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On the detection of non-methane total hydrocarbons by gas chromatography - Master's thesis - Dissertation
Non-Methane Hydrocarbons (NMHC) refer to all volatile hydrocarbons except methane, primarily ranging from C2 to C8. These compounds are also known as non-methane total hydrocarbons and can have significant environmental and health impacts when their concentration in the atmosphere exceeds certain thresholds. In addition to direct harm to human health, NMHCs can react under sunlight to form photochemical smog, which poses serious threats to both the environment and public well-being.
Monitoring NMHC levels in ambient air and industrial waste gas is essential for environmental protection and regulatory compliance. While various methods exist, most countries [1, 2] rely on gas chromatography due to its precision and reliability. The standard method involves using a gas chromatograph equipped with a dual-column system and two hydrogen flame ionization detectors (FID). The total hydrocarbon and methane content are measured separately, and the difference between these two values represents the NMHC content. This measurement reflects the total amount of hydrocarbons excluding methane and is highly responsive to the FID, particularly in terms of carbon detection.
In nature, NMHCs include a wide variety of hydrocarbons that differ from methane. Due to their high photochemical reactivity, they serve as precursors to the formation of photochemical smog. A large portion of these emissions comes from natural sources, such as terpenoids released by plants, which account for approximately 65% of total NMHC emissions. Key compounds like isoprene and monoterpenes contribute significantly to the formation of photochemical oxidants and aerosol particles in urban and rural areas through atmospheric reactions.
Anthropogenic sources of NMHCs are mainly associated with human activities, including gasoline combustion, incineration, solvent evaporation, petroleum refining, and transportation losses. These sources contribute to about 96% of total anthropogenic hydrocarbon emissions, highlighting the importance of controlling them to reduce environmental impact.
**Gas Chromatographic Method for Determining Non-Methane Total Hydrocarbons in Fixed-Source Exhaust Gas:**
The Junqi instrument offers a reliable and efficient solution for analyzing NMHCs in fixed-source exhaust gases. It includes the following key components:
1. **GC9890A Gas Chromatograph Host (220V, 50Hz):**
- Imported HP high-sensitivity FID detector
- Packed column inlet
- Double six-way injection valve
- Five independent temperature control systems with intelligent rear door
- Data power-off protection and fault self-diagnosis
- Includes an accessory kit
2. **V2008 Chromatography Data Station:**
- Dual-channel capture card and software
- (Dual-channel, gas-liquid universal) analysis software
3. **Column:**
- Total hydrocarbon analysis packed column
**Main Features:**
- The main unit features a two-way valve control system, enabling convenient online automatic injection.
- An inter-column compensation circuit electronically compensates for baseline drift during program temperature operations, simplifying the second column, detector, and auxiliary flow system.
- The detector signal, heater value, furnace temperature, flow sensor reading, or stored column compensation baseline signal can be assigned to an analog output channel.
- Self-detection and fault diagnosis, power-off protection for experimental data, stopwatch, and running timer functions are included.
- Can be connected to a counter-control workstation for real-time control and can store 100 sets of experimental conditions and spectra.
- Compatible with the U.S. HP-5890 gas chromatograph micro-thermal conductivity detector for full integration.
- Supports installation of two flow sensing channels and two single column compensation channels.
**Heating Furnace System:**
- Temperature range: Ambient temperature +5°C to 400°C, third-order programmed temperature, heating rate 0–50°C/min, with increments of 0.1°C/min.
- Temperature control accuracy: ±0.05°C, allowing users to recalibrate and set maximum temperatures.
- Intelligent rear door opening system with stepless variable inlet and outlet air volume, reducing system stabilization time after temperature changes.
- Oven cooling from 300°C to 50°C takes less than 6 minutes.
**Injection System:**
- Packed column sampler suitable for various packed columns and large diameter capillary columns.
- Capillary injector with optional split/dispersed system controlled by a programmed valve.
- Optional headspace sampler and thermal analyzer available.
**Detector System:**
1. **Hydrogen Flame Ionization Detector (FID):**
- Easy to disassemble, install, clean, or replace nozzles.
- Input signal can be logarithmically amplified, reducing interference.
- High sensitivity, good linearity, and wide measuring range.
- Sensitivity: Type A Mt ≤ 5 × 10â»Â¹Â¹ g/s (n-hexadecane)
- Baseline noise: ≤6 × 10â»Â¹Â² A/H
- Linear range: ≥10âµ
- Stabilization time: <0.5 hours
2. **Thermal Conductivity Detector (TCD):**
- Sensitivity: Type A ≥ 4000 mv·ml/mg (n-hexadecane)
- Baseline noise: ≤30 μV (with helium as carrier gas at 99.999% purity)
- Stabilization time: Type A <1.5 hours
- Gas barrier protection included
For detailed national standards and configuration methods, please contact us at 021-57786311.
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