offered by process intensification give access to new options for the tar refiners. Beyond the most obvious opportunities for decreasing the refinery footprints by using some smaller and less energy demanding equipments that are offered by intensified devices, the implementation of these new technologies offers new production alternatives for recovery of chemicals of interest which were given up due to uncompetitive operational costs vs. synthetic routes.
A typical example is considering the so called tar acids. This family of compounds gathers phenol and its homologue molecules (cresols and xylenols). The traditional recovery route is based on a series of reactions with strong bases and strong acids. In a first step, the oil is treated with caustic soda to recover an aqueous phenolate liquor which is then reacidified to reform an organic phenol blend. Such a process is usually either a batch process or a continuous Lurgi phenoraffin process. In the first case, due to the nature of the chemicals involved, a significant investment is required: glass lined reactors, graphite heat exchangers Serious industrial safety concerns are also raised. This leads to the definition of an economical bottom line which restraint these applications to large coal tar refineries (beyond 400 ktpy whereas most refineries are nowadays within 200-300 ktpy size range). As a matter of fact, shall the phenolate liquor be removed for some process constraints in the distillation train, they are either qualified as a waste or as a low value byproduct which shall be sold to another industry. In such a latter case, these streams are collected throughout many refineries and treated in a single central facility; thanks to economies of scale, these downstream treatment centers can afford moving to continuous processes such as phenoraffin.
The potential for the recovery of phenols and other tar acids has been investigated at laboratory scale in a microchannel reactor. The process consisted in a two steps:
- A neutralization of a carbolic oil/naphtha fraction with diluted caustic soda
- An acidification with sulfuric acid for forming back phenols for sodium phenolates.
These reactions show some distinctive features such as:
- Large exothermicity both due to the reaction and the dilution of acid or base in the media
- Extremely fast kinetics
- Undesirable formation of bright red coloring agent for uncontrolled temperature rise
- Polyphasic systems
The use of microchannel reactor has been found to be a good alternative to the traditional processing routes. High control of the exothermy has been achieved and phenol recovery has allowed achieving satisfactory yields with decreased water consumption. This technology opens a route for compact reactor systems perfectly compliant with continuous operation in refineries even for small capacities. This new generation of compact reactors opens opportunities for renewal of coal tar refining business model, assisting refiners into a move toward higher value chemicals whatever the size of the distillation train might be.
 Franck H.-G., National meeting of American Chemical Society, 13 Jan. 1963, Vol 7:1 Conference 143.
 Franck H.-G., Stadelhofer J.W., in Industrial aromatic chemistry, 1988, Springer-Verlag, Berlin-Heidelberg-N.-Y.
Keywords: reaction intensification, compact reactor, coal tar.