• Energy Research

Abstract Liquefaction is an attractive technology for converting biomass into bio-oil without the requirement for drying feedstock, and the process can be conducted at relatively low temperatures. In the practical application, the treated biomass feedstocks are composed of a mixture of agricultural waste, forestry waste and some organic solid waste. The utilization of co-liquefaction technology is suitable for biomass as it can fully utilize different types of feedstocks and enhance the liquefaction degree of each feedstock. During the co-liquefaction of these blending biomass feedstocks, the individual biomass species can degrade according to their own reaction network that is governed by the unique structural compositions. Furthermore, the reaction intermediates from the degradation of different biomasses can potentially interact with each other. This will affect the reaction characteristics and alter the chemical constituents and properties of the bio-oil produced. The understanding of interaction for the blending biomasses during the co-liquefaction process is of significance for tuning the chemical species and yield of the resulting bio-oil. Thus, this review work focuses on the co-liquefaction behavior of the various biomass feedstocks including lignocellulose, organic solid waste and algae. The influences of the essential operation parameters including solvent types, catalyst types, reaction temperature and time, and the mixing ratio of different biomasses on co-liquefaction behavior are also evaluated in detail. The choice of the proper reaction parameters is dependent on the structural characteristics of mixed feedstocks. Additionally, the co-liquefaction impact on the composition and formation mechanism of bio-oils are investigated.

Marine macroalgae Enteromorpha prolifera, one of the main algae genera for green tide, was converted to bio-oil by hydrothermal liquefaction in a batch reactor at temperatures of 220−320 °C. The liquefaction products were separated into a dichloromethane-soluble fraction (bio-oil), water-soluble fraction, solid residue, and gaseous fraction. Effects of the temperature, reaction time, and Na2CO3 catalyst on the yields of liquefaction products were investigated. A moderate temperature of 300 °C with 5 wt % Na2CO3 and reaction time of 30 min led to the highest bio-oil yield of 23.0 wt %. The raw algae and liquefaction products were analyzed using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, gas chromatography−mass spectrometry (GC−MS), and 1H nuclear magnetic resonance (NMR). The higher heating values (HHVs) of bio-oils obtained at 300 °C were around 28−30 MJ/kg. The bio-oil was a complex mixture of ketones, aldehydes, phenols, alkenes, fatty acids, esters, aromatics, and nitrogen-cont...

The resource utilization of food waste is crucial, and single-cell protein (SCP) is attracting much attention due to its high value. This study aimed to convert food waste to SCP by Yarrowia lipolytica. It was found the chemical oxygen demand (COD) removal rate 77 ± 1.70% was achieved at 30 g COD/L with the protein content of biomass only 24.1 ± 0.4% w/w biomass dry weight (BDW) in one-stage fermentation system. However, the protein content was significantly increased to 38.8 ± 0.2% w/w BDW with the COD removal rate 85.5 ± 0.7% by a two-stage fermentation process, where the food waste was firstly anaerobically fermented to volatile fatty acids and then converted to SCP with Yarrowia lipolytica. Transcriptomic analysis showed that the expression of SCP-producing genes including ATP citrate (pro-S)-lyase and fumarate hydratase class II were up-regulated in the two-stage transformation, resulting in more organic degradation for SCP synthesis.

AbstractFlash Joule heating (FJH) is an emerging and profitable technology for converting inexhaustible biomass into flash graphene (FG). However, it is challenging to produce biomass FG continuously due to the lack of an integrated device. Furthermore, the high-carbon footprint induced by both excessive energy allocation for massive pyrolytic volatiles release and carbon black utilization in alternating current-FJH (AC-FJH) reaction exacerbates this challenge. Here, we create an integrated automatic system with energy requirement-oriented allocation to achieve continuous biomass FG production with a much lower carbon footprint. The programmable logic controller flexibly coordinated the FJH modular components to realize the turnover of biomass FG production. Furthermore, we propose pyrolysis-FJH nexus to achieve biomass FG production. Initially, we utilize pyrolysis to release biomass pyrolytic volatiles, and subsequently carry out the FJH reaction to focus on optimizing the FG structure. Importantly, biochar with appropriate resistance is self-sufficient to initiate the FJH reaction. Accordingly, the medium-temperature biochar-based FG production without carbon black utilization exhibited low carbon emission (1.9 g CO2-eq g−1 graphene), equivalent to a reduction of up to ~86.1% compared to biomass-based FG production. Undoubtedly, this integrated automatic system assisted by pyrolysis-FJH nexus can facilitate biomass FG into a broad spectrum of applications.

It is challenging to handle heavy-metal-rich plants that grow in contaminated soil. The role of heavy metals in biomass on the physicochemical structure and electrochemical properties of their derived carbon has not been considered in previous research. In this study, Cu-ion hybrid nanoporous carbon (CHNC) is prepared from Cu content-contaminated biomass through subcritical hydrocharization (HTC) coupling pyrolytic activation processes. The CHNCs are used as advanced electrode material for energy storage applications, exhibiting an impressively ultrahigh capacitance of 562 F g−1 at a current density of 1 A g−1 (CHNC-700-4-25), excellent energy density of 26.15 W h kg−1, and only 7.59% capacitance loss after enduring 10,000 cycles at a current density of 10 A g−1, making CHNCs rank in the forefront of previously known carbon-based supercapacitor materials. These comprehensive characterizations demonstrate that copper ions introduce new electrochemically active sites and enhance the conductivity and charge transport performance of the electrode material, elevating the specific capacitance of CHNC from 463 to 562 F g−1. These findings offer valuable insights into the effective energy storage application of heavy-metal-contaminated biomass wastes.

The liquefaction of “green tide” macroalgae Enteromorpha prolifera in sub-/supercritical alcohols in a batch reactor had been investigated. Effects of the temperature and algae/solvent ratio on the liquefaction yields in methanol and ethanol were studied. The results showed that, under the conditions of the reaction time of 15 min and algae/solvent ratio set at 1:10, the macroalgae in methanol at 280 °C produced a bio-oil yield at 31.1 wt % of dry weight and the ethanol at 300 °C yielded bio-oil at 35.3 wt %. Different from bio-oils obtained by hydrothermal liquefaction of microalgae as well as macroalgae in our previous work, the bio-oils obtained by liquefaction of macroalgae in alcohols are mainly composed of ester compounds. A variety of fatty acid (C3–C22) esters (methyl or ethyl) in the bio-oils obtained in methanol and ethanol, respectively, were qualified by gas chromatography–mass spectrometry, and their relative contents are above 60% of the total area for each bio-oil. In addition, some N-conta...

Dichloromethane (DCM) is a solvent commonly used in laboratories for microalgae hydrothermal liquefaction (HTL) product separation. The addition of DCM would lead to an ���overestimation effect��� of biocrude yield and diminish biocrude quality. However, it is currently not clear to what extent this overestimation effect will impact a continuous HTL process. In this study, Chlorella vulgaris microalgae was processed in a continuous stirred tank reactor at different temperatures (300, 325, 350, 375, and 400 ��C) at 24 MPa for 15 min holding time. Two separation methods were applied to investigate the effect of using DCM in a cHTL product separation procedure in terms of product yield, biocrude elemental content, and aqueous product (AP) composition. Subsequently, the feasibility of reusing AP for algae cultivation has been evaluated. Results suggest that 350 ��C is the optimal temperature for cHTL operation, leading to the highest biocrude yield, and an average increase in biocrude yield of 9 wt % was achieved when using DCM in cHTL product separation. Within the temperature range investigated, an average biocrude yield estimation can be proposed by yield$_{non-DCM}$ ��� 0.818 �� yield$_{DCM}$. The AP has been characterized by total organic carbon and total nitrogen, high-performance liquid chromatography, and inductively coupled plasma optical emission spectroscopy. Results show that at 350���375 ��C more nitrogen and other ions were directed into the AP, which could be advantageous in nutrient recovery. With the help of optical density testing, algae was shown to exhibit a better growth using AP with activated carbon absorption purification treatment as compared to the standard medium. The recovery of water and nutrients from the HTL-AP could improve the economics of a microalgae biorefinery process.

Abstract Using inexpensive and high-quality oil feedstock is an effective means to produce low-cost biodiesel. This work investigated the production and fuel properties of biodiesel derived from Hodgsonia macrocarpa (HM). The oil content of HM seed was 71.65 wt%, which is much higher than that of many potential oil plants. With traditional base-catalyzed transesterification, biodiesel was readily prepared from HM seed oil. The biodiesel yield was 95.46 wt% from HM seed oil. Biodiesel derived from HM met all ASTM D6751 and EN 14214 specifications, except for oxidative stability (OS). The OS specifications of the two biodiesel standards were met after treatment of HM biodiesel with 400 ppm tertbutyl hydroquinone. The biodiesel exhibited excellent transportation safety and cold flow properties, with flash point of 153 °C, pour point of −9 °C, and cold filter plugging point of −7 °C.

Two-stage nanofiltration (TSNF) process was proposed for recovering high-value chemicals, including monophenols, cyclopentenones, glucose and acetic acid, from hydrolysates of lignocellulosic biomass (rice straw) through hydrothermal liquefaction (HTL). The separation performances of three single nanofiltration (NF) processes and three TSNF processes were studied. Results showed that at the first stage of (DL + DK) TSNF process, DL membrane had high glucose rejection of 97.12%, and lower acetic acid rejection as well as lower aromatics rejections than DK membrane. At the second stage, DK membrane had rather low acetic acid rejection of 5.04% to ensure acid separation from aromatics. Unlike glucose or acetic acid, aromatics were unable to be recovered into one fraction due to scattered rejections of different aromatic compounds on NF membrane. The (DL + DK) TSNF process was proved to be a feasible way to fractionate hydrolysates into three parts: glucose concentrate, monophenols and cyclopentenones concentrate, and acetic acid permeate.