mercaptan removal from natural gas & LPG using molecular sieve desiccant What is LPG ?
Liquefied Petroleum Gas.
Its Colorless & Odorless. —
I— ts compositions of Methane, Propane 60% ,Ethane & butanes 40%.
—ropane & butane % ages P changes according to seasons, Winters – More propane & in summer more butanes.
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What is LPG ? 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 fuelOnly 19% CO2 per Kwh than oils. — Its having Calorific value of 26.1 kWh/m³ than natural Gas methane 10.6 kWh/m³.Its also called as C3C4 Hydrocarbon. LPG replaces Chloro fluoro carbons as Aerosol propellants.
LPG 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 present at a concentration of approximately 0.9-1.3 pound/million standard cubic feet of gas . • SH group which are low molecular weight gives Bad odor.
Specification of LPG
Aerosols • Aerosols are very fine particles of liquid or solid substances suspended in air. Fog, for example, is a normal aerosol. • The aerosol package is a self-contained dispensing system with three main elements: Active Ingredients (soap or disinfectant, etc.) Inert or Inactive ingredients (water) Propellant. • The propellant is a gaseous compound which pushes the product out of the container and produces a spray or foam. In most cases, the propellant also acts as a solvent to keep the product at the proper strength. • Aerosols operates at 30-50psig & does have 90% propellant
Mercaptan removal • 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 like phosphoric acid, boric acid & sulfuric acid, where Mercaptans gets convert to Sulfides & later discharge the eff luent as Gas phase & Liquid phase.
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Adsorption Molecular Sieves & Spherical active Alu-Silica Gel technique, in which all Typical Mercaptans are selectively trapped on Bed.
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Cracking Reaction :-Technique in which there is sulfur absorption at elevated temperatures where all disulfides & CO2 are removed.
Adsorption Process
Loading According to Mechanism
Comparison of Relative Humidity Effect on Various Desiccant
Adsorption Method •
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Bed is prepared with Active Molecular Sieves or Alu-Gel spherical beads & then LPG flow is initiated top to down. Adsorption capacity is directly related to Molecular weight & Boiling point of the gas. Which means H2O & high MW components are more strongly hold on bed than lighter components. C5-C6 is near to discharge side of bed, if more feed is applied than C5 will escape followed by C6 H2O is getting removed at entrance only. Mercapatans are held up more strongly than C6.
Molecular Sieve for Mercaptan Removal •
Molecular sieve is widely used for the purification process of petroleum products. These products have strong compounds such as water, carbon dioxide, hydrogen sulphide and mercaptan that need to be removed to obtain the pure product.
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The adsorption process is carried out by passing the petroleum product from the bed of zeolite for the specific period of time depending on the amount of impurity required to be removed.
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The adsorbed contaminants can be easily removed from the molecular sieve at a certain temperature range i.e. from 200 °C and 325 °C. The sodium based Type 13X molecular sieve brings excellent outcome when removing mercaptan and other unwanted compounds with the help of drying and purifying certain types of liquids and gases.
Molecular Sieve for Mercaptan Removal • The main purpose of molecular sieve is to reduce or eliminate the water content to the predetermined level. 13X desiccants contain Type X crystal structure and also has much larger pore size than the Type A crystals. The feature of removing the impurities that cannot be possible with Type A crystal, 13X is used for the desired dehydration process of removing the Mercaptan. It can adsorb all types of materials which have less than 10 angstrom molecular diameter. Mercaptan removal is done from natural gas, LPG and various other liquid hydrocarbons using the most appropriate pore size of the sieve type. • This adsorbent has the ability to trap the typical mercaptans in number of gaseous or liquid applications to obtain high percentage of pure and clean products. In case of liquid hydrocarbon and natural gas sweetening, removal of H2S and mercaptan is required in the dehydration process to get the clean natural gas without any kind of impurities.
Reference Links • • • • • • • • • • • • • • • • •
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