Method development and evaluation of pyrolysis oils from mixed waste plastic by GC-VUV.

The conversion of waste streams into a useable material through a recycling process is a hot topic. Waste streams can originate from domestic and industrial sources and range from plastic waste to medical waste to various industrial waste streams, both solid and liquid. In addition to waste circularity, circularity for bio-based waste streams and renewable sources are also being investigated. To simplify this complexity, this article presents a case study evaluating the output from the feedstock recycling of plastic waste originating from municipal solid waste. Plastic waste entering the environment is undesired, and many initiatives are working towards a plastics circular economy. Once disposed of, ideally, plastic waste should be either re-used or recycled in order to avoid incineration or disposal in landfills. Recycling waste plastic can occur either via mechanical recycling or feedstock (chemical) recycling, where feedstock recycling can occur for example, through gasification or pyrolysis technologies. This article will focus only on the oils obtained from the pyrolysis of mixed waste plastic. The output from pyrolysis has a different composition than traditional fossil-based hydrocarbon streams, and therefore, must be evaluated to correctly process as feedstock. The authors have previously shown that gas chromatography coupled to vacuum ultraviolet detection (GC-VUV) provides accurate identification and quantification of the hydrocarbon composition (paraffins, isoparaffins, olefins, naphthenes, and aromatics - PIONA) of fossil-based liquid hydrocarbon streams.1 Therefore, GC-VUV was evaluated for analysis of the pyrolysis oils from plastic waste. Using an in-house modified spectral library in combination with the PIONA+ software, accurate identification and quantification of the hydrocarbon composition of pyrolysis oils from C4 through C30+ was possible with a limit of detection of 0.1 wt.%. To the best of our knowledge, this article is the first example of accurate PIONA-type quantification of pyrolysis oils by GC-VUV.

A reversed-flow differential flow modulator for comprehensive two-dimensional gas chromatography.

A simple and reliable differential flow modulator has been demonstrated which reverses the flow during the flush step. The modulator is constructed with commercially available capillary flow technology tees which simplifies the apparatus and permits wide range of column dimensions to be used because the modulator volume is adjustable. Using a reverse flush arrangement the tailing of the peak at the base (baseline rise between modulations) is reduced 10-20 fold as compared to forward flush modulation. This is most easily observed for peaks overloaded in the first dimension. Excellent reproducibility (<2% RSD) of area measurements has been demonstrated with a complex fragrance sample as well as the capacity to handle significant overloading without loss of resolution in the second dimension. Further demonstrating the flexibility of this modulator, separation of C1-6 alkanes and olefins are demonstrated with two porous layer open tubular columns.

One-pot microwave derivatization of target compounds relevant to metabolomics with comprehensive two-dimensional gas chromatography.

Metabolomics has been defined as the quantitative measurement of all low molecular weight metabolites (sugars, amino acids, organic acids, fatty acids and others) in an organism's cells at a specified time under specific environmental/biological conditions. Currently, there is considerable interest in developing a single method of derivatization and separation that satisfies the needs for metabolite analysis while recognizing the many chemical classes that constitute the metabolome. Chemical derivatization considerably increases the sensitivity and specificity of gas chromatography-mass spectrometry for compounds that are polar and have derivatizable groups. Microwave-assisted derivatization (MAD) of a set of standards spanning a wide range of metabolites of interest demonstrates the potential of MAD for metabolic profiling. A final protocol of 150 W power for 90 s was selected as the derivatization condition, based upon the study of each chemical class. A study of the generation of partially derivatized components established the conditions where this could potentially be a problem; the use of greater volumes of reagent ensured this would not arise. All compounds analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry in a standard mixture showed good area ratio reproducibility against a naphthalene internal standard (RSD<10% in all but one case). Concentrations tested ranged from 1 microg/mL to 1000 microg/mL, and the calibration curves for the standard mixtures were satisfactory with regression coefficients generally better than 0.998. The application to gas chromatography-quadrupole mass spectrometry and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry for a typical reference standard of relevance to metabolomics is demonstrated.

Analysis of low levels of oxygen, carbon monoxide, and carbon dioxide in polyolefin feed streams using a pulsed discharge detector and two PLOT columns.

A gas chromatography (GC) method is developed for rapid analysis of polyolefin feed streams for the catalyst poisons CO, CO(2), and O(2). The method uses an HP MoleSieve column in parallel with a CP-PoraPLOT Q column and a pulsed discharge detector (PDD). Detection limits for each of the potential poisons are between 50 and 250 ppb. For a 10-ppm standard, the precision of the method was +/- 4.2% for oxygen, +/- 7.8% for carbon dioxide, and +/- 2.0% for carbon monoxide. In addition to the polyolefin feed stream, nitrogen and hydrogen feed streams are also analyzed. In each case, sampling is observed to be a critical issue, with air contamination of the sample cylinder often the limiting step in determining the true level of oxygen. It is also noted that large amounts of argon are present in the standards when nitrogen is used as a balance gas. Because the trace oxygen peak partly coelutes with the larger argon peak, it is suggested that helium be used as the balance gas for all standards. This general experimental arrangement should be effective when applied to feed streams for other polymers as well.