Comparative study on pyrolysis of lignocellulosic and algal biomass using a thermogravimetric and a fixed-bed reactor

Microalgal biochar assisted simultaneous removal of particulate matter, formaldehyde, and total volatile organic compounds (TVOC's) from indoor air

Biochar-based materials for air treatment have gained significant attention for removing health-detrimental volatile organic compounds (VOCs) and particulate matter (PM) in indoor air settings. However, high turnaround time, multiple pretreatment processes involved, and high pore size and low surface area (>10 μm, <100 m2 g-1) of lignocellulosic feedstocks demand alternative biochar feedstock material. Considering this, we designed a simple first-of-its-kind indoor air scrubbing material using diatoms-enriched microalgae biochar. In the present study, the microalgae were cultivated on waste anaerobic digestate (biogas slurry) and were pyrolyzed at three different temperatures: 300 °C (BC300), 500 °C (BC500), and 700 °C (BC700). The BC500 and BC700 showed the highest removal efficiencies (99 %) for total volatile organic carbons (TVOCs) and formaldehyde (HCHO) at concentrations of 1.22 mg m-3 HCHO and 8.57 mg m-3 TVOC compared to 50% efficiency obtained with commercially available surgical, cloth, and N95 masks. The biochar obtained showed a high Brunauer-Emmett-Teller (BET) surface area of 238 m2 g-1 (BC500) and 480 m2 g-1 (BC700) and an average pore size of 9-11 nm due to the mesoporous characteristic of diatom frustules. The comparatively poor performance of BC300 was due to lower surface area (150 m2 g-1) arising from incomplete organic removal, as evidenced by FESEM-EDX and FTIR. The high removal efficiencies in BC500 and BC700 were also attributed to the presence of reactive functional groups such as -OH and R-NH2. Concurrently, the average particulate matter (PM10, PM2.5, and PM1) removal efficiency for BC500 and BC 700 ranged between 66 and 82.69 %. The PM removal performance of BC500 and BC700 was lower (15-20%) than commercially available masks. Overall, the present study highlights the importance of diatoms (reactive Si) present inside the pores of microalgal biochar for enhanced removal of PM, TVOCs, and HCHO at temperatures above 500 °C. This complete approach signifies a step towards establishing a self-sustainable and circular process characterized by minimal waste generation for indoor air treatment.

MgO-modified biochar by modifying hydroxyl and amino groups for selective phosphate removal: Insight into phosphate selectivity adsorption mechanism through experimental and theoretical

Metal oxides-modified biochars have been widely studied as promising adsorbents for removing phosphate from wastewater discharge. Yet, the low adsorption selectivity towards phosphate severely limits its potential in practical applications. In this study, MgO-modified biochar modified by hydroxyl and amino groups (OH/NH2@MBC) is developed for selective phosphorus recovery from wastewater. As major results, the OH/NH2@MBC exhibits favorable phosphate adsorption performance is superior to that of MBC resin in the presence of co-existing anions (NO3-, Cl-, HCO3- and SO42-) and natural organic matter (humic acid) even actual wastewater, suggesting its superior selectivity towards phosphate. The OH/NH2@MBC shows an excellent phosphate adsorption capacity (43.27 mg/g) and desorption ratio (82.34 %) after five cycles under the condition of anion coexistence (100 mg/L). The experimental and DFT theoretical study reveals that attaching hydroxyl and amino groups onto the MBC surface, which facilitates to inhibiting the side effects of anions (NO3-, Cl-, HCO3-, and SO42-) through Lewis acid-base sites, hydrogen bonds, and metal affinity, and preferentially select adsorption P, contributing greatly to improve phosphate adsorption selectivity. Importantly, the presence of amino and hydroxyl groups can reduce the Fermi level of OH/NH2@MgO(220) and OH/NH2@MgO(200) and improve the adsorption selection for HPO42-. This study provides an effective strategy for enhancing the adsorption selectivity of metal oxides-modified biochars towards phosphate through modifying functional groups.

Efficient removal of heavy metal and antibiotics from wastewater by phosphate-modified hydrochar

The preparation, characterization and adsorption performance of the phosphate-modified hydrochar (P-hydrochar) for Pb(II) and ciprofloxacin removal are investigated. Pb(II) and ciprofloxacin adsorption behavior fit well with the Hill model with the adsorption capacity of 119.61 and 98.38 mg/g, respectively. Pb(II) and ciprofloxacin adsorption kinetic process are accurately described by the Pseudo-second-order. Pb(II) and ciprofloxacin have synergy in the binary contaminant system, which reveals that Pb(II) adsorption amount is augmented. While ciprofloxacin adsorption amount is also augmented at low Pb(II) concentration and hindered at high Pb(II) concentration. Pb(II) adsorption mechanisms on P-hydrochar (e.g. precipitation, π-π interaction and complexation) are different from the ciprofloxacin (e.g. hydrogen bonding, pore filling, electrostatic attraction). Pb(II) and ciprofloxacin adsorption process are further analyzed by the density functional theory. The coexisted ions have little influenced on Pb(II) and ciprofloxacin adsorption. P-hydrochar still has large Pb(II) and ciprofloxacin adsorption capacity after five cycles. This result indicates that poplar sawdust waste can be converted into an efficient adsorbent to remove Pb(II) and ciprofloxacin from wastewater,.

Recent advancements and challenges in emerging applications of biochar-based catalysts

The sustainable utilization of biochar produced from biomass waste could substantially promote the development of carbon neutrality and a circular economy. Due to their cost-effectiveness, multiple functionalities, tailorable porous structure, and thermal stability, biochar-based catalysts play a vital role in sustainable biorefineries and environmental protection, contributing to a positive, planet-level impact. This review provides an overview of emerging synthesis routes for multifunctional biochar-based catalysts. It discusses recent advances in biorefinery and pollutant degradation in air, soil, and water, providing deeper and more comprehensive information of the catalysts, such as physicochemical properties and surface chemistry. The catalytic performance and deactivation mechanisms under different catalytic systems were critically reviewed, providing new insights into developing efficient and practical biochar-based catalysts for large-scale use in various applications. Machine learning (ML)-based predictions and inverse design have addressed the innovation of biochar-based catalysts with high-performance applications, as ML efficiently predicts the properties and performance of biochar, interprets the underlying mechanisms and complicated relationships, and guides biochar synthesis. Finally, environmental benefit and economic feasibility assessments are proposed for science-based guidelines for industries and policymakers. With concerted effort, upgrading biomass waste into high-performance catalysts for biorefinery and environmental protection could reduce environmental pollution, increase energy safety, and achieve sustainable biomass management, all of which are beneficial for attaining several of the United Nations Sustainable Development Goals (UN SDGs) and Environmental, Social and Governance (ESG).

Modelling hydrogen production from biomass pyrolysis for energy systems using machine learning techniques

In the context of Industry 4.0, hydrogen gas is becoming more significant to energy feedstocks in the world. The current work researches a novel artificial smart model for characterising hydrogen gas production (HGP) from biomass composition and the pyrolysis process based on an intriguing approach that uses support vector machines (SVMs) in conjunction with the artificial bee colony (ABC) optimiser. The main results are the significance of each physico-chemical parameter on the hydrogen gas production through innovative modelling and the foretelling of the HGP. Additionally, when this novel technique was employed on the observed dataset, a coefficient of determination and correlation coefficient equal to 0.9464 and 0.9751 were reached for the HGP estimate, respectively. The correspondence between observed data and the ABC/SVM-relied approximation showed the suitable effectiveness of this procedure.

Microalgae bio-oil production by pyrolysis and hydrothermal liquefaction: Mechanism and characteristics

Microalgae have great potential in producing energy-dense and valuable products via thermochemical processes. Therefore, producing alternative bio-oil to fossil fuel from microalgae has rapidly gained popularity due to its environmentally friendly process and elevated productivity. This current work aims to review comprehensively the microalgae bio-oil production using pyrolysis and hydrothermal liquefaction. In addition, core mechanisms of pyrolysis and hydrothermal liquefaction process for microalgae were scrutinized, showing that the presence of lipids and proteins could contribute to forming a large amount of compounds containing O and N elements in bio-oil. However, applying proper catalysts and advanced technologies for the two aforementioned approaches could improve the quality, heating value, and yield of microalgae bio-oil. In general, microalgae bio-oil produced under optimal conditions could have 46 MJ/kg heating value and 60% yield, indicating that microalgae bio-oil could become a promising alternative fuel for transportation and power generation.

Complication Rates after Breast Surgery with the Motiva Smooth Silk Surface Silicone Gel Implants-A Systematic Review and Meta-Analysis

BACKGROUND

In an era where textured devices are being phased out due to concerns about BIA-ALCL, the Motiva SilkSurface breast implants intend to alleviate historical prosthesis-related complications. However, its safety and feasibility remain unelucidated.

METHODS

An analysis of Pubmed, Web of Science, Ovid, and Embase databases was performed. A total of 114 studies were identified initially, and 13 of these met the inclusion criteria and were assessed regarding postoperative parameters such as complication rate or follow-up period.

RESULTS

In 4784 patients who underwent breast augmentation with Motiva SilkSurface breast implants, a total of 250 (5.2%) complications were observed. Short- and medium-term complication rates ranged from 2.8-14.4% and 0.32-16.67%, respectively. The most common complication was early seroma (n = 52, overall incidence = 1.08%), followed by early hematoma (n = 28, overall incidence = 0.54%). The incidence of capsule contracture was 0.54% and breast implant-associated-anaplastic large cell lymphoma was not observed.

DISCUSSION

Although the majority of the studies in the current literature suggest the distinction of the Motiva SilkSurface breast implants in terms of postoperative complications and capsular contracture, its safety and feasibility need to be further elucidated with well-designed, large-scale, multicenter, prospective case-control studies. Other: No funding was received.

Effect of the Iron Component on Microcrystalline Structure Evolution of Hydrochloric Acid-Demineralized Lignite during the Pyrolysis Process

Hydrochloric acid-demineralized Shengli lignite (SL⁺) and iron-added lignite (SL⁺-Fe) were thermally degraded using a fixed-bed device to better understand the effect of the iron component on the microcrystalline structure transformation properties of lignite during the pyrolysis process. The primary gaseous products (CO₂, CO, H₂, and CH₄) were detected by pyrolysis-gas chromatography. X-ray diffraction and Raman spectra were adopted to analyze the microcrystalline structure of lignite and chars. The results indicated that the iron component had a catalysis effect on the pyrolysis of SL⁺ below 602.6 °C. The pyrolysis gases released in the order of CO₂, CO, H₂, and CH₄, and the addition of the iron component did not change the sequences. The iron component promoted the generation of CO₂, CO, and H₂ in the low-temperature stage. During the high-temperature stage, the iron component inhibited the formation of CO and H₂. The formation of CH₄ was inhibited by the iron component throughout the pyrolysis process. The evolution characteristics of -OH, C=O, C=C, and C-H functional groups were not significantly affected, and the fracture of aliphatic functional groups and C-O functional groups was inhibited by the iron component during the pyrolysis process. The iron component restricted the spatial regular arrangement tendency of aromatic rings and facilitated the decrease in the small-sized aromatic ring but inhibited the formation of large aromatic rings (≥6 rings) and the content decrease in side chains during the pyrolysis process. Notably, the effects of the iron component on the formation of gaseous products were associated with the microstructure evolution of lignite.

Sequential washing and eluent regeneration with agricultural waste extracts and residues for facile remediation of meta-contaminated agricultural soils

Washing with organic acids and dissolved organic carbon (DOC) is a promising technique for effective removal of potentially toxic metals from agricultural soils and the two key factors are the screening of inexpensive, high-efficiency, and environmentally friendly washing agents and the safe treatment of waste eluent. We used extracts from agro-forestry wastes (pineapple peel, lemon peel, grapefruit peel and gardening crabapple fruit) to develop a facile two-stage sequential washing method (extracts and/or citric acid (CA) and coupled with extracts) and regenerated waste eluent. The washing efficiencies of Cd and Cu were significantly increased by pineapple peel (PP) using two-stage sequential washing with the sequence of PP + CA-PP > CA-PP > PP-PP. The potential pollution risk from soil Cd was lowered by 33.0% from moderate to low risk, and soil nutrient contents increased. 80.9% of Cd and 81.3% of Cu in waste eluent were efficiently removed by the PP residues. The removal mechanisms of metals in soils and eluents by PP washing agents and residues can be attributed to acid activation, cation exchange and complexation between metal ions and carboxyl groups. Therefore, the PP extracts and residues are potentially suitable for the removal of Cd and Cu from polluted agricultural soils and washing waste eluents.

Pyrolysis characteristics of biodried products derived from municipal organic wastes: Synergistic effect of bulking agents and modification of biodegradation

Derived from the biodrying of municipal organic wastes (MOWs), biodried products (BPs) are widely identified as renewable energy sources. In this study, for efficient energy recovery, the pyrolysis characteristics of BPs were investigated by comprehensive kinetic analysis, with special focus on the synergistic effect of bulking agents and the influence of biodegradation. Compared with theoretical raw materials (RMs), it was suggested that the synergistic effect of organics and lignocelluloses in RMs promoted decomposition in Stage 1 (400-570 K), especially for the pyrolysis of RM using sawdust, during which the positive effect achieved decomposition in advance with lower overlap ratio (0.9264) and ΔW (-9.50% at 619.0 K) values. Furthermore, compared with RMs, it was indicated that the kinetic indices (E_a and ln A values) of the BPs were upward in Stage 1 and decreased in Stage 2 due to biodegradation. The results of ΔH, ΔG and ΔS indicated that BP pyrolysis required more heat supply as the reaction progressed but formed a more organized activated complex. In addition, biodegradation observably decreased the generation of gas products and typical functional groups of volatiles during BP pyrolysis, such as CO₂ and CO, which presented decreasing ratios of 32.18-42.47% and 30.25-46.47%, respectively. In general, the pyrolysis of BPs was intensified by bulking agents and modified by biodegradation.

Pyrolysis of low-value waste switchgrass: Physicochemical characterization, kinetic investigation, and online characterization of hot pyrolysis vapours

The present study is dedicated to physicochemical characterization, kinetic, thermal degradation behaviors, and online characterization of vapour products through Py-GC-MS and TGA-FTIR. The feasibility study was attained via proximate, ultimate, fibre analysis, and extractive analysis, whereas Vyazovkin (VM), Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), Coats-Redfern (CR), and Distributed Activation Energy Model (DAEM) were employed for kinetics exploration. The feasibility study showed its tremendous ability to be used as pyrolysis feedstock. TGA-FTIR documented the maximum release of CO₂ (26.22%), carbonyls (25.04%), and hydrocarbons (15.93%). Further, kinetic investigation of SWG documented an increased trend of activation energy against progressive conversion. The apparent average activation energy from KAS, OFW, DAEM, and VM was found to be 126.03, 137.54, 130.33, 134.26 kJ mol^-1, respectively. Also, kinetics reaction mechanisms are exposed to the multi-nature of decomposition of biomass. Furthermore, the Py-GC-MS investigation established increased hydrocarbons (6.49-11.54%) and reduced oxygen-containing products (24.17-17.27%) with an increased temperature.

Sustainable valorization of algae biomass via thermochemical processing route: An overview

Biofuels have become an attractive energy source because of the growing energy demand and environmental issues faced by fossil fuel consumption. Algal biomass, particularly microalgae, has excellent potential as feedstock to be converted to bio-oil, biochar, and combustible syngas via thermochemical conversion processes. Third-generation biofuels from microalgal feedstock are the promising option, followed by the first-generation and second-generation biofuels. This paper provides a review of the applications of thermochemical conversion techniques for biofuel production from algal biomass, comprising pyrolysis, gasification, liquefaction, and combustion processes. The progress in the thermochemical conversion of algal biomass is summarized, emphasizing the application of pyrolysis for its benefits over other processes. The review also encompasses the challenges and perspectives associated with the valorization of microalgae to biofuels ascertaining the potential opportunities and possibilities of extending the research into this area.

Co-pyrolysis of microalgae and other biomass wastes for the production of high-quality bio-oil: Progress and prospective

Microalgae are the most prospective raw materials for the production of biofuels, pyrolysis is an effective method to convert biomass into bioenergy. However, biofuels derived from the pyrolysis of microalgae exhibit poor fuel properties due to high content of moisture and protein. Co-pyrolysis is a simple and efficient method to produce high-quality bio-oil from two or more materials. Tires, plastics, and bamboo waste are the optimal co-feedstocks based on the improvement of yield and quality of bio-oil. Moreover, adding catalysts, especially CaO and Cu/HZSM-5, can enhance the quality of bio-oil by increasing aromatics content and decreasing oxygenated and nitrogenous compounds. Consequently, this paper provides a critical review of the production of bio-oil from co-pyrolysis of microalgae with other biomass wastes. Meanwhile, the underlying mechanism of synergistic effects and the catalytic effect on co-pyrolysis are discussed. Finally, the economic viability and prospects of microalgae co-pyrolysis are summarized.

Machine learning prediction of pyrolytic gas yield and compositions with feature reduction methods: Effects of pyrolysis conditions and biomass characteristics

This study aimed to utilize machine learning algorithems combined with feature reduction for predicting pyrolytic gas yield and compositions based on pyrolysis conditions and biomass characteristics. To this end, random forest (RF) and support vector machine (SVM) was introduced and compared. The results suggested that six features were adequate to accurately forecast (R² > 0.85, RMSE < 5.7%) the yield while the compositions only required three. Moreover, the profound information behind the models was extracted. The relative contribution of pyrolysis conditions was higher than that of biomass characteristics for yield (55%), CO₂ (73%), and H₂ (81%), which was inverse for CO (12%) and CH₄ (38%). Furthermore, partial dependence analysis quantified the effects of both reduced features and their interactions exerted on pyrolysis process. This study provided references for pyrolytic gas production and upgrading in a more convenient manner with fewer features and extended the knowledge into the biomass pyrolysis process.

Combustion Behavior of Algal Biochars Obtained at Different Pyrolysis Heating Rates

In this work, the combustion performance of Chlorella vulgaris (CV), Dunaliella salina (DS), and Haematococcus pluvialis (HP) algal biochars was analyzed based on the multicomponent method. The biochars were obtained via nonisothermal pyrolysis of raw algal biomasses at three different heating rates (i.e., 30, 40, and 50 °C/min), and biochar combustion was performed from 200 to 700 °C at a heating rate of 5 °C/min. The complex oxidative reaction of algal biochar was resolved into combined reactions of multiple pseudo-components based on the peak deconvolution method using a bi-Gaussian model. The activation energies (E _a) for each pseudo-component (PC) of all biochar samples were calculated by the Coats-Redfern isoconversional method and four kinetic models (i.e., diffusion, nucleation, order-based, and shrinking core models). The results showed that the highest E _a values were predicted by the diffusion model. Except that the E _a for the first PC of CV biochar decreased by 16.45%, the E _a values for all other biochar samples generally increased with increasing the pyrolysis heating rate. Moreover, when the diffusion model was used, the E _a for the second PC of CV biochar increased by 50.87%, that for the first PC of DS biochar increased by 16.85%, and those for the first and third PCs of HP biochar increased by 4.66 and 11.66%, respectively. In addition, the combustibility index (S_n ) was evaluated based on the ignition and burnout temperatures as well as the mean and maximum weight loss rates. Generally, the combustion performance of all biochar samples was good at a low temperature but deteriorated toward a high temperature. As the pyrolysis heating rate increases, an overall increase in the combustion quality was also seen for the second PC of CV biochar and the first PCs of DS and HP biochars because their S_n increased from 2.70 × 10^-15 to 3.07 × 10^-15 °C^-5, 2.53 × 10^-13 to 3.88 × 10^-13 °C^-5, and 3.00 × 10^-13 to 3.26 × 10^-13 °C^-5, respectively.

Graphitic bio-char and bio-oil synthesis via hydrothermal carbonization-co-liquefaction of microalgae biomass (oiled/de-oiled) and multiple heavy metals remediations

Thermochemical transformation of microalgae biomass into graphitic bio-chars entices as proficient bio-adsorbents for heavy metal contaminants. This study explores the synergistic impact of Chlorella sorokiniana on biomass generation and wastewater remediation in high rate algae pond (HRAP). Biomass produced was applied for hydrothermal carbonization-co-liquefaction (HTCL). The structural and morphological characteristics of HTCL products (i.e. bio-chars and bio-oils) have been systematically studied by XRD, Raman, FTIR, elemental analyzer, SEM, BET, and ¹H NMR spectroscopy. The crystallite size of the graphite 2H indexing planes was to be 4.65 nm and 14.07 nm in the bio-chars of oiled biomass (MB-OB) and de-oiled biomass (MB-DOB), respectively. The increase in the I_D/I_G ratio of MB-DOB indicated the highly disordered graphitic structure due to the appearance of carbonyl, hydroxyl, and epoxy functionalities in the line of high C/N and low C/H ratio. Also, the multiple heavy metals remediation of MB-DOB revealed better efficiency as ~100% in 720 min. The kinetics analysis shows the correlation coefficient of pseudo-second-order is well fitted compared to the pseudo-first-order. The Langmuir adsorption model signifies the adsorption of heavy metal ions in a monolayer adsorption manner. The study proposes the microalgae bio-char potential for multiple heavy metals remediation alongside bio-oils.

Detoxification of sisal bagasse hydrolysate using activated carbon produced from the gasification of açaí waste

Due to its recalcitrance and difficult disruption, biomass requires severe treatment conditions to produce bioproducts. These processes also generate substances that inhibit microbial metabolism, resulting in low conversion of sugars into bioproducts. To minimize this, in this work the sisal bagasse acid hydrolysate was detoxified using the activated carbon obtained from residues of the gasification of açaí endocarp. The adsorbent properties were analyzed, and the effects of experimental parameters related to furfural adsorption were evaluated. Then, the validation of the adsorption experiments was carried out in acid hydrolyzed liquor from sisal bagasse, the fermentation tests being performed with Saccharomyces cerevisiae. Overall, the furfural adsorption in the activated carbon was fast since most of the furfural was removed in the first minutes of the experiment. The Sips isotherm fit the experimental data best, with maximum adsorption capacity of 48.02 mg.g^-1. Kinetic data fitted LDF, QDF and FD models, and diffusivity parameters were obtained. After detoxification, the activated carbon from açaí waste removed 52% of furfural, 100% of HMF and 40.4% of acetic acid with moderate loss of sugars (17%). The results confirmed that the adsorbent is effective and promising for removing furfural and other fermentation inhibitors.

A comprehensive review on the factors affecting thermochemical conversion efficiency of algal biomass to energy

Algae are one of the most viable feedstock options that can be converted into different bioenergies viz., bioethanol, biobutanol, biodiesel, biomethane, biohydrogen, etc. owing to their renewable, sustainable and economic credibility features. Algal biomass to fuel biorefining process is generally classified into three categories as chemical, biochemical and thermochemical methods. The present article aims to provide a state-of-the-art review on the factors affecting the thermochemical conversion process of algal biomass to bioenergy. Further, reaction conditions of each techniques (torrefaction, pyrolysis, gasification and hydrothermal process) influence biochar, bio-oil and syngas yield were discussed. Reaction parameters or factors such as reactor temperature, residence time, pressure, biomass load/feedstock composition, catalyst addition and carrier gas flow affecting process efficiency in terms of product yield and quality were spotlighted and extensively discussed with copious literature. It also presents the novel insights on production of solid (char), liquid (bio-oil) and gaseous (syngas) biofuel through torrefaction, pyrolysis and gasification, respectively. It is found that the energy intensive drying was more efficient mode involved in thermochemical process for wet algal biomass. However other modes of thermochemical process were having unique feature on improving the product yield and quality. Among the various factors, reaction temperature and residence time were relatively more important factors which affected the process efficiency. The other factors signposted in this review will lay a roadmap to researchers to choose an optimal thermochemical conditions for high quality end product. Lastly, the perspectives and challenges in thermochemical conversion algae biomass to biofuels were also discussed.

Recent advances in thermochemical methods for the conversion of algal biomass to energy

Thermochemical techniques are being operated for the complete conversion of diverse biomasses to biofuels. Among the feedstocks used for thermochemical processes, algae are the promising biomass sources owing to their advantages over other feedstocks such as biomass productivity, renewability and sustainability. Due to several advantages, algal biomass is considered as a source for third generation biofuel. This review work aims to provide a state-of-the-art on the most commonly used thermochemical methods namely torrefaction, pyrolysis, and gasification processes. Furthermore, the production of biofuels from algal biomass was comprehensively articulated. Different algal strains used in thermochemical techniques and their conditions of operation were compared and discussed. The yield and quality of solid (char), liquid (bio-oil) and gaseous (syngas) products obtained through thermochemical methods were reviewed and analysed to understand the efficacy of each technique. End product percentage, quality and advantages of the torrefaction, pyrolysis, and gasification were summarized. It is found that the biofuel produced from the torrefaction process was easy to store and deliver and had higher utilization efficiency. Among the existing thermochemical methods, the pyrolysis process was widely used for the complete conversion of algal biomass to bio-oil or char. This study also revealed that the gasification (supercritical) method was the most energy efficient process for conversion of wet algal biomass. The reactor used in the thermochemical process and its subprocess was also highlighted. This study revealed that the fixed bed reactor was suitable for small scale production whereas the fluidized bed reactor could be scaled up for industrial production. In addition to that environmental impacts of the products were also spotlighted. Finally, the perspectives and challenges of algal biomass to bioenergy conversion were addressed.

Optimization of the nitrogen and oxygen element distribution in microalgae by ammonia torrefaction pretreatment and subsequent fast pyrolysis process for the production of N-containing chemicals

In this work, ammonia (NH₃) torrefaction pretreatment (ATP) was developed to optimize the nitrogen and oxygen element distribution of microalgae via the N-doping and oxygen removal reaction, which could obviously improve the potential use of microalgae as a feedstock for the production of N-heterocyclic chemicals through fast pyrolysis technology. The nitrogen content increased from 8.3% of raw microalgae to 11.51% at 300 °C of ATP, while the oxygen content decreased from 35.96% to 21.61%, because of the Maillard reactions. In addition, the nitrogen-doping ratio and oxygen removal ratio of ATP was much higher than the conventional nitrogen torrefaction pretreatment (NTP). With the increase of ATP torrefaction temperature or the pyrolysis temperature, the relative content of the N-containing compounds increased, while the O-containing compounds decreased. For the N-heterocyclic chemicals, higher pyrolysis temperature favored the formation of pyrroles, while inhibited the formation of pyridines and indoles.

Pyrolysis of algal biomass: Determination of the kinetic triplet and thermodynamic analysis

Microalgae Spirulina has good potential for bio-oil production. Therefore, kinetic and thermodynamic analysis of its pyrolysis process was performed. The activation energy values were estimated using both differential (109-340 kJ/mol) and integral (102-272 kJ/mol) isoconversional methods. Kinetic model was determined using master plot approach and the pyrolysis reaction appeared to transition between nucleation, diffusion and order-based kinetic models. Based on sigmoidal equations, a novel kinetic model equation was proposed which can define the pyrolysis process of algal biomass showing single differential thermogravimetric peak. The proposed kinetic triplet predicted the weight loss evolution quite precisely. Additionally, the thermodynamic feasibility of the reaction was examined based on enthalpy, entropy and Gibbs free energy. It was revealed that heat is consumed to make the raw sample reach a 'more orderly' state until a fractional conversion of 0.35. Moreover, bio-char and the remaining lipids at high temperature impede the reaction spontaneity towards the end.

On the pyrolysis of different microalgae species in a conical spouted bed reactor: Bio-fuel yields and characterization

The aim of this work was to study fast pyrolysis of three microalgae species in a continuous bench-scale conical spouted bed reactor at 500 °C. Bio-gas, bio-oil and bio-char yields have been determined and characterized by using GC, GC/MS, elemental analyzer and SEM. Bio-oil was the main product obtained through pyrolysis of microalgae. The non-condensable gaseous stream is made up of mainly hydrogen, carbon monoxide and carbon dioxide, apart from other light hydrocarbons detected in lower concentration, as are methane, ethane, ethylene, propane and propylene. The compounds identified in the bio-oil have been categorized into hydrocarbons, nitrogen containing compounds, ketones, alcohols, acids, lactones, phenols and aldehydes. The nitrogen and carbon contents of the microalgae bio-chars are higher than those for bio-chars derived from other biomasses. Pyrolysis improved the morphology and porous structure of microalgae. Finally, the mechanism involving microalgae pyrolysis has been approached and the main reaction pathways have been proposed.

Algal biodiesel production with engineered biochar as a heterogeneous solid acid catalyst

This study evaluates the use of engineered biochar as a heterogeneous solid acid catalyst for transesterification of algal oil derived from a native microalgal consortium. Biochar derived from sugarcane bagasse, coconut shell, corncob and peanut shell were evaluated for catalytic activity following surface modification. Peanut shell pyrolyzed at 400 °C with the sulfonic acid density of 0.837 mmol/g having 6.616 m²/g surface area was selected for efficient catalysis. The efficiency of transesterification was evaluated with 1-7 wt% catalyst loading, methanol: oil ratio of 6:1 to 30:1 at 55-85 °C over 2-8 h. Biodiesel yield of 94.91% was obtained with 5 wt% catalyst loading, MeOH: oil ratio of 20:1 at 65 °C after 4 h. Spectral analysis of algal biodiesel showed the presence of functional groups corresponding to esters. GC-MS analysis revealed the prominent presence of palmitic and oleic acids, further advocating the suitability of the technology for commercial application.

Synchronous removal of ammonium and phosphate from swine wastewater by two agricultural waste based adsorbents: Performance and mechanisms

Two agricultural wastes, Chinese medicinal herbal residue and spent Pleurotus ostreatus substrate, were developed to remove ammonium and phosphate from swine wastewater. These adsorbents were mesoporous materials with abundant smooth layered pores, and rough protuberances and grooves, respectively. Their adsorption capacities were 1131.65 and 1631.79 mg N g^-1, and 63.41 and 62.58 mg P g^-1 at pH 8.0, dosage of 0.2 g L^-1 and contact time of 360 min. And kinetics data of ammonium and phosphate fitted best with the intra-particle diffusion and pseudo-second-order models, respectively. Based on the point of zero charge, FTIR and XPS analyses, ammonium was removed mainly by electrostatic attraction, ion exchange and surface precipitation, while phosphate was by ligand exchange, surface complexation and precipitation. Therefore, the two agricultural wastes have great potential to synchronously remove ammonium and phosphate from swine wastewater.

Catalytic reforming of palm kernel shell microwave pyrolysis vapors over iron-loaded activated carbon: Enhanced production of phenol and hydrogen

This study addresses the in-situ microwave catalytic reforming of volatile matter from palm kernel shell (PKS) over iron-loaded activated carbon (Fe/AC) catalysts. The impacts of catalyst composition on the secondary gas-phase reactions and distribution of products were studied at 500 °C. It was found that the Fe/AC catalyst promoted the yield of light gases. Using the 1%-Fe/AC catalyst, the yield of gaseous fraction peaked at 37.09 wt%. The selectivity of the deoxygenated products was promoted in the presence of Fe. Catalytic reforming of PKS pyrolysis vapors over Fe/AC drastically enhanced the generation of phenol and H2, the concentrations of which reached 75.09 area% and 75.12 vol%, respectively. Catalytic pyrolysis of syringol and guaiacol as model compounds showed that Fe/AC catalyst promoted the demethoxylation and deoxygenation reactions to selectively generate phenol which was explained by oxophilic reactivity of the active Fe sites.

Removal of lead, zinc and cadmium from contaminated soils with two plant extracts: Mechanism and potential risks

Screening appropriate washing agents to remediate soils contaminated with heavy metals is crucial for decreasing metal hazards posing to environment and human health. In this study, two plant washing agents-water-extracted from Fagopyrum esculentum and Fordiophyton faberi, were applied to remove soil Pb, Zn, and Cd by washing. Results indicated that metal removals augmented with increase of washing solution concentrations, decreased with increasing pH values of the solution and followed the pseudo-second-order model depending on contact duration. At concentration of 50 g/L, pH 3 and contact duration of 120 min, F. esculentum had higher removals of Pb (5.98-6.83%), Zn (21.82-27.94%), and Cd (39.90-40.74%) than those of F. faberi. And metal ions could be removed by binding with carboxyl, hydroxyl, amide, amine and aromatic groups in washing solutions. The potential risks of residual metals declined by 51.35-52.12% for mine soil and 48.51-49.96% for farmland soil with exchangeable and carbonate-bound fractions obviously extracted after a single washing (P < 0.05). And soil organic carbon and nutrients increased to some extent except for total phosphorus and available potassium. Moreover, soil phytotoxicity lowered except that some adverse effects on seed germination existed. Therefore, the water extract from F. esculentum is a promising washing agent for heavy metal removal.

Reaction engineering and kinetics of algae conversion to biofuels and chemicals via pyrolysis and hydrothermal liquefaction

A state-of-the-art review on pyrolysis and hydrothermal liquefaction of algae to fuels and chemicals with emphasis on reaction chemistry and kinetics.

Kinetic triplet of Colombian sawmill wastes using thermogravimetric analysis

The potential of sawmill wastes as a raw material in pyrolysis process is presented in this study. Non-isothermal thermogravimetric analysis (TGA and DTG) and isoconversional methods were employed to determine triplet kinetic (activation energy, reaction model and pre-exponential factor). Through TGA and DTG, the conversion degree is described as a function of temperature for five heating rates (10, 20, 30, 40 and 50o C/min) and four model-free methods (Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Friedman, and Vyazovkin) with temperatures ranging from 25 to 1000^°C were employed. Isoconversional lines were built for every method at different isoconversional degrees α∈[0,1]. The activation energy E was found as a function of α in the interval χII=[0.2,0.7] where each isoconversional methods were in agreement and the estimated error was sufficiently small. Findings show the same activation energy profile independently of the isoconversional method. In particular the total variation of E in χII was as follows: 209.909–228.238 kJ/mol (FWO); 211.235–229.277 kJ/mol (KAS); 223.050–188.512 kJ/mol (Friedman), and 211.449 kJ/mol-229.512 kJ/mol (Vyazovkin). The reaction model of the process in χII matched with a two-dimensional diffusion (D2) by using a master-plot analysis. The calculated and reported parameters are fundamental information for the pyrolysis reactor design using Sawmill wastes as feedstock.

Experimental studies on high-quality bio-oil production via pyrolysis of Azolla by the use of a three metallic/modified pyrochar catalyst

In this study, the potential of the pyrolysis method to overcome the negative effects of Azolla-filiculoides in infected areas was thoroughly investigated. Non-catalytic pyrolysis experiments were conducted at a temperature range of 400-700 °C. The highest possible bio-oil yield (35 wt%) was attained at 500 °C. To achieve the best chemical composition of bio-oil and higher amount of synthesis gas the catalytic pyrolysis were conducted in a dual-bed quartz reactor at the optimum temperature (500 °C). Although, all three catalysts (pyro-char, modified pyro-char (MPC), and Mg-Ni-Mo/MPC) showed almost an impressive performance in promotion of the common reactions, Mg-Ni-Mo/MPC catalyst have illustrated the stunning results by increasing the percentage of furan compounds from 5.25% to 33.07%, and decreasing the acid compounds from 25.56% to 9.09%. Using GC-MS and GC-FID liquid and gaseous products were fully analyzed. The carbon-based catalysts were also evaluated via FTIR, FESEM, EDX, and BET analyses.

Experimental Investigation on the Energy Consumption, Physical, and Thermal Properties of a Novel Pellet Fuel Made from Wood Residues with Microalgae as a Binder

Co-pelletization of waste biomass and microalgae is an attractive option for using bioenergy efficiently. This work investigates the potential of microalgae as a binder to improve the energy consumption and physical and thermal properties of a novel pellet. Wood waste biomass was blended with microalgae in proportions of 15%, 30%, and 50% to investigate its properties using a single pelleting device and thermodynamic analysis. The results showed that, under the conditions of temperature (80–160 °C), pressure (120–200 MPa), and moisture content (6%–14%), blending microalgae can effectively increase the bulk density and mechanical durability of the pellets by 9%–36% and 0.7%–1.6%, respectively, and can significantly reduce the energy consumption of pelleting by 23.5%–40.4%. Blending microalgae can significantly reduce the energy consumption of pelleting by 23.5%–40.4%. Moreover, when the amount of Chlorella vulgaris powder (CVP) is 50%, a maximum bulk density (BD) of 1580.2 kg/m3, a durability (DU) of 98%, and a minimum energy consumption of 25.2 kJ/kg were obtained under the optimum conditions of temperature (120 °C), pressure (120 MPa), and moisture content (10%), respectively. Besides, the interaction between the microalgae and sawdust does exist, and their effect on the co-combustion process is inhibitive (0–300 °C) and accelerative (300–780 °C). When the amount of microalgae was 15%, the average activation energy of the pellet was a minimum value, which was 133.21 kJ/mol and 134.60 kJ/mol calculated by the Kissinger–Akahira–Sunose method and Ozawa–Flynn–Wall method, respectively. Therefore, the energy consumption, physical, and thermal properties of the novel pellet could be improved and meet the ISO standard (International Organization for Standardization of 17225, Geneva, Switzerland, 2016) by blending 15% of microalgae. Overall, the use of microalgae as a binder can indeed improve pellet quality, and it can be considered a significant way to utilize microalgae in the future.

Kinetic study and pyrolysis characteristics of algal and lignocellulosic biomasses

A comparative kinetic study on the pyrolysis of six algal and lignocellulosic biomasses was performed and six heating rates were employed to obtain the kinetic equations and analyze the compensation effect. Due to complexity, the whole pyrolysis process of algal biomass was divided into two reaction zones in which the analysis was carried out individually. The activation energies were first evaluated within the conversion range of 0.05 to 0.95, which were 125-147 kJ/mol and 113-138 kJ/mol for lignocellulosic biomass and zone-1 of algal biomass, respectively. Regression analysis was also conducted to determine the appropriate kinetic model. Moreover, Z(α) master plots suggested that the nucleation model was dominant at lower and higher temperatures for lignocellulosic biomass. Besides, the pre-exponential factor was calculated and a compensation effect between activation energies and pre-exponential factors was completely observed in zone-2 of algal biomass and partially seen in zone-1 of algal biomass and lignocellulosic biomass.

Speciation and transformation of nitrogen for spirulina hydrothermal carbonization

Nitrogen conversion (N-conversion) mechanism of spirulina (SP) in hydrothermal carbonization (HTC) was investigated under medium-low temperature (180-280 °C). N-conversion in bio-char, liquid and bio-oil were studied by FTIR, XPS, GC-MS and other analytical methods. Results indicated that the temperature could significantly affect the evolution of nitrogen. At 180-200 °C, the content of protein-N and pyridine-N in bio-char fell 23.01% and 9.51% respectively. In contrast, the contents of inorganic-N and quaternary-N increased by 16.99% and 16% respectively. Protein-N hydrolysis and Maillard reaction produced the key intermediate compounds, including amines, amides and N-heterocyclic compounds during the HTC. At 200-280 °C, the inorganic-N was obviously converted from solid to liquid. With the increased of temperature, it would enhance the polymerization of pyrrole-N and pyridine-N, which could cause the significant increase of aromatic N-heterocyclic compounds (e.g., nitriles and indole derivatives) in bio-oil. A N-conversion mechanism of SP HTC was proposed in this study.

Kinetics, thermodynamics, and physical characterization of corn stover (Zea mays) for solar biomass pyrolysis potential analysis

Solar pyrolysis of agricultural waste has huge potential for sustainable production of fuel and chemical feedstock. In this paper, the kinetics, thermodynamics, and physical characterization of corn stover (CS) collected from Wyoming, USA was conducted with respect to solar pyrolysis. The kinetics and thermodynamics of the CS pyrolysis was analyzed in detail using the methods described by KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa), from which the activation energy, Gibbs energy, Arrhenius pre-exponential factor, enthalpy, and entropy were derived.14 other kinetics models based on reaction order, diffusion, nucleation, geometric contraction, power models were also examined, and models based on diffusion was found to be best suited. The CS was used for solar pyrolysis of biomass and the products were analyzed by mass spectroscopy, ICP-MS, GPC, micro-GC, and Elemental analyzer. The results show that CS is suitable for solar pyrolysis to produce chemicals and other fuels.

Thermal characteristics and product formation mechanism during pyrolysis of penicillin fermentation residue

This work studied thermal characteristics and product formation mechanism during pyrolysis of penicillin fermentation residue (PR). Results showed that PR pyrolysis proceeded in four stages. The kinetic triplet of each stage was calculated using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and integral master-plot methods. The kinetic model for stage 1 was the three-dimensional diffusion model, the simple reaction order model for stage 2 and stage 4, and the nucleation-growth model for stage 3. FTIR analysis suggested that the intensities of absorption peaks of NH, CO, CH, CN, and CO in chars weakened gradually with increasing temperature, corresponding to the production of CH₄, CO, NH₃, and HCN. GC-MS results indicated that the high protein content in PR resulted in a high fraction of nitrogenated compounds (amides and amines, nitriles, and N-heterocyclic species) in bio-oil. The formation mechanism of these compounds was discussed. Besides, bio-oil also contained large quantities of oxygenated compounds and a few hydrocarbons.

Comparative study on characteristics of the bio-oil from microwave-assisted pyrolysis of lignocellulose and triacylglycerol

Microwave-assisted pyrolysis of Camellia oleifera shell (COS) and stillingia oil (SO) was performed in the temperature range of 400-600 °C. The effects of feedstock and pyrolysis temperatures on product yield and bio-oil composition were discussed in detail. The bio-oil yield from COS pyrolysis varied from 37.30 wt% to 40.27 wt%, which was 11.32 wt% to 21.62 wt% lower than that from SO pyrolysis. Gas chromatography-mass spectrometry analysis indicated that SO bio-oil was rich in hydrocarbons, whereas COS pyrolysis produced mainly oxygen-containing compounds predominantly comprising phenols and acids. Fourier transform infrared and ¹H-nuclear magnetic resonance spectra showed significant differences in the chemical structure of bio-oils from COS and SO pyrolysis. Elemental-composition and physical-property analyses further revealed that SO bio-oils were similar to gasoline and heavy fuel oil.

A review on the production of nitrogen-containing compounds from microalgal biomass via pyrolysis

Nitrogen-containing compounds (NCCs) which may be produced from nitrogen-rich biomass such as microalgae, may find important biochemical and biomedical applications. This review summarizes the recent knowledge about the formation mechanism of NCCs during pyrolysis of microalgae. The key technical and biological aspects of microalgae and pyrolysis process parameters, which influence the formation of NCCs, have been analyzed. The mechanism of formation of NCCs such as indole, pyridine, amides, and nitriles during primary and secondary pyrolysis reactions are elaborated. It has been emphasized that the pyrolysis conditions and the use of catalysts had significant impacts on the yields and compositions of NCCs. The available information shows that the transformation of nitrogen and nitrogen functionalities during pyrolysis are strongly associated with the formation process of NCCs. The challenges in the development of pyrolysis technologies for the production of NCCs from microalgae are identified with future research needs identified.

The transformation of nitrogen during pressurized entrained-flow pyrolysis of Chlorella vulgaris

The transformation of nitrogen in microalgae during entrained-flow pyrolysis of Chlorella vulgaris was systematically investigated at the temperatures of 600-900 °C and pressures of 0.1-4.0 MPa. It was found that pressure had a profound impact on the transformation of nitrogen during pyrolysis. The nitrogen retention in bio-char and its content in bio-oil reached a maximum value at 1.0 MPa. The highest conversion of nitrogen (50.25 wt%) into bio-oil was achieved at 1.0 MPa and 800 °C, which was about 7 wt% higher than that at atmospheric pressure. Higher pressures promoted the formation of pyrrolic-N (N-5) and quaternary-N (N-Q) compounds in bio-oil at the expense of nitrile-N and pyridinic-N (N-6) compounds. The X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results on bio-chars clearly evidenced the transformation of N-5 structures into N-6 and N-Q structures at elevated pressures. The nitrogen transformation pathways during pyrolysis of microalgae were proposed and discussed.

Characterization of herb residue and high ash-containing paper sludge blends from fixed bed pyrolysis

High ash-containing paper sludge which is rich in various metal oxides is employed in herb residue pyrolysis to enhance the yield of fuel gas and reduce tar yield in a drop tube fixed bed reactor. Effects of heat treatment temperature and blending ratio of paper sludge on the yields and composition of pyrolysis products (gas, tar and char) were investigated. Results indicate that paper sludge shows a significantly catalytic effect during the pyrolysis processes of herb residue, accelerating the pyrolysis reactions. The catalytic effect resulted in an increase in gas yield but a decrease in tar yield. The catalytic effect degree is affected by the paper sludge proportions, and the strongest catalytic effect of paper sludge is noted at its blending ratio of 50%. At temperature lower than 900 °C, the catalytic effect of paper sludge in the pyrolysis of herb residue promotes the formation of H₂ and CO₂, inhibits the formation of CH₄, but shows slight influence on the formations of CO, while the formation of the four gas components was all promoted at 900 °C. SEM results of residue char show that ash particles from paper sludge adhere to the surface of the herb residue char after pyrolysis, which may promote the pyrolysis process of herb residue for more gas releasing. FT-IR results indicate that most functional groups disappear after pyrolysis. The addition of paper sludge promotes deoxidisation and aromatization reactions of hetero atoms tars, forming heavier polycyclic aromatic hydrocarbons and leading to tar yield decrease.

Pressurized entrained-flow pyrolysis of microalgae: Enhanced production of hydrogen and nitrogen-containing compounds

Pressurized entrained-flow pyrolysis of Chlorella vulgaris microalgae was investigated. The impact of pressure on the yield and composition of pyrolysis products were studied. The results showed that the concentration of H₂ in bio-gas increased sharply with increasing pyrolysis pressure, while those of CO, CO₂, CH₄, and C₂H₆ were dramatically decreased. The concentration of H₂ reached 88.01 vol% in bio-gas at 900 °C and 4 MPa. Higher pressures promoted the hydrogen transfer to bio-gas. The bio-oils derived from pressurized pyrolysis were rich in nitrogen-containing compounds and PAHs. The highest concentration of nitrogen-containing compounds in bio-oil was achieved at 800 °C and 1 MPa. Increasing pyrolysis pressure promoted the formation of nitrogen-containing compounds such as indole, quinoline, isoquinoline and phenanthridine. Higher pyrolysis pressures led to increased sphericity, enhanced swelling, and higher carbon order of bio-chars. Pressurized pyrolysis of biomass has a great potential for poly-generation of H₂, nitrogen containing compounds and bio-char.