The need for micro-process gas-chromatography (µGC)

Process Gas Chromatography (PGC) exists from the early 1960s. Compared to a laboratory gas-chromatograph  a process GC differs in the unattended and automated operation, its environmental conditions, and the demand of its applications. A conventional process gas-chromatograph consists of an electrical and mechanical system. With the development of the Micro Electrical & Mechanical Systems (MEMS) the micro gas-chromatograph (µGC) was introduced. Micro gas-chromatography is an analytical technique that lends itself to process analysis. Reasons for this perspective could be addressed as follows:

1. The high speed of the analysis
2. The small size, high robustness and reliability of the instrument
3. The low consumption of utilities (power and carrier) and sample
4. The advantage towards EMC and ATEX certification and integration
5. The modular design for the ease of adaption of laboratory applications 

As discussed in other studies (6) the need for micro-process gas-chromatography (µGC) can be found in the fast detailed analyses in various industrial processes, for the fast control of product yield and quality. A few examples:

• Oil exploration during drilling, a quick answer is obtained if hydrocarbons above a certain level are present (mud-logging).
• Real-time feedforward in the control of a chemical/petrochemical plant or refinery.
• Field installation in a (remote) location like on and off-shore natural gas fields for the fast analyses and energy calculation of natural gas.
• Environmental exhaust guarding against greenhouse gasses like CO₂ and CH₄ or emissions of toxic gasses like SO₂ and H₂S.

A number of µGCs are developed over the last decade, a brief overview is displayed below:

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Although the start of this chapter reports the abilities of a µGC to be uses for process analysis, none of the µGCs can be installed in a process environment just like that. Even some of them are not valid  to be installed in an industrial setup. Those are designed for a off-line (laboratory) use where the environment and utilities are under controlled and ideal conditions. The ability of a GC to be used in a process environment, a harsh and explosion danger environment, depends on a number of factors. These abilities of the instrument and the conditions under which it must operate can be addressed as follows:

1.     Its performance specifications (like speed, repeatability, bias, dynamic range etc.),

2.     The continuous and unattended operation (reliability),

3.     The ability to handle a wide variety of unknown samples (applications),

4.     The explosion proof certification (ATEX, CSA),

5.     The environmental conditions.

We look again at the µGC list but now from a perspective with above displayed criteria:

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A number of the µGCs in the table fail immediately the above selection criteria in Table 2. This can be explained as some of the µGCs only have a narrow application frame or lack of independency and inability to be operate unattended. All of the µGCs have performance specifications which are reported by the manufacturer and are therefore hard to compare. The selection of which instrument is eventually ready for  process control purpose is partly based on these performance specifications. In order to generalize the choice and make the µGCs comparable a request was formulated by a number of the µGC manufacturers to perform such a general performance specification.

Varian, SLS and C2V are further discussed as possible process µGCs. They cover a wide range of promising application features for process control. Due to universal detectors, wide dynamic range and flexible and modular instrumental setup they all apply as a potential process analyser.

The reason for the selection of the 3 µGCs from Varian, SLS and C2V in respect to the other brands can be further addressed as follows:

• The application frame is extensive and applications can be selected and extended by adding/combining modules with different columns. A feature to flush out components not of interest is available on all three brands.
• All have heated injectors, sample lines and inlets with a temperature up to 110°C to handle high boiling point samples in the gas phase. The sample inject volume is variable and can be reconfigured in seconds.
• They have µTCDs which allows for a wide dynamic range (ppmv – vol%) and universal detection of components.
• ATEX certification (for explosion safe operation) and environmental protection is available.
• Long term hardware field tests are performed and confirm suitability for process installation.
• All three manufacturers made a choice to make the instrument suitable for process analyses.

All other brands as displayed in Table 1 fail to one or more of the above described selection criteria and are therefore not selected for further testing.

Notes:

Due to confidentiality the detailed test results are not published and can only be obtained from the individual manufacturers.

Recently Varian Inc. was acquired by Agilent Technologies Inc; C2V was acquired by Thermo Scientific and SLS was acquired by Elster GmbH.