Hydrocarbon Processing - December 2022 - 41

Process
Optimization
P. LE GRANGE, K. TEKEBAYEV, F. LEBLANC
and M. SHEILAN, Amine Experts International,
Amsterdam, the Netherlands, and Calgary, Alberta,
Canada; and M. ADOLFSSON, D. YARNOLD and
G. THEVENET, Preemraff Lysekil, Goteborg, Sweden
The other sulfides: Organic sulfur species
in amine solvents
This article examines the behavior of
carbonyl sulfide (COS), C1
tans (R1
-C5
mercapSH-R5SH),
methyl ethyl sulfide
(MES), dimethyl sulfide (DMS) and
dimethyl disulfide (DMDS) in amine
solvent systems. The objective here is to
explore the current state of open industry
knowledge in this area and compare it to
gathered field test data. This article will
highlight what is and what is not known
and is a good starting point for future
study on this topic, as not much field
data has been previously published. The
article contains:
1. A review of the chemistry
of organic sulfur species
in amine systems
2. Trending and analysis of key
operating parameters for data
from 50 industrial amine
solvent absorbers
3. A study of the organic sulfur
challenge at a European refinery.
Optimizing the removal of organic sulfur
species can eliminate the need for, or
reduce the size of, downstream gas conditioning
units in new facilities. In existing
systems, this offers the advantage of
extending cycle times on molecular sieves
and reducing the consumption of caustic
and the volume of mercaptide and disulfide
waste streams requiring disposal.
Note: The removal of sulfide species
from liquefied petroleum gases (LPG)
through liquid-liquid extraction is not covered
here. Carbon disulfide (CS2
) is also
not included in this study, as its presence in
gas streams is thought to be mostly limited
to tail gas treating units (TGTUs). The
authors' company has extensive field data
for LPG treaters and CS2
data will be the subject of future work.
Background. The non-hydrogen sulfide
(H2
S) sulfide species COS, C1
mercaptans (R1
SH-R5SH), methyl ethyl
sulfide (MES), dimethyl sulfide (DMS)
and dimethyl disulfide (DMDS) are frequently
present in hydrocarbon streams
in the oil, natural gas and biogas industries
and are commonly called 'organic
sulfur.' The behavior of organic sulfur species
in amine systems is generally poorly
predicted but can have a major impact on
plant operations. This has been highlighted
during work on two recent projects.
The first, an ultra-sour natural gas plant
in the Middle East, contained ~1,000
ppmv of non-H2
S sulfide in its feed. Units
were built downstream of the amine absorber
to remove the organic sulfur from
the gas product. When the authors' company
commissioned and performed guarantee
testing on the plant, it became apparent
that the amine system was almost
entirely removing the organic sulfur species
from the gas. This effectively rendered
the downstream mol sieve organic sulfur
removal units unnecessary at start-of-run
(SOR) operating conditions. Details on
this project are provided by Schulte, et al.1
The second project was a European
refinery, Preemraff Lysekil, where compliance
with strict internal and governmental
environmental standards on stack
sulfur dioxide (SO2
) emissions was limit-C5
removal,
and this
ing throughput. The refinery initiated an
analytical testing program to determine
the primary sources of the SO2
emissions.
This was traced back to the treated gas
from a specific amine absorber (one of
the 12 onsite). Specifically, the visbreaker
LPG fraction (which contains significant
mercaptan sulfur) was being added into
the feed to this absorber-when burned,
this fuel gas accounted for a large portion
of the refinery sulfur emissions. Similar
emissions resulting from mercaptans have
subsequently been found at four other refineries
in Europe and three in the U.S.,
all of which also vaporize a large portion
of the visbreaker/coker LPG fraction into
their refinery fuel gas.
Both projects experienced a significant
economic impact because the behavior of
organic sulfur species in amine systems
is not well-developed in industry. This
article will present the information available
to the industry and from the authors'
company, and highlight areas where work
is needed to improve understanding.
The theory of organic sulfur species
removal with alkanolamine solvents.
In an amine absorber tower, the
gas being treated is contacted countercurrently
with an amine solvent. These
solvents are alkaline in nature and remove
target species-which are acidic in aqueous
solutions-such as H2
dioxide (CO2
S and carbon
) by chemical absorption.
Non-dissociating species (e.g., hydrogen,
nitrogen, methane) can also be partially
absorbed in the amine solution through
Hydrocarbon Processing | DECEMBER 2022 41
Hydrocarbon Processing - December 2022

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