Hydrothermal Liquefaction Of Algae Research Articles

Optimization of bio-oil production from macroalgae, caulerpa lentillifera via hydrothermal liquefaction

Abstract An environmentally friendly method of producing bio-oil through the hydrothermal liquefaction (HTL) of algae has emerged, providing a path toward renewable energy and reducing greenhouse gas emissions. Algae is currently received a lot of interest as biomass feedstock due to its long growing season in warm climate area, does not require arable land, and relatively rapid growing rate. This study aims to optimize the HTL process of macroalgae (Caulerpa lentillifera) for bio-oil production, focusing on optimizing the bio-oil yield based on three parameters (operating temperature, the loading size of catalyst sodium hydroxide (NaOH), and algae-to-water ratio) using Box Behnken Design (also generally known as Response Surface Methodology). The results showed that an ideal reaction temperature of 277 °C, a 1:10 algae-to-water ratio, and 0.88 wt% catalyst loading led to an optimal experimental bio-oil yield of 11.65 wt%. Sensitivity study also revealed that the temperature is the second most important component, after the algae-to-water ratio. The difference in the catalyst loading showed low impact on the HTL of algae. Slight improvement to the bio-oil yield under the presence of NaOH is mainly due to the alkali environment provided by NaOH. The FTIR spectrum revealed the existence of various functional groups in the bio-oil. In summary, HTL has been effective in turning Caulerpa lentillifera into useful bio-oil. Overall, this study contributes to the growing body of research on algae-based bio-oil production. The results highlighted the potential of HTL as a promising technology for sustainable biofuel production, offering a pathway towards a greener and more energy-efficient future.

Catalytic aqueous hydrodeoxygenation of palmitic acid with in-situ hydrogen donor

Algal bio-oil obtained from hydrothermal liquefaction of algae contains a large amount of water and long-chain fatty acids. High acidity and corrosiveness seriously restrict the application of algal bio-oil. The aqueous-phase catalytic upgrading was a promising approach to solve this problem, and the hydrogen donor was one of the most important parameters to the conversion of the algal bio-oil and the quality of the products. Catalytic transfer hydrogenation (CTH) reaction was an efficient, economical and green method for hydrogenation reaction, which can directly transfer hydrogen from the hydrogen donor to the reaction substrate. In this work, the CTH reaction of algal bio-oil model compound palmitic acid was investigated to deal with the problem of high oxygen content in the algal bio-oil. Several common hydrogen donors, included methanol, ethanol, formic acid, and isopropanol, as well as different reaction conditions were experimented to study the CTH process of palmitic acid. The results showed that, with the reaction conditions of 350 °C and 10 h, formic acid achieved the best oxygen removal, carbon retention and energy efficiency, the C16 selectivity reached the highest at 33.3 % as the formic acid addition ratio was 1:2, and the C15 selectivity reached the highest at 48.3 % as the formic acid addition ratio was 1:3. In general, the best ratio of formic acid added was 1:3, which showed the highest yield of C15 and above alkanes of 79.6 %. This result indicates that the catalytic transfer hydrogenation reaction of formic acid has practical value in improving the combustion performance of algal bio-oil.

Hydrocarbon biolubricants from hydrotreated renewable and waste derived liquid intermediates

There is a need to support the biofuel sector by utilizing waste materials for its production and utilizing co-products through an integrated approach. Due to bio-oil's diverse composition, its applications for foams and resins syntheses are emerging, but most importantly, as biolubricants, product with increasing global demand. In this study, four hydrocarbon biolubricants (HBL) were produced via a hydrotreatment process. Two samples were produced using hydrothermal liquefaction (HTL) of algae (HAL) and sewage sludge (HSS). Additional samples included animal fat (poultry fat; HPF) and non-edible oil (carinata; HCA). All four samples were evaluated for their tribological properties and compared with the mineral base oil (MBO). These potential biolubricants samples had viscosity indices (VI) ranging from 197 to 254, pour points (PP) from −10 °C to −20 °C, and Noack volatilities between 16% and 23%. The coefficient of friction (COF) for HAL and HSS was lower than MBO, HPF, and HCA, but the wear was higher than HPF. Large amounts of oxygenates and olefins imparted higher VI and lowered PP to HPF. Even though both HSS and HAL demonstrated higher amounts of paraffin, they exhibited lower thermo-oxidative stability, higher PP, and higher volatility than other samples. In the case of HAL and HSS, the aromatics could have played a more prominent role in determining the lubricating properties than the paraffin alone. The HPF had the lowest wear, highest VI, and lower PP but higher COF. The volatility and COF predominantly dependent on the cyclic structures, unsaturation, and heteroatoms. The results indicated that the hydrotreated bio-oil from HTL biocrude and waste precursors could be considered as eco-friendly hydrocarbon biolubricant blend stock.

Kinetics studies and performance analysis of algae hydrothermal liquefaction process

Kinetics studies and performance analysis of algae hydrothermal liquefaction process

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).

Influence of Red Mud Catalyst and Reaction Atmosphere on Hydrothermal Liquefaction of Algae

Algae are a diverse group of aquatic organisms and have a potential to produce renewable biofuel via hydrothermal liquefaction (HTL). This study investigated the effects of reaction environments on biocrude production from “Tetraselmis sp.” algae strain by HTL process using red mud (RM) based catalyst. The inert (N2), ethylene (C2H4), reducing (10% H2/90% N2), and oxidizing (10% O2/90% N2) environments were applied to the non-catalytic as well as catalytic HTL treatments with two forms of RM catalysts: RM reduced at 500 °C (RRM) and nickel-supported RM (Ni/RM). Under nitrogen, ethylene and reducing environments, the biocrude yield increased by the following trend: No Catalyst < RRM < Ni/RM. The Ni/RM catalyst produced the highest biocrude yield (37 wt.%) in an ethylene environment, generated the lowest total acid number (14 mg KOH/g) under inert atmosphere, and lowered sulfur (33–66%) and oxygen (18–30%) from biocrude products irrespective of environments. The RRM catalyst maximized the biocrude carbon content (61 wt.%) under a reducing environment and minimized the heavy metal and phosphorus transfer from the feedstock to biocrude in studied ambiences. The reducing environment facilitated mild hydrotreatment during HTL reaction in the presence of RRM catalyst. Among the non-catalytic experiments, the reducing atmosphere optimized carbon content (54.3 wt.%) and calorific value (28 MJ/kg) with minimum oxygen amount (27.2 wt.%) in biocrudes.

The effect of chlorella hydrothermal products on the heavy oil upgrading process

In-situ upgrading can improve the scale of heavy oil development, but the efficiency of in-situ hydrothermal hydrogen supply is limited. In this paper, the combination of algae hydrothermal liquefaction and heavy oil upgrading and viscosity reduction process is proposed. The liquefaction products of hydrothermal liquefaction are used to supply hydrogen to the heavy oil upgrading and viscosity reduction process, thereby enriching the supply path of active hydrogen. The effects of hydrothermal liquefaction temperature of Chlorella and the addition of 5% Fe/HZSM-5 catalyst on the liquefaction rate and product distribution of Chlorella were investigated, and the upgrading and viscosity reduction process of heavy oil with the participation of hydrothermal liquefaction products was discussed. The results show that when the temperature of upgraded heavy oil is 280 °C and 5 wt% of hydrothermal liquefaction products are added and reacted for 24 h can make the viscosity reduction rate of heavy oil reach 84.32%, and 31.2% of resin in heavy oil was converted into aromatic hydrocarbon. Elemental analysis showed that the upgraded heavy oil H/C ratio increased, and GC–MS analysis showed that the distribution of algae hydrothermal liquefaction products could be adjusted by the catalyst, and more aromatics were produced after the addition of the catalyst, which confirmed that the aromatics in hydrothermal liquefaction products had a significant effect on the quality improvement and viscosity reduction of heavy oil. Its molecular weight was also found to be reduced from 853 to 326 in the average molecular weight test (GPC). The efficient carbon sequestration of algae is combined with the demand for carbon dioxide emission reduction in oilfields to realize the recycling of carbon resources.

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.

Influence of Red Mud Catalyst and Reaction Atmosphere on Hydrothermal Liquefaction of Algae

Influence of Red Mud Catalyst and Reaction Atmosphere on Hydrothermal Liquefaction of Algae

Machine learning prediction and optimization of bio-oil production from hydrothermal liquefaction of algae

Hydrothermal liquefaction (HTL) of algae is a promising biofuel production technology. However, it is always difficult and time-consuming to identify the best optimal conditions of HTL for different algae by the conventional experimental study. Therefore, machine learning (ML) algorithms were applied to predict and optimize bio-oil production with algae compositions and HTL conditions as inputs, and bio-oil yield (Yield_oil), and the contents of oxygen (O_oil) and nitrogen (N_oil) in bio-oil as outputs. Results indicated that gradient boosting regression (GBR, average test R2 ∼ 0.90) exhibited better performance than random forest (RF) for both single and multi-target tasks prediction. Furthermore, the model-based interpretation suggested that the relative importance of operating conditions (temperature and residence time) was higher than algae characteristics for the three targets. Moreover, ML-based reverse and forward optimizations were implemented with experimental verifications. The verifications were acceptable, showing great potential of ML-aided HTL for producing desirable bio-oil.

Techno-economic uncertainty analysis of wet waste-to-biocrude via hydrothermal liquefaction

Wet waste hydrothermal liquefaction (HTL) has the potential to make economically competitive and environmentally sustainable biocrude. However, there are few studies available on the continuous-flow wet waste HTL process. Therefore, stochastic techno-economic analysis (TEA) is needed to evaluate the economic feasibility and risks of the wet waste HTL process. This work leveraged our previous uncertainty quantification work on algae HTL and in-house wet waste HTL continuous system testing data. A “component additivity” model was developed to predict HTL product yields and qualities from different wet waste compositions. With the established HTL yield model, a process reduced-order model (ROM) coupled with an economic model was built in Microsoft Excel® to replace the rigorous but computationally intensive Aspen Plus® model for uncertainty analysis. The proposed stochastic TEA approach using the ROM reduces the computational time for the analysis by 2000 times, compared to the full Aspen-based model. Monte Carlo simulation was conducted to quantify the uncertainties from feedstock composition, HTL yield model, aqueous-phase product treatment, utility consumption, and equipment sizing and costing. The stochastic TEA indicates that the MBSP for wet waste HTL ranges from $2.65/gge ($0.75/L) to $4.93/gge ($1.41/L) (10th and 90th percentiles) with a median of $3.55/gge ($1.01/L). Feed moisture, HTL reactor model, and capital investment are the main contributors to the economic uncertainty of the wet waste HTL process. Uncertainty in the MBSP could be reduced by roughly 50% if uncertainties in the feed moisture and HTL reaction yield model can be effectively controlled or decreased.

Electrochemical oxidation of nitrogen-rich post-hydrothermal liquefaction wastewater

The aqueous phase co-product from the hydrothermal liquefaction of algae contains a significant fraction of the decomposed feedstock components that are suspected of having detrimental effects on the environment, requiring treatment before reutilisation or disposal. We used for the first time an electrochemical oxidation process to decrease the soluble organics content in the aqueous phase co-product from the hydrothermal liquefaction of microalgae Chlorella sp. using boron-doped diamond as the anode. The original aqueous phase co-product contained relatively high levels of chemical oxygen demand (36,000 mg·L−1), ammonia (1500 mg N·L−1), and organic nitrogen (3000 mg N·L−1). The process removed up to 99% of the carbon and attained a 96% discolouration of the wastewater. Nitrogen was converted from organic to inorganic forms, predominantly remaining in solution as ammonia and nitrate. The global current efficiency was 85% at a constant current density of 30 mA·cm−2, and the specific energy consumption to remove dissolved carbon was 28 kWh per kg of chemical oxygen demand.

Nutrient recycle from algae hydrothermal liquefaction aqueous phase through a novel selective remediation approach

Algae have received increasing interest in the past several decades as a biofuel feedstock source. However, sustainable nutrient supply has presented algal biofuels with a major obstacle in the value chain. At a scale where algal biofuels would meet a significant portion of transportation fuel needs, the demand for nutrients, specifically nitrogen and phosphorus, would exceed current global agricultural production. One downstream conversion pathway, hydrothermal liquefaction (HTL), produces bio-crude oils from wet algal biomass with a waste aqueous phase (HTL-AP), containing a significant amount of carbon and nitrogen. While this stream is rich in organic content and nutrients, it also contains toxic components, which include heterocyclic nitrogen compounds and phenolic compounds. Thus, the recyclability and potential toxicity of HTL-AP need to be studied in detail. The feasibility of utilizing nutrients available in HTL-AP was experimentally determined for Chlorella vulgaris and Desmodesmus armatus monocultures. Our work focused on determining the tolerance of these algae species toward HTL-AP toxicity through varying dilutions. Nitrogen replacement in the growth media was varied from a low of 18% to a high of 141% across both species. The most notable of these results show that addition of a 100× dilution (35% nitrogen replacement) of untreated HTL-AP decreased growth in C. vulgaris by 47 ± 7% with respect to a control medium. Adsorption treatments, including activated carbon and various resins, were introduced to remediate the HTL-AP toxic effects. Treatment of the HTL-AP portion with an ion-exchange resin, Dowex 50WX8, supported C. vulgaris growth at a 100× dilution (35% nitrogen replacement) with no statistical change compared to the control. An in-depth molecular profiling demonstrated for the first time the selective removal of high‑nitrogen containing components by resin treatment. This work provides a foundation for studying the toxic components of HTL-AP and possible mechanisms by which treatments can remove these components.

Engine performance and emissions of high nitrogen-containing fuels

Nitrogen (N) content in algae hydrothermal liquefaction (HTL) biocrude is high (5–8 wt%) and generally presumed to result in high NOx emissions during combustion. However, to our knowledge a very limited previous work on diesel engine performance and emissions of N-containing fuels. In order to investigate this issue, pyridine, an N-heterocyclic compound commonly found in algae biocrude, was blended with diesel fuel. This study investigated the influence of N in fuels, using a surrogate fuel to simulate algal biocrude, to determine the combustion behavior and emissions profile of an industrial multi-cylinder diesel engine. The presence of N in the fuel affected its physical properties. Density was slightly higher than neat diesel, while the viscosity, the flash point and the higher heating value (HHV) of the N-containing fuels reduced with increasing N content. The flash point of N-containing fuels were reduced, which affects the storage and transportation of the fuel. The engine load between 25 and 75% was observed to have an effect on engine performance parameters. Compared to diesel, N-containing fuels emitted both lower carbon monoxide (CO) and unburned hydrocarbons (HC). Increasing nitrogen oxides (NOx) emissions were observed with increasing N content in the fuels. At 50% and 75% loads, NOx emissions from N0.1 (0.1 wt% N), N0.5 (0.5 wt% N) and N2 (2 wt% N) were lower than for EUROIII. Particulate matter (PM) was lower for N-containing fuels compared to diesel fuel except for N0.1.

Understanding catalytic mechanisms of HZSM-5 in hydrothermal liquefaction of algae through model components: Glucose and glutamic acid

Hydrothermal liquefaction (HTL) of algae has attracted great interest as a thermal conversion for biofuels. In an effort to understand the catalytic mechanism by which algae undergoes HTL in the presence of HZSM-5, the different roles of the major components (carbohydrates and proteins) were investigated. Glucose and glutamic acid were selected as model compounds of carbohydrates and proteins, respectively. Glucose, glutamic acid, and their binary mixtures were processed under hydrothermal conditions in the presence of HZSM-5 over a temperature range of 220–330 °C. The products were analyzed using a combination of elemental analysis (EA), thermal gravimetric analysis (TGA), gas chromatography mass spectrometry (GC-MS), and Fourier transform infrared (FT-IR) spectroscopy to characterize the physicochemical properties. The effects of HZSM-5 on the yield and quality of bio-oil were investigated. Results indicated that the addition of HZSM-5 did not significantly affect the bio-oil yield of glutamic acid but increased the bio-oil yields from glucose and their binary mixtures. The hydrogen-to-carbon (H/C) ratio and the higher heating values (HHVs) of the bio-oils were all greatly increased in the presence of HZSM-5. The addition of HZSM-5 reduced the contents of undesirable oxygenated compounds, nitrogenous compounds, and increased the hydrocarbon content. Maillard reactions between glucose and glutamic acid were also strengthened by HZSM-5.

Hydrothermal liquefaction of Galdieria sulphuraria grown on municipal wastewater

Two strains of Galdieria sulphuraria algae, 5587.1 and SOOS, were grown on municipal wastewater to develop energy-positive treatment systems. Hydrothermal liquefaction (HTL) of 5–10 wt% algal biomass solids was conducted at 310–350 °C for 5–60 min to produce bio-crude oil. HTL product yields and energy recovery were compared to those from previous studies using G. sulphuraria grown on a modified Cyanidium medium. Total bio-crude oil yields were lower (11.2–23.0 wt%) and char yields were higher (22.6–36.4 wt%) for HTL of algae grown on actual wastewater compared with that grown on media (31.4 wt% and 4.8 wt%, respectively), indicating a potential limitation for using yields from media-based studies. High-resolution mass spectroscopy of bio-crude oil provides new insights into differences in composition based on growth media. Energy recovery in total bio-crude oil and char at 350 °C was 17–28% and 14–19%, respectively, for the 5587.1 strain, and 23–27% and 14–25%, respectively, for the SOOS strain.

Techno-economic analysis of alternative aqueous phase treatment methods for microalgae hydrothermal liquefaction and biocrude upgrading system

An economic analysis was conducted for an algae hydrothermal liquefaction (HTL) and biocrude upgrading system with alternative aqueous phase treatment methods. Using experimental data, three different methods were modeled and compared: 1) direct recycle of HTL aqueous phase to the algae farm, 2) catalytic hydrothermal gasification (CHG), and 3) anaerobic digestion (AD). Direct recycle consumes the most natural gas because unlike AD and CHG, no methane is generated from the aqueous phase organics conversion. However, direct recycle has the lowest cost compared to other two cases because it only requires the addition of pumps and buffer tankage related to the aqueous phase recycle. The CHG and AD cases require significant capital and operating costs for aqueous phase treatment, which increase the minimum fuel selling price (MFSP) over the direct recycle case by 11% and 2.9%, respectively. The CHG and AD respectively increase the conversion cost only (excludes the cost to grow, harvest, and dewater algae) by 75% and 21%. Sensitivity analysis suggests that the key factors affecting the total cost of fuel production are the feedstock cost, the biocrude yield, the plant scale, and the method of aqueous phase treatment.

Techno-economic uncertainty quantification of algal-derived biocrude via hydrothermal liquefaction

Using microalgae for fuel production via hydrothermal liquefaction (HTL) has received increasing attention in recent years because of its high biocrude productivity and quality, cultivation flexibility, and potential for large scale operation. Most of the current knowledge on algae HTL is based on laboratory benchtop findings and/or simulation models, while yield correlations or simplified kinetics models were usually developed based on small batch equipment. In this work, the lack of commercial experience and knowledge gaps of algae HTL process were addressed through techno-economic uncertainty quantification. Particularly, a “component additivity” model was developed to predict the yields and qualities of biocrude derived from a variety of algal biomass via HTL process with model uncertainty quantified based on the operating data of PNNL's continuous flow HTL system. Impacts of algae types on the biocrude yield and process economic were investigated by performing sensitivity analysis. Monte Carlo simulations were conducted using rigorous process and economic models developed in Aspen Plus and Excel to determine the process uncertainty. The results indicate that higher total lipid content (including membrane lipid) yields more biocrude, which directionally reduces biocrude production cost. For the base case scenario (Chlorella with 18.2 wt% lipid, capacity of 200 tpd daf algae, dewatered algae price of $1171/dry ton), the modeled biocrude production cost is approximately $11/gge, of which 90% is attributed to feedstock cost of dewatered algae. According to the Monte Carlo simulation, the modeled production cost for HTL biocrude production is between $5/gge and $16/gge when the algae price ranges from $400 to $1800/daf ton, of which an uncertainty (range between 10% and 90% percentiles) up to ±12% is observed. Tornado analysis suggested that the algae composition and capital investment are the two main contributors to the economic uncertainties of the algae conversion via HTL.

Strategies for recovery and recycling of nutrients from municipal sewage treatment effluent and hydrothermal liquefaction wastewaters for the growth of the microalga Scenedesmus sp. AMDD

Developing reliable processes for recycling nutrients obtained from hydrothermal liquefaction of algae could improve the sustainability and scalability of algae based biofuels. In this study, hydrothermal liquefaction (HTL) wastewater was obtained from continuous liquefaction experiments in plug flow reactor and two strategies were evaluated to recycle both phosphorous and nitrogen for the growth of Scenedesmus sp. AMDD. The first strategy involved using HTL wastewater as a source of nitrogen while minimizing the algae growth inhibitors present in wastewater using hydrothermal gasification and activated carbon adsorption. The second strategy focused on recovering nitrogen as ammonia and phosphorous as struvite from HTL wastewater and recycling only the nutrients thereby decoupling the HTL wastewater and most inhibitors from nutrient recycle process. Water samples obtained from these two strategies were analyzed using various techniques (elemental analysis, gas chromatography, and hydrogen NMR) and potential growth inhibitors were identified as nitrogen containing heteroaromatics. The second approach relied solely on activated carbon treatment to remove these heteroaromatics. Although comparable growth rates were obtained using the first approach after strong dilution, algae growth and biomass yields obtained using the latter approach was much more robust as indicated by less variability, similar rates and biomass yields as compared to the synthetic medium. Apparent nitrogen and phosphorous removal rates for this case were > 99% and 68 ± 5.7%, respectively. This approach of decoupling nitrogen and phosphorous nutrients from HTL water offers a flexible, reliable, and scalable process for recycling nutrients without the inhibitors in HTL water and an important step towards the commercial production of algae for biofuels.

Influence of Fe/HZSM-5 catalyst on elemental distribution and product properties during hydrothermal liquefaction of Nannochloropsis sp.

Hydrothermal liquefaction (HTL) is a promising thermochemical technology to produce biocrude oil from algae; however, further improvement of the process efficiency is still required. In this study, we used a cost-effective catalyst (Fe/HZSM-5) during HTL of microalgae Nannochloropsis sp. The highest biocrude oil yield (38.1 ± 3.2%) was achieved at 365 °C with the inclusion of Fe/HZSM-5, which improved the biocrude oil yield by 25% compared with the non-catalyzed group. In addition, Fe/HZSM-5 showed a positive effect on influencing element migration during the HTL process. An increase of carbon in the biocrude oil and increase of nitrogen in the aqueous phase were observed, which would benefit downstream processing, including biocrude oil upgrading and nutrients recovery. Furthermore, the presence of low-molecular weight ketones, acids, amides and phenols in the biocrude oil indicated improvement of the oil quality. Hence, Fe/HZSM-5 could be a promising catalyst for the HTL of algae, enhancing biocrude oil production and regulating the distribution of carbon and nitrogen in the product fractions.