On-line monitoring of methanol and methyl formate in the exhaust gas of an industrial formaldehyde production plant by a mid-IR gas sensor based on tunable Fabry-Pérot filter technology

Abstract

On-line monitoring of key chemicals in an industrial production plant ensures economic operation, guarantees the desired product quality, and provides additional in-depth information on the involved chemical processes. For that purpose, rapid, rugged, and flexible measurement systems at reasonable cost are required. Here, we present the application of a flexible mid-IR filtometer for industrial gas sensing. The developed prototype consists of a modulated thermal infrared source, a temperature-controlled gas cell for absorption measurement and an integrated device consisting of a Fabry-Pérot interferometer and a pyroelectric mid-IR detector. The prototype was calibrated in the research laboratory at TU Wien for measuring methanol and methyl formate in the concentration ranges from 660 to 4390 and 747 to 4610 ppmV. Subsequently, the prototype was transferred and installed at the project partner Metadynea Austria GmbH and linked to their Process Control System via a dedicated micro-controller and used for on-line monitoring of the process off-gas. Up to five process streams were sequentially monitored in a fully automated manner. The obtained readings for methanol and methyl formate concentrations provided useful information on the efficiency and correct functioning of the process plant. Of special interest for industry is the now added capability to monitor the start-up phase and process irregularities with high time resolution (5 s).

Towards Integrated Mid-Infrared Gas Sensors

“…Gas sensors using optical detectors, to measure I(λ), have been successfully implemented for a variety of gases: acetone (C3H6O) [63], ammonia (NH3) [63], carbon dioxide (CO2) [19,40,43,47,54,58,59,61,64,73], formaldehyde (CH2O) [48], nitric oxide (NO) [53], carbon monoxide (CO) [59,64,74], methane (CH4) [56,59,60,62,64,75,76], or methanol (CH3OH) [77]. Various strategies have been implemented to fabricate gas sensors based on optical detection, Table 1 (Figure 3a–c,e–g).…”

“…These include designs based on tube-like gas cells formed between face-to-face configured emitters and detectors [19,43,48,53,54,58,63,75,76,77] (Figure 3a–c,e), dome-like gas cells with planar configured emitters and detectors [47,59] (Figure 3f), open cells [40,64,73] (Figure 3e), cavity-enhanced cells [56], or waveguides based on evanescent-field interaction [60,61,62] (Figure 3g). Different light sources have been used such as MEMS heaters [19,43,54,63,64,73,77], LEDs [40,47,48,53,76], distributed feedback lasers (DFBs) [62,75], or QCLs [61], and detectors such as photodiodes [47,48,53,62,76], thermopiles [19,43,54,63], pyroelectric detectors [59,64,77], or photoconductive detectors [56,60,61]. Thus far the most popular configuration is based on face-to-face configured tube-like cells for CO2 detection [19,56,60].…”

On-chip readout plasmonic mid-IR gas sensor

“…Conventionally, the gas sensing system needs a bulky gas chamber to ensure a strong light-gas interaction for low detection limit [36][37][38] . As is well known, micro-resonators are usually used to enhance the light-matter interaction 30 , which is able to reduce the sensor dimensions for distributed or low-load platform while keeping a high performance.…”

A pocket-sized 3D-printed attenuated total reflection-infrared filtometer combined with functionalized silica films for nitrate sensing in water

“…27 A micro-electro-mechanical system (MEMS)-based mid IR filter using a FP air resonator combined with a pyroelectric detector was first reported in 2003 and is now commercially distributed in several MIR wavelength ranges. 28,29 FP filterdetectors have been successfully paired with miniaturized pulsed MIR emitters were employed for process gas monitoring in transmission gas cells, [30][31][32] for liquid sensing, 33 imaging systems 34 as well as paired with a supercontinuum laser for standoff IR spectroscopy. 32 These reports achieved adequate analytical performance without the high spectral resolution and the full spectral coverage provided by FTIR spectrometers while reducing the costs and size of the respective sensing system.…”