Qualitative Characterization of the Aqueous Fraction from Hydrothermal Liquefaction of Algae Using 2D Gas Chromatography with Time-of-flight Mass Spectrometry

Summary

A two-dimensional gas chromatography-time-of-flight mass spectrometry method is described for characterization of the aqueous fraction of bio-crude produced from hydrothermal liquefaction of algae. This protocol can also be employed to analyze the aqueous fraction of liquid products from fast pyrolysis, catalytic fast pyrolysis, catalytic deoxygenation and hydro-treating.

Abstract

Two-dimensional gas chromatography coupled with time-of-flight mass spectrometry is a powerful tool for identifying and quantifying chemical components in complex mixtures. It is often used to analyze gasoline, jet fuel, diesel, bio-diesel and the organic fraction of bio-crude/bio-oil. In most of those analyses, the first dimension of separation is non-polar, followed by a polar separation. The aqueous fractions of bio-crude and other aqueous samples from biofuels production have been examined with similar column combinations. However, sample preparation techniques such as derivatization, solvent extraction, and solid-phase extraction were necessary prior to analysis. In this study, aqueous fractions obtained from the hydrothermal liquefaction of algae were characterized by two-dimensional gas chromatography coupled with time-of-flight mass spectrometry without prior sample preparation techniques using a polar separation in the first dimension followed by a non-polar separation in the second. Two-dimensional plots from this analysis were compared with those obtained from the more traditional column configuration. Results from qualitative characterization of the aqueous fractions of algal bio-crude are discussed in detail. The advantages of using a polar separation followed by a non-polar separation for characterization of organics in aqueous samples by two-dimensional gas chromatography coupled with time-of-flight mass spectrometry are highlighted.

Introduction

Steady growth in demand for liquid fuels, finite fossil fuel resources, uncertainty of fossil fuel supplies, and concerns over the increasing concentration of greenhouse gases in the atmosphere have increased global awareness for renewable resources¹. Solar energy (including photovoltaics and solar-thermal), wind energy, hydropower, geothermal, and biomass are the primary renewable sources that could potentially replace fossil-derived energy². Of these, biomass is the only carbon-based alternative energy resource for the production of liquid transportation fuels and high-value chemicals³. Biomass includes any organic material such as f....

Protocol

1. Sample Preparation

1. Generate a mixed aqueous/organic product stream via continuous flow HTL of algae according to the reactor design and experimental procedure found in the literature^10,11.
2. Use a gravity separator to separate the product stream into an aqueous phase and organic phase.
3. Filter 10 ml of the HTL aqueous phase using a 0.45 µm syringe filter and store in a refrigerator maintained at 4 °C for GC × GC–TOF-MS analysis.

2. Instrument Components

1. Use a gas chromatograph (GC) equipped with a quad-jet dual stage cooling-based modulator and time-of-flight....

Results

A total ion chromatogram (TIC) obtained for the aqueous fraction of algae bio-crude analyzed with a column combination of polar × non-polar is shown in Figure 4. Retention times and similarity or match factor values of compounds identified by searching against a National Institute of Standards and Technology (NIST) library are tabulated in Table 1. Oxygenates (such as cyclopenatanone, furanic compounds and dianhydromannitol) and organic acids (including a.......

Discussion

Results clearly illustrate the ability of the column combination of polar × non-polar to resolve polar compounds and light volatiles present in the aqueous fraction of algae bio-crude without prior sample preparation techniques. Drastic peak tailing was observed for organic acids and N-compounds while using the non-polar× polar column combination. This peak tailing was not observed for the early eluting light organics. This behavior has been reproducible when verifying the instrument is free of leaks (the vacuu.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
GC × GC–TOF/MS	Leco	PEG4D11DLN15	Commercial Pegasus 4D
ChromaTOF version 4.50	Leco		Data analysis software
Rxi-5MS GC column	Restek	13420	2.3 m column was used from this column.
Stabilwax GC column	Restek	10626
HP-5 GC column	Agilent	19091J-416
Stabilwax GC column	Restek	15121
Presstight Connector	Restek	20430
GC injector liner	Restek	23305.5
GC Injector ferrules	Agilent	5181-3323
Non-stick liner O-rings	Agilent	5188-5365
Transfer line ferrules	Restek	20212
Ethanol	Sigma-Aldrich	459844	Chromatography grade
Acetone	Sigma-Aldrich	414689	Chromatography grade
Acetic acid	Sigma-Aldrich	320099	Chromatography grade
2-butanone	Sigma-Aldrich	360473	Chromatography grade
Propanoic acid	Sigma-Aldrich	402907	Chromatography grade
Butanoic acid	Sigma-Aldrich	19215	Chromatography grade
Pyridine	Sigma-Aldrich	270970	Chromatography grade
Pyrazine	Sigma-Aldrich	65693	Chromatography grade
Acetamide	Sigma-Aldrich	695122	Chromatography grade
2,5-pyrrolididione	Sigma-Aldrich	S9381	Chromatography grade
N-methylsuccinimide	Sigma-Aldrich	325384	Chromatography grade
N-(2-hydroxyethyl)succinimide	Sigma-Aldrich	444073	Chromatography grade