Peigao Duan

Hydrothermal processing of duckweed: Effect of reaction conditions on product distribution and composition

Influences of operating conditions such as temperature (270-380 °C), time (10-120 min), reactor loading (0.5-5.5 g), and K2CO3 loading (0-50 wt.%) on the product (e.g. crude bio-oil, water soluble, gas and solid residue) distribution from the hydrothermal processing of duckweed were determined. Of the four variables, temperature and K2CO3 loading were always the most influential factors to the relative amount of each component. The presence of K2CO3 is unfavorable for the production of bio-oil and gas. Hydrothermal processing duckweed produces a bio-oil that is enriched in carbon and hydrogen and has reduced levels of O compared with the original duckweed feedstock. The higher heating values of the bio-oil were estimated within the range of 32-36 MJ/kg. Major bio-oil constituents include ketones and their alkylated derivatives, alcohols, heterocyclic nitrogen-containing compounds, saturated fatty acids and hydrocarbons. The gaseous products were mainly CO2 and H2, with lesser amounts of CH4 and CO.

Co-liquefaction of micro- and macroalgae in subcritical water.

Co-liquefaction of microalgae (Spirulina platensis, SP) and macroalgae (Entermorpha prolifera, EP) was studied in subcritical water by using a stainless-steel batch reactor at different temperature (250 to 370°C), time (5 to 120 min), SP/EP mass ratio (0 to 100%), and water/algae mass ratio (1:1 to 6:1). The results suggested that a positive synergetic effect existed during the co-liquefaction of SP and EP, and this synergetic effect was dependent on reaction conditions. Co-liquefaction alleviated the severe reaction conditions compared to the separate liquefaction of SP and EP and also promoted the in situ deoxygenation of the bio-oil. The higher-heating-value of bio-oil produced from the co-liquefaction of SP and EP (wSP:wEP=1) is 35.3 MJ/kg. The energy recovery from the co-liquefaction is larger than the average value from the separate liquefaction of SP and EP. Co-liquefaction did not affect the molecular composition but affect the relative amount of each component in the bio-oil.

Thermo-chemical conversion of Chlorella pyrenoidosa to liquid biofuels

The aim of the present study is to find how the solvent polarity affects the liquefaction behavior of Chlorella pyrenoidosa and subsequently using the most suitable solvent identified to explore the solvent/biomass ratio, time, and temperature on the products yield and properties of the bio-oil. The products yield was significantly affected by the solvent type, and ethanol was proven to be the most suitable solvent to convert C. pyrenoidosa into bio-oil from the yield and economic points of view. Temperature is the most influential factor on the products yield and properties of the bio-oil. The HHVs of the bio-oils produced under different reaction conditions are within the range of 27.68-36.45 MJ/kg. The major compounds in bio-oil were esters, fatty acids, alkenes, aldehydes, and amides, and fatty acid ethyl esters were the largest portion.

Hydrothermal liquefaction of Litsea cubeba seed to produce bio-oils

Hydrothermal liquefaction (HTL) of Litsea cubeba seed was conducted over different temperature (250-350°C), time (30-120 min), reactor loading (0.5-4.5 g) and Na2CO3 loading (0-10 wt.%). Temperature was the most influential factor affecting the yields of product fractions. The highest bio-oil yield of 56.9 wt.% was achieved at 290°C, 60 min, and reactor loading of 2.5 g. The presence of Na2CO3 favored the conversion of the feedstock but suppressed the production of bio-oil. The higher heating values of the bio-oil were estimated at around 40.8 MJ/kg. The bio-oil, which mainly consisted of toluene, 1-methyl-2-(1-methylethyl)-benzene, fatty acids, fatty acid amides, and fatty acid esters, had a smaller total acid number than that of the oil obtained from the direct extraction of the starting material. It also contained nitrogen that was far below the bio-oil produced from the HTL of microalgae, making it more suitable for the subsequent refining.

Lewis acid-catalyzed in situ transesterification/esterification of microalgae in supercritical ethanol.

The activities of several Lewis acid catalysts such SnCl2, FeCl3, ZnCl2, AlCl3, and NbCl5 for the in situ transesterification/esterification of lipid contained within a microalga (Chlorella pyrenoidosa) in ethanol at 350°C were examined to identify the most suitable catalyst in term of crude biodiesel (CBD) yield. Of those catalysts tested, ZnCl2 showed the highest performance toward the CBD production. Using ZnCl2 as catalyst, effects of reaction temperature (200-370 °C), time (0-120 min), ethanol to microalga ratio (EtOH:MA) (5/5-40/5), catalyst loading (0-30 wt.%), and algae moisture (0-80 wt.%) on the yields of product fractions and the properties of CBD were studied. The presence of ZnCl2 not only promoted the production of CBD but also showed activities toward the deoxygenation and denitrogenation of CBD. The moisture content in the starting material is the most influential factor affecting the yield and properties of CBD.

Non-catalytic hydropyrolysis of microalgae to produce liquid biofuels.

Non-catalytic hydropyrolysis of Chlorella pyrenoidosa was studied by using a stainless-steel batch reactor at different temperature (150-450 °C), time (5-120 min) and initial hydrogen pressure (1 atm-8 MPa), aiming to find how these parameters affect the product (oil, gas and solid) yields and properties of the hydropyrolysis oil (HPO). Temperature was the most influential factor to the relative amount of each product and properties of the HPOs. The hydrogen favored the stabilization of the active intermediates but cannot guarantee to produce HPOs in higher hydrogen at its higher initial pressure. The HPO, which showed much difference in component strongly depending on the reaction conditions, mainly consisted of aromatics and straight-chain hydrocarbons, amides, amines, nitriles and carboxylic acids at moderate temperatures. The main gas products detected during the hydropyrolysis were unreacted H2, CO2, CO and CH4. About 85% of energy originally present in the microalgae was recovered as oil under the optimal conditions.

Catalytic upgrading of duckweed biocrude in subcritical water.

Herein, a duckweed biocrude produced from the hydrothermal liquefaction of Lemna minor was treated in subcritical water with added H₂. Effects of several different commercially available materials such as Ru/C, Pd/C, Pt/C, Pt/γ-Al₂O₃, Pt/C-sulfide, Rh/γ-Al₂O₃, activated carbon, MoS₂, Mo₂C, Co-Mo/γ-Al₂O₃, and zeolite on the yields of product fractions and the deoxygenation, denitrogenation, and desulfurization of biocrude at 350°C were examined, respectively. All the materials showed catalytic activity for deoxygenation and desulfurization of the biocrude and only Ru/C showed activity for denitrogenation. Of those catalysts examined, Pt/C showed the best performance for deoxygenation. Among all the upgraded oils, the oil produced with Ru/C shows the lowest sulfur, the highest hydrocarbon content (25.6%), the highest energy recovery (85.5%), and the highest higher heating value (42.6 MJ/kg). The gaseous products were mainly unreacted H₂, CH₄, CO₂, and C₂H6.

Catalytic hydrothermal upgrading of crude bio-oils produced from different thermo-chemical conversion routes of microalgae

This study presents experimental results that compare the use of hydrothermal liquefaction (HTL), alcoholysis (Al), pyrolysis (Py) and hydropyrolysis (HPy) for the production of bio-oil from a microalga (Chlorella pyrenoidosa) and the catalytic hydrothermal upgrading of crude bio-oils produced by these four conversion routes. The yields and compositions of bio-oil, solid residue, and gases were evaluated and compared. HTL resulted in a bio-oil that has a higher energy density and superior fuel properties, such as thermal and storage stabilities, compared with the other three conversion routes. The N in crude bio-oils produced from Py and HPy is more easily removed than that in the bio-oils produced from HTL and Al. The upgraded bio-oils contain reduced amounts of certain O-containing and N-containing compounds and significantly increased saturated hydrocarbon contents. All of the upgraded bio-oils have a larger fraction boiling below 350°C than their corresponding crude bio-oils.

Catalytic hydropyrolysis of microalgae: Influence of operating variables on the formation and composition of bio-oil

Catalytic hydropyrolysis of microalgae has been studied by using a batch reactor. Nine different heterogenous catalysts of Pd/C, Pt/C, Ru/C, Rh/C, CoMo/γ-Al2O3, Mo2C, MoS2, and activated carbon were screened. Mo2C was identified as the most suitable catalyst. With Mo2C catalyst, influence of reaction conditions on the yield and properties of the hydropyrolysis oil (HPO) was examined. Temperature was the most influential factor affecting the yield and quality of the HPO. Higher temperature will produce HPO with higher C and H content and lower N and O content but at the cost of lowering the yield of HPO. Mo2C promoted the in situ deoxygenation and desulfurization of the HPO which has a HHVs varying between 35.3 and 39.3 MJ/kg. The highest energy recovery of 87.5% was achieved. Thus, this work shows that the catalytic hydropyrolysis is an effective way to produce high quality bio-oil from microalgae.

Supercritical water gasification of microalgae over a two-component catalyst mixture

Supercritical water gasification (SCWG) of the microalga Chlorella pyrenoidosa was examined with a catalyst mixture of Ru/C and Rh/C in a mass ratio of 1:1. The influences of temperature (380-600°C), water density (0-0.197g/cm3), and catalyst loading (0-20wt%) on the yields and composition of the gaseous products and the gasification efficiency were examined. The temperature and water density significantly affected the SCWG of the microalgae. The hydrogen gasification efficiency was more dependent on the temperature, while the carbon gasification efficiency was more dependent on the water density. The gaseous products mainly consisted of CH4, H2, CO, and CO2, with smaller amounts of C2-C3 hydrocarbons. CH4 made up half of the mole fraction of the gaseous products under most reaction conditions. A synergistic effect between Ru/C and Rh/C existed during the SCWG of the microalgae, and this effect favored the production of CH4. The role of the catalyst mixture became indistinct at higher temperatures. Hydrogen atoms from the water were transferred to the gaseous products during the SCWG, leading to hydrogen gasification efficiencies that exceeded 100%. The main components of the bio-oil were aromatics and nitrogen-containing compounds, and the main aromatics consisted of azulene and anthracene. The nitrogen-containing compounds are potential poisons to the catalyst mixture.