Full Length ArticleFT-ICR MS analysis of blended pine-microalgae feedstock HTL biocrudes
Introduction
Hydrothermal liquefaction is an effective process for conversion of wet biomass feedstocks to oil [1], [2], [3]. Among feedstock choices, microalgae has been studied as an HTL candidate feed through the recent interest in that material for biofuel development [4], [5], [6], [7], [8]. Harvested algal cultures are well-suited as HTL feedstock because they do not require significant sample preparation, can contain relatively high lipid content and additional water is not needed to generate a pumpable slurry [1].
Nonetheless, the availability of algal biomass for biofuel production is limited by seasonal harvest variability (among other cultivation challenges), with higher summer productivity than that of winter [3]. Techno-economic analysis reveals that the under-utilization of equipment during winter results in significant costs penalties for production economics [3]. In fact, feedstock costs limit the viability of commercial-scale HTL biocrude production regardless of feedstock and single biomass sources are not available in sufficient quantity to support a large-scale HTL operation, let alone a cost-effective upgrading unit.
Mixed-biomass HTL addresses feedstock supply limitations and allows for development of regionally significant biomass sources. The use of multiple biomass sources provides a means to tailor feedstock composition to maximize throughput and mitigate production issues. Hydrothermal liquefaction of mixed microalgal species and/or microalgae mixed with other biomass has been shown to improve the economic prospect of HTL operations [9]. Chen et al. generated HTL biocrude from mixed swine mature/algae blends to determine the feasibility of mixed feeds [10]. The abundant nutrients within swine manure were used to enhance the growth of algae and co-liquefaction was determined to be economically advantageous [10]. Brilman et al. studied the co-liquefaction of microalgae, wood, and sugar beet pulp [11]. Similarly, Madsen et al. preformed quantitative analysis on composition of HTL biocrudes from lignocellulosic, macroalgae, microalgae, residues, and mixtures of the later [12]. Results from both studies show that biocrudes generated from mixed lignocellulosic/microalgal feedstocks differed from the calculated values (linear average for neat feeds) and suggest the need for further research on the co-liquefaction of mixed feeds [11], [12].
Here, Pacific Northwest National Laboratory (PNNL) has generated several HTL biocrudes from a mixture of pine waste and microalgal feedstocks in variable ratios to determine the yields and biocrude quality that result from HTL of mixed lignocellulosic/algal feedstock. We utilize one of the most advanced mass spectrometers in existence, a custom-built 9.4 Tesla Fourier transform ion-cyclotron resonance mass spectrometer (FT-ICR MS) at the national FT-ICR user facility at the National High Magnetic Field Laboratory, to map compositional differences for HTL biocrudes generated from 100% pine, 100% algae, 75:25 pine:algae, and 50:50 pine:algae feeds. The FT-ICR MS analysis identifies thousands of compounds simultaneously within complex mixtures [13] and has been successfully applied to the analysis of HTL biocrudes from various feedstocks [5], [14], [15], [16], [17], [18], [19], [20], [21]. In general, FT-ICR MS analysis of biocrudes generated from lignocellulosic sources reveal oxygenated species (degradation of carbohydrates) are present in the highest relative abundance whereas biocrudes generated from algal sources contain higher relative abundances of nitrogen-containing species (degradation of protein) [5], [14], [15], [16], [17], [18], [19], [20]. To our knowledge, this study represents the first analysis of mixed lignocellulosic/algal feeds by FT-ICR MS. Ultimately, the detailed molecular fingerprint of each mixed feed biocrude allows direct comparison of chemical composition for biocrudes derived from different feed make-up and can be used to predict and determine upgrading strategies and decipher thermochemical processes with occur during the HTL process.
Section snippets
Biocrude production
Biocrude samples were prepared using bench-scale, continuous HTL process equipment that has been previously described [2]. The 50:50 pine:algae and 100% algae tests used a system configuration with tube-in-tube plug-flow reactors only. The continuous stirred tank reactor (CSTR) was bypassed. For the 100% pine test, the CSTR was added between the preheater and main tubular reactor as insurance against plugging in the main reactor but the feed was heated to 320 °C in the tubular preheater at a
Biocrude yield, composition, and properties
Each of the HTL tests yielded gravity-separable biocrude and the overall mass balance during the sampling window ranged from 99 to 105%. Table 2 contains mass and carbon yields with associated mass balances. Reported yields are normalized to the mass balance percentage, which is computed by the mass (overall or by element) of products out divided by the mass of feed input. The highest yield is noted for the 50:50 pine:algal blend, with 0.46 g biocrude/g feed (dry, ash free). This result
Conclusion
FT-ICR MS analysis of the HTL biocrudes generated from pine and algal feedstocks demonstrates the composite nature of the pine/algal HTL biocrude blends as well as the formation of novel compounds compared to the pure feedstock biocrudes. Both the 75:25 and 50:50 pine:algal HTL biocrudes contain heteroatom classes with lower oxygen/higher nitrogen contents than the pine HTL biocrude and higher oxygen/lower nitrogen contents than the algal HTL biocrude. Compositionally, the blends tend to appear
Acknowledgments
This work was supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (Bioenergy Technologies Office), the United States National Science Foundation (IIA-1301346 and MRI-1626468), the Center for Animal Health and Food Safety at New Mexico State University, and NSF Division of Materials Research (DMR-11-57490). The authors thank the ICR staff at National High Magnetic Field for their help with instrument set-up and data collection.
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