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Guidelines For BTX Distillation Revamps
Karl KolmetzGTC Technology
Singapore
Joseph C. GentryGTC Technology
Guidelines For BTX Distillation Revamps
GTC TechnologyHouston
Jeff N GrayKLM Technology Group
Malaysia
1. Introduction – Page 4
2. Processing Schemes – Page 8
3. Critical Success Factors – Page 21
Guidelines For BTX Distillation Revamps
4. Solvent Selection – Page 23
5. Equipment Design - Page 29
6. Equipment Inspection – Page 38
7. Conclusions – Page 53
There are many reasons to revamp aprocess unit. These include;
1. Increased purities,
2. Increased recoveries,
Introduction
2. Increased recoveries,
3. Decreased environmental impacts
4. And increased capacity.
The best revamps will include each of thelisted items.
Steps of A Revamp – Papers by Karl Kolmetz
• The High Load Test (AIChE 2005)
• Process Simulation (Thailand PROII UsersConference 2005)
Introduction
• Rate the Existing Equipment
• Equipment Design (AIChE 2002)
• Equipment Inspection (AIChE 2007)
• Tower Commissioning
With the current environmental mandatesto reduce the benzene in the gasoline pool,the production of benzene for use in otherproducts is increasing.
In the United States the benzene in the
Introduction
In the United States the benzene in thegasoline pool is regulated to very lowlevels, whereas in other parts of the worldthe standard is 1.0 weight percent.
As this world standard is lowered thisbenzene will need to be purified fordownstream reprocessing.
Currently many of the benzeneseparation units are utilizingliquid-liquid extraction which canbe revamped to extractive
Introduction
be revamped to extractivedistillation for all of the previousmentioned goals of a revamp.
Benzene, Toluene and Xylenes (BTX)contained in the olefin plant pyrolysisgasoline, refinery catalytic reformerproducts, or other hydrocarbons streamscannot be used directly in the downstreamprocesses due to the impurities in the raw
Processing Schemes
processes due to the impurities in the rawreactor products.
Solvent-based extractive techniques whichutilize the polar nature of benzene and itspreferential solubility in polar solvents arerequired to separate the aromatics from thenon-polar non-aromatics.
Since heavier aromatics such astoluene and xylenes are co-producedwith the benzene-containing streams, itis sensible to purify the heavieraromatics along with benzene.
Processing Schemes
aromatics along with benzene.
There are two main processes than areused for this purpose: liquid-liquidextraction and extractive distillation.
Liquid-liquid extraction processes,although reliable and prevalent in theindustry for a long period of time, havenot been able to offer improvementsthat make them competitive against the
Processing Schemes
that make them competitive against thecurrent extractive distillation process.
The configurations for the twoprocesses are compared next.
Processing Schemes
Raffinate
ExtractExtract
Raffinate
H2O
Liquid-liquid Extraction Extractive Distillation
Extract
Solvent
Feed
Feed
Solvent
In the liquid-liquid extraction systems, thesolvent makes an incomplete separation ofthe components at both ends of theextraction column, thus requiring theadditional steps of extractive stripping andwater washing of the raffinate.
Processing Schemes
water washing of the raffinate.
A particular problem for liquid-liquid systemsis methyl-cyclopentane which has a polarmoment.
MCP can component trap in the bottom of theextractor and recycle back from the flashdrum and stripper column.
Extractive distillation, which is the use of asolvent in distillation to enhance theseparation efficiency, is recognized as auseful means to separate close-boilingmixtures.
Processing Schemes
Extractive distillation is a vapor-liquidprocess unit operation.
The extractive solvent creates or enhancesthe relative volatility difference between thecomponents to be separated.
In BTX extractive distillation, the polararomatics and the polar solvent combine tofrom a heavy boiling species.
Processing Schemes
The extractive solvent and the now lowervolatile component flow to the bottom of thedistillation column as a liquid.
The liquid is the recovered by a subsequentdownstream vacuum distillation, where thevacuum separates the polar compounds.
Processing Schemes
The non-extracted non-polar species aredistilled as a vapor to the top of theextractive distillation tower.
In the extractive distillation system, theextractive distillation column cleanlyremoves the non-aromatics from thearomatics; and the aromatics and solventfrom the raffinate in a single columnoperation.
Processing Schemes
operation.
Therefore, the extractive distillation designrequire fewer pieces of equipment and amuch lower capital cost than a liquid-liquidsystem or other extractive distillationsystems that require washing of products, orreprocessing of the raffinate.
Processing Schemes
Revamp of Glycol Extraction Units
Feed
Raffinate
Hybrid Design for Incremental Feed
H2O
Ra
ffin
ate
Wa
ter
Wa
sh
Ex
tra
cto
r
AromaticsExtract
Raffinate #1
Raffinate #2
So
lve
nt
Re
co
ve
ryExtractorReflux
Rich Solvent
Ex
tra
cti
ve
Dis
till
ati
on
Co
lum
n
Techtiv-100 Solvent System
Ex
tra
cti
ve
Str
ipp
er
Steam
HydrocarbonFeed
IncrementalFeed
So
lve
nt
Re
co
ve
ryC
olu
mn
Hybrid Design to Double Unit Capacity
Techtiv-100 Solvent
AromaticsExtract
Non-aromaticsRaffinate
Ra
ffin
ate
Wa
ter
Wa
sh
H2O
Ra
ffin
ate
Ex
tra
cto
r
HydrocarbonFeed
ExtractorReflux
Extract
Steam
OldExtractiveStripper
Steam
Ra
ffin
ate
Ex
tra
cto
r
So
lve
nt
Re
co
ve
ryC
olu
mn
So
lve
nt
Re
co
ve
ryC
olu
mn
Ex
tra
cti
ve
Dis
till
ati
on
Co
lum
n
In each type of revamp there aresome critical success factors.
Some are consistence fromrevamp to revamp – others are
Critical Success Factors
revamp to revamp – others arerevamp specific.
For BTX Revamps there arethree critical success factors.
1. Solvent Selection
Critical Success Factors
2. Equipment Design
3. Equipment Inspection
Traditionally, unit operators have reliedon liquid-liquid extraction technologiesfor aromatics recovery.
This is because the older generationsof extractive distillation solvent could
Solvent Selection
of extractive distillation solvent couldnot produce acceptable performance ofproduct recovery and purity acrossmultiple carbon numbers.
The first generation of solvents wasglycol based and was utilized in liquid-liquid extraction.
The second generation of solventswere sulfur and nitrogen based andcommissioned in extractive distillationwith limited success.
The second generations of extractive
Solvent Selection
The second generations of extractivedistillation solvents was not selectiveenough to cleanly separate more thanone aromatic species at a time, andwere plagued by ineffectiveperformance due to 3-phase distillationfoaming issues.
Some of the second generationprocesses used nitrogen basedsolvents which are poisons in manydownstream benzene consuming units.
Some nitrogen based solvents are an
Solvent Selection
Some nitrogen based solvents are anenvironmental and safety hazard asthey easily hydrolyze with water totoxic compounds – i.e. morpholinewhich is toxic to humans in ppm levels
These concerns are no longer an issue withthe third generation of blended solvents,which are commercially used to recover BTXat higher efficiencies, with no productcontamination or toxic hazards because nonnitrogen based solvents are compatible with
Solvent Selection
nitrogen based solvents are compatible withwater.
The selectivity of the third generation ofblended solvents has a large advantage overthe first and second generation of solvents.
The third generation blended solvent is40% more selective than the firstgeneration solvents and 20% moreselective than the second generation of
Solvent Selection
selective than the second generation ofsolvents and is foaming resistant.
Solvent S/FRelative volatility (α)
n-C7/benzene
Techtiv-100 (GT-BTX®) 3.0 2.44
Comparison of Different Solvent Systemsfor Aromatics Recovery
Techtiv-100 (GT-BTX®) 3.0 2.44
Sulfolane 3.0 2.00
N-methyl pyrrolidone 3.0 1.95
N-formyl morpholine 3.0 1.89Tri-ethylene glycol 3.0 1.44
Tetra-ethylene glycol 3.0 1.39
Glycol blends (CAROM) 3.0 1.35
No solvent 0 0.57
It is important to review each design toconform to distillation fundamentals.
Even though a design has been successfulin the past, a review of each new
Equipment Design
in the past, a review of each newapplication needs to be completed.
Some small deviation could restrict thecolumn from obtaining design goals