UNIVERSITY OF LAGOSProcess description for the production of Mtbe

A Presentation by Group 10 consisting:

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Department of Chemical Engineering

Submitted in partial fulfillment of the requirement for Master Degree in Process Engineering

Date: 15th of May 2010

Process of producing MTBE (Metyl tert-Butyl Ether)

What is MTBE?

Methyl tert-butyl ether, also known as methyl tertiary butyl ether and MTBE, is a chemical compound with molecular formula C5H12O. MTBE is a gasoline additive, used as oxygenate and to raise the octane number in petrol. It also acts as a volume extender by adding volume to the petrol pool and by reducing the severity of the naphtha reforming and related conversion operations (Muddaris and Pettman). MTBE is also used in organic chemistry as a relatively inexpensive solvent. It is also used medically to dissolve gallstones.

Why MTBE?

Petrol is a mixture of compounds of carbon and hydrogen called hydrocarbons; most of the hydrocarbons in petrol are alkanes. In modern car engines, the petrol vapour-air mixture is highly compressed before it is sparked, in order to get the maximum energy from the burning fuel. However, some hydrocarbons tend to ignite under pressure before they are sparked, so that the engine runs roughly; this is known as "knocking". Branched-chain alkanes tend to resist this pre-ignition better than alkanes with unbranched chains. Alkanes and fuel mixtures are given Octane ratings depending on their knocking tendency. 2,2,4-trimethylpentane (which contains 8 carbons and so is an isomer of octane) has an Octane rating of 100; heptane has a rating of 0. The Octane number of a petrol is the % of 2, 2, 4-trimethylpentane in a mixture with heptane that has the same knocking characteristics as the petrol under test. Lead compound tetraethyl lead, Pb (CH2CH3)4, was added to petrol. Particles of lead and lead oxide PbO are formed on combustion. This helps the petrol to burn more slowly and smoothly, preventing knocking and giving higher Octane ratings. 1, 2-dibromoethane is also added to the petrol to remove the lead from the cylinder as PbBr2, which is a vapour and removed from the engine. (This is how lead is released into the environment from leaded fuels). Lead however is poison to human health. That is why MTBE was thought of as alternative.

How does it reduce CO levels?

The toxic gas carbon monoxide is formed by incomplete combustion of petrol. The oxygen atom in MTBE helps provide extra oxygen for complete combustion, and helps give it an Octane rating of 116.

Formulae

IUPAC Name: 2-methoxyl, 2-methyl propane

Physical Properties of MTBE

MTBE is a volatile, flammable and colorless liquid that is immiscible with water. MTBE has a minty odor vaguely reminiscent of diethyl ether leading to unpleasant taste and odor in water.

Molecular formula C5H12OMolar mass 88.15 g/molDensity 0.7404 g/cm³Melting point -109 °C, 164 K, -164 °FBoiling point 55.2 °C, 328 K, 131 °F

NFPA 704blue = health,

red = flammability, yellow = reactivity

310

Chemical Properties

Being an ether, MTBE is a Lewis base. However, unlike other ethers such as diethyl ether or THF, it does not coordinate well enough with magnesium to be used for making Grignard reagents. The tert-butyl group is easily cleaved off under strongly acidic conditions (forming a moderately stable carbocation), particularly if heated (isobutylene is lost), something which can limit the use of MTBE as a solvent.

NFPA = National Fire protection Agency. 704, means in section 704. All the colored section use scale 0 to 4. 3 on the blue diamond - Material that on short exposure could cause serious temporary or residual injury. 1 on the red diamond - Material must be pre-heated before ignition can occur. 0 on the yellow diamond means - Material that in itself is normally stable, even under fire exposure conditions, and is not reactive with water.

Reaction:

CH3OH + (CH3)2C=CH2 (CH3)3C-O-CH3

The reason why this technology is chosen over the c

Process Flow Diagram Description

The technology used is called CDMbte (R) or CATALYTIC DISTILLATIONMtbe

We use a basis of 165tonnes/day in our analysis

Stream 1/4: Methanol stored as a liquid at the desired pressure of the reaction, and stream from reflux captured in Vessel V-901

Equipment V-901: feed vessel for methanol, and also to capture reflux methanol from Methanol Recovery Tower T-903

Stream 2/16: Assume pure Methanol from T-903 Methanol recovery Tower

Stream 3: Mixed Butene stream obtained from a refinery stream OSBL(Outside Battery Limits) – 23% iso-butene, 20% 1-butene, 57% trans 2-butene. Usually gaseous at room temperature but liquid for the purpose of our system. Usually washed with water to remove catalyst poisons such as nitrogen compounds and metal ions

Stream 5: Mixed feed 4 & 3, heading for R-901.

Equipment P-901A/B: This is a pump used to increase the pressure of the liquid mixture to the reactor R-901 feed pressure this is 3,000kpa or 30atm. It has a Flow Integral Controller

Stream 6: running at 3,000kpa is the mixed feed Methanol and Butene mixtures

Equipment E-901: Shell and Tube heat exchanger used to raise the feed mixture temperature to the reactor R-901 feed temperature. This is 90oC. It is an LPS – low pressure steam

Stream 7: This is the feed stream running at 30atm pressure and 90oC.

Equipment R-901: This is where the reaction occurs. It is a fixed bed reactor, packed with sulfonic acid resin catalyst which is active at room temperature. The reactor is adiabatic and the reaction is exothermic. But the heat generated by the reaction cannot leave the system hence the temperature of the exit stream is raised. The exit temperature is a function of its conversion. Methanol must be present in the reactor feed at a minimum 200% excess to suppress side reaction that produces undesired products. As more and more feed is processed through the unit, catalytic activity gradually decreases in the reactor due to neutralization of the active sites from

residual impurities entering the feedstock. Raising the temperature or pressure of the system however will give a high degree of conversion.

The Problem with fixed Bed Reactors

The problem is that the catalyst eventually loses activity, and conversion level falls accordingly. The catalyst continually loses activity due to thermal degradation. The major culprit however is catalyst poison in the Butene feedstock which neutralizes the active sites. After some time the catalyst will have to be dumped, and replaced.

Feed Entry requirement into Reactor R-901:

Pressure: 30 atm. Temperature: 90oC.

Stream 8: Consists essentially of MTBE with unreacted methanol, 1-butene and trans 2-butene. Because the reaction is exothermic, one might expect to have vapour at the exit stream of R-901. If you desire to have only liquid stream at and not a vapour-liquid stream, you might want to flash the vapour at stream by dropping pressure at stream 8 from 30 atm to about 1 atm. A valve can do that.

Equipment T-901: MTBE Tower. This is a catalytic distillation tower where the MBTE is separated from Methanol. The partially vaporized reactor R-901 effluent stream enters this T-901 MTBE column from feed plate somewhere in the middle (Tray 25). Once in the column, the reaction continues and the MTBE product separates from unreacted butenes. Due to its high boiling point MTBE is easily separated from isobutene and methanol, as a result, the equilibrium reaction is shifted to higher conversion

Methanol and Butenes form a minimum boiling azeotrope, i.e. B.P of mixture is less than individual B.Ps. so that the methanol in the column feed up to the azeotropic limit is carried up to the tower reaction zone which comprises of three catalytic beds. MTBE formed is removed from the reaction zone by distillation, hence allowing the reaction to proceed well beyond the limit set by chemical equilibra.

MTBE and Methanol also form a minimum boiling azeotrope, whereby methanol is stripped from the MTBE product in the stripping section of the column.

Equipment E-902: here the bottom of the distillation tower contains essentially MTBE and the butenes with methanol. Some of the content of the stream leaving the bottom of T-901 are reboiled and vaporized, to return to the column. It is an HPS – high pressure steam

Stream 9: is mainly MTBE product 95w% pure. The Liquid Level Indicator control measures the level of MTBE in the tower and certain level triggers the valve, hence stream 9.

Equipment V-902: serves as a collection vessel of saturated liquid MTBE and other impurities.

Equipment P-902A/B: pumps reflux to tower with a flow rate indicator controller that monitors the flow rate into tower.

Stream 10/11: Essentially Methanol Vapour and the Butene vapours in the stream pressure is drop to 5atm.

Equipment T-902: This is a Methanol Absorber operating at 90 OC and 5atm. Process water is introduced from top of Absorber while the gas is introduced from bottom. Methanol vapour dissolves in water and is collected at the bottom.

Stream 12: This is the Absorbing Agent which is water.

Stream 13: Undissolved inert gas (1-butene, Trans 2-butene) as waste Butenes, exit

Stream 14: This is the Methanol with impurities running at 90 OC, but the pressure has drop to say 3atm

Equipment P-903A/B: normal pump for raising pressure to 5 atm

Stream 15: running at 5atm, 90 OC into T-903 Methanol recovery tower

Equipment T-903: Methanol Recovery Tower. This tower runs at 5atm, and this is where methanol is separated from water.

Equipment E-904: in this boiler, the contents of the stream leaving the bottom of T-903 going to this equipment are vaporized and returned to the column. This is essentially a heat exchanger. Methanol boils at 64.7 OC water boils at 100 OC or more due to dissolved impurities. Its an MPS – medium pressure steaam

Methanol vapour is collected at the top, while we have water at the bottom.

Stream 17: is controlled by a valve with a liquid level indicator controller and its essentially waste water.

Equipment E-905: in this heat exchanger the methane vapour from the top leaving the T-903 are completely condensed from saturated vapor to saturated liquid and stored in a Methanol reflux tank V-903

Equipment P-904A/B: Pumps reflux into tower an FIC controls flow rate into Tower

Stream 16/2: Methanol recycled into feed Vessel V-901