What is the source of iron carbonyl in synthetic methanol?

Let me start by saying this: the methanol synthesis system is basically made of stainless steel. The crude methanol and iron carbonyl are produced at temperatures over 300 degrees Celsius, using iron-manganese desulfurization agents or carbon steel equipment from the conversion system, and then transported to the synthesis process via the feed gas. The positive component in pure methanol must have come from crude methanol.

Mist in the circulating gas can erode the inner surface of the equipment, resulting in uneven surfaces; liquid accumulating in these areas can lead to carbide corrosion, especially at the welds.

This is mainly due to gases containing acidic substances such as CO2, along with a saturated water vapor concentration, which causes corrosion; this effect is particularly severe in systems where there is circulation

Ferrocarbonyl is formed when the temperature of the tower wall is too high, causing a chemical reaction between CO and the iron present in the tower wall, and this occurs at temperatures above 130°C. By suppressing the formation of iron carbonyl, the tower wall temperature can be well controlled. Hehe

Reply to 1# yangzhi5114: Ferrocene may be formed when the inlet pipes of the methanol synthesis system are exposed to high CO concentrations, causing a chemical reaction between CO and the iron in the carbon steel pipes to produce ferrocene.

1.1 Reasons for formation To date, there are no systematic studies on the formation mechanisms of Fe(CO)5 and Ni(CO)4. According to research, the main sources of carbonyl iron and carbonyl nickel are as follows. (1) CO in the feed gas causes corrosion of equipment and pipelines, leading to the formation of Fe(CO)5 and Ni(CO)4. Among metals, only iron and nickel can react directly with CO gas under milder conditions to form carbonyl compounds. Its reaction formula is as follows. Fe(s) + 5CO(g) → Fe(CO)5(g) Ni(s) + 4CO(g) → Ni(CO)4(g) (2) During the gas generation process, CO reacts with Fe and Ni to form Fe(CO)5 and Ni(CO)4; the amounts produced depend on the contents of Fe and Ni in the raw materials as well as the partial pressure of CO. 1.2 Effect on the performance of methanol catalysts It is well known that the surface properties of catalysts are not uniform; their surfaces do not possess identical catalytic activity and adsorption characteristics, but rather consist of a series of active centers. The active centers are not scattered randomly on the catalyst surface, but follow a certain pattern that is suitable for the catalyst. Once these active centers are damaged, the catalyst loses its activity or causes other side reactions. Catalyst poisoning is generally considered to be the result of catalyst toxins forming a film on the catalyst surface, thereby rendering the surface inactive. But in many cases, the dose of toxins that poison the catalyst is very small; they are not even capable of forming a monolayer. Such toxins adhere firmly to the active centers, causing the catalyst to lose its activity or leading to other side reactions. Fe(CO)5 and Ni(CO)4 are formed at temperatures lower than those in the reactor, and they decompose at the reactor temperature to deposit on the catalyst surface. This decomposition reaction is likely catalyzed by the catalyst itself; as substances are gradually adsorbed on the catalyst’s surface, this blocks the surface and pores of the catalyst, resulting in a decrease in its activity. Since the heat of reaction cannot be removed in time, it causes the temperature of the catalyst bed to rise, thereby affecting the industrial service life of the catalyst. Robert et al. investigated the effect of iron carbonyl and nickel carbonyl on the catalyst activity for methanol, demonstrating that the decline in catalyst activity is proportional to the amount of poisons deposited on the catalyst. At the same time, since iron and nickel are the active components in the Fischer-Tropsch reaction, the presence of iron and nickel carbonyls can also cause numerous side reactions, such as those that produce hydrocarbons and paraffinic hydrocarbons, thereby complicating the separation process. The methanol production plant for residue oil gasification, with a capacity of 100 kt/year, which was introduced by a domestic fertilizer factory from the German company Lurgi, experienced issues during operation as the activity of the methanol catalyst declined rapidly, thereby affecting the normal production of methanol. Analysis shows that one of the main reasons is the presence of impurities such as iron carbonyl and nickel in the methanol synthesis gas, which causes poisoning and deactivation of the methanol catalyst. Side reactions caused by iron and nickel carbonyls increase the impurity content in crude methanol and raise the difficulty of purification, affecting product quality.

What is iron carbonyl? What are the hazards of impurities in methanol?

Large amounts of carbonyl iron and carbonyl nickel can poison the catalyst, while small amounts of them can increase methanol side reactions, leading to the formation of large quantities of higher alkanes

Hehe, I'm currently studying the issue of iron carbonyl. Thank you all

1. When the system contains excessive rust impurities, Fe(CO)5 can be formed at 130–150°C. 2. Methanol synthesis gas contains a small amount of H2S, which can corrode pipelines and equipment, causing rust to form; the presence of this rust facilitates the occurrence of the carbonylation reaction. If the system is not thoroughly purged before operation, the residual rust remaining in the equipment and pipes will accelerate the carbonylation reaction, resulting in the formation of Fe(CO)5, Ni(CO)4, and a small amount of Mo(CO)4, thereby promoting the waxing reaction.