Pumps High-Pressure Dosing Pumps
The Berlin-based manufacturer of laboratory measuring instruments Knauer Wissenschaftliche Geräte recently reported that its high-pressure metering pumps played an important role in the development of the groundbreaking new manufacturing process of methane sulfonic acid (MSA) directly from methane and sulfur trioxide, which was successfully realised by researchers from Duisburg's Grillo-Werke.
Currently methane sulfonic acid is already produced on an industrial scale. Its strongly acidic but non-oxidising properties make it an interesting catalyst for many reactions in organic chemistry, especially in polymerisations. Methane sulfonic acid is also used in electroplating and increasingly also in industrial cleaners, where it is used as a substitute for phosphoric, hydrochloric or sulfuric acid, because it is less harmful to the environment as compared to the mineral acids used previously. The preparation of methane sulfonic acid is currently relatively expensive, because of multi-stage processes, which are partly dependent on toxic intermediates such as dimethyl disulfide.
The direct reaction of methane with sulfur trioxide would be the most obvious solution. Researchers worldwide have long been experimenting with the direct activation of methane. As early as in the 1950s, a US patent was filed using sulfur trioxide, however, the achieved yields of methane sulfonic acid were low and the number of unwanted by-products high.
The Grillo researchers took a different approach than most other researchers. They relied on relatively mild temperatures below 100 degrees Celsius and pressures around 50 bar only. The cunning in their process is an activator molecule that triggers sulfonation and can easily be re-synthesized from MSA and sulfuric acid in a secondary process. By the way, sulfuric acid serves as a solvent in the process.
A tricky part of the new MSA synthesis is the precise metering of sulfur trioxide (SO3) into the chemical reactor. Sulfur trioxide is only liquid in a narrow temperature range between 32°C and 44°C, reacts violently when in contact with water and chars most plastics very quickly. This means that it is very difficult to handle.
Knauer high-pressure dosing pumps are based on the HPLC technology and inherently provide high chemical resistance, excellent flow rate precision, and low pulsation. However, pumping liquid sulfur trioxide required customisation, especially with regard to plastic parts in the flow path. Another important prerequisite for the success was the powerful pump head heating offered by Knauer in order to keep sulfur trioxide in the fluid state even at low flow rates or necessary stops, states the firm.
The special feature of the methane sulfonic acid production process developed by the Grillo researchers is that it works much more efficiently than previous processes and makes methane usable as a carbon source for sulfonation. Certainly, with this process methane is becoming more important as a raw material. Wasting methane through flaring will hopefully become less common. Using biogas as a source of methane, the process can do without a fossil carbon source. A recently published comparative life cycle assessment (LCA) study from the University of Zurich concludes that the new process has a three times smaller environmental impact than previous methods. Greenhouse gas emissions are 85 % lower.
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