Oxygen Measurement in Reactor Feed Gas Ensures Reliable Formaldehyde Production
Problem
Oxygen is commonly measured in reactor feed gases or reactor head spaces. One such application is the industrial production of formaldehyde. Formaldehyde is produced by mixing specific amounts of methanol vapor with oxygen in a reactor in the presence of a catalyst, most commonly metal oxides. This method keeps the methanol vapor below the explosive limit that would be surpassed by more traditional techniques using a silver catalyst. With 80% of the production cost of formaldehyde being made up of the raw material used in the reaction, the oxygen content within the reactor must be controlled at an optimum level to produce a successful yield.
Application
| Application | 0% to 21% O₂ in N₂ saturated with methanol vapors |
|---|---|
| Temperature | Ambient |
| Pressure | 5 psig (≈0.34 bar) |
Benefits:
- No moving parts to be fouled by liquid carryover
- Sensor is not consumed as with galvanic fuel cells
- Simple field calibration
- Turnkey sample conditioning system
Challenge
The challenge in this application relates to the potential for liquid carryover to the oxygen analyzer, along with the reliability of the measurement. Traditional dumbbell-type paramagnetic sensors have been used in the past for these applications; however, they required extensive maintenance. Liquid carryover is extremely damaging to these units, so the challenge is to use an oxygen analyzer with minimal maintenance requirements and the durability to recover from process upsets.
Solution
Air is used as the source of oxygen in the formaldehyde production process. The air and methanol vapor mixture is sampled at the inlet to the reactor. The XMO2pro thermoparamagnetic oxygen transmitter verifies that the optimal amount of oxygen — typically 9.8% — is present to achieve a complete reaction with minimal waste. The sample system is mounted near the sample point to prevent measurement lag time. A typical installation includes the thermoparamagnetic oxygen transmitter, a display/controller and a sample system. The sample system components — including the inlet and calibration valves, a filter/coalescer assembly, pressure gauge and flowmeter — are normally plate-mounted.
Source: Panametrics Application Note PANA059AN (panametrics.com) — © Panametrics LLC. Localized and prepared by INTECH CONTROL, the official Panametrics representative in Slovakia and Hungary.