Organic Dimethyl DME LPG Compressed Liquid Chemical Intermediate

Product Specification

Overview

molecular formula: CH3OCH3, DME It is a derivative of the dehydration condensation of two molecules of methanol. At room temperature, it is a colorless, non-toxic gas or compressed liquid . It is an important organic chemical product and chemical intermediate.

Properties

DME is very stable in the air, non-corrosive, slightly toxic, and non-carcinogenic. It has good miscibility and can be miscible with most polar and non-polar organic solvents.

As an important chemical intermediate, DME undergoes an alkylation reaction with benzene in the presence of a catalyst. It reacts with carbon monoxide to produce methyl acetate; homologation reactions can also produce ethyl acetate and acetic anhydride. It reacts with carbon dioxide to produce methoxyacetic acid. It reacts with fuming sulfuric acid or sulfur trioxide to produce dimethyl sulfate. It reacts with hydrogen cyanide to produce acetonitrile.

Preparation

In the laboratory, trimethyl orthoformate is generally used, which is prepared using ferric chloride as a catalyst. Or it can be obtained by thermal decomposition of sodium methyl carbonate at 320°C. High-purity DME is prepared by the Williamson synthesis method using iodomethane and sodium methoxide. The reaction conditions are harsh and must be reacted under anhydrous conditions.

In industry, DME was first separated and recovered from the by-products of methanol synthesis. After that, the production methods of DME mainly include the two-step method (methanol dehydration to DME) and the one-step method (syngas directly synthesizes DME). In addition, there are methods for preparing DME from carbon dioxide and biomass.

Synthesis Methods of DME

The synthesis methods of DME primarily include the one-step method and the two-step method. Below are detailed introductions to these two methods:

One-Step Method

The one-step method involves the direct synthesis of DME from feedstock gas in a single step. This method simultaneously completes the two reaction processes of methanol synthesis and methanol dehydration under the action of a specific catalyst, directly generating DME.

1. Reaction Principle:
   • Methanol synthesis: CO + 2H₂ → CH₃OH
   • Methanol dehydration: 2CH₃OH → CH₃OCH₃ + H₂O
     These two reactions can occur simultaneously in one reactor, producing DME and a small amount of by-products.
2. Catalyst:
   • The one-step method typically uses a bifunctional catalyst, which is physically mixed from two types of catalysts. One type is a methanol synthesis catalyst, such as Cu-Zn-Al(O)-based catalysts, BASFS3-85, and ICI-512. The other type is a methanol dehydration catalyst, such as alumina, porous SiO₂-Al₂O₃, Y-type zeolite, ZSM-5 zeolite, mordenite, etc.
3. Reaction Conditions:
   • The reaction temperature is usually between 280~340°C.
   • The reaction pressure is in the range of 0.5~0.8 MPa or higher (e.g., 4.2 MPa in the Topsøe process).
4. Process Characteristics:
   • The process flow is short, with less equipment investment and lower operating costs.
   • The product quality is high, with DME selectivity greater than 98%.
   • However, the one-step synthesis of DME involves relatively complex technology and has high requirements for catalysts and reactors.
5. Representative Processes:
   • Danish Topsøe Process: Uses a multi-stage adiabatic reactor with interstage cooling, and the catalyst is a mixed bifunctional catalyst for methanol synthesis and dehydration to DME.
   • U.S. Air Products Process: Developed the Liquid Phase LPDME™ process, using a slurry bubble column reactor with fine catalyst particles forming a slurry with inert mineral oil.
   • Japanese NKK Process: Also adopts the liquid phase DME method.

Two-Step Method

The two-step method involves first synthesizing methanol from syngas and then dehydrating it to produce DME. This method is relatively simple in operation and produces high-purity products.

1. Methanol Synthesis:
   • The feedstock gas undergoes methanol synthesis in the presence of a methanol synthesis catalyst, generating methanol.
2. Methanol Dehydration:
   • Methanol undergoes dehydration in the presence of a methanol dehydration catalyst, generating DME.
3. Catalyst:
   • The methanol synthesis catalyst is the same as in the one-step method.
   • In the gas-phase method for methanol dehydration, solid acid catalysts such as ZSM-5 zeolite are commonly used. In the liquid-phase method (sulfuric acid method), liquid acid catalysts such as concentrated sulfuric acid are used (but this method has been gradually phased out due to environmental pollution issues).
4. Reaction Conditions:
   • Methanol synthesis typically occurs at higher pressures and temperatures.
   • The temperature and pressure for methanol dehydration depend on the specific catalyst and process conditions.
5. Process Characteristics:
   • The two-step synthesis of DME involves relatively mature technology and simple operation.
   • The product purity is high, with good DME selectivity.
   • However, the production process is longer, with greater equipment investment, and is affected by fluctuations in methanol market prices.
6. Representative Processes:
   • Gas-phase Method: Uses solid acid catalysts such as ZSM-5 zeolite in a fixed-bed reactor for methanol dehydration.
   • Liquid-phase Method (Sulfuric Acid Method): Uses concentrated sulfuric acid as a catalyst for methanol dehydration in the liquid phase (but has been gradually phased out).