Molecular Sieve Mercaptans Removal from LPG

Complied by SORBEAD INDIA Technical Department

www.sorbeadindia.comwww.sorbeadindia.com

What is LPG ?What is LPG ? Liquefied Petroleum Gas.

Its Colorless & Odorless.

Its compositions of Methane, Propane 60% ,Ethane & butanes 40%.

Propane & butane % ages changes according to seasons, Winters –More propane & in summer more butanes.

Small concentration of propylene & butylenes in small conc.

Powerful odorant Ethane thiols CH3CH2SH are added for leak test.

At normal temperatures and pressures, LPG will evaporate.

Its is low emitting carbon fuel- Only 19% CO2 per Kwh than oils.

Its having Calorific value of 26.1 kWh/m³ than natural Gas methane10.6 kWh/m³.

Its also called as C3-C4 Hydrocarbon. LPG replaces Chlorofluorocarbons as Aerosol propellants.


LPG CompositionsLPG Compositions Its consist of Methane , butane , propane ,ethane.

Acid components' like CO2 ,H2S ,COS & H2O.

RSH- Mercaptans.

Methyl Mercaptans CH3SH.

Ethyl Mercaptans C2H5SH.

Propyl Mercaptans C3H7SH.

Butyl Mercaptans C4H9SH.

Longer Chain 6 Ring Mercaptans.

Tertiary Butyl Mercapatans Blends are added in LPG which is presentat a concentration of approximately 0.9-1.3 pound/million standard cubicfeet of gas .

-SH group which are low molecular weight gives Bad odor.


<-Methyl Mercaptans

<-Tert Butyl Mercaptans

<-Propyl Mercaptans

Specification of LPG.Specification of LPG.


AerosolsAerosols Aerosols are very fine particles of liquid or solid

substances suspended in air. Fog, for example, isa normal aerosol.

The aerosol package is a self-containeddispensing system with three main elements:

a. Active Ingredients (soap or disinfectant, etc.)

b. Inert or Inactive ingredients (water)

c. Propellant.

The propellant is a gaseous compound whichpushes the product out of the container andproduces a spray or foam. In most cases, thepropellant also acts as a solvent to keep theproduct at the proper strength.

Aerosols operates at 30-50 psig & does have90% propellant.


MercaptanMercaptan removalremoval

Deaciding – By virtue of solvents Alkanol amines & Diethanol amines,where CO2,H2S can be removed to Max 2%.

Ammonia treatment- Reaction of Gas feed with Olefins likephosphoric acid, boric acid & sulfuric acid, where Mercaptans getsconvert to Sulfides & later discharge the effluent as Gas phase & Liquidphase.

Adsorption Molecular Sieves & Spherical active Alu-Silica Geltechnique, in which all Typical Mercaptans are selectively trapped onBed.

Cracking Reaction Technique in which there is sulfur absorption atelevated temperatures where all disulfides & CO2 are removed.


1

The vapor is absorbed in Gelsurfaces and changes with the

water.

The absorption to be advanced, 695kilogram calories/kg The adsorption heat

occurs.

The vapor moves toward a low-endterritory from the territory where the

humidity is high and is absorbed

Activated Alumina Gel or MolecularSieves with respect to vapor hasgot wide surface area

DESICCANT BEAD

AIR FLOWHigh H2O

Low H2O

AIR FLOW

Vapor

AIR FLOWHigh

H2O,CO2,H2S

LowMercaptans

AIR FLOW

AIR FLOWReaching to Gel when saturated states until,to be continued, when absorbs the vapor ofabove that, shifts Desiccants must go for

regeneration.

2

3

4

5

6

Adsorption ProcessAdsorption Process

The vapor elements contact andDesiccants surfaces and they come to beabsorbed.


Surface Loading

Vapor

Loading According to MechanismLoading According to Mechanism

Capillary Condensation

Vapor

COPYRIGHT 2006 © AIR LINEALL RIGHTS RESERVEDComplied by SORBEAD INDIA Technical Department

Loading According to MechanismLoading According to Mechanism

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 30 40 50 60 70 80 90 100

Relative Humidity, wt%

Wa

ter

Ca

pa

cit

y,

wt%

Capillary Loading

SurfaceLoading


Adsorbent Gel DataAdsorbent Gel Data

ParametersParametersAluminaAlumina

GelGelSilica GelSilica Gel

MolecularMolecularSievesSieves

ActivatedActivatedAluminaAlumina

Size mmSize mm 2 ~ 6.4 2 ~ 5 1.5 ~ 5 2-6

Al2O3 / SiO2Al2O3 / SiO2 97 / 3 % 0.3 / 99 % - 93%/ 0.30

Surface AreaSurface Area 360 m2/g 750 m2/g 480 415

Total PoreTotal PoreVolumeVolume

0.5 cc/g 0.37 cc/g 0.4 cc/g 0.42 cc/g

Bulk DensityBulk Density 770 g/l 750 g/l 700 g/l 890-930 g/l

Crush StrengthCrush Strength 25 ~ 32 kg - 18-20 kg 29-35 kg

RegenerationRegenerationTemp.Temp.

175 ~250 ℃

150 ~ 180 ℃ 200 ~ 320 ℃ 180-220℃

Attrition LossAttrition Loss < 0.5% <0.3% <0.4% <0.8%

Not Crack inNot Crack inBoiled WaterBoiled Water

Yes No Partly No


0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 40 50 60 65 70 75 80 85 90 95 100

Relative Humidity, wt%

Wa

ter

Ca

pa

cit

y,

wt%

0

5

10

15

20

25

30

35

40

45

Alumina

MolecularSieves

Silica

Comparison of Relative Humidity Effect on Various DesiccantComparison of Relative Humidity Effect on Various Desiccant

COPYRIGHT 2006 © AIR LINEALL RIGHTS RESERVEDComplied by Sorbead India Technical Department

Adsorption MethodAdsorption Method Bed is prepared with Active Molecular

Sieves or Alu-Gel spherical beads &then LPG flow is initiated top todown.

Adsorption capacity is directly relatedto Molecular weight & Boiling point ofthe gas. Which means H2O & highMW components are more stronglyhold on bed than lighter components.

C5-C6 is near to discharge side of bed,if more feed is applied than C5 willescape followed by C6.

H2O is getting removed at entranceonly.

Mercapatans are held up morestrongly than C6.


Regeneration of AdsorbentsRegeneration of Adsorbents

Once saturated the bed isthermally regenerated bypassing hot steam of feed gasthrough bed, followed bycooling & cycle repeats.

Thermal swing is adopted inwhich vapor phases out as waterfrom wet natural gas.

3 bed techniques are mostfavored 1-Alu gel & 2 MolecularSieves, 8 Hours time is goodenough for regeneration ofadsorbents.


Molecular SievesMolecular Sieves Molecular sieves are transition metal alumino silicates with a uniform pore

crystalline structure.

Molecular sieves operate on the size exclusion principle. Smaller molecules thatfit into the pores are adsorbed while larger molecules pass through.

Molecular sieves have regular pore openings of 3, 4, 5, or 10 Angstroms.

Polarity of the molecules matter because the highly polarized molecules areadsorbed more readily into the pores than non-polar molecules. Molecules areselectively removed in this manner.

Mercaptans are removed to tune of 7-8% by Special treated Macro porousMolecular Sieves from LPG.

Pellets does have better surface area as compared to beads.

Pellets high surface area but more dust & Beads less dust less brakages.


AluAlu--Gel Spherical BeadsGel Spherical Beads The Spherical Silica Alu gel does have more water tolerant properties,

it is also called at Water resistant adsorbents.

Highest affinity towards water molecule with capacity of 40-45% of itsown weight.

It does adsorbs some ammonia & carbon dioxide molecules.

Its having high mechanical strength& assures resistant to channeling's.

Highly Water resistant & tolerant.


Adsorption TechniquesAdsorption Techniques The adsorption technique is used to purify process & separate

components.

Mercaptans are non soluble in water but they do mix with CO2 & H2S.

CO2 & H2O removal is critical if mercaptans needed to be trapped overbed, because CO2 adsorption capacity is lower than water with respectto Molecular Sieves.

Removal of H2S is must before hydrocarbon is released out.

Natural gas always contain CO2 & there will be always some reactionsof H2S prior to HC recovery.

CO2 +H2S -> COS +H2O…Here COS always goes with recoveredpropane & H2S fractionates with Ethane.

Sometimes Methane is present in HC , which fractionates & thusconcentrates with propane.

Molecular Sieves 4A for such applications are best suited.

The VariousThe Various MercaptansMercaptans does have pore diameter between 12does have pore diameter between 12--15A for15A forwhich special grade of 13X is prepared for best adsorption.which special grade of 13X is prepared for best adsorption.


Molecular Sieve Ageing ?Molecular Sieve Ageing ?The aging of molecular sieves leads to loss of adsorption capacityand deterioration of mechanical properties

Causes of Aging :Causes of Aging :

– Insoluble water– Liquid entrainment (hydrocarbon, water)– High water partial pressure at high temperature (above 150°C)– Amine carryover– CO2 , Carbonic acid formation– H2CO3 + (Na+, Ca++, K+) Na2CO3 - NaHCO3 - Ca CO3 –K2CO3– Decomposition of mercaptans during regeneration– Presence of chlorides– Mercury


Safety & trouble shootingSafety & trouble shooting Periodic recharging & replacements required.

Adsorbent will age with time & will became less effective.

Ageing reduces the differential loading & slows down themass transfer rate.

Leakage of Contamination in bed may occur.

Mechanical failure will lead wrong performance.

Poor mechanical design will destroy the bed support in notime.

Improper adsorbent installation will offer ir-ratic results.“Like side wall of column will leak through”.

Non compactness of bed will lead to channels & moreescape of LPG with out having correct contact withadsorbents.

Low crushing strength of Adsorbents will offer morepowder formation inside the bed.

Presence of trace un known components in Process Feed.

Regeneration fluid not initially identified.


Our clients:Our clients: Accra Pack Vapi.

Vanessa Cosmetics Himachal Pradesh.

ITW signode ( India ) Medak AP.

Mosil Lubricants Mumbai.

Chem Verse Consultants Mumbai.

Asian Aerosols Pvt Ltd Mumbai

SOBO international USA.

Dishman Pharma Ahmedabad

B.R.Labs Anand



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Molecular Sieve Mercaptans Removal from LPG