Quality Of Bio-oil Research Articles

Cement Catalyzed Valorization of Rice Straw into Upgraded Bio-Oil and Fuel Gases Using Pyrolysis Reactions

ABSTRACT Rice straw is one of the major agricultural residues that is generated enormously in Asian countries. Thus, it is critical to develop an efficient process of converting this residue into valuable compounds in replacing fossil-based products. Herein, we developed an economically viable cement catalyst to pyrolyze the rice straw into bio-oil and fuel gas in a batch-type reactor. Under the optimized conditions, the maximum bio-oil yield of 41.07 wt.%, and gas yield of 30.53 wt.% along with a biochar yield of 28.41 wt.% is achieved at 600°C. The catalyst showed a considerable effect on the bio-oil composition. It improved hydrocarbons quantities while using the optimum cement dosage at 600°C, and enhanced H2 from 18.79% to 25.57. By further increasing the catalyst dosage to 15 wt.%, the H2 yield was enhanced to 28.35%. The BET specific surface area of char at the optimum temperature was 76.42 m2/g and fine pore size. Catalyst improved both the yield and quality of the bio-oil. The bio-oil quality was enhanced by lowering the oxygen contents to a smaller value as 7.0098% and no water at all.

Chemical looping staged conversion of microalgae with calcium ferrite as oxygen carrier: Pyrolysis and gasification characteristics

Aiming to take full advantage of biomass featuring high volatiles and high oxygen content, we propose two chemical looping staged conversion (CLSC) schemes by decoupling pyrolysis and gasification into two distinct stages. In current work, the pyrolysis and gasification characteristics of microalgae Nannochloropsis sp. with calcium ferrite as oxygen carrier were performed by TG-FTIR analysis and experiments in a tubular reactor. Meanwhile, the gained bio-oils and gaseous products were analyzed using GC-MS and GC, respectively. The results suggested that both the oxidized and reduced calcium-ferrite oxygen carrier could enhance the quality of bio-oil in the pyrolysis stage by decreasing the oxygenated and nitrogenized compounds dramatically. Furthermore, the CO-rich or H2-rich syngas was generated in the gasification stage via the reactions between oxygen carrier and pyrolytic char. In the pyrolysis stage, the oxidized oxygen carrier facilitated the formation of chemicals (such as aromatics and alcohols), while the reduced oxygen carrier promoted the quality of bio-oil as the liquid fuel with the heating value high to 34.18 MJ/kg. Meanwhile, the content of H2 in pyrolytic gas was up to 50 %. In the gasification stage, CO-rich syngas was generated without the steam gasification agent, while H2-rich syngas was produced with the steam gasification agent. It proves that CLSC will provide a promising approach for high effective and clean utilization of biomass.

A study of optimization of solar pyrolysis and catalyst recovery and reuse

The use of renewable energy sources in the pyrolysis process for bio-oil production has gained a renewed interest. In this work, ex-situ catalytic solar pyrolysis (ECSP) of microalgae was performed using Mg-Al mixed oxides catalyst derived from hydrotalcite. The effects of biomass loading, reaction time, and catalyst percentage on the pyrolysis product were investigated. The condition that maximizes simultaneously the bio-oil yield and its hydrocarbon content was obtained in an optimization study. A study of the effect of catalyst reuse on the pyrolysis process was also performed. The results showed that high yields of bio-oil were found when intermediary values of independent variables were used. The use of the catalyst derived from hydrotalcite improved the quality of bio-oil, promoting a reduction of oxygenated compounds and forming aromatic and long-chain aliphatic hydrocarbons. High bio-oil yield (38.55%) with high hydrocarbon content (32.65%) was achieved under the optimal conditions. The study of the catalyst reuse showed that the structure and surface area of fresh and regenerated catalyst were very similar. In addition, the hydrocarbon content of bio-oil did not significantly change after three pyrolysis cycles.

Kinetic studies and performance analysis of Indonesian rice husk pyrolysis

Rice husk is abundantly available biomass in Indonesia and it can be a potential source of high-value energy source. In the present work, pyrolysis of rice husk was subjected to various temperature and used as a method to produce bio-oil. The decomposition profile of rice was examined at different heating rates (10, 20, 30, and 40°C/min) using a thermogravimetric analysis (TGA) method. The pyrolysis kinetics were evaluated using three different kinetic models: Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW), and Coats-Redfern (CR). The activation energy for KAS, OFW, and CR was centered at 251.62 kJ/mol, 253.32 kJ/mol, and 33.92 kJ/mol, respectively. Varying activation energy with conversion was observed, which reveals that the pyrolysis of rice husk processes through complex reaction. The production of bio-oil from rice husk using pyrolysis method was studied at different temperature conditions (300, 400, 500, 600°C). Results showed that bio-oil and gas products increase at higher temperature. The highest yield of bio-oil was produced at 600°C with 46.3 grams (37%-wt). The specific test showed that the density, viscosity, and acid value of bio-oil decreased at higher temperatures indicating that different pyrolysis conditions might lead to the different bio-oil quality.

Wheat straw based polygeneration systems integrating the electricity, heating and transport sector

To achieve a 100% renewable energy system, plants integrating the electricity, heating and transport sectors in a Smart Energy System are required. In this work, three different polygeneration plants producing biofuels and heat, while interacting with the electricity grid are presented. All plants were based on wheat straw gasification in a low temperature circulating fluidized bed gasifier. High quality bio-oil was produced by catalytically upgrading and condensing the tars in the produced gas. Additionally, bio-ash containing carbon was produced, which acts as fertilizer and carbon sequestration when returned to the fields. The three plants used the tar-free gas to produce electricity, synthetic natural gas (SNG) and dimethyl ether (DME), respectively. The electricity producing plant delivered electricity to the grid, while the SNG and DME production plants used electricity for producing electrolytic hydrogen to boost the fuel production. The plants were evaluated using energy and carbon efficiencies. The analysis showed that all plants achieved total energy efficiencies >83%, including process heat and district heating as by-products. The SNG production plant yielded the highest carbon efficiency (91%) of carbon bound in bio-fuels and bio-ash, followed by the DME (50%) and the electricity production plant (23%).

Effect of acid treatment and Na2CO3 as a catalyst on the quality and quantity of bio-products derived from the pyrolysis of granular bacteria biomass

The intense growth rate of granular bacteria biomass (GB) in anaerobic wastewater treatment units has made environmental problems with its disposal. In this research the potential of pyrolysis method to convert granular bacteria biomass to biofuels was completely investigated. The non-catalytic experiments were performed in a temperature range of 400 to 700 °C and the maximum liquid product yield on dry ash-free basis (55.0 %wt.) was obtained at optimum temperature of 550 °C. Pyrolysis of pretreated granular bacteria with 5 wt% HCl (PGB) and then impregnation with Na2CO3 (IPGB) was studied to improve the bio-oil quality as well as higher amount of synthesis gas. Feedstock pretreatment with acid decreased the gas yield in 550 °C while Na2CO3 pretreatment had reverse effect, with H2 yield (mmol/g feed) of 2.9, 2.4 and 1.8 for IPGB, GB and PGB respectively. It means Na2CO3 exhibited excellent catalytic activity toward producing hydrogen-rich hydrocarbons. Acid treatment increased bio-oil weight percent with little effect on the quality, while the IPGB pyrolysis resulted 8.3% and 8.6% decrease in the oxygenates and nitrogenates respectively and 19.5% increase in the hydrocarbons which improved the higher heating value (HHV) from 32.6 MJ/kg to 33.7 MJ/kg in comparison with GB. The raw and treated biomass was characterized by using thermogravimetric analysis (TGA-DTG), X-ray fluorescence (XRF), elemental analyses (CHNS), field emission scanning electron microscope (FESEM) and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). The bio-products were analyzed by a gas chromatography-thermal conductivity detector (GC-TCD), a gas chromatography-mass spectrometry (GC–MS) and CHNS.

Ex-situ catalytic upgrading of corncob pyrolysis vapors into furans and phenols over Pt-Re/AC: Effect of Pt/Re ratio and process parameter

In order to improve the quality of bio-oils, catalytic fast pyrolysis of corncob over Pt/Re supported activated carbon (AC) catalysts was conducted to produce bio-furans and bio-phenols. The effect of Pt/Re ratio on the catalytic pyrolysis performance was evaluated. Pt and Re are uniformly dispersed on AC, but it results in the decrease of specific surface area. In addition, the amount of weak acidic sites increased and higher total weak acidity of Pt-Re/AC was contributed to the production of target products at low catalytic upgrading temperature. AC and Pt/AC inhibited the formation of phenols, and Re/AC and Pt-Re/AC promoted the formation of phenols. The relative peak area of furans over 1Pt-3Re/AC and Re/AC is 44.36 % and 41.98 %, respectively. Pt-Re/AC catalysts have a high selectivity for methylfurans (MFs) and phenol (P), remaining at 19 % ∼ 33 % and 17 % ∼ 21 %, respectively. Finally, 1Pt-3Re/AC showed good reuse performance.

Accelerating the production of bio-oil from hydrothermal liquefaction of microalgae via recycled biochar-supported catalysts

As a highly effective nanocomposite for hydrothermal liquefaction (HTL) of microalgae, the recycled biochar synthesized from Spirulina platensis and impregnated into CeO2 has been demonstrated. The order of in situ >ex situ > biochar nanocomposites for higher bio-oil. The highest bio-oil conversion of 33% was achieved at the optimum temperature of 250 °C. The use of the biochar nanocomposite also resulted in a decrease in the oxygen and nitrogen content of the bio-oil and an increase in its heating value, which was found to be high at 35.64 MJ/kg. With the inclusion of the in situ biochar nanocomposite, energy recovery was increased by up to 65.34%. The current study has shown that low biochar nanocomposite concentrations (0.20 g), low temperature (250 °C), and short residence time (30 min) are essential for improved bio-oil yield and quality of bio-oil.

A review on catalytic pyrolysis for high-quality bio-oil production from biomass

Biomass is a renewable source and potentially sustainable fossil fuel replacement due to its availability, lower processing cost, high conversion, and lower life cycle carbon emissions. Pyrolysis can be used to convert biomass into bio-oil, but the quality of bio-oil is usually poor exhibiting high viscosity, thermal instability, and corrosiveness. This review article is focused on the application of catalytic pyrolysis towards obtaining high-quality bio-oil and advanced techniques for bio-oil characterisation. Structural arrangement (i.e., mesoporous, microporous), number of acid sites (Lewis and Bronsted acid sites), and amount of metal loading play a key role on deoxygenation reactions and selective production of aromatic hydrocarbons. Hierarchical zeolites doped with noble metals favour hydrogenation of C▬O or C〓O and reduce coke deposition in the production of polycyclic aromatics. Overall reaction mechanisms, aromatic yield and selectivity, the effect of Si/Al ratio, and process challenges of metal loaded zeolites are summarized. The advantages and disadvantages of different types of advanced analytical techniques for bio-oil characterisation are also discussed. The results showed that two-dimensional gas chromatography (2D GC) technique can identify 70% of chromatograph from bio-oil analysis. However, there is need to combine analytical techniques to accurately quantify bio-oil components.

Synergetic effect and primary reaction network of corn cob and cattle manure in single and mixed hydrothermal liquefaction

Agricultural waste is a good choice to produce biofuels because of its abundance and environmental friendliness. In this work, corn cob and cattle manure were studied by hydrothermal liquefaction (HTL) in a batch reactor with reaction temperatures from 300 °C to 360 °C alone and in mixtures. HTL products, including bio-oil, aqueous phase, and gas were comparatively analyzed. The maximum bio-oil yields were 22.2% at 300 °C for corn cob and 19.3 % at 360 °C for cattle manure, respectively. Besides, the bio-oil from cattle manure had lower oxygen, higher H/C ratios, and higher HHVs than that from corn cob. N-Heterocycles could be taken as the characteristic compounds of bio-oils from cattle manure, yet organic acids and aldehydes were only detected from corn cob. Although benzenediols and N-heterocycles were major products in water-soluble organic matter (WSOM) for both two feedstocks, the pH values of aqueous phase products are acidic for corn cob and alkali for cattle manure, respectively. This is attributed to the generation of some ammonia from the decomposition of protein in cattle manure pyrolysis. The synergistic effect in mixtures could promote the decomposition of lignin by generating more phenols and benzenediols that improved the quality of bio-oil and increased the yields of WSOM. It could also affect the product of protein decomposition and transfer more N into the aqueous phase. The major component in the gaseous product was all CO2. These results indicate that different compositions could not only react with each other but also change the pH values of the reaction environment and further affect the reaction pathways of other compositions. A predicted primary reaction network of different components from corncob and cattle manure in the HTL was also proposed.

Comparative Investigation of Yield and Quality of Bio-Oil and Biochar from Pyrolysis of Woody and Non-Woody Biomasses

This study investigated the quantitative and qualitative attributes of liquid product and biochar obtained from pyrolysis of woody biomass (rubberwood sawdust (RWS)) and non-woody biomasses (oil palm trunk (OPT) and oil palm fronds (OPF)). The prepared biomass was pyrolyzed at temperatures of 500 °C, 550 °C, and 600 °C by using an agitated bed pyrolysis reactor, and then the yields and characteristics of liquid product and biochar were determined. The results showed that liquid product and biochar yields were in the respective ranges of 35.94–54.40% and 23.46–25.98% (wt.). Pyrolysis of RWS at 550 °C provided the highest liquid yield. The energy content of the water free liquid product was in the range 12.19–22.32 MJ/kg. The liquid product had a low pH and it mainly contained phenol groups as indicated by GC-MS. The biochars had high carbon contents (75.07–82.02%), while their oxygen contents were low (14.22–22%). The higher heating value (HHV) of biochar was in the range 26.42–29.33 MJ/kg. XRF analysis revealed that inorganic elements had higher contents in biochar than in the original biomass. The slagging and fouling indexes of biochar were also different from those of the biomass. High carbon content of the biochar confirms potential for its use in carbon sequestration. The specific surface of biochar was lower than that of biomass, while the average pore diameter of biochar was larger than for raw biomass as revealed by BET and SEM. These results on liquid product and biochar obtained from RWS, OPT, and OPF demonstrate that they are promising feedstocks for biofuels and other value-added products.

Effect of solvent on hydro-solvothermal co liquefaction of sugarcane bagasse and polyethylene for bio-oil production in ethanol–water system

This study aims to investigate the role of water and ethanol in ethanol/water mixed solvent system, co-liquefaction of high-density polyethylene (HDPE) and sugarcane bagasse (SCB) to produce high quality bio-oil. It was revealed that various ethanol/water mixing ratios led to various reaction mechanisms, which indicates that there is a clear synergy effect between water and ethanol liquefaction process in three reaction media. The conversion and bio-oil yield approach were in the order of pure water < pure ethanol < water/ethanol mixed solvent regardless of the feedstock composition. Furthermore, detailed analysis of bio-oils was preformed such as CHNS/O analysis, chemical composition, 13C and 1H NMR analysis, higher heating value (HHV), TGA and FTIR analysis. The sugarcane bagasse-plastics derived bio-oil was found effective to enhance the qualitative properties of bio-oils compared from the pure sugarcane bagasse. The co-liquefaction of HDPE and SCB in mixed solvent was found more effective to enhance the qualitative and quantitative features of bio-oils compared to sole water and ethanol solvent.

Solar pyrolysis of waste biomass: A comparative study of products distribution, in situ heating behavior, and application of model-free kinetic predictions

A fixed-bed based solar pyrolysis of three waste biomass types: waste wood (WW), waste straw (WS), and sewage sludge (SS) was performed with emphasis on heating behaviour description, products yields, and quality. Laboratory solar pyrolysis reactor setup consists of a copper block indirectly heated by research-grade 1.6 kW xenon lamp radiation. Actual heating rates observed for 90, 95 and 100% xenon lamp power are 4.51, 5.32, and 5.49 K/min for WS; 5.10, 5.19, and 5.37 K/min for WW; and 3.95, 4.48, and 5.25 K/min for SS, respectively. Solar pyrolysis product yields (bio-oil, gas, char) were 51.68, 9.53, and 38.79 wt% for SS, 69.23, 9.18, and 21.59 wt% for WW, 62.30, 10.64, and 27.06 wt% for WS, denoted for the specific heating rates in ascending order. The highest quality bio-oil was obtained from WW pyrolysis with the lowest oxygen to carbon fraction and higher heating value (HHV) of 21.99 MJ/kg. Obtained chars, especially after solar pyrolysis of lignocellulosic biomass, presented HHV of 27.09 MJ/kg and 22.02 MJ/kg for WW and WS respectively, showed significant potential for renewable solid fuel. The increase of the lamp power, and long process time, caused degradation of porous structures within the biomass, where among the samples the highest specific surface area (BET) was denoted for WW samples at 5.2 K/min with 145.09 m2/g. Correlation between model-free kinetic predictions and gaseous species evolution was found, proving the value of apparent isoconversional activation energy profiles in describing actual solar pyrolysis gas compound formation at the laboratory scale.

Spent fluid catalytic cracking (FCC) catalyst enhances pyrolysis of refinery waste activated sludge

Catalytic pyrolysis is an effective innocuity, volume reduction and resource recovery technology for petroleum refinery waste activated sludge (rWAS). However, the high cost of catalysts hinders its application. In the present study, the spent fluid catalytic cracking catalyst (sFCCc) was reused to catalytically pyrolyze rWAS for the first time. The pyrolytic kinetics, yields and characteristics of pyrolytic products were investigated. sFCCc reduced the low-temperature (139–390 °C) and high-temperature (390–540 °C) average activation energy by 12.9% and 6.6% compared to rWAS alone. sFCCc and metallic oxides in rWAS jointly catalyzed the decomposition of rWAS and primary vapor via a series of thermochemical reactions. sFCCc promoted the conversion of rWAS into bio-oil and non-condensable gases. The lowest yield of biochar was 40.6 wt % and the highest content of H2 in non-condensable gases was up to 38.4 vol %. sFCCc significantly improved the quality of bio-oil. The content of saturated hydrocarbons increased from 37.3 wt % to 45.7 wt % and H/C molar ratios increased from 1.4 to 1.6. The O mobility from rWAS to bio-oil decreased from 22.1 wt % to 14.9 wt %. The pyrolytic residue presented a low environmental risk and showed a catalytic potential in ozonation treatment of refractory refinery wastewater. This study provides a new “wastes-treat-wastes” method for petroleum refinery waste management with the advantages of value-added energy recovery and resources reuse.

Effects of aqueous phase circulation and catalysts on hydrothermal liquefaction (HTL) of penicillin residue (PR): Characteristics of the aqueous phase, solid residue and bio oil

Hydrothermal liquefaction (HTL) is a promising thermochemical technology for the treatment of hazardous wastes such as penicillin residue (PR). For the treatment of aqueous waste produced by PR in the HTL process, aqueous phase circulation is an attractive solution, both environmentally and economically. The present study shows that aqueous phase circulation can promote the transfer of organic matter from the aqueous phase to bio–oil. The content of organic acids and alcohols in the aqueous phase decreased significantly, and the bio–oil yield and energy recovery efficiency also increased. Under non–catalytic conditions, the bio–oil yield increased from 26.09 wt% to 33.72 wt%. The use of Na2CO3 as a catalyst further improved the bio–oil yield. After a single aqueous phase circulation, the bio–oil yield increased to 34.63 wt%, and the energy recovery efficiency increased to 66.94%. Under catalytic hydrothermal conditions, the content of organic acids in the bio–oil was reduced using aqueous phase circulations, which improved the quality of the bio–oil. At the same time, the Na2CO3 catalyst promoted the hydrolysis of PR to form small molecule organic matter, inhibited the formation of coke, and reduced the content of carbon, hydrogen and oxygen in the solid residue. An increase of cycle times led to excessive accumulation of Na2CO3, which had a negative impact on the yield of bio–oil. Nitrogen–containing compounds in the bio–oil increased to a certain extent, which renders it necessary to consider denitrification treatments in the future. The work provides a useful reference for further research on the preparation of high quality bio–oil by PR hydrothermal liquefaction.

Catalytic co-pyrolysis palm oil empty fruit bunch and low-density polyethylene of plastic waste into high grade bio-oil

Bio-oil produced from biomass pyrolysis is still acidic and has a low heating value. Co-pyrolysis is a process of pyrolysis of biomass and material that has a higher (H/C) effective. Low-density polyethylene (LDPE) is a type of plastic waste that has a higher hydrogen index than empty fruit bunch (EFB). To improve the quality of bio-oil, it is necessary to co-pyrolysis EFB and LDPE using a calcium oxide catalyst. The purpose of this research is to produce bio-oil from a mixture of EFB and LDPE, to determine the effect of the CaO catalyst ratio and temperature on the bio-oil yield, and to determine the physical and chemical characteristics of the bio-oil product. The catalytic co-pyrolysis process uses 10 grams of EFB/LDPE mixture (EFB/LDPE ratio 50%:50%), CaO catalyst with a variation of CaO/raw material ratio (1%, 2%, 3%, 4%, and 5% w/w) and temperature variations (400°C, 450°C, 500°C,550 and 600 °C), with nitrogen gas flowing at a flow rate of 400 mL/min for 45 minutes. The highest yield generated on the use of CaO/raw material ratio of 5% w/w and temperature of 550 °C was 35.2%. The characteristics of the bio-oil obtained were the density of 0.948 g/mL, the viscosity of 4.18 cSt, pH of 4.04, and heating value of 43.4 MJ/Kg. The results of GC-MS analysis showed that bio-oil contained 37.05% phenol compounds, 27.88% hydrocarbon, 20.27% ketones, 7.21% alcohol, 4.36% aldehydes, and 1.08% ester.

Robust ZSM-5 Membranes for Efficient Bio-Oil Dehydration: Transport Mechanism and Its Implication on Structural Tuning

Effective water removal from bio-oil is very important for upgrading bio-oil quality via esterification because water strongly inhibits the conversion and simultaneously lowers the heating value. In the present study, ZSM-5 zeolite membranes are applied to make bio-oil pervaporation dehydration more efficient. An investigation of the permeation performance demonstrated that water mainly permeated through ZSM-5 membranes via intercrystalline pores, whereas intracrystalline pores in the membrane were almost completely blocked because of intensive membrane fouling. The above result showed that tuning water transport paths was significantly important when designing high-performance ZSM-5 membranes for bio-oil pervaporation. A decrease in membrane fabrication time successfully created loose membrane structures with abundant intercrystalline pores and resulted in highly selective and stable ZSM-5 membranes with significantly improved permeation flux in bio-oil dehydration. These robust ZSM-5 membranes show great potential for bio-oil refining in industrial applications.

Catalytic flash pyrolysis of Monoraphidium sp. before and after lipid extraction

The use of biomass from Monoraphidium sp. microalgae before and after lipid extraction was investigated using flash catalytic pyrolysis to generate a bio-oil with improved characteristics. The biomass was obtained from intensive outdoor crops and exhibited an attractive biochemical composition to be used in thermochemical processes with high protein and carbohydrate content remaining after lipid extraction. Flash pyrolysis of biomass before and after extraction was developed at 500 °C in an analytical micro-pyrolyzer coupled to a gas chromatography/mass spectrometry (Py-GC/MS) instrument and the pyrolysis vapors were transported to a catalytic bed at 300 °C. Pyrolysis vapors were improved in the catalytic pyrolysis using zeolite HZSM-5 which promoted the deoxygenation and complete denitrogenation of the products. Furthermore, the formation of aromatics in the biomass was increased before and after extraction to 87.45% and 95.08%, respectively, thus demonstrating the potential of this process to generate a high quality bio-oil which can be used in several applications in chemical and fuel industries.

Catalytic pyrolysis of ulva lactuca macroalgae: Effects of mono and bimetallic catalysts and reaction parameters on bio-oil up-gradation

Catalytic pyrolysis of ulva lactuca (UL) macroalgae was studied over a series of ZrO2 supported metal such as Co, Ni and Co-Ni metal catalysts at temperature range of 300–500 °C. Highest bio-oil yield (47.8 wt%) was found with Co-Ni/ZrO2 (10 wt%) catalyst while non-catalytic yielded 42.5 wt% bio-oil. Moreover with increases the metal amount to 15 wt%, the bio-oil yield slightly increased (49.2 wt%). The bio-oil quality significantly improved with using the catalysts compared to the non-catalytic pyrolysis. Catalytic pyrolysis also revealed that introducing Co-Ni into the ZrO2 could result in higher surface area and which increased active sites. Catalytic bio-oils were consisted of mainly long chain hydrocarbon in the range of C6-C16. Moreover, the catalytic bio-oils were showed the higher ‘high heating value’ (HHV) 38.1 MJ/kg as compare to non-catalytic bio-oils (29.4 MJ/kg). Catalysts have been showed excellent recyclability on bio-oil yield and compounds selectivity.

Synergistic effects on co-pyrolysis of low-temperature hydrothermally pretreated high-protein microalgae and polypropylene

Protein-rich (58.50%) Chlorella sp. was hydrothermally pretreated at 175 °C to remove part of N, and the obtained solid residue (ChSR) was then co-pyrolyzed with polypropylene (PP) to reduce O content and improve bio-oil quality. About 48.25% of N was enriched into the aqueous phase during hydrothermal pretreatment (HTP) process, and about 15.70% of bio-oil with low N content (3.45%) was obtained. Compared with that of raw sample, the structure of ChSR was further aromatized as revealed by 13C NMR analysis. The interaction between ChSR and PP was deeply investigated with the help of online TG-FTIR-MS and Py-GC/MS. The co-pyrolysis process of ChSR-PP blends was generally divided into two thermal decomposition stages. The first stage (150–400 °C) was mainly associated with decomposition of ChSR, while the second stage (400–550 °C) was the results of combination of thermal degradations of ChSR and PP, with the primary contribution from the degradation of PP. The addition of PP accelerated pyrolysis of ChSR and inhibited the release of C2H5O+/COOH+ and NH3 but promoted CO2 releasing at the first stage. However, ChSR delayed the pyrolysis of PP and prohibited release of H2 and light hydrocarbons (i.e., CH4, C2H2, C2H6, C3H7, and so on) from PP at the second stage. Kinetic analysis based on the Flynn-Wall-Ozawa (FWO) method revealed that the average activation energy (E) of the blends at the two decomposition stages were 159.10–164.12 kJ/kg and 194.20–219.86 kJ/kg, respectively. Results of Py-GC/MS indicated that, the synergistic effect between ChSR and PP significantly enhanced the formation of hydrocarbons (i.e., cyclohexane derivatives and 2,4-Dimethyl-1-heptene), and the interaction achieved maximum when the ratio of ChSR:PP was 80:20. The yields of O-containing compounds (alcohols, and phenols) and BTEXs (Benzene series) were decreased. It should be noted that both the amounts and kinds of N-heterocyclic compounds were decreased. Finally, the possible mechanism on interaction between ChSR and PP was also proposed. This work will provide useful information on better utilization of high-protein microalgae.