Comprehensive two-dimensional gas chromatography for biogas and biomethane analysis

Exploring the hidden chemical landscape: Non-target and suspect screening analysis for investigating solid waste-associated environments

Solid waste is an inevitable consequence of urbanization. It can be safely managed in municipal landfills and processing plants for volume reduction or material reuse, including organic solid waste. However, solid waste can also be discarded in (un-)authorized dumping sites or inadvertently released into the environment. Legacy and emerging contaminants have the potential to leach from solid waste, making it a significant pathway to the environment. Non-target screening (NTS) and suspect screening analysis (SSA) have become helpful tools in environmental science for the simultaneous analysis of a wide range of chemical compounds. However, the application of these analytical approaches to environmental samples related to Raw or Processed Solid Waste (RPSW) has been largely neglected so far. This perspective review examines the potential and policy relevance of NTS and SSA applied to waste-related samples (liquid, gaseous and solid). It addresses the hurdles associated with the chemical safety of solid waste accumulation, processing, and reuse, and the need for landfill traceability, as well as effectiveness of leachate treatments. We reviewed the current applications of NTS and SSA to environmental samples of RPSW, as well as the potential adaptation of NTS and SSA techniques from related fields, such as oilfield and metabolomics, to the solid waste domain. Despite the ongoing technical challenges, this review highlights the significant potential for the implementation of NTS and SSA approaches in solid waste management and related scientific fields and provides support and guidance to the regulatory authorities.

Two-dimensional chromatography for the analysis of valorisable biowaste: A review

Various everyday areas such as agriculture, wood industry, and wastewater treatment yield residual biowastes in large amounts that can be utilised for the purpose of sustainability and circular economy. Depending on the type of biowaste, they can be used to extract valuable chemicals or converted into alternative fuels. However, for efficient valorisation, these processes need to be monitored, for which thorough chemical characterisation can be highly beneficial. For this aim, two-dimensional (2D) chromatography can be favourable, as it has a higher peak capacity and sensitivity than one-dimensional (1D) chromatography. Therefore, here we review the studies published since 2010 involving gas chromatography (GC) or liquid chromatography (LC) as one of the dimensions. For the first time, we present the 2D chromatographic characterisation of various biowastes valorised for different purposes (chemical, fuels), together with future prospects and challenges. The aspects related to the 2D chromatographic analysis of polar, poorly volatile, and thermally unstable compounds are highlighted. In addition, it is demonstrated how different 2D setups can be applied for monitoring the biowaste conversion processes.

State-of-the-art and challenges in the analysis of renewable gases

The development of renewable and low-carbon gases for injection into the gas grid obtained by different processes such as anaerobic digestion, pyrogasification, hydrothermal gasification, and methanation, followed by upgrading steps, increases the demand for analysis and characterization in order to fully manage their integration into the gas value chain. If the analysis of the main compounds (methane, carbon dioxide, hydrogen, and carbon monoxide) is well described, the analysis of impurities in renewable gases remains more challenging due to their various natures and quantities. After a brief description of renewable and low-carbon methane production processes, the review focuses on the methods used for the analysis of the different compounds in renewable gases, from the main ones to impurities at ppbv levels. Gas chromatography (GC), coupled with different detectors, is the preferred technique, enabling the analysis and quantification of siloxanes, terpenes, oxygenates, and sulfur compounds. Recently, comprehensive two-dimensional GC has been applied to renewable gases, increasing the number of compounds detected. Non-chromatographic techniques are also reviewed. As sampling is of major importance in the search for reliable analyses, a whole section is devoted to this aspect. Among the available methods, pre-concentration on adsorbent tubes emerges as the most relevant solution.

Preparation of Thermodesorption Tube Standards: Comparison of Usual Methods Using Accuracy Profile Evaluation

In order to quantify organic impurities in gas produced from renewable sources, thermal desorption coupled with GC-MS or GC×GC-MS is very useful. However, the preparation of the standard tubes appears not to be trivial. For that, different strategies, based on commercial setups, have been developed. The goal of this study was to compare the classical manual deposit of a liquid standard solution with other commercial methods such as gas stream assisted deposit and vaporization followed by adsorption assisted by gas stream. A standard mixture of 48 compounds from different families was used for the comparison of the performances of the three strategies using the accuracy profile methodology. A global validation score was attributed to each strategy as well as a score according to family of compounds and boiling point range, in order to provide a detailed comparison of the techniques. On the set of studied molecules, commercial setups were found to be more efficient than the manual deposit.

Novel field-portable high-pressure adsorbent tube sampler prototype for the direct in situ preconcentration of trace compounds in gases at their working pressures: application to biomethane

In Europe, renewable energy gases such as biomethane are aimed at substituting natural gas provided their stringent compliance to natural gas quality standards stipulating maximal levels of several chemical trace compounds (TC). Preconcentration is generally required to detect TC and inasmuch as biomethane is compressed for injection in the natural gas grid, preconcentration is commonly either done by collecting the bulk pressurized gas in a high-pressure cylinder or by first depressurizing it to collect a bulk volume in e.g. a gas sampling bag. Such whole gas samples are then transported to the lab and transferred to a preconcentration unit, entailing contamination and TC loss risks. Therefore, here a novel handy field-portable device for the direct in situ high-pressure preconcentration of TC is presented, enabling to sample gases at pressures up to 200 bar_a through a self-assembled Tenax®TA + Carbopack™X multibed adsorbent tube. The effect of the gas sampling pressure on the preconcentration of TC on adsorbent tubes was evaluated using a synthetic gas mixture containing 41 halogenated volatile organic compounds each at 1 ppm_mol in N₂. At given normalized sampled volumes and in the pressure range 5–100 bar_a handled in French gas transport grids, the pressure had no influence on the preconcentration when the gas circulates through the adsorbent tubes and as long as the adsorbents are not saturated. Next, for the first time, a real biomethane stream was sampled using the novel direct high-pressure preconcentration method on Tenax®TA + Carbopack™X multibed adsorbent tubes, allowing to preconcentrate, in a single sampling run, a wide range of volatile organic TC. More than 26 distinct TC were detected, belonging to seven chemical families: alkenes, aromatics, alkanes (linear, cyclic and polycyclic), sulphur-compounds and terpenes, with linear alkanes (pentane, heptane, octane) and terpenes predominating. Semi-quantification indicated pentane, dimethylcyclopropane, hexane, heptane, octane, α-pinene and camphene are present at a ≤1 ppm_mol concentration threshold in the biomethane.

The circulating gas sampling pressure had no impact on the preconcentration of trace compounds on adsorbent tubes.

Comprehensive Screening of Polycyclic Aromatic Hydrocarbons and Similar Compounds Using GC-APLI-TIMS-TOFMS/GC-EI-MS

In the present work, a novel workflow based on complementary gas-phase separations for the identification of isomeric PAHs from complex mixtures is described. This is the first report on the coupling of gas chromatography (GC), atmospheric pressure laser ionization (APLI), and trapped ion mobility spectrometry-mass spectrometry (TIMS-MS) for the characterization of polycyclic aromatic hydrocarbons. Over a hundred known unknowns are uniquely identified based on the molecular ion retention indices I (5%), mobility (RSD < 0.6% and R = 50-90 with S_r = 0.18 V/ms), mobility-based theoretical candidate assignment (<3%), accurate mass chemical formula assignment (<2 ppm), and electron impact fragmentation pattern and database search. The advantages of theoretical modeling of PAHs and similar compounds were evaluated using candidate structures ranked by retention indices and fragmentation pattern from GC-EI-MS data sets. Over 20 PAH isomeric and deuterated standards were utilized for the GC-APLI-TIMS-TOF MS workflow validation. Noteworthy is the analytical capability for untargeted screening of isomeric and isobaric compounds with additional characterization metrics not available in traditional GC-EI-MSⁿ workflows.

Analysis of Natural Gas Using a Portable Hollow-Core Photonic Crystal Coupled Raman Spectrometer

The low accessibility of natural gas fields and transporting pipelines requires portable online analyzers of the composition of natural gas, ensuring nearly chromatographic precision and capable of in situ analysis of a wide range of gases, including infrared-inactive ones (hydrogen, oxygen, nitrogen, chlorine). We have developed an express method of gas analysis meeting all the requirements for analysis of natural gas and its derivative mixtures using a portable 532 nm Raman spectrometer rigidly connected to a hollow-core crystal photonic fiber.

Advanced mono- and multi-dimensional gas chromatography-mass spectrometry techniques for oxygen-containing compound characterization in biomass and biofuel samples

A wide variety of biomass, from triglycerides to lignocellulosic-based feedstock, are among promising candidates to possibly fulfill requirements as a substitute for crude oils as primary sources of chemical energy feedstock. During the feedstock processing carried out to increase the H:C ratio of the products, heteroatom-containing compounds can promote corrosion, thus limiting and/or deactivating catalytic processes needed to transform the biomass into fuel. The use of advanced gas chromatography techniques, in particular multi-dimensional gas chromatography, both heart-cutting and comprehensive coupled to mass spectrometry, has been widely exploited in the field of petroleomics over the past 30 years and has also been successfully applied to the characterization of volatile and semi-volatile compounds during the processing of biomass feedstock. This review intends to describe advanced gas chromatography-mass spectrometry-based techniques, mainly focusing in the period 2011-early 2020. Particular emphasis has been devoted to the multi-dimensional gas chromatography-mass spectrometry techniques, for the isolation and characterization of the oxygen-containing compounds in biomass feedstock. Within this context, the most recent advances to sample preparation, derivatization, as well as gas chromatography instrumentation, mass spectrometry ionization, identification, and data handling in the biomass industry, are described.

Analytical methods for the determination of oil carryover from CNG/biomethane refueling stations recovered in a solvent

Vehicle gas is often compressed to about 200 bar at the refueling station prior to charging to the vehicle's tank. If a high amount of oil is carried over to the gas, it may cause damage to the vehicles; it is therefore necessary to accurately measure oil carryover. In this paper, three analytical methods for accurate quantification of the oil content are presented whereby two methods are based on gas chromatography and one on FTIR. To better evaluate the level of complexity of the matrix, 10 different compressor oils in use at different refueling stations were initially collected and analysed with GC and FTIR to identify their analytical traces. The GC traces could be divided into three different profiles: oils exhibiting some well resolved peaks, oils exhibiting globally unresolved peaks with some dominant peaks on top of the hump and oils exhibiting globally unresolved peaks. After selection of three oils; one oil from each type, the three methods were evaluated with regards to the detection and quantification limits, the working range, precision, trueness and robustness. The evaluation of the three measurement methods demonstrated that any of these three methods presented were suitable for the quantification of compressor oil for samples. The FTIR method and the GC/MS method both resulted in measurement uncertainties close to 20% rel. while the GC/FID method resulted in a higher measurement uncertainty (U = 30% rel.).

Experimental study on high-purity hydrogen generation from synthetic biogas in a 10 kW fixed-bed chemical looping system

The utilization of locally available renewable resources is crucial for the creation of a sustainable energy system in the future. Biogas, a product of the anaerobic digestion of biogenic residues, exhibits great potential as feedstock to generate hydrogen for fuel cell mobility applications. A 10 kW fixed-bed chemical looping research system, to-date the largest in the world, was operated to prove the applicability of this versatile process for synthetic biogas utilization. In this experimental study, the focus was laid on examining the influence of different operating parameters (biogas composition, steam co-feeding, process temperature) on the attainable hydrogen purity and system efficiency. The generated hydrogen, between 90 to 230 g per cycle, was characterized online by ppm-range gas analysis and exhibited a product gas quality between 99.8% and 99.998%. The difference observed is attributed to carbon deposition if synthetic biogas with an increased share of carbon dioxide was supplied. This study involved the longest uninterrupted period of operation of a lab prototype system for fixed-bed chemical looping with 250 hours of time-on-stream, four months of discontinuous service and 50 consecutive experimental cycles.

Experimental proof of synthetic biogas utilization for high-purity hydrogen generation (99.998%) with a 10 kW fixed-bed chemical looping system.

Ultrafine Particle Emissions from Natural Gas, Biogas, and Biomethane Combustion

Biogas and biomethane (=purified biogas) are major renewable fuels that play a pivotal role in the evolving global energy economy. Here, we measure ultrafine particle (UFP; D_p (particle diameter) < 100 nm) emissions from the combustion of biomethane and biogas produced from five different representative sources: two food waste digesters, two dairy waste digesters, and one landfill. Combustion exhaust for each of these sources is measured from one or more representative sectors including electricity generation, motor vehicles, and household use. Results show that UFP emissions are similar when using biomethane and natural gas with similar sulfur and siloxane content. Approximately 70% of UFPs emitted from water heaters and cooking stoves were semivolatile, but 30% of the UFPs were nonvolatile and did not evaporate even under extremely high dilution conditions. Photochemical aging of biomethane combustion exhaust and natural gas combustion exhaust produced similar amounts of secondary organic aerosol (SOA) formation. The results of the current study suggest that widespread adoption of biogas and biomethane as a substitute for natural gas will not significantly increase ambient concentrations of primary and secondary UFPs if advanced combustion technology is used and the sulfur and siloxane content is similar for biogas/biomethane and natural gas.