Liquefaction Of Microalgae Research Articles

Hydrothermal Liquefaction of Microalgae to Bio-oil Using Zeolite Catalysts

Mesoporous zeolite silica-alumina catalysts were investigated for their impact on the hydrothermal liquefaction (HTL) to convert Nannochloropsis oculata into bio-oil. The commercial catalysts were characterized using characterization instruments which are XRD, SAP, and TPD-NH3 analysis, revealing distinctive structural and physicochemical properties. The catalytic screening was conducted at varied reaction temperatures (160–240 °C), durations (60–120 min), and catalyst loadings (1–5 wt.%). The result revealed that ZSM-5 demonstrates effectiveness as a catalyst for the HTL of Nannochloropsis oculata, yielding high bio-oil production under optimized conditions. Strong acid sites and high surface area density are highlighted as the key factors contributing to the catalyst's enhanced performance in promoting valuable bio-oil components.

Catalytic and solvent hydrothermal liquefaction of microalgae: a strategy for recovering fine chemicals

Catalytic and solvent hydrothermal liquefaction of microalgae: a strategy for recovering fine chemicals

Hydrothermal liquefaction of microalga with and without seawater: Effects of reaction temperature on yield and hydrocarbon species distribution in biocrude

AbstractA halophytic microalga Tetraselmis sp. biomass diluted with deionized water and seawater was converted to biocrude with the hydrothermal liquefaction (HTL) process in a batch reactor at 310, 330, 350, and 370°C, 15 min with %w/w solids. The biocrude yield, carbon, and energy recovery in biocrude and hydrocarbon species distribution from deionized water base HTL (DW HTL) and seawater base HTL (SW HTL) were evaluated. The results revealed that irrespective of reaction medium, the yield in biocrude increased with an increase in temperature, reaching a maximum of 50–56 wt% at 350°C, characterized by a higher heating value of up to 35.6 MJ/kg. The carbon and energy recovery at 350°C were 85% and 89% respectively, for SW HTL, while the DW HTL stream was 10% and 12% lower. Also, the GC MS analysis of biocrude obtained from both streams contains a complex mixture of compounds such as hydrocarbons, phenolics, and large amounts of nitrogenated and oxygenated compounds. The metallic constituents in biocrudes derived from both steams showed no substantial variations. The study showed a marginal increase in biocrude yield and its HHV with a reduction in oxygen and nitrogen contents from the SW HTL stream, suggesting the potential of seawater as a reaction medium.

Orthovanadate intercalated CuFe-LDO catalyzed hydrothermal liquefaction of microalgae for low nitrogen bio-oil production

Hydrothermal liquefaction (HTL) of microalgae for bio-oil production is a promising strategy to avoid extensive fossil fuel utilization, while tandem amidation and Maillard reactions during hydrolysis of cellular compounds unavoidably result in formation of nitrogen containing (N-containing) compounds, reducing quality of bio-oil. Accordingly, VO43− intercalated Cu–Fe layered double oxides named as Cu2Fe-VO4-LDO is firstly synthesized to both catalyze hydrolysis of cellular compounds and block N-containing compounds formation. The results indicate Cu2Fe-VO4-LDO can improve bio-oil yield from 19.32 to 20.32 wt%, with decrease of N/C ratio from 0.70 of control to 0.67 of experimental group, and increase of H/C ratio from 0.129 to 0.132. The insert of VO43− provides more strong-acid sites, which are beneficial to hydrolysis of cellular compounds. Meanwhile, more strong-base sites of Cu2Fe-VO4-LDO promote decarboxylation of fatty acids and removing amino-group of amino acids, subsequently improve production of alkanes. Furthermore, the reversible oxidation of VO43− promotes oxidation of reducing sugars, blocking tandem amidation and Maillard reaction between intermedia of hydrolyzed lipids, carbohydrates, and proteins. This work reports a methodology for synthesis of Cu2Fe-VO4-LDO with strong acid-base sites and reversible oxidize interlayer sites, providing a strategy to simultaneously improve bio-oil yield and reduce its N/C ratio.

Optimization of process parameters for bio-crude and value-added chemical recovery through hydrothermal liquefaction of microalgae

Optimization of process parameters for bio-crude and value-added chemical recovery through hydrothermal liquefaction of microalgae

Effects of solvent phase recycling on microalgae liquefaction in ethanol: Bio-oil production and nitrogen transformation

Liquefaction of microalgae in ethanol offers an eco-friendly bio-oil alternative, but solvent recycling is crucial for sustainability due to extra costs. In this work, Chlorella vulgaris was liquefied in supercritical ethanol at 260 °C, and the solvent phase (SP) separated from bio-oil was recovered and reused. Five liquefaction cycles were performed at identical temperature and pressure conditions to investigate the effects on oil production and nitrogen transformation. The findings demonstrated a gradual increase in water content in recycled SP. Ethanol-water co-solvent as the reaction medium promoted the decomposition and re-polymerization of protein in raw material, thus increasing the bio-oil yield (76.84 %) and higher heating value (33.53 MJ/kg) to some extent. Simultaneously, the relative nitrogen content of bio-oil rose from 8.03 % to 8.52 %, predominantly in the form of nitrogen heterocycles. The potential pathway for nitrogen conversion was revealed, which establishes a theoretical basis for the subsequent denitrification of bio-oil.

Catalytic Hydrotreatment of Algal HTL Bio‐Oil over Phosphide, Nitride, and Sulfide Catalysts

AbstractGlobal energy demand and environmental concerns about limiting CO2 emissions have been growing recently. This is why fuel production from renewable resources has become a priority. In this context, microalgae represent an attractive alternative carbon source. In this work, different supported catalysts, including metal phosphide, nitride, and sulfide, were tested for the hydroconversion of bio‐oil issued from the hydrothermal liquefaction of microalgae. Supported Ni phosphide catalysts promoted the decarboxylation and decarbonylation route, while NiMo nitride promoted the hydrodeoxygenation pathway. NiW sulfide catalysts were the most performant, producing a hydrotreated oil with the best higher heating value (HHV), lower aromaticity degree, and lower average molar mass. Among sulfide catalysts, NiWS/SiO2−Al2O3 was the least active, probably due to the inhibition of acid sites by the nitrogen compounds. However, NiWS/Al2O3 performed better, showing high hydrogenation performances, which contributed to the conversion of refractory compounds.

Off-line two-dimensional separation involving supercritical fluid chromatography for the characterization of the wastewater from algae hydrothermal liquefaction

An off-line multidimensional method involving liquid chromatography combined with supercritical fluid chromatography was developed for the characterization of the wastewater of hydrothermal liquefaction of microalgae Chlorella sorokiniana. The first dimension consisted of a phenyl hexyl column operated in reversed-phase mode, whereas the second dimension was performed on a diol stationary phase. Optimization of the kinetic parameters of the first and second dimensions were performed, taking into account the fraction collection system. The beneficial effect of working at high flow rate in both dimensions, as well as the need to work with short columns (50 mm) in the second dimension was evidenced. Injection volume was also optimized in both dimensions. The first dimension benefited from on-column focusing, while in the second dimension, untreated water-rich fractions could be injected without peak deformation. The performances of offline LCxSFC were compared to LC-HRMS, SFC-HRMS and LCxLC-HRMS for the analysis of the wastewater. Despite a long analysis time of 3.3h, the off-line separation coupled to high-resolution mass spectrometry exhibited a very large orthogonality with 75 % occupation rate of the separation space, reaching an effective peak capacity of 1050. While other evaluated techniques were faster, one-dimensional techniques failed to separate the numerous isomers while LCxLC exhibited lower orthogonality (45% occupation rate).

Catalytic hydrothermal liquefaction of microalgae over reduced graphene oxide support Ni catalyst

In this study, a reduced graphene oxide (RGO) material loaded with nickel was prepared, and to the best of the authors' knowledge, it was the first time that RGO material used as a catalyst in the hydrothermal liquefaction (HTL) of microalgae. The effect of RGO support Ni catalyst on the yield and quality of bio-oil derived from HTL of Spirulina was studied in this research. The results showed that the catalyst could improve the yield of bio-oil, and the performance in improving the quality of bio-oil was significantly increased. GC–MS analysis showed that RGO catalyst could promote the formation of hydrocarbons. When the loading amount of Ni was 5%, the oxygen content of bio-oil was the lowest (14.79%), and when the loading amount of Ni was increased to 25%, the content of hydrocarbons was the highest (11.41%). In addition, RGO catalyst also increased the content of low boiling point components (<400°C) in bio-oil from 68% to 81%. This study can provide valuable information for the further application of graphene in microalgae HTL and the production of high-quality bio-oil in the future.

Microalgae liquefaction in ethanol to produce high-quality fuels: Effect of magnetic nanoparticles on nitrogen transformation

As the representative of the 3rd generation feedstock of biodiesel, microalgae show extraordinary advantages for energy demands. Magnetic separation is a proven and effective method for microalgae harvesting. This study aims to investigate the effect of unrecovered magnetite-based nanoparticles (Fe3O4 NPs) after microalgae harvesting on the bio-oil quality, especially nitrogen content in the subsequent production. Co-liquefaction of Chlorella Vulgaris mixed with three residual amounts (1 wt%, 5 wt%, and 10 wt% of microalgae addition) Fe3O4 NPs in ethanol at 220 and 260 °C were performed. Ethanol can provide hydrogen in situ during liquefaction, and the catalytic activity of Fe3O4 to hydrogenation reaction enhances the yield and quality of bio-oil. At 260 °C and 5 wt% NPs dosage, the bio-oil yield can reach up to 79.71%. The addition of NPs reduces the relative N content of bio-oil by more than 16.90%. GC/MS analysis shows that the nitrogen heterocyclic compounds are significantly reduced about 60%; instead, hydrocarbons are increased in the bio-oil. It implies that Fe3O4 NPs are beneficial to the denitrogenation of bio-oil during microalgae liquefaction in ethanol.

Reducing nitrogen content in bio-oil from hydrothermal liquefaction of microalgae by using activated carbon-pretreated aqueous phase as the solvent

Hydrothermal liquefaction (HTL) is a promising thermochemical technology for converting wet biomass into liquid fuels, with aqueous phase (AP) as one main by-product. The strategy for recycling AP into the HTL process is extensively studied due to its potential to enhance bio-oil production. However, an increased concentration of nitrogen elements in the bio-oil has been reported in recycling cases. In the current work, the aqueous phase was first pretreated with activated carbon to solve this problem before recycling it back into the liquefaction system. Results showed that nitrogen content was decreased, and bio-oil quality was improved due to pre-adsorption. The optimal pretreatment conditions were 160 mg activated carbon and 40 min adsorption time. Although the bio-oil yield obtained from the recycling HTL with the pretreated solvent (35.75 wt%) was lower than the untreated case (39.77 wt%), the nitrogen content of the bio-oil was also reduced up to 39% simultaneously. Moreover, the bio-oil's higher-heating value (HHV) was increased slightly when using the pretreated solvent. And the content of n-hexadecanoic acid in the bio-oil was expanded due to the decline of N-based compounds. This study concluded that liquefaction of biomass with the activated carbon-pretreated AP solvent leading to high conversion efficiency and bio-oil quality would be more favorable from an economic point of view.

Integrated route of fast hydrothermal liquefaction of microalgae and sludge by recycling the waste aqueous phase for microalgal growth

In this study, waste aqueous phase after hydrothermal of sludge was used to cultivate the green microalga Chlorella sp. Results showed that waste aqueous phase can be used as a medium for Chlorella sp, with nitrogen and phosphorus removal efficiency of more than 90 %. At the same time, it was found that the introduction of CO2 during microalgal cultivation can effectively promote the growth of Chlorella sp and increase the lipid content respectively, comparing to the control. Further, based on response surface methodology, the optimal cultivation conditions of Chlorella sp were 5 % CO2, BG-11/SAP = 1:1 mixed medium and growth for 8 days. Chlorella sp was cultivated under the optimal aforementioned conditions followed by hydrothermal liquefaction, then the differences between the bio-oil and aqueous phase obtained by fast hydrothermal liquefaction and hydrothermal liquefaction were compared. This study showed that Chlorella sp can effectively remove N and P in waste aqueous phase after hydrothermal of sludge. At the same time, the addition of CO2 was beneficial to increase the unit biomass of Chlorella sp and promote the accumulation of lipids. Further comparison of different hydrothermal liquefaction processes showed that fast hydrothermal liquefaction can obtain bio-oil with higher quality in a shorter reaction time.

Fractional distillation of biocrude from hydrothermal liquefaction of microalgae: Upgrading of fuel properties

The use of hydrothermal liquefaction (HTL) biocrude as commercial fuels remains challenging due to its complex composition, particularly the presence of heteroatomic nitrogen and sulfur containing compounds and oxygenates. In this study, a semi-automatic fractional distillation system was developed for the upgrading of biocrude from hydrothermal liquefaction of microalgae biomass. The fractional distillation produced ten liquid fractions (F1–F10 below 325 °C), which made up above 48.91 wt% of the biocrude. Through the distillation, the contents of N, O, and S were reduced by 0.12 %–22.70 %, 27.71 %–69.34 %, and 24.30 %–64.02 %, respectively. The GC–MS results showed that lighter fractions (F1–F3) were mainly composed of N-heterocyclics while heavier fractions (F5–F10) were dominated by saturated hydrocarbons and olefins, which was further evidenced by the thermogravimetric analysis (TGA) and Gel Permeation Chromatography (GPC) results. In addition, a significant reduction in metal contents (up to 94.26 %) was observed, and the alkalis metals (89.63 % of Ca and 96.17 % of K) and heavy metals (91.32 % of Pb and 59.08 % of As) mainly remained in the distillation residue. This study indicates that fractional distillation is a potential green method for the upgrading of HTL biocrude.

Production of acid-free bio-oil through improved co-HTL of sludge and microalgae: Experiment and life cycle assessment

Sludge and microalgae have been reported as the main residues of microalgal-bacterial symbiosis wastewater treatment, characterized by high moisture content and large output. Effective utilization is still a challenging task. Aiming to find out the most optimized and applicable process, eight co-hydrothermal conversion schemes were investigated in this study. It was found that using hydrothermal carbonization as pretreatment of sludge, co-hydrothermal liquefaction of two raw materials could have 45.65% bio-oil, 5.07% more than conventional co-hydrothermal liquefaction with simple mixing of sludge and microalgae in the reactor. The acid content of bio-oil was reduced by 14.4% at the same time. In another improved process, all acid of bio-oil was eliminated when the co-hydrothermal liquefaction occurred between microalgae and hydrochar obtained by sludge hydrothermal carbonization. This is more conducive to equipment material selection and reduces the difficulty of upgrading. Furthermore, the mechanism of acid transformation was explored by the hydrothermal experiment of model compounds. Based on experiment data, three optimal co-hydrothermal liquefaction systems were evaluated through conception process construction and life cycle assessment. The Global Warming Potential of co-hydrothermal liquefaction of sludge and microalgae was 39.97 kg CO2eq, while the Global Warming Potential of co-hydrothermal liquefaction of microalgae with hydrochar obtained by sludge hydrothermal carbonization was only 25.49 kg CO2eq, which showed that sludge hydrothermal carbonization exhibited the largest environmental benefits. And sensitivity analysis showed that combining hydrothermal carbonization with co-hydrothermal liquefaction could reduce the influence of various environmental impact categories and improve environmental stability.

Biofuel potential of liquid products from protein- and lipid-rich biomass hydrothermal liquefaction

Hydrothermal liquefaction (HTL) of oleaginous microorganisms is an economical method with which to transform all compounds of wet biomass into competitive biofuels without the need for pretreatments such as feedstock drying and lipid extraction. In the present work, liquefaction of microalgae or yeasts in subcritical water is investigated in a self-built HTL system. Fractional yield distribution of the end-products and characterization of biocrudes from algae HTL are studied by considering the effects of the reaction temperature and residence time. The identified compounds in the biocrudes are compared to those in yeast-derived HTL biocrudes and the reaction scheme is reported. The present work reveals that no significant quality change of algae-derived HTL biocrudes is observed in a moderate temperature range thus the N-containing compounds vary complicatedly at different residence times. Compared to the pyrolysis biocrudes of algae and yeast, the collected HTL biocrudes do not perform the advantage, in terms of biofuel potential of a high portion of N-containing compounds, especially heterocyclic compounds. It should be noted that the low protein content in the feedstocks cannot definitely be proven to have led to the reduced heterocyclic compounds in HTL biocrudes. If lipids had been present, this would have enhanced the formation of N-containing heterocyclic compounds. Instead, amino acid degradation was accelerated by the high level of carbohydrates, forming amides. This paper presents a promising effort to develop an efficient route to transform oleaginous microorganisms into biofuels.

Hydrothermal Liquefaction of Microalgae for the Production of Biocrude and Value-added Chemicals

Hydrothermal Liquefaction of Microalgae for the Production of Biocrude and Value-added Chemicals

Catalytic hydrothermal liquefaction of microalgae to bio-oil with in-situ hydrogen donor formic acid

Hydrothermal liquefaction (HTL) can directly convert high water content microalgae into bio-oil, but the bio-oil quality needs to be improved before the actual utilization. In this paper, the influences of hydrogen donor formic acid and catalysts on bio-oil properties via HTL of Chlorella were investigated. The results showed that the addition of formic acid and catalysts decreased the bio-oil yield slightly but increased the carbon, hydrogen content and higher heating values of the bio-oil. The carbon content and heating value of bio-oil derived from Au/C3N4 catalyst with formic acid were 74.66% and 38.34MJ/kg, respectively. Nitrogen heterocyclic and amine compounds were the main components of the bio-oil in the blank experiment, and the peak area percentages of them were 31% and 28% respectively. When formic acid was added as hydrogen donor, the content of nitrogen heterocyclic compounds decreased while the content of amine compounds increased. Furthermore, Ru/C or Au/C3N4 increased the content of hydrocarbons in the bio-oil, and the highest peak area percentage of hydrocarbons in Au/C3N4 bio-oil was 42%. Besides, thermogravimetric analysis of the bio-oil indicated that the distillates below 200 °C enhanced 10% compared with the blank bio-oil, and the fraction below 400 °C reached 84% after addition of formic acid and Au/C3N4. The results of this study showed that the introduction of formic acid and catalyst to HTL could improve the quality of bio-oil obviously.

Full utilization of marine microalgal hydrothermal liquefaction liquid products through a closed-loop route: towards enhanced bio-oil production and zero-waste approach.

The present study aimed to evaluate the potential of aqueous phase after hydrothermal liquefaction of microalgae (Aq-P), enriched with seawater, as a growth medium coupled with crude bio-oil production by the halophyte Dunaliella salina. Results showed that Aq-P showed higher content of total organic carbon (TOC) and total nitrogen (10.24, and 5.11g L-1, respectively), while seawater showed higher anions and cations content. At the 12th day of microalgae incubation, the Aq-P growth medium showed 15.9% higher dry weight than the control (f/2 medium), with enhanced lipid content by 21.2% over the control, and 5.7% significant reduction in carbohydrates. The bio-oil yields of microalgal biomass cultivated in f/2 and Aq-P were 28.74% and 29.54%, respectively. Using Aq-P enhanced the fatty acids/esters and hydrocarbons in the crude bio-oil by 12.6% and 1.7times, respectively, comparing to f/2-derived bio-oil. However, nitrogen-containing compounds in the Aq-P-derived bio-oil reduced by 60.7% comparing to f/2 medium. Interestingly, diesel carbon-range represented the majority of the products in both f/2- and Aq-P-derived bio-oil (69.1% and 78.3%, respectively). The findings of the present study provide a new approach for development of sustainable microalgal cultivation system for crude bio-oil production through a closed-loop route using Aq-P and seawater.

Study on synergistic mechanism of Co-hydrothermal liquefaction of microalgae and macroalgae

The mechanism of Co-hydrothermal liquefaction (Co-HTL) between microalgae (Chlorella vulgaris) and macroalgae (Enteromorpha clathrata) was studied, and the effects of different mass ratios of microalgae and macroalgae on the yield of Co-HTL products and the distribution of nitrogen-contained compounds were discussed. The study found that Co-HTL has a positive effect on the increase of bio-oil yield, with a maximum increase of 15.0 wt%. The ultimate analysis, FTIR, GC-MS and other means were carried out to investigate the composition liquefied oil products. Compared with the bio-oil obtained from Enteromorpha, the nitrogen compounds content of amides in the bio-oil prepared by mixed sample increased significantly, and maximum yield increased from 0.9% to 13.6%, while pyrazine and piperazine significantly decreased by 5.1% and 11.0%, respectively. This could be due to the intensification of the amidation reaction in the Co-HTL, and consequently interfering with the Maillard pathway. Except for at the ratio of 1/1, the content of nitrogen compounds in the oil phase at all ratios was lower than the theoretical value. At the ratio of 3/1, the content of nitrogen compounds decreased the most compared with the theoretical value, which is reduced by 7.5%, and the content was 41.0%. When the mixing ratio was 1/3, the nitrogen content of aqueous phase was the highest (85.7%), and the total nitrogen content in aqueous phase was 2669.2 mg/L.

Catalytic hydrothermal liquefaction of microalgae cultivated in wastewater: Influence of ozone-air flotation on products, energy balance and carbon footprint

The use of ozone-air flotation for microalgae harvesting was investigated, in terms of its environmental feasibility and use in catalytic HTL. The environmental feasibility was determined by the Net Energy Ratio (NER) and carbon footprint metrics following a life cycle assessment (LCA). The effect of the variables in the catalytic HTL process (catalyst load, temperature, time), on the distribution of bio-crude and hydrocarbons, was experimentally evaluated using a mixed microalgae culture dominated by Scenedesmus sp. grown in wastewater and harvested by ozone-air flotation or gravity-sedimentation, respectively. Liquefaction was carried at three temperatures (325 °C, 350 °C and 370 °C), three reaction times (30, 60 and 120 min) and two HZSM-5 catalyst loads (0, 5 and 7 wt%). The bio-crude yields obtained (17 to 20%) were similar with both harvesting methods; however, the production of aliphatic compounds was doubled, when using ozone-air flotation, and further increased when using a HZMS-5 catalyst. The highest bio-crude quality (N: 3.0%, O: 5.6%, S: 0.1%) and high heat values (42.3 MJ/kg) were produced at 325 °C, 60 min and 5 wt%, in contrast with sedimented microalgae (6.0%, 7.0%, 1.0%, and 39.3 MJ/kg, respectively). Energy and carbon footprint were quantified with a LCA approach for a scenario using a functional unit (FU) of 1 GJ of bio-crude production and its possible bio-jet fuel conversion as a potential product. HTL microalgae conversion required the highest amount of energy among evaluated cultivation and harvesting processes. Harvesting via ozone-air flotation, gave a NER value and carbon footprint of 2.7 and 30.5 kg CO2 eq/GJ of bio-jet fuel, respectively. The proposed novel system had significantly lower greenhouse gas equivalent emissions (by 65%) and NER values (by 48%) than for conventional jet fuel.