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