Integrated process for catalytic upgrading of hydrothermal liquefaction aqueous phase in the supercritical state

Production and characterization of biocrude from Persian Gulf Sargassum angustifolium using hydrothermal liquefaction: Process optimization by response surface methodology

• Hydrothermal Liquefaction (HTL) process has the ability to convert all kinds of biomasses to biocrude, which is comparable to fossil crude oil and can be upgraded in existing refinery set-up. • Article identifies various design, scale-up and operational challenges in HTL technology and proposes potential ways to mitigate those challenges. • Key challenges in the post processing of biocrude to make it refinery ready are the high amount of heteroatoms, moisture, ash, and acid content. Renewables are going to play an important role in meeting the greenhouse gas (GHG) emission targets to mitigate the effects of climate change. Most of the bioenergy production processes available today can be broadly categorized into two types of technologies - biological and thermochemical processes. Worldwide, the major practiced methods are Combustion/Incineration, Pyrolysis, Gasification, Anaerobic digestion, Fermentation etc. These methods have their own benefits and limitations based on their capability and capacity to process various feed stocks, energy efficiency, operational challenges, product quality and economics. Hydrothermal liquefaction (HTL) process is one such method, which has recently attracted attention of many scientific and practicing community across the world on various platforms. HTL process has the ability to convert all kinds of biomasses to crude bio-oil, which is comparable to fossil crude oil and can be upgraded in existing refinery set-up. Although it has significant benefits over other conversion technologies, HTL process is yet to be commercialized. Several technical and operational challenges have been reported in literature that need to be addressed for successful scale-up and design of continuous scale HTL process. Large number of review and research articles pertaining to batch and pilot scale are available on the process and product development aspect of HTL process. However, limited information is available on the design and scale-up issues that are envisaged in the scale-up of HTL technology. This review article identifies various design, scale-up and operational challenges in HTL technology and proposes potential ways to mitigate those challenges.

Synthetic polymers constitute one of the largest fractions of solid waste worldwide. From 1950 to 2015, roughly 12 Gton of these materials were deposited either in landfills or in the environment. The absolute majority of these materials are energetically dense, fossil-derived and non-biodegradable, which causes accumulation in the environment, threatening both marine and terrestrial ecosystems. Chemical recycling of these materials can be a management strategy to alleviate pollution and to reuse otherwise wasted energy in the form of solid materials. Agricultural crop residues are composed of both wet and dry streams, summing up to 3600 Mton year-1 (2013 estimate) of wasted resources globally. Besides that, around 3120 MTon year-1 (2017 estimate) of animal manure is generated worldwide. Nowadays, these agribusiness byproducts are underutilized and their conversion to liquid biofuels may present an untapped opportunity to provide the sustainability needed in sectors dependent on liquid hydrocarbons as an energy source. This thesis focuses on understanding how synthetic polymers and agricultural waste interact under hydrothermal liquefaction (HTL) conditions, identifying opportunities and evaluating the engineering challenges to apply the technology in combined processing of waste streams. This work evaluates the possibility of recovering monomer-like structures from synergistic combined HTL (co-HTL) of synthetic materials and lignocellulosic biomasses. It also evaluates how biocrudes derived from highly synergistic co-HTL behave in downstream processing for biofuel production when compared to single-feedstock biocrudes. HTL uses the reactivity of hot-compressed water in near-critical conditions to convert carbon-based materials into useful short chain organic compounds. The interaction of different feedstock materials under this condition allows a beneficial process efficiency and enlarges the opportunities to apply this process in waste handling scenarios. Literature about HTL processing of synthetic polymers present significant achievements within the field, however the non-standardized approach for several studies lead to contradictory results, generating a knowledge gap between laboratory results and practical applications. Here, results of subcritical HTL processing are presented for the 12 most used synthetic polymers worldwide, both individually and combined with lignocellulosic materials. When evaluating synthetic polymers alone, it is found that materials containing heteroatoms in the backbone of the polymer structure are prone to hydrolysis under subcritical water, while carbon-carbon bonds are preserved. In practice, polymers derived from addition polymerization such as polyolefins and polystyrene do not depolymerize under subcritical water, while condensation polymers and others containing heteroatoms in the backbone are decomposed into molecules similar to their original monomers. When these materials are combined with lignocellulosic ones, the synthetic parts containing nitrogen heteroatoms tend to synergistically interact with the organic-derived molecules and act synergistically increasing biocrude production. The reactivity of nitrogen species in synthetic polymers was directly proportional to the intensity of the synergies verified. The largest synergy identified was for polyurethane combined processing due to the presence of highly reactive amines bonded to aromatic groups. This finding led to an improved combinedprocessing of polyurethane foam and lignocellulosic materials, reaching pilot processing carbon and energy efficiencies of 71 and 75%, respectively. The combination of wet and dry agribusiness waste fractions in HTL processing was evaluated using cow manure and wheat straw, respectively, as representatives. Their combination also leads to enhanced biocrude and carbon recovery during subcritical HTL processing through nitrogen species reactions with lignocellulosic-derived compounds. The formation of heteroatom-containing aromatics acts as a carbon carrier to the biocrude products. With this approach, pilot HTL processing carbon yields were enhanced from 40 to 60 wt%, while also providing superior total energy efficiencies (up to 50% based on organic input and output including heating utilities). This increase in carbon efficiency generates further benefits in the production of hydrotreated products, with biomass-to-hydrotreated products carbon balances increasing from 34 wt% for wheat straw in single HTL to 43 wt% in co-HTL of wheat straw and cow manure. The distillation of hydrotreated products depicts that the nitrogen-containing molecules tend to have higher concentration in heavier fractions, which may be an opportunity for more targeted processing of these fractions. Overall, production of biofuels enlarged via co-HTL mainly due to HTL superior carbon and energy yields. Both synthetic-organic and organic-organic waste combined HTL, the reactions involving nitrogen compounds generate high synergistic effects towards biocrude formation. When increasing product stability through nitrogenated species, a consequent increased difficulty for their removal in following hydrotreatment oil upgrading is also verified. Nevertheless, the enhanced carbon and energy recovery and enlarged scope of HTL technologies attainedvia combination of waste materials is an opportunity to take advantage of these sub-utilized streams.

Aqueous phase recycling in catalytic hydrothermal liquefaction for algal biomass and the effect on elemental accumulation and energy efficiency

Hydrothermal liquefaction of Cd-enriched Amaranthus hypochondriacus L. in ethanol–water co-solvent: Focus on low-N bio-oil and heavy metal/metal-like distribution

Hydrothermal liquefaction (HTL) is a promising thermochemical processing technology for converting wet biomass into liquid fuels, with aqueous phase (AP) as one main by-product. Recycling the AP into the HTL process is under extensive research due to its improvement in bio-oil production. However, an increased concentration of nitrogen in the bio-oil has been reported during recycling. In this work, the AP obtained from HTL of Spirulina Platensis was first pretreated by activated carbon to reduce nitrogen concentration and improve bio-oil quality from the circulating HTL. The optimal conditions for pretreating the AP were 160 mg activated carbon and 40 min adsorption time. Although the bio-oil yield obtained from the circulating HTL with the pretreated AP (35.15 wt. %) was lower than that from the untreated case (39.77 wt. %), the nitrogen content of the bio-oil was significantly reduced (7.95%), indicating an improved bio-oil quality. Moreover, the higher-heating value (HHV) of the bio-oil was increased slightly when the AP was pretreated before recycled. Interestingly, the content of n-hexadecanoic acid in the bio-oil from the pretreated case was found significantly higher than that in pure water and the untreated case. This study concluded that the HTL with recycled AP pretreated by activated carbon would be more favorable for the economic concern due to high conversion efficiency and high bio-oil quality.

Insights into valuing the aqueous phase derived from hydrothermal liquefaction

The hydrothermal liquefaction (HTL) of composite household waste (CHW) was investigated at different temperatures in the range of 240-360 °C, residence times in the range of 30-90 min, and co-solvent ratios of 2-8 ml/g, by utilising ethanol, glycerol, and produced aqueous phase as liquefaction solvents. Maximum biocrude yield of 46.19% was obtained at 340 °C and 75 min, with aqueous phase recirculation ratio (RR) of 5 ml/g. The chemical solvents such as glycerol and ethanol yielded a biocrude percentage of 45.18% and 42.16% at a ratio of 6 ml/g and 8 ml/g, respectively, for 340 °C and 75 min. The usage of co-solvents as hydrothermal medium increased the biocrude yield by 35.30% and decreased the formation of solid residue and gaseous products by 19.82% and 18.74% respectively. Also, the solid residue and biocrude obtained from co-solvent HTL possessed higher carbon and hydrogen content, thus having a H/C ratio and HHV that is 1.01 and 1.23 times higher than that of water as hydrothermal medium. Among the co-solvents, HTL with aqueous phase recirculation resulted in higher carbon and energy recovery percentages of 9.36% and 9.78% for solid residue and 52.09% and 56.75% for biocrude respectively. Further qualitatively, co-solvent HTL in the presence of obtained aqueous phase yielded 33.43% higher fraction of hydrocarbons than the pure water HTL and 7.70-17.01% higher hydrocarbons when compared with ethanol and glycerol HTL respectively. Nitrogen containing compounds, such as phenols and furfurals, for biocrudes obtained from all HTL processes, were found to be present in the range of 8.30-14.40%.

Elemental nitrogen balance, reaction kinetics and the effect of ethanol on the hydrothermal liquefaction of soy protein

This chapter focuses on the hydrothermal liquefaction (HTL) process and describes the basic structure, reaction pathway, and kinetics of breakdown of major components in the feedstock during HTL process. It discusses the effect of some of the important operating parameters on bio-oil yield. Products of HTL process include a high heating value biocrude or bio-oil, an aqueous fraction, gases, and solid residues. HTL is a very promising technology for high moisture feedstock conversion. The high solids content is unfavorable for proper mixing in the HTL reactor and reduces the heat and mass transfer, which results in lower conversion and bio-oil yields. The products obtained in bio-oil from cellulose HTL are different under acidic, neutral, and alkaline conditions. The nitrogen gets incorporated in bio-oil during the HTL process. Temperature is an important factor in depolymerization of biomass which is a dominant reaction during initial stages of HTL and requires sufficient temperatures to overcome the activation energies of bond cessation.

Azolla as a Feedstock for Bio-Refinery: Cultivation, Conversion and Application

Hydrothermal liquefaction of sewage sludge into biocrude: Effect of aqueous phase recycling on energy recovery and pollution mitigation

The National Advanced Biofuels Consortium is working to develop improved methods for producing high-value hydrocarbon fuels. The development of one such method, the hydrothermal liquefaction (HTL) process, is being led by the Pacific Northwest National Laboratory (PNNL). The HTL process uses a wet biomass slurry at elevated temperatures (i.e., 300 to 360°C [570 to 680°F]) and pressures above the vapor pressure of water (i.e., 15 to 20 MPa [2200 to 3000 psi] at these temperatures) to facilitate a condensed-phase reaction medium. The process has been successfully tested at bench-scale and development and testing at a larger scale is required to prove the viability of the process at production levels. Near-term development plans include a pilot-scale system on the order of 0.5 to 40 gpm, followed by a larger production-scale system on the order of 2000 dry metric tons per day (DMTPD). A significant challenge to the scale-up of the HTL process is feeding a highly viscous fibrous biomass wood/corn stover feedstock into a pump system that provides the required 3000 psi of pressure for downstream processing. In October 2011, PNNL began investigating commercial feed and pumping options that would meet these HTL process requirements. Initial efforts focused on generating a HTL feed and pump specification and then providing the specification to prospective vendors to determine the suitability of their pumps for the pilot-scale and production-scale plants. Six vendors were identified that could provide viable equipment to meet HTL feed and/or pump needs. Those six vendors provided options consisting three types of positive displacement pumps (i.e., diaphragm, piston, and lobe pumps). Vendors provided capabilities and equipment related to HTL application. This information was collected, assessed, and summarized and is provided as appendices to this report.

Hydrothermal liquefaction (HTL) processing of unhydrolyzed solids (UHS) for hydrochar and its use for asymmetric supercapacitors with mixed (Mn,Ti)-Perovskite oxides

Use of microalgae to recycle nutrients in aqueous phase derived from hydrothermal liquefaction process