Hydrocarbon Processing - January 2022 - 68

Bio-Based Processing
mate salts. Formates have been shown to
be corrosive to carbon steel in liquid and
vapor states. Formamides do not appear
to be corrosive, but they do increase viscosity
and reduce amine available for acid
gas removal.13
Field test results from several facilities
coprocessing biofeed in their DHT
showed an increase in CO in the hydrogen
gas being amine treated from zero
to the order of 1,500 ppmv-4,500 ppmv,
with one facility showing a CO content
of more than 10,000 ppmv. Therefore,
the partial pressure of CO in the amine
unit will normally be less than 100 kPa
with current coprocessing levels. Based
on observations in synthesis gas-treating
amine systems, significant formate formation
from CO does not normally occur at
partial pressures less than 400 kPa.
Current biodiesel feedstocks contain
large quantities of long-chain fatty acids.
In their unprocessed form, these will have
a major negative impact on the surface
tension and viscosity of an amine solvent.
In turn, this may cause the amine solvent
to foam (or emulsify in the case of LPG
treating). Conventional silicon and polyglycol
anti-foams have had some success
in mitigation of this foam.
The FCCU biofeedstock coprocessFIG.
4. Examples of corrosion caused by
excessive CO2
in various locations of
an amine unit.
ing route appears especially vulnerable
to foaming and emulsification problems.
The authors are aware of five refineries
coprocessing biofeedstock in their
FCCUs, four of which experienced significant
LPG emulsion issues as a result.
Unlike the other two routes where hydrotreating
is employed, there are many
potential breakdown products that can
be formed from catalytically cracking
biofeedstocks. A summary of these is
presented in TABLE 3. Tests on extracted
phases of sour FCCU LPG have also indicated
that high-oxygen content polymers
may be present in the LPG.
Dealing with the emulsified FCCU
LPG is a challenge, and conventional
TABLE 3. Fatty acids known to be present in vegetable oils, and their FCCU breakdown
products
Fatty acids in vegetable oil
Lauric, myristic, palmitic, palmitoleic,
stearic, oleic, linoleic, linolenic, erucic,
hexadecenoic, arachidic, eicosenoic,
belienic, docosadienoic and lignoceric
FCCU breakdown products
(fatty acids and triglycerides)
Methanol, ethanol, propanol, butanol, formic acid,
acetic acid, propionic acid, butanoic acid, acetone,
formaldehyde, acetaldehyde, acrylaldehyde, ethers,
cyclic species, cresols, phenols, substituted morpholines
and indoles
Note: A significant amount of the information in this table was provided by MPR Services
techniques (anti-foams and carbon beds)
do not appear to be adequate. Tailored
demulsifiers injected into the sour LPG
feeding the column have shown some
success at reducing the emulsification;
however, this treats the symptoms rather
than removing the cause. Some success
has also been achieved using proprietary
absorbents on the LPG and the
amine sides. In practice, a combination
of absorbents and demulsifiers on the
FCCU LPG treater seems to be required
to achieve FCCU biofeed coprocessing
blends of more than a few percent.
Impacts on sour water stripping.
Refinery biodiesel production often results
in a significant increase in sour water
volume as a result of the deoxygenation
of biofeed with hydrogen and the water
emulsified with the biofeedstock. The
extra water may require debottlenecking
of the sour water system or the installation
of additional stripping capacity. The
optimal strategy for debottlenecking is
plant-specific and dependent on the preexisting
system. A holistic approach to
the review of the complete refinery water
system may reveal an opportunity to substantially
reduce the use of fresh water.
A good process water strategy can have
the following additional benefits:
* Reduced phenols in refinery
effluent water
* Reduced fractionator overhead
corrosion or less corrosion
inhibitor use
* Reduced sodium in residue
feeds, which may enable longer
thermal cracker unit runs
* Reduced desalter emulsion issues
FIG. 5. A conventional SWS design (left) compared to the Lieberman low-CAPEX SWS design (right).
68 JANUARY 2022 | HydrocarbonProcessing.com

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Hydrocarbon Processing - January 2022

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