Micro Gas Chromatograph

POKE meeting Tallin, Sabrina Schmidt, Laboratory of Industrial Chemistry and Reaction Engineering,

Åbo Akademi

Classical Gas Chromatograph (GC)

•Injection

•Separation

•Detection

Micro-GC Agilent 3000A

Micro-GC : Elements

Each element contains:

Micro-injector

Sample column (+pre column)

Reference column

Detector

Electronic pressure control

Gas flow solenoids

Hardware

Control board

The portable module

• Delivered also as portable module with a battery

and an inbuilt gas-cylinder

For workers/rescuers in coal mines

• Coal mine explosion: indicated by C2H6, C2H4 and C2H2.

• Micro GC can analyze these compounds in less than 60 seconds at the necessary detection limit of 1ppm

General features

• Mobile

• Modular setup, easy exchange of column types

• Online analysis with programmable sampling intervals

• Very fast analysis, typically less than 180 s

General features

• Fixed/variable volume injector

• Back flush: removes unwanted contaminants from your analysis

• Thermal conductivity detector: 10 times more sensitive than traditional TCDs, allowing you to detect common gas components in the low ppm range.

General features: Precautions

• Only for clean gas samples Micro injector is sensitive towards plugging

• No liquids, no condensibles

• No particles

• Agilent supplies sample filters and conditioners

• Gas liquid separator

• Pressure reducer

Our micro GC

• Four separate modules

• Self-made valve system to connect two reactor setups and two calibration gases

Columns

• Plot U: hydrocarbons, CO2, air/CO, water, polar compounds

• OV-1: Hydrocarbons, phenol, amines, non-polar

• Alumina: petrochemicals (acetylene, ethylene, propadiene)

• Molesieve 5A : Hydrogen, CO, oxygen, nitrogen, methane

Two practical examples from our lab:

Online Analysis

Example 1: Online analysis for methyl chloride synthesis

Analysis of methanol, dimethyl ether, methyl chloride

No liquids: Lines are heated to 95 °C to prevent condensation of methanol

GC signals and analysis time

13

• Sample analysis in less than 1 min

• Separation is not optimal

PlotU

OV-1

Stability of methanol flow

14

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0 200 400

Are

a /

µV

*s*1

06

flow

stop

t/min

•Standard deviation from average flow: 1.6 %

•Fixed injection volume is reliable: easy calibration

•Information on residence time distribution

Switch to standard GC due to breakdown of micro GC

Analysis using a standard GC

Separation: +

Sample analysis : - (10 min instead of 1 min)

Sampling: - (running from the reactor to the GC with a gas tight

syringe heated to 100 °C)

Maintenance: - (septum of reactor sampling unit and GC)

Standard GC is sufficient

Micro GC vs. normal GC

Example 2: Aqueous phase reforming of sugar alcohols

Analysis of CO, CO2, H2 , CH4, linear hydrocarbons C1-C4,

He, N2

All analyzed in one sample/run

Inert gas: 1 wt% He in N2 as internal standard for micro GC

Analysis works perfectly – No change in signal since four years

Summary: Advantages /Disadvantages

• Modular Design: Column, Injector and Detector in a box

No possibility to self-repair

• Micro injector is delicate! Micro injector was plugged

– The whole module has to be replaced

• Mobile

• Online analysis

• Easy calibration due to fixed injection volume

• Parallel analysis with four columns

Thank you for your attention!