(328a) 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, [1]… The associated coal tar
distillation industry has been the flag ship for the development of industrial
chemistry up to the 50’s. If this industrial area is nowadays considered as
being mature the well established associated technology portfolio [2] 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.

[1]
Franck H.-G., National meeting of American Chemical Society, 13 Jan. 1963, Vol
7:1 Conference 143.

[2]
Franck H.-G., Stadelhofer J.W., in “Industrial aromatic chemistry”, 1988,
Springer-Verlag, Berlin-Heidelberg-N.-Y.

Keywords: reaction intensification,
compact reactor, coal tar.