Name: NguyễnThịKhánhHuyền
Class: K4
Student code: CTTT13210133
HOMEWORK ASSINGMENT NO.2
ADECH 04
ETHYLENE GLYCOL PRODUCTION FROM SYNTHESIS GAS:
I. Interpret production of Ethyleneglycol (EG) from synthesis gas via dimethyl oxalate (DMO).
Ethylene glycol is an with the formula (CH2OH)2, also known as Mono Ethylene Glycol (MEG).It is a major chemical commodity, mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for formulations. It is odorless, colorless, sweet-tasting syrup. Ethylene glycol is moderately toxic.
These materials, in turn, are used to manufacture textiles, soft drink and water bottles, tire cords and more. MEG was first synthesized via the hydrolysis of ethylene glycol di-acetate. Now, it can be made from multiple raw materials, such as coal, natural gas and ethylene. Globally, it is mainly produced from ethylene via an ethylene oxide intermediate. This process generates di and tri-ethylene glycol along with MEG.
The process essentially consists of several stages of reaction and resulting products separation,ethylene glycol is produced from synthesis gas (syngas), a gaseous mixture of carbon monoxide (CO) and hydrogen (H2). There are 3 steps: carbonylation, DMO hydrogenation and purification.
1.Carbonylation:This isthe initial step,in this step CO is converted to dimethyl oxalate (DMO), which is then hydrogenated to form ethylene glycol.CO and H2 in the feed syngas are separated. The recovered CO is fed to the carbonylation reactors along with a recycled stream from the nitrite regeneration sectionthat contains an intermediate (methyl nitrite). Methyl nitrite reacts with CO in the gaseous phase in the presence of proprietary Pd catalyst to produce a mixture of DMO and nitric oxide (NO). The two reaction products are separated from each other by condensing dimethyl oxalate in a methanol scrubbed column. The product from the carbonylation reactors is partially condensed, generating a gaseous stream, rich in unconverted CO and NO, and a liquid stream, rich in DMO. The former is directed to the nitrite regeneration section, and the latter is directed to the DMO hydrogenation section.
2.DMO hydrogenation:In the second step, nitric oxide formed in the first step is converted back to methyl nitrite by reacting with methanol and oxygen. Water is also formed in this reaction. The reaction takes place in a countercurrent gas-liquid column, with nitric oxide and oxygen entering from the bottom and methanol spraying down the column from the top. The light gases (mainly unconverted NO), unconverted O2, CO, CO2, N2 …etc.., leaving from the top of the column are cooled, and after purging a small portion thereof, recycled to the first-stage dimethyl oxalate reactor. An aqueous solution of methanol is removed from the bottom of the column.The DMO-rich stream is fed to the hydrogenation reactors along with H2 recovered from the syngas feed. DMO reacts with H2 to produce the final product, ethylene glycol and methanol. A few byproducts from undesired side reactions also form. The product stream from the hydrogenation reactors is partially condensed, and the condensate is directed to the purification section. Uncondensed vapor (mostly H2) is compressed and recycled to the hydrogenation reactors.
3.Purification:The third reaction step consists of converting dimethyl oxalate to ethylene glycol (EG) in an excess of H2. Methanol for producing methyl nitrite is also regenerated in this reaction. This is a vapor-phase process in which a proprietary type of copper-zinc chromite is used as a catalyst. Some impurities/by-products such as methyl glycolate, dimethyl carbonate, methyl formate, 1,2-butanediol, etc., are also produced in small amounts. While most of the impurities are removed from the EG without serious difficulties, 1,2-butanediol is likely to pose a problem for producing fiber-grade EG.
 The purification system consists of a series of distillation steps to separate fiber-grade ethylene glycol from methanol and other byproducts formed during DMO hydrogenation. Methanol is recovered from an intermediate distillation column and is recycled to the nitrite-regeneration section. The recovered NO stream from the carbonylation section is mixed with O2 and contacted in a reactive absorber with methanol, which is recycled from the purification section, as well as from a distillation column downstream. These chemicals react to produce methyl nitrite and water. The top product stream from the nitrite reactor is partially condensed to remove most of its water and the resulting methyl-nitrite-rich stream is recycled to the carbonylation section. The reactor bottom product is directed to a water-removal distillation column.
II. Block diagram of EG from synthesis gas via dimethyl oxalate.
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Note: Reactor 1 is Carbonylation reactor, Reactor 3 is hydrogenation reactor.
III. The advantage and disadvantage of hydration, carbonylation and Shell OMEGA technologies.
• In hydration, the advantages are: continuous process, need few worker and fast at reaction rate, no by-product made; but the disadvantage are: uses non-renewable material (from crude oil), occurs at high temperature (300°C) and high pressure (