Technical Manual - Section 3 (Safety Hazards)

Table III:2-8 SOLVENT DEWAXING PROCESS
Feedstocks From Process Typical products................To
Lube basestock Vacuum tower Treating Dewaxed lubes or wax....... Hydrotreating
Spent agents....................... Treatment or recycle
SOLVENT DEWAXING
Solvent dewaxing is used to remove wax from either distillate
or residual basestocks at any stage in the refining process.
There are several processes in use for solvent dewaxing, but
all have the same general steps, which are: (1) mixing the
feedstock with a solvent, (2) precipitating the wax from the
mixture by chilling, and (3) recovering the solvent from the
wax and dewaxed oil for recycling by distillation and steam
stripping. Usually two solvents are used: toluene, which
dissolves the oil and maintains fluidity at low temperatures,
and methyl ethyl ketone (MEK), which dissolves little wax at
low temperatures and acts as a wax precipitating agent. Other
solvents that are sometimes used include benzene, methyl
isobutyl ketone, propane, petroleum naphtha, ethylene
dichloride, methylene chloride, and
sulfur dioxide. In addition, there is a catalytic process used
as an alternate to solvent dewaxing.
HEALTH AND SAFETY CONSIDERATIONS
Fire Prevention and Protection
Solvent treatment is essentially a closed process and,
although operating pressures are relatively low, the potential
exists for fire from a leak or spill contacting a source of
ignition such as the drier or extraction heater. In solvent
dewaxing, disruption of the vacuum will create a potential
fire hazard by allowing air to enter the unit.
Health
Because solvent extraction is a closed process, exposures are
expected to be minimal under normal operating conditions.
However, there is a potential for
exposure to extraction solvents
such as phenol, furfural, glycols,
methyl ethyl ketone, amines, and
other process chemicals. Safe work
practices and/or the use of
appropriate personal protective
equipment may be needed for
exposures to chemicals and other
hazards such as noise and heat, and
during repair, inspection,
maintenance, and turnaround
activities.
III:2-22