Pyrolysis Of Microalgae Research Articles

Fast pyrolysis of microalgae in a falling solids reactor: Effects of process variables and zeolite catalysts

Non-catalytic and catalytic pyrolysis of microalgae were carried out to generate an organic liquid fuel precursor. The impacts of several process variables on the fast pyrolysis in a falling solids reactor are reported, including temperature, particle size, flow rate, and atmosphere (N2, H2O and CO2). Experiments were carried out with duckweed as the biomass to provide some comparison. The speciated organic phase product data were classified according to the different compound types including hydrocarbons, alcohols, oxygenates, and nitrogenates. In-situ catalytic pyrolysis produced an organic phase with an increased fraction of hydrocarbons and decreased fraction of oxygenates, evidence for carbon removal chemistries such as decarboxylation and decarbonylation. The noncatalytic pyrolysis gave the highest total liquid yield while catalytic pyrolysis resulted in the highest yield of the desired hydrocarbon fraction. A comparison of four exchanged ZSM-5 catalysts (H-, Fe-, Cu-, and Ni-) indicates that the protonated zeolite provided the largest enhancement among the catalysts of the liquid product yield and composition: H-ZSM-5 increased the yield of the hydrocarbon fraction in the organic phase from 21% to 43%, a 100% relative increase, and exhibited the least coking. The effects of biomass weight hourly space velocity, and comparisons between H-ZSM5 powder and monolithic catalysts are also reported. The implications of the findings for the conversion of microalgae to liquid fuels are discussed.

Deoxygenation of microalgal oil into hydrocarbon with precious metal catalysts: Optimization of reaction conditions and supports

Deoxygenation of microalgal oil obtained by pyrolysis of microalgae was carried out for the production of hydrocarbon fuel from biomass by metal supported catalyst. Oleic acid was used as a model reactant to select an optimized catalyst. Effects of support, metal species, and metal loading on catalytic performance were investigated. Activated carbon showed better performance than silica as a support. Considering various factors in model reaction, such as metal loading, reaction temperature, activity for deoxygenation, and selectivity for decarboxylation, 5wt% platinum supported on activated carbon (5wt% Pt/C) was selected as an optimized catalyst. Based on these results, deoxygenation of the pyrolysis oil from Chlorella sp. KR-1 was conducted at 623 and 673K over this selected catalyst. The product after catalytic deoxygenation was mainly composed of pure hydrocarbons, and its oxygen content was below 2.0%. The fraction in the product of which the boiling point was less than 623K was about 90%. These properties could allow this upgraded oil to be used for transportation fuel. However, the degree of oxygen removal with microalgal pyrolysis oil was lower than that with oleic acid, implying that impurities in the pyrolysis oil may inhibit the deoxygenation reaction.

Thermogravimetric–mass spectrometric analysis of lignocellulosic and marine biomass pyrolysis

The pyrolysis characteristics of three lignocellulosic biomasses (fir wood, eucalyptus and pine bark) and a marine biomass (Nannochloropsis gaditana microalgae) were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA–MS). Thermal degradation of lignocellulosic biomass was divided into four zones, corresponding to the decomposition of their main components (cellulose, hemicellulose and lignin) and a first step associated to water removal. Differences in volatile matter and cellulose content of lignocellulosic species resulted in different degradation rates. Microalgae pyrolysis occurred in three stages due to the main components of them (proteins), which are greatly different from lignocellulosic biomass. Heating rate effect was also studied. The main gaseous products formed were CO2, light hydrocarbons and H2O. H2 was detected at high temperatures, being associated to secondary reactions (char self-gasification). Pyrolysis kinetics were studied using a multiple-step model. The proposed model successfully predicted the pyrolytic behaviour of these samples resulting to be statistically meaningful.

A study on experimental characteristic of microwave-assisted pyrolysis of microalgae

The microwave-assisted pyrolysis of Chlorella vulgaris was carried out under different microwave power levels, catalysts and contents of activated carbon and solid residue. The products, pyrolysis temperature and temperature rising rate were analyzed in order to obtain the optimal conditions. The results indicated that the higher the microwave power level was, the higher the maximum temperature rising rate and pyrolysis temperature were. The maximum bio-oil yield (35.83wt.%) and gas yield (52.37%) were achieved under the microwave power of 1500W and 2250W, respectively. And 2250W was the optimal power to obtain bio-fuel product. High microwave power level and catalyst can enhance the production of gas. Catalysts can promote the pyrolysis of C. vulgaris, and activated carbon was the best among the tested catalysts followed by the solid residue. The optimal content of activated carbon is 5% with the maximum bio-fuel yield of 87.47%.

Catalytic pyrolysis of microalgae to high-quality liquid bio-fuels

The pyrolytic conversion of chlorella algae to liquid fuel precursor in presence of a catalyst (Na2CO3) has been studied. Thermal decomposition studies of the algae samples were performed using TGA coupled with MS. Liquid oil samples were collected from pyrolysis experiments in a fixed-bed reactor and characterized for water content and heating value. The oil composition was analyzed by GC-MS. Pretreatment of chlorella with Na2CO3 influences the primary conversion of chlorella by shifting the decomposition temperature to a lower value. In the presence of Na2CO3, gas yield increased and liquid yield decreased when compared with non-catalytic pyrolysis at the same temperatures. However, pyrolysis oil from catalytic runs carries higher heating value and lower acidity. Lower content of acids in the bio-oil, higher aromatics, combined with higher heating value show promise for production of high-quality bio-oil from algae via catalytic pyrolysis, resulting in energy recovery in bio-oil of 40%.

Microwave-assisted pyrolysis of microalgae for biofuel production

The pyrolysis of Chlorella sp. was carried out in a microwave oven with char as microwave reception enhancer. The results indicated that the maximum bio-oil yield of 28.6% was achieved under the microwave power of 750W. The bio-oil properties were characterized with elemental, GC–MS, GPC, FTIR, and thermogravimetric analysis. The algal bio-oil had a density of 0.98kg/L, a viscosity of 61.2 cSt, and a higher heating value (HHV) of 30.7MJ/kg. The GC–MS results showed that the bio-oils were mainly composed of aliphatic hydrocarbons, aromatic hydrocarbons, phenols, long chain fatty acids and nitrogenated compounds, among which aliphatic and aromatic hydrocarbons (account for 22.18% of the total GC–MS spectrum area) are highly desirable compounds as those in crude oil, gasoline and diesel. The results in this study indicate that fast growing algae are a promising source of feedstock for advanced renewable fuel production via microwave-assisted pyrolysis (MAP).

Fast pyrolysis of microalgae to produce renewable fuels

In the present study, fast pyrolysis tests of microalgae were performed in the fluid bed reactor. The experiments were completed at temperature of 500 °C with a heating rate of 600 °C s −1 and a sweep gas (N 2) flow rate of 0.4 m 3 h −1 and a vapour residence time of 2–3 s. In comparison with the previous studies on slow pyrolysis from microalgae in an autoclave, a greater amount of high quality bio-oil can be directly produced from continuously processing microalgae feeds at a rate of 4 g min −1 in the present work, which has a potential for commercial application of large-scale production of liquid fuels. The liquid product yields of 18 and 24% from fast pyrolysis of Chllorella protothecoides and Microcystis aeruginosa were obtained. The saturated and polar fractions account for 1.14 and 31.17% of the bio-oils of microalgae on average, which are higher than those of bio-oil from wood. The H/C and O/C molar ratios of microalgae bio-oil are 1.7 and 0.3, respectively. The gas chromatograph analyses showed that the distribution of straight-chain alkanes of the saturated fractions from microalgae bio-oils were similar to diesel fuel. Bio-oil product from fast pyrolysis microalgae is characterized by low oxygen content with a higher heating value of 29 MJ/kg, a density of 1.16 kg l −1 and a viscosity of 0.10 Pa s. These properties of bio-oil of microalgae make it more suitable for fuel oil use than fast pyrolysis oils from lignocellulosic materials.