Foreign Gas Detection in High-Purity Ethylene
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for determining foreign gases in ethylene with high purity (above 99%) are inadequate for quickly measuring small concentrations, as they are complicated by strong ethylene absorption and interference from other gases, limiting detection precision and accuracy.
Innovation Solution
A method using tunable diode laser absorption spectroscopy with four lasers operating in different wavelength ranges to selectively scan absorption lines of acetylene, carbon dioxide, carbon monoxide, and ammonia, allowing for precise measurement of these gases with a detection limit of up to 10 ppb, without requiring individual light sources with a wide enough tuning range, by employing semiconductor lasers like quantum cascade or surface-emitting lasers and utilizing wavelength modulation spectroscopy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single laser with wide tuning range is used to scan absorption lines of multiple impurity gases, then device complexity is reduced, but measurement precision deteriorates due to insufficient spectral resolution and interference from strong ethylene absorption
Solution Approach 1:
The patent divides the measurement task into separate wavelength ranges, assigning one semiconductor laser to each range (3.0-3.1 μm for acetylene, 4.2-4.3 μm for CO2, 4.6-4.7 μm for CO, and 6.1-6.4 μm for ammonia). This segmentation allows each laser to be optimized for its specific wavelength range, achieving high spectral resolution and detection precision without requiring a single complex wide-tuning-range laser system.
Solution Approach 2:
The patent employs a multi-functional measurement system where four separate semiconductor lasers collectively cover the entire spectral range needed for detecting all four impurity gases. Each laser serves its specific function at its optimized wavelength range, and the system as a whole achieves universal detection capability across multiple gas types with high precision.
2Measurement precision
If wavelength modulation spectroscopy is used to improve detection precision, then measurement precision improves, but device complexity and difficulty of detecting and measuring increase due to additional modulation and evaluation requirements
Solution Approach 1:
The patent implements wavelength modulation spectroscopy by periodically varying the laser wavelength across the absorption lines of the impurity gases. This periodic action enables the system to distinguish between weak absorption signals from trace impurities and the strong continuous absorption from ethylene, thereby improving detection precision and spectral resolution through frequency-domain analysis.
Solution Approach 2:
The measurement system incorporates feedback mechanisms where the modulated laser wavelength is carefully controlled and adjusted based on the detection signals. This feedback allows the system to optimize the measurement process in real-time, improving both detection precision and the ability to resolve spectral features in the presence of strong ethylene absorption.
3Manufacturing precision
If high purity levels (above 99%) are required for ethylene, then manufacturing precision improves, but measurement precision deteriorates because the concentration of foreign gases becomes too small to detect accurately
Solution Approach 1:
The patent changes the measurement parameters by operating at optimized wavelength ranges for each impurity gas, using appropriate laser power levels, and adjusting the modulation frequency and amplitude. These parameter changes enable the system to detect trace concentrations of impurities (down to 10 ppb or lower) even in highly purified ethylene streams with >99% purity, resolving the contradiction between high manufacturing precision requirements and the resulting difficulty in measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise measurement of foreign gases like acetylene, carbon dioxide, carbon monoxide, and ammonia in ethylene with high purity, achieving a detection limit of up to 10 ppb, while minimizing interference from ethylene and other gases, thus ensuring the quality and usability of ethylene in polymerization processes.
Implementation Method 1
a sample of the ethylene is irradiated with light in a measuring cell, the wavelength of the light is varied in order to scan selected absorption lines of the impurity gases acetylene, carbon dioxide, carbon monoxide and ammonia in a wavelength-dependent manner, the light is detected after irradiation of the sample and the concentrations of the impurity gases are determined on the basis of the wavelength-specific absorption of the light
Implementation Method 2
the concentrations of the impurity gases are determined on the basis of the wavelength-specific absorption of the light at the locations of the scanned absorption lines
Implementation Method 3
the wavelength of light from a tunable diode laser is periodically varied across the absorption line of interest and additionally modulated sinusoidally at a high frequency and small amplitude. The intensity of the light is detected after passing through the acetylene-contaminated ethylene and evaluated at twice the modulation frequency (2f-WMS)
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
For the purposes of determining foreign gases in ethylene with a purity of up to more than 99%, light (14) is passed through a sample (2) of the ethylene in a measuring cell (1), when the wavelength of the light (14) is varied in order to scan selected absorption lines of the foreign gases in a wavelength-dependent manner. The light (14) is detected after passing through the sample (2) in order to determine the concentrations of the foreign gases on the basis of the wavelength-specific absorption of the light (14) at the locations of the scanned absorption lines. The concentrations of the foreign gases of acetylene, carbon dioxide, carbon monoxide and ammonia are determined on the basis of the absorptions at respectively one of their following absorption lines: – acetylene absorption lines at 3.02575 µm, 3.0223 µm, 3.0099 µm or 7.423 µm, – carbon dioxide absorption lines at 4.2347 µm, 4.2396 µm, 4.23225 µm or 4.2875 µm, – carbon monoxide absorption lines at 4.61 µm, 4.58765 µm or 4.74515 µm, – ammonia absorption lines at 6.1496 µm, 6.4046 µm, 6.4066 µm or 6.18425 µm.