PolymerizationPolymerizationOf gasolineOf gasoline

Mohamed Salah Abu-Hamad

Refining and Petrochemical Engineering

Overview A Brief History Description ID card Explanation of the process Catalyst Principal Reactions Health and Safety Considerations Comparison of polymerization and alkylation

A Brief History

It was widely used in the 1930's and 1940's, but was replaced by the alkylation process after WWII. It did make a comeback due to the mandated phase out of leaded gasoline and the demand for high octane fuel.

THE REFINERY

Description  Polymerization in the petroleum industry is the process of

converting light olefin gases including ethylene,propylene, and butylene into hydrocarbons of higher molecular weight and higher octane number that can be used as gasoline blending stocks.

Polymerization combines two or more identical olefin molecules to form a single molecule with the same elements in the same proportions as the original molecules.

Polymerization may be accomplished thermally or in the presence of a catalyst at lower temperatures.

ID card

Feedstock From Typical products

To

Olefins Cracking processes

High octane naphtha

Gasoline blending

Petrochem. feedstock

Petrochemical

Liquefied petro. gas

Storage

Drawing

Explanation of the process The olefin feedstock is pretreated to remove sulfur and

other undesirable compounds.

In the catalytic process the feedstock is either passed over a solid phosphoric acid catalyst or comes in contact with liquid phosphoric acid, where an exothermic polymeric reaction occurs.

This reaction requires cooling water and the injection of cold feedstock into the reactor to control

temperatures between 300° and 450° F . pressures from 200 psi to 1,200 psi.

Cont…

The reaction products leaving the reactor are sent to stabilization and/or fractionator systems to separate saturated and unreacted gases from the polymer gasoline product.

Catalyst

The above reactions are caalyzed by phosphoric acid on an inert support. Sulfur in the feed poisons the catalyst and basic compounds neutralize the acid and increase its consumption. Also, oxygen dissolved in the feed strongly affects the reactions and must be removed..

Principal Reactions

olefin + olefin --> olefin

C=C-C + C=C-C --> C-C-C=C-C

  C=C-C-C + C=C-C --> C-C-C-C-C=C-C

NOTE In the petroleum industry, polymerization is used to indicate the

production of gasoline components, hence the term "polymer" gasoline. Furthermore, it is not essential that only one type of monomer be involved.

If unlike olefin molecules are combined, the process is referred to as "copolymerization." Polymerization in the true sense of the word is normally prevented, and all attempts are made to terminate the reaction at the dimer or trimer (three monomers joined together) stage.

However, in the petrochemical section of a refinery, polymerization, which results in the production of, for instance, polyethylene, is allowed to proceed until materials of the required high molecular weight have been produced.

Health and Safety Considerations a. Fire Prevention and Protection.

Polymerization is a closed process where the potential for a fire exists due to leaks or releases reaching a source of ignition.

b. Safety. The potential for an uncontrolled exothermic reaction exists

should loss of cooling water occur. Severe corrosion leading to equipment failure will occur

should water make contact with the phosphoric acid, such as during water washing at shutdowns.

Corrosion may also occur in piping manifolds, reboilers, exchangers, and other locations where acid may settle out.

Cont…

c. Health. Because this is a closed system, exposures are expected

to be minimal under normal operating conditions. There is a potential for exposure to caustic wash

(sodium hydroxide), to phosphoric acid used in the process or washed out during turnarounds, and to catalyst dust.

Safe work practices and/or appropriate personal protective equipment may be needed for exposures to chemicals and other hazards such as noise and heat, and during process sampling, inspection, maintenance, and turnaround activities.

Comparison of alkylation and polymerization

Process POLYMERIZATION ALKYLATIONPurpose  polymerize propene and

butenes to form a high octane gasoline.

produce a high octane gasoline by reactine light olefins with light iso-paraffins.

Feed Propene and butene primarily a mixture of (propylene and butylene) with isobutane

Operating Conditions

Pressure 200-1200 psi Space Velocity 0.3 gal/lb Temperature 300-450 F

Lower temperatures

(yield a higher quality) Strong acid strength

Catalyst phosphoric acid

(H2SO4 and HF)

The concentrations must be greater than 88%

Products 1. Liquefied petro. gas

2. High octane naphtha

3. Petrochem. Feedstock

1. LPG grade propane liquid

2. Normal butane liquid

3. C5 + alkylate(want to maximize its production)

Gasoline Specification

MON = 83 RON = 97

MON = 88-94 RON = 94-99

Major Refinery Products LPG (Propane/Butane)

GASOLINE (hundreds of blends) JET FUELS DIESEL FUELS HEATING OILS GREASES ASPHALTS COKE (not the kind you drink )

Gasoline SpecificationsGasoline must meet many criteria which change with the time

of year and geographic location. Some critical specifications are:

Vapor Pressure

Octane Aromatics / Benzene Content Sulfur Content

Gasolines are always a blend of a number of streams in the refinery

Specifications

Product gasoline (olefin) MON = 83

RON = 97

Summary

Comparison of alkylation/polymerization with catalytic cracking:

Alkylation/polymerization combines shorter chains (C3, C4) to get C7 and C8.

Catalytic Cracking breaks long chain n-alkanes to make branched alknaes.

The final product for each process is branch chain alkanes.

ReferencesWeb http://www.hghouston.com http://www.eoearth.org http://nptel.iitm.ac.in

Books Petroleum refining technology and

economics_James H. Gary