Methanol section: One question per day. What impurities are present in crude methanol? 2016.04.11

In crude methanol, in addition to methanol, there is also water along with dozens of trace organic impurities, including aldehydes, ketones, ethers, acids, esters, alkanes, amines, and iron carbonyl. In the low-pressure synthesis of methanol, when a copper-based catalyst is used, dimethyl ether is the most abundant organic impurity.

The main impurities are water, ethanol, dimethyl ether, and isobutanol.

1. Reducing substances: mainly aldehydes, amines, iron carbonyl, etc. 2. Soluble impurities: (1) Water-soluble impurities such as ethers, C1–C5 alcohols, aldehydes, ketones, organic acids, and amines have high solubility in water; when a methanol solution is diluted, these substances do not precipitate or cause the solution to become cloudy. (2) Alcohol-soluble impurities: C6–C15 alkanes, C6–C16 alcohols. Such impurities are soluble only in methanol at high concentrations; as the methanol concentration in the solution decreases, they precipitate out of the solution or cause it to become turbid. (3) Insoluble impurities: Alkanes with C16 and above, and alcohols with C17 and above. It is insoluble in methanol and water at room temperature; it will crystallize out in liquids or cause the solution to become turbid. 3. Inorganic impurities 4. Electrolytes and water. The conductivity of pure methanol is approximately 4×107 Ω·cm; the presence of water and electrolytes reduces this conductivity. In crude methanol, the electrolytes mainly include organic acids, organic amines, ammonia, and metal ions such as copper, zinc, iron, sodium, etc., as well as trace amounts of sulfides and chlorides.

1) Moisture and electrolytes: mainly water, organic acids, organic amines, ammonia, as well as metal ions, along with trace amounts of sulfides, ammoniates, and metal ions. 2) Organic impurities: water-soluble impurities (ethers, C1–C5 alcohols, aldehydes and organic acids, amines, etc.), alcohol-soluble impurities (C6–C15 alkanes, C6–C10 alcohols), and insoluble impurities (alkanes with 16 carbon atoms or more, alcohols with 10 carbon atoms or more). 3) Inorganic impurities: trace amounts of ions and complexes of iron, metals, etc.

The main impurities are water, ethanol, dimethyl ether, and isobutanol.

Water, ethanol, dimethyl ether, isobutanol.

In crude methanol, in addition to methanol, there is also water along with dozens of trace organic impurities, including aldehydes, ketones, ethers, acids, esters, alkanes, amines, and iron carbonyl. In the low-pressure synthesis of methanol, when a copper-based catalyst is used, dimethyl ether is the most abundant organic impurity.

What impurities are present in crude methanol? Answer: Due to an imbalance in the hydrogen-to-carbon ratio and the dehydration of ZnO, dimethyl ether and higher alcohols may be formed; high water vapor content in the feed stream facilitates the formation of organic acids. Incomplete desulfurization can easily lead to the formation of thiols. Excessively high reaction temperatures can lead to the formation of carbonyl compounds. Therefore, the main impurities in crude methanol are: 1) water and electrolytes: mainly water, organic acids, organic amines, ammonia, as well as metal ions, along with trace amounts of sulfides, ammoniates, and metal ions. 2) Organic impurities: water-soluble impurities (ethers, C1–C5 alcohols, aldehydes and organic acids, amines, etc.), alcohol-soluble impurities (C6–C15 alkanes, C6–C10 alcohols), and insoluble impurities (alkanes with 16 carbon atoms or more, alcohols with 10 carbon atoms or more). 3) Inorganic impurities: trace amounts of ions and complexes of iron, metals, etc.

Main impurities: water, ethanol, dimethyl ether, isobutanol