Effect of essential inorganic metals on primary thermal degradation of lignocellulosic biomass

Colored cotton crop wastes valorization through pyrolysis: a study of energetic characterization and analytical Py-GC/MS

The present work aimed to study different parts of colored cotton waste through energetic characterization and analytical flash pyrolysis. Stalks and bolls of BRS cotton cultivars from Sementes do Brasil (Green, Ruby, Topaz and Jade) were studied, using white cotton (BRS 286) as a comparison. The energetic potential of biomass was evaluated by bulk density, High Heating Value (HHV), proximate and ultimate analysis, compositional and thermogravimetric analysis (TGA). Pyrolysis was performed in a micro-pyrolyzer and the products were identified by gas chromatography and mass spectroscopy (Py-GC/MS). The results indicated a significant energetic potential, suggesting that can be used as an alternative energy source for thermochemical processes. The results of conventional pyrolysis indicated the presence of oxygenated compounds of different organic groups: aldehydes, ketones, phenols, furans and ethers, characteristic of the decomposition of lignocellulosic materials. Light organic acids in the C1-C4 range stood out the most, followed by phenols that appeared in a considerable proportion. Finally, it is concluded that the energy potential and pyrolysis products of the different parts (stalks and bolls) of colored cotton waste can be used to generate bioenergy and various chemical compounds of plant origin from green chemistry.

Magnetic Multienzyme@Metal-Organic Material for Sustainable Biodegradation of Insoluble Biomass

Biodegradation of insoluble biomass such as cellulose via carbohydrase enzymes is an effective approach to break down plant cell walls and extract valuable materials therein. Yet, the high cost and poor reusability of enzymes are practical concerns. We recently proved that immobilizing multiple digestive enzymes on metal-organic materials (MOMs) allows enzymes to be reused via gravimetric separation, improving the cost efficiency of cereal biomass degradation [ACS Appl. Mater. Interfaces 2021, 13, 36, 43085-43093]. However, this strategy cannot be adapted for enzymes whose substrates or products are insoluble (e.g., cellulose crystals). Recently, we described an alternative approach based on magnetic metal-organic frameworks (MOFs) using model enzymes/substrates [ACS Appl. Mater. Interfaces 2020, 12, 37, 41794-41801]. Here, we aim to prove the effectiveness of combining these two strategies in cellulose degradation. We immobilized multiple carbohydrase enzymes that cooperate in cellulose degradation via cocrystallization with Ca2+, a carboxylate ligand (BDC) in the absence and presence of magnetic nanoparticles (MNPs). We then compared the separation efficiency and enzyme reusability of the resultant multienzyme@Ca-BDC and multienzyme@MNP-Ca-BDC composites via gravimetric and magnetic separation, respectively, and found that, although both composites were effective in cellulose degradation in the first round, the multienzyme@MNP-Ca-BDC composites displayed significantly enhanced reusability. This work provides the first experimental demonstration of using magnetic solid supports to immobilize multiple carbohydrase enzymes simultaneously and degrade cellulose and promotes green/sustainable chemistry in three ways: (1) reusing the enzymes saves energy/sources to prepare them, (2) the synthetic conditions are "green" without generating unwanted wastes, and (3) using our composites to degrade cellulose is the first step of extracting valuable materials from sustainable biomasses such as plants whose growth does not rely on nonregeneratable resources.

Energetic, bio-oil, biochar, and ash performances of co-pyrolysis-gasification of textile dyeing sludge and Chinese medicine residues in response to K2CO3, atmosphere type, blend ratio, and temperature

Hazardous waste stream needs to be managed so as not to exceed stock- and rate-limited properties of its recipient ecosystems. The co-pyrolysis of Chinese medicine residue (CMR) and textile dyeing sludge (TDS) and its bio-oil, biochar, and ash quality and quantity were characterized as a function of the immersion of K2CO3, atmosphere type, blend ratio, and temperature. Compared to the mono-pyrolysis of TDS, its co-pyrolysis performance with CMR (the comprehensive performance index (CPI)) significantly improved by 33.9% in the N2 atmosphere and 33.2% in the CO2 atmosphere. The impregnation catalyzed the co-pyrolysis at 370°C, reduced its activation energy by 77.3 kJ/mol in the N2 atmosphere and 134.6 kJ/mol in the CO2 atmosphere, and enriched the degree of coke gasification by 44.25% in the CO2 atmosphere. The impregnation increased the decomposition rate of the co-pyrolysis by weakening the bond energy of fatty side chains and bridge bonds, its catalytic and secondary products, and its bio-oil yield by 66.19%. Its bio-oils mainly contained olefins, aromatic structural substances, and alcohols. The immersion of K2CO3 improved the aromaticity of the co-pyrolytic biochars and reduced the contact between K and Si which made it convenient for Mg to react with SiO2 to form magnesium-silicate. The co-pyrolytic biochar surfaces mainly included -OH, -CH2, C=C, and Si-O-Si. The main phases in the co-pyrolytic ash included Ca5(PO4)3(OH), Al2O3, and magnesium-silicate.

Catalytic torrefaction effect on waste wood boards for sustainable biochar production and environmental remediation

Wood boards used in construction are generally treated with toxic chemicals, making them unsuitable for further use and causing environmental pollution. This study evaluates the possibility of using catalytic torrefaction as a pretreatment to improve wood pyrolysis and combustion for greener biochar production. Waste beech boards were impregnated with different K2CO3 solutions (0-0.012 M), then torrefied between 5 and 60 min at 275 °C. The ICP-AES showed that the board's surface held more potassium than the core. Torrefaction coupled with potassium decreased the C-O and -OH stretches. Thermogravimetric analysis of torrefied wood showed that the board's internal heating degraded the core more than the surface. The exothermic reactions made potassium's catalytic action more efficient in the core. Interactions between the potassium content and torrefaction duration decreased the pyrolysis' maximum devolatilization temperature. During combustion, potassium decreased the ignition temperature by up to 9% and 3% at the surface and core, respectively, while the torrefaction increased it. The catalytic torrefaction significantly decreased the devolatilization peak during combustion, thus making the wood's combustion similar to that of coal, having only the char oxidation step. These findings highlight the advantages and challenges of waste wood's catalytic-torrefaction for biochar production to reduce environmental pollution.

Analysis of Interactions Occurring during the Pyrolysis of Lignocellulosic Biomass

This paper presents a review of the recent advances in research on the interactions between the components of lignocellulosic biomass. The literature reports on the effects of interaction between lignocellulosic biomass components, such as cellulose-lignin, lignin-hemicellulose, and hemicellulose-cellulose, were discussed. The results obtained by other researchers were analyzed from the viewpoint of the interactions between the pyrolysis products formed along with the impact effects of the organic and inorganic components present or added to the biomass with regard to the yield and composition of the pyrolysis products. Disagreements about some statements were noted along with the lack of an unequivocal opinion about the directivity of interactions occurring during biomass pyrolysis. Based on the data in the scientific literature, it was suggested that the course of the pyrolysis process of biomass blends can be appropriately directed by changes in the ratio of basic biomass components or by additions of inorganic or organic substances.

Analysis of the Catalytic Effects Induced by Alkali and Alkaline Earth Metals (AAEMs) on the Pyrolysis of Beech Wood and Corncob

The catalytic pyrolysis of beech wood and corncob was experimentally investigated considering six additives containing alkali and alkaline earth metals (Na2CO3, NaOH, NaCl, KCl, CaCl2 and MgCl2). Thermogravimetric analyses (TGA) were carried out with raw feedstocks and samples impregnated with different concentrations of catalysts. In a bid to better interpret observed trends, measured data were analyzed using an integral kinetic modeling approach considering 14 different reaction models. As highlights, this work showed that cations (Na+, K+, Ca2+, and Mg2+) as well as anions (i.e., CO32−, OH−, and Cl−) influence pyrolysis in selective ways. Alkaline earth metals were proven to be more effective than alkali metals in fostering biomass decomposition, as evidenced by decreases in the characteristic pyrolysis temperatures and activation energies. Furthermore, the results obtained showed that the higher the basicity of the catalyst, the higher its efficiency as well. Increasing the quantities of calcium- and magnesium-based additives finally led to an enhancement of the decomposition process at low temperatures, although a saturation phenomenon was seen for high catalyst concentrations.

Generation Mechanism of Persistent Free Radicals in Lignocellulose-Derived Biochar: Roles of Reducible Carbonyls

Persistent free radicals (PFRs) in biochar can influence biochar reactivity, promoting organic contaminant degradation or even causing certain toxic impacts. However, the PFR generation mechanism is not still well understood. An investigation of the relationship between PFR formation and the chemical structure of biochar is essential for understanding the PFR formation mechanism. Our in situ measurement results showed that PFR intensities increased from 0-509.5 to 146-5678 a.u. after being pyrolyzed at 300 °C for 60 min. The significant positive correlation between PFR intensities and the peak areas of C═O and aromatic C═C groups indicated that the generation of PFRs was highly dependent on the C═O and aromatic C═C structures. The reduction of biochars by KBH₄ resulted in a 32.2 ± 2.49% decrease in the C═O content and a relative increase in the C-O content, while other physicochemical properties did not change. Thus, the observed 49.3% decrease in PFR signals after this reduction suggested that the reducible C═O groups, possibly in aldehydes, aromatic ketones, and quinones, were closely associated with PFRs in biochars. This study provides an in situ insight into the PFR generation mechanism and guides the corresponding biochar design and property manipulation.

Influence of Densification on the Pyrolytic Behavior of Agricultural Biomass Waste and the Characteristics of Pyrolysis Products

TG/FT-IR techniques, UV-spectroscopy, microwave extraction, XRD and SEM were used to study how densification of the three types of agricultural biomass wastes (wheat straw, soft wood, and sunflower husk) changes the composition and structure of their pyrolysis products. It was determined that densification changes the composition of volatile products of pyrolysis at the temperature of 420 °C: sunflower husk emits 4.9 times less saturated and unsaturated hydrocarbons and 1.9 times less compounds with carbonyl group; soft wood emits 1.8 times more saturated and unsaturated hydrocarbons and compounds with carbonyl groups and 1.3 times more alcohols and phenols; and wheat straw emits 2 times more compounds with carbonyl groups. These changes are probably caused by the differences in interaction of formed volatiles with the surface of chars. These differences can be caused by distinct places of cumulation of inorganic components in the densified samples. In the densified char, the inorganics cumulate on the surface of sunflower husk whereas for wheat straw they cumulate inside the sample. In the case of soft wood, the inorganics cumulate both inside and on the surface. The decreased contribution of hydrocarbons in volatiles can be connected with the morphology of nano-particles formed in inorganics.

Co-pyrolysis of sewage sludge and metal-free/metal-loaded polyvinyl chloride (PVC) microplastics improved biochar properties and reduced environmental risk of heavy metals

Co-pyrolysis of sewage sludge and plastics have been utilized for producing biochars as a strategy to fix plastic pollution. However, comparative studies on the characteristics and environmental risk of heavy metals in biochars obtained by the co-pyrolysis of sludge and microplastic with/without metal additives are seldom. Here we demonstrated the effects of simulated co-pyrolysis (at 400 °C) of sewage sludge and metal-free or metal-loaded polyvinyl chloride (PVC) microplastics at different mass ratios (1:0, 19:1, 3:1, 1:3, sewage sludge: PVC (w/w)) respectively. Results revealed that co-pyrolysis of metal-loaded PVC and sewage sludge resulted in higher electrical conductivity, ash content, and an acidic pH of biochars as compared to the co-pyrolysis of metal-free PVC and sewage sludge. Addition of metal-loaded PVC increased total concentrations of calcium (Ca), magnesium (Mg), cadmium (Cd), and lead (Pb) in biochars, but reduced the bioavailability of Cd, chromium (Cr), nickel (Ni), and zinc (Zn) in biochars. Analysis of chemical speciation showed that heavy metals (except Pb) in biochars derived from co-pyrolysis of sewage sludge and metal-loaded PVC had higher percentage of more stable fraction (residual fraction) and lower potential ecological risk index (RI) value. S1AP3 (sludge: metal-loaded PVC = 1:3) biochar had the lowest environmental risk based on RI value (14.41). To sum up the present study suggests that the addition of metal-loaded PVC microplastic in sewage sludge had a positive impact on the immobilization of heavy metals during co-pyrolysis process.

Reactivity Effects of Inorganic Content in Biomass Gasification: A Review

This review article discusses the effects of inorganic content and mechanisms on raw biomass and char during gasification. The impacts of the inherent inorganics and externally added inorganic compounds are summarized based on a literature search from the most recent 40 years. The TGA and larger-scale studies involving K-, Ca-, and Si-related mechanisms are critically reviewed with the aim of understanding the reaction mechanisms and kinetics. Differences between the reaction pathways of inorganic matter, and subsequent effects on the reactivity during gasification, are discussed. The present results illustrate the complexity of ash transformation phenomena, which have a strong impact on the design of gasifiers as well as further operation and process control. The impregnation and mixing of catalytic compounds into raw biomass are emphasized as a potential solution to avoid reactivity-related operational challenges during steam and CO2 gasification. This review clearly identifies a gap in experimental knowledge at the micro and macro levels in the advanced modelling of inorganics transformation with respect to gasification reactivity.

Valorization of rubberwood sawdust and sewage sludge by pyrolysis and co-pyrolysis using agitated bed reactor for producing biofuel or value-added products

This study investigated experimentally pyrolysis of rubberwood sawdust (RWS), sewage sludge (SS), and their blends (25:75, 50:50, and 75:25 by weight) in an agitated bed pyrolysis reactor. The yields and characteristics of liquid product and biochar were determined for pyrolysis at 450, 500, and 550 °C and were affected both by temperature and feedstock type. The liquid and biochar yields were in the ranges 27.30-52.42 and 21.43-49.66 (wt%). Pyrolysis of RWS at 550 °C provided the highest liquid yield, while SS gave a high biochar yield. Co-pyrolysis of SS with RWS improved yield and quality of liquid and biochar products. The liquid product had 57.54-70.70 wt% of water and a low hydrocarbon content. The higher heating value (HHV) of water-free liquid product was 14.73-22.45 MJ/kg. The major compounds of liquid product included acetic acid, 2-propanone, 1-hydroxy, and phenols according to GC-MS. The biochar from RWS had a high carbon content (83.37 wt%) and a high HHV (33.57 MJ/kg), while SS biochar was mainly ash (67.62 wt%) with low carbon content. The SS biochar also had high contents of Si, Ca, Fe, K, and Mg as determined by XRF. Co-pyrolysis of SS with RWS improved the biochar by increasing its carbon content and reducing ash and inorganic elements. The surface of RWS biochar was more porous, while SS biochar had the larger specific surface according to SEM and BET. Based on these results, co-pyrolysis of 75:25 feedstock mix is recommended for further studies on applications of liquid product and biochar.

Effect of potassium on the pyrolysis of biomass components: Pyrolysis behaviors, product distribution and kinetic characteristics

Potassium is an inorganic mineral element in biomass and has a significant catalytic effect on biomass pyrolysis. In this work, the effect of potassium on the pyrolysis of biomass components (cellulose, xylan and lignin) was investigated with the help of thermogravimetric analyzer coupled to fourier transform infrared spectrometer (TG-FTIR) and pyrolysis-gas chromatography coupled to mass spectrometry (Py-GC/MS). The results showed that potassium accelerated the start of the main pyrolysis stage of the biomass components, reduced the weight loss rate for cellulose and lignin, and increased the weight loss rate for xylan. On the other hand, potassium presented a promotion effect on the formation of char for cellulose but a suppression effect for lignin. In addition, an increasing potassium content promoted the release of volatile products for xylan. Product distribution analysis found that potassium promoted the scission of glycosidic bonds and the decomposition of glucose units, resulting in a sharp yield decrease of carbohydrates and a yield increase of furans, aldehydes and ketones. In addition, an increased production of CO₂ was obtained, indicating that potassium favors the cleavage and reforming of carboxyl (COOH) and carbonyl (CO) groups. Furthermore, the effect of potassium on the pyrolysis of cellulose and xylan was stronger than that on lignin pyrolysis. The effect on the pyrolysis reaction also resulted in a higher activation energy for the decomposition of biomass components, especially at high temperature intervals. Moreover, the higher the content of potassium added, the greater the increase was in the activation energy.

Influence of Biomass Inorganics on the Functionality of H+ZSM-5 Catalyst during In-Situ Catalytic Fast Pyrolysis

In this study, the contamination of H+ZSM-5 catalyst by calcium, potassium and sodium was investigated by deactivating the catalyst with various concentrations of these inorganics, and the subsequent changes in the properties of the catalyst are reported. Specific surface area analysis of the catalysts revealed a progressive reduction with increasing concentrations of the inorganics, which could be attributed to pore blocking and diffusion resistance. Chemisorption studies (NH3-TPD) showed that the Bronsted acid sites on the catalyst had reacted with potassium and sodium, resulting in a clear loss of active sites, whereas the presence of calcium did not appear to cause extensive chemical deactivation. Pyrolysis experiments revealed the progressive loss in catalytic activity, evident due the shift in selectivity from producing only aromatic hydrocarbons (benzene, toluene, xylene, naphthalenes and others) with the fresh catalyst to oxygenated compounds such as phenols, guaiacols, furans and ketones with increasing contamination by the inorganics. The carbon yield of aromatic hydrocarbons decreased from 22.3% with the fresh catalyst to 1.4% and 2.1% when deactivated by potassium and sodium at 2 wt %, respectively. However, calcium appears to only cause physical deactivation.

Integrated Leaching and Thermochemical Technologies for Producing High-Value Products from Rice Husk: Leaching of Rice Husk with the Aqueous Phases of Bioliquids

It remains challenging to develop a techno-economically feasible method to remove alkali and alkaline earth metal species (AAEMs) from rice husk (RH), which is a widely available bioresource across the world. In this study, the AAEMs leaching effect of aqueous phases of both bio-crude prepared by hydrothermal liquefaction (AP-HT) and bio-oil prepared by pyrolysis (AP-Pyro) of RH were systematically investigated. The results indicated that although the acidity of AP-HT and AP-Pyro are much lower than that of HCl, they performed a comparable removal efficiency on AAEMs (Na: 56.2%, K: 96.7%, Mg: 91.0%, Ca: 46.1% for AP-HT, while Na: 58.9%, K: 96.9%, Mg: 94.0%, Ca: 86.3% for AP-Pyro) with HCl. The presence of phenolics in bio-oil could facilitate the penetration of water and organic acids into the inner area of RH cells, thus enhancing the AAEMs removal via chelate reactions. The thermal stability of leached RH during thermochemical conversions was studied via TG and Py-GC-MS. The results showed that the heat conduction efficiency in leached RH was enhanced with a high pyrolysis rate, resulting in a narrow carbon chain distribution (C5–C10) of derived chemical compounds.

Components and Persistent Free Radicals in the Volatiles during Pyrolysis of Lignocellulose Biomass

Persistent free radicals (PFRs) may cause negative impacts to human health and the environment because of the induced reactive oxygen species. We expect that PFRs could be generated in the condensable volatiles formed during lignocellulose biomass pyrolysis. Elucidating the structural origin and the formation mechanism of PFRs is important for an in-depth understanding of air pollutants from the pyrolysis or combustion of lignocellulose biomass. This work selected rice straw and pine sawdust to represent agricultural and forest biomass residues. The pyrolysis mechanism, volatile components, and PFR generation were discussed based on the analysis of thermogravimetry-Fourier transform infrared spectroscopy-mass spectrometry (MS), pyrolysis-gas chromatography/MS, and electron spin resonance (ESR). Levoglucosan, furans, and 2-methoxyphenols were the main pyrolytic compounds for cellulose (CL), hemicellulose (HC), and lignin (LG), respectively. Obvious ESR signals were detected in the condensable volatiles of LG, while no ESR signals were detected for those of CL and HC. Higher ESR signals were detected in lignocellulose with a higher content of LG. Therefore, LG was the main structural basis to generate PFRs in lignocellulose condensable volatiles, mostly attributed to the methoxyphenol components. This study provides useful information regarding the generation mechanisms of and the structures related to PFRs, which is essential to understand the risks of lignocellulose pyrolytic volatiles.

Engineered biochar via microwave CO2 and steam pyrolysis to treat carcinogenic Congo red dye

We developed an innovative single-step pyrolysis approach that combines microwave heating and activation by CO₂ or steam to transform orange peel waste (OPW) into microwave activated biochar (MAB). This involves carbonization and activation simultaneously under an inert environment. Using CO₂ demonstrates dual functions in this approach, acting as purging gas to provide an inert environment for pyrolysis while activating highly porous MAB. This approach demonstrates rapid heating rate (15-120 °C/min), higher temperature (> 800 °C) and shorter process time (15 min) compared to conventional method using furnace (> 1 h). The MAB shows higher mass yield (31-44 wt %), high content of fixed carbon (58.6-61.2 wt %), Brunauer Emmett Teller (BET) surface area (158.5-305.1 m²/g), low ratio of H/C (0.3) and O/C (0.2). Activation with CO₂ produces more micropores than using steam that generates more mesopores. Steam-activated MAB records a higher adsorption efficiency (136 mg/g) compared to CO₂ activation (91 mg/g), achieving 89-93 % removal of Congo Red dye. The microwave pyrolysis coupled with steam or CO₂ activation thereby represents a promising approach to transform fruit-peel waste to microwave-activated biochar that remove hazardous dye.

Synergetic effect of magnesium citrate and temperature on the product characteristics of waste lotus seedpod pyrolysis

To understand the synergetic effect of magnesium citrate (MC) and temperature on biomass pyrolysis, co-pyrolysis of lotus seedpod (LS) and MC was carried out in a fixed bed reactor. With the addition of MC, CO2 become the dominate composition in gas (55.83-90.75 vol%). And with temperature increasing, the main components in bio-oil converted from carboxylic acid to phenols and aromatics. Meanwhile, the mesoporous carbon was formed, with the BET specific surface area up to 514.66 m2/g, and pore diameter mainly focused at 3-8 nm. For the catalytic effect, the secondary cracking of pyrolytic volatiles (acetic acid and anhydrosugar) was inhibited, therefore the gas releasing was inhibited below 550 °C. However, at higher temperature, MgO catalysts favored the reduction of acids and deoxygenation via ketonization and aldol condensation reactions. The formed MgO as a template and the catalysis of MgO during co-pyrolysis contributed to the mesoporous structure of solid char.

Influence of Mineral Composition of Chars Derived by Hydrothermal Carbonization on Sorption Behavior of CO2, CH4, and O2

The doping of SiO₂ and Fe₂O₃ into hydrochars that were produced by the hydrothermal carbonization of cellulose was studied with respect to its impact on the resulting surface characteristics and sorption behavior of CO₂, CH₄, and O₂. During pyrolysis, the structural order of the Fe-doped char changed, as the fraction of highly ordered domains increased, which was not observed for the undoped and Si-doped chars. The Si doping had no apparent influence on the oxidation temperature of the hydrochar in contrast to the Fe-doped char where the oxidation temperature was reduced because of the catalytic effect of Fe. Both dopants reduced the micro-, meso- and macroporous surface areas of the chars, although the Fe-doped chars had larger meso- and macroporosity than the Si-doped char. However, the increased degree in the structural order of the carbon matrix of the Fe-doped char reduced its microporosity relative to the Si-doped char. The adsorption of CO₂ and CH₄ on the chars at temperatures between 273.15 and 423.15 K and at pressures up to 115 kPa was slightly inhibited by the Si doping but strongly suppressed by the Fe doping. For O₂, however, the Si doping promoted the observed adsorption capacity, while Fe doping also showed an inhibiting effect.

Formation of persistent free radicals in biochar derived from rice straw based on a detailed analysis of pyrolysis kinetics

The presence of persistent free radicals (PFR) in biochars may greatly broaden the application of biochars in pollution control, but may also cause negative impacts to the environment. Understanding the structural basis and the formation mechanisms of PFR is essential for a targeted biochar production and application. This study used rice straw (RS), a ubiquitous agricultural waste, to investigate the generation processes of PFR in relation to RS pyrolysis kinetics. Based on a detailed thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis, the activation energy was calculated by Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods. This work combined pyrolysis kinetics analysis and solid particle characterization. Our results showed that lignin started to pyrolyze at a lower temperature than cellulose and hemicellulose. Lignin was the main factor for PFR generation. Chemical bond breaking contributed only slightly to PFR formation. The reconfiguration of the carbonaceous structures may be a more important contributor to PFR formation, while the cross-linking between different compositions and the interactions between the chemical compositions and inorganic minerals may play a significant role for PFR generation and stabilization in RS. This study provides useful theoretical basis to understand the thermal pyrolysis process of RS and the manipulation of biochar properties.

Enhancing levoglucosan production from waste biomass pyrolysis by Fenton pretreatment

Levoglucosan is served as a significant versatile product to generate high value-added chemicals and pharmaceutical additives. Levoglucosan was predominately produced from pyrolysate of cellulose. However, the direct fast pyrolysis of waste biomass produces a small quantity of levoglucosan in comparison with the theoretical value of cellulose. This study explored Fenton pretreatment as a possible route to enhance levoglucosan yield during the fast pyrolysis of the waste corncob. The experimental results showed that different Fenton pretreated conditions and pyrolytic temperatures played vital roles in the formation of levoglucosan. The levoglucosan yield from fast pyrolysis at 500 °C of corncob pretreated by Fenton reaction of 14 mL/g H₂O₂ and 16 mM FeSO₄ was about 95% higher than that of the untreated corncob. Additionally, Fenton pretreated corncob was capable of obtaining the levoglucosan at a low pyrolytic temperature (300 °C). It was mainly attributed to the effective disrupting of biomass structures and the selective degradation of lignin and hemicellulose during pretreatment. Furthermore, the powerful removal of alkali and alkaline earth metals during Fenton pretreatment was beneficial to increasing the levoglucosan yield. These findings demonstrate that Fenton pretreatment can provide a novel effective method to enhance levoglucosan yield during biomass fast pyrolysis.

Overview of biochar production from preservative-treated wood with detailed analysis of biochar characteristics, heavy metals behaviors, and their ecotoxicity

Concerns over the disposal of preservative-treated wood waste and its related environmental problems are the main driving forces of research into the recycling of preservative-treated wood. Preservative-treated wood waste composed of cellulose, hemicellulose, and lignin with several types of heavy metals can be recycled in various ways, such as wood-based composites, heavy metal extraction, energy recovery, etc. In particular, thermochemical conversion has attracted considerable attention recently because energy can be recovered from biomass as liquid fuel and bio-oil, as well as produce bio-char with a high carbon content, which can be applied to valuable products, such as soil amendment, adsorbents, solid fuels, and catalyst supports. On the other hand, environmental issues, such as heavy metal volatilization and heavy metal leaching, are still a challenge. This review reports the state-of-the-art knowledge of biochar production from preservative-treated wood with the main focus on the feedstock, process technology, biochar characteristics, application, and environmental issues. This review provides important information for future studies into the recycling of preservative-treated woods into biochar.

Suppressed formation of polycyclic aromatic hydrocarbons (PAHs) during pyrolytic production of Fe-enriched composite biochar

The pyrolytic production of Fe-enriched composite biochar is receiving increasing attention. However, understanding of the environmental risk from the polycyclic aromatic hydrocarbons (PAHs) potentially generated during composite biochar production is lacking. This study investigated the formation of PAHs from the pyrolysis of barley straw impregnated with FeCl₃ or Fe(NO₃)₃ at 350 °C, 500 °C, and 650 °C. The total amount of PAHs formation increased with increasing heating temperature. Most of the PAHs were concentrated in bio-oil (72.7-94.6%), with only a small fraction retained in biochar (1.7-11.1%) and in biogas (2.2-16.2%). Preloading FeCl₃ or Fe(NO₃)₃ onto the biomass greatly reduced PAH formation by up to 33% and 21%, respectively, compared to that obtained with biomass alone. The suppressed formation of PAHs was due to the generation of more reductive forms of Fe, such as Fe⁰ and FeO, in the O₂-starved pyrolysis atmosphere, which reduced C₂H₂ and C₆H₅OH, two important PAH precursors in hydrogen abstraction acetylene addition reactions. Although Fe loading reduced the amounts of PAHs in biochar, the toxic equivalent value increased because Fe induced more accumulation of high-molecular-weight PAHs in the biochar. This study proved that Fe loading suppresses PAH generation during biomass pyrolysis, which can guide the design of composite biochar production.

Co-carbonization of biomass and oily sludge to prepare sulfamethoxazole super-adsorbent materials

Different biomass materials (walnut shell, coconut shell or cottonwood sawdust) were co-pyrolyzed with carbon-enriched oily sludge to produce aqueous phase sulfamethoxazole (SMZ) adsorption materials. The co-pyrolysis char was activated with K₂CO₃ to modify its micro-structure and functional groups. Results show that ACs prepared from the mixture contained more mesopores than biomass-based ACs, more porous and higher yield than oily sludge-based ACs. One-step activation method was more attractive than two-step activation in larger specific surface area (up to almost 4 times), wider pore size distribution (2-3 nm), stronger SMZ adsorption ability (higher than 2 times). The maximum BET surface area was 1342 m²/g for the ACs prepared from the mixture of walnut shell and oily sludge by one-step activation and it had the maximum SMZ adsorption capacity up to 361.9 mg/g, which is higher than previous reported values. The capacity of SMZ adsorption of ACs was mainly attributed to pore size distribution, specific surface area and functional groups. Among them, the appropriate content of CO and CO functional groups, larger specific area and more pores range from 2 to 3 nm lead to higher adsorption capacity.

Effects of process water recirculation on solid and liquid products from hydrothermal carbonization of Laminaria

Hydrothermal carbonization (HTC) is a promising thermo-chemical technology to treat wet biomasses for production of hydrochars but produces excessive process water. In this study, recirculation of process water from HTC of macroalgae Laminaria was investigated for 12 rounds. Recycling process water increased the hydrochar yield, carbon recovery rate and high heating value from 13.3% to 17.1%, from 22.9% to 32.6%, and from 18.4 MJ/kg to 20.5 MJ/kg after 12 rounds, respectively. The process water recirculation could partly alleviate the toxicity of process water through seed germination test. Volatile fatty acids (VFAs) predominantly accumulate with process water recirculation. The increased proportion of VFAs on chemical oxygen demand could promote methane production of diluted process waters, a 12.3% increase was observed in the round 10, compared with initial process water. These results showed that recycling the process water could reduce water consumption significantly and enhance energy recovery efficiency.

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.

About the Influence of Doping Approach on the Alkali Metal Catalyzed Slow Pyrolysis of Xylan

In this study, we highlighted how the catalytic effect of alkali metals on xylan pyrolysis is strongly affected by the adopted doping approach. Thermogravimetric and pyrolysis tests, up to 973 K and at a heating rate of 7 K/min, were conducted on a set of potassium- or sodium-doped xylan samples containing controlled amounts of KCl or NaCl introduced, starting from a demineralized xylan sample, through a conventional wet impregnation approach. Pyrolysis product yields from xylan-doped samples were compared with those related to the demineralized xylan sample. The performances of the doping procedure were assessed through a comparison with the data collected on raw xylan and a xylan sample doped with potassium ions by a cationic exchange approach. The results showed that the introduction of potassium ions by wet impregnation using a chloride salt negligibly affected the pyrolytic behaviour of the demineralized sample and indicated that the doping approach based on wet impregnation using chloride salts is not appropriate for the study of the effect of alkali metals on the pyrolysis of polysaccharides bearing acidic functional groups as xylan.

Fast pyrolysis characteristics of two typical coastal zone biomass fuels by thermal gravimetric analyzer and down tube reactor

This study aimed at investigating fast pyrolysis behavior and products distribution of two typical coastal zone biomass fuels (Jerusalem artichoke stalk (JAS) and reeds (Re) by TGA and a homemade down tube reactor. The kinetic analysis with different ramping rates was conducted by FWO and DAEM models. The liquid, gaseous and solid products are characterized to study the influence of temperature. Results indicate that high heating rates may be overcome some resistances to mass or heat transfer inside the particles of biomass, and lead to a higher conversion rates and Re species is preferable to JAs in terms of thermochemical conversion because of the lower apparent activation energy for total conversion. Moreover, the pyrolysis conditions - temperature under fast pyrolysis in a down tube pyrolysis unit will make the covalent bonds in the biomass degradation more rapidly, gave significant influence on the yields and properties of liquid, gaseous and solid products.

Investigation of the relevance between biomass pyrolysis polygeneration and washing pretreatment under different severities: Water, dilute acid solution and aqueous phase bio-oil

Washing pretreatments of rice straw were performed using three different solutions, namely water, dilute hydrochloric acid solution (HCl solution, pH = 2.9), and aqueous phase bio-oil (APBO, pH = 2.9). The raw and pretreated samples were pyrolyzed at 550 °C in a fixed bed reactor. Results showed that among the three pretreatments, washing with APBO had the highest removal efficiency of alkali metal and alkaline earth metals (AAEMs). Among the pyrolysis products, bio-oil from APBO washed sample had the highest mass, energy, and carbon yields, lowest water content of 36.9%, highest HHV of 17.2 MJ/kg, and highest relative content of anhydrosugars of 31.2%. Its biochar had the lowest ash content of 27.3% and highest specific surface area of 98.6 m²/g, and its non-condensable gases had the highest HHV of 11.9 MJ/m³. Therefore, APBO washing was effective in improving the quality of biomass and its subsequent pyrolysis products.

Online photoionization mass spectrometric evaluation of catalytic co-pyrolysis of cellulose and polyethylene over HZSM-5

The hydrogen-deficient and oxygen-rich nature of lignocellulosic biomass prohibits effective conversions of biomass to fuels and chemicals via catalytic pyrolysis due to significant coking of the catalysts. Co-feeding of biomass feedstock with hydrogen-rich and oxygen-deficient thermoplastics could improve the process. Herein, thermal and catalytic co-pyrolysis of cellulose and polyethylene (PE) was studied via thermogravimetry combined with an online photoionization time-of-flight mass spectrometry (PI-TOF-MS). No notable synergetic effect was found in the thermal co-pyrolysis process while a considerable synergetic effect was observed during the catalytic co-pyrolysis. In the case of catalytic pyrolysis, co-feeding of cellulose with PE significantly improved the aromatic formation. Detailed reaction intermediates and products were detected by PI-TOF-MS and the process of aromatization could be ascribed to aromatization of small oxygenates and olefins, as well as Diels-Alder reaction and dehydration by HZSM-5. Moreover, this study provides a reliable tool for screening and optimizing of catalytic co-pyrolysis.

Influence of inherent hierarchical porous char with alkali and alkaline earth metallic species on lignin pyrolysis

This study aimed to explore the influence of inherent hierarchical porous char with alkali and alkaline earth metallic species (AAEMs) during pyrolysis of lignin derived from agricultural crop residues in a laboratory fixed-bed at 550 °C. A catalytic strategy was implemented to investigate volatile-char interactions based on ex situ lignin pyrolysis. The physico-chemical properties of the AAEMs-loaded char were characterized by FTIR, XRD, SEM-EDX and N₂ nitrogen adsorption analyses. Results indicated that AAEMs-loaded char had a large specific surface area, hierarchical porosity, amorphous carbon structure, surface-active functional groups and highly dispersed metal species. Specifically, the specific surface area of AAEMs-loaded char was significantly reduced owing to coke deposition after interaction with pyrolysis vapours. Bio-oil composition revealed substantial increases in phenol, o-cresol, p-cresol and catechol. These increases were mainly attributed to demethylation, demethoxylation, or alkyl substitution reaction. The experimental results confirmed the occurrence of significant volatile-char interactions during lignin pyrolysis.

Comparative investigation of rice husk, thermoplastic bituminous coal and their blends in production of value-added gaseous and liquid products during hydropyrolysis/co-hydropyrolysis

The hydropyrolysis/co-hydropyrolysis of rice husk (RH) and thermoplastic bituminous coal (BC) was carried out using a fixed-bed reactor to investigate the effects of atmosphere and hydrogen pressure on product distributions. RH produced more carbon oxides, phenolics and acids. BC yielded more methane and BTX (benzene, toluene and xylene) during hydropyrolysis. Compared with hydropyrolysis of RH, the co-hydropyrolysis promoted the higher heating value of gaseous product and the yield of BTX by 19% and 57% respectively, while it reduced the yield of corrosive acids by 89% under 5 MPa H₂. The yields of methane, BTX and phenolics during co-hydropyrolysis were 1.5, 6.4 and 4.0 times as much as those obtained during co-pyrolysis under 5 MPa. The co-hydropyrolysis reformed the structure of heavy oil/tar, benefiting the development of aromaticity. High hydrogen pressure synergistically reduced yields of char and acids, and enhanced yields of tar and light aromatics via the secondary reactions.

Effect of inorganic species on torrefaction process and product properties of rice husk

The objective of this study was to evaluate the effect of inorganic species on torrefaction process and product properties. Torrefaction process of raw and leached rice husk was performed at different temperatures between 210 and 270 °C. Inorganic species have significant effect on the torrefaction process and properties of torrefaction products. The results indicated that solid yield increased, gas yield decreased and liquid yield remained unchanged for leached rice husk when compared to raw rice husk. Gas products from torrefaction process mainly contained CO₂ and CO, and leaching process slightly reduced the volume concentration of CO₂. Removal of inorganic species slightly decreased water content and increased organic component content in liquid products. Acetic acid, furfural, 2,3-dihydrobenzofuran and levoglucosan were the dominant components in liquid product. Inorganic species enhanced the effect of deoxygenation and dehydrogenation during torrefaction process, resulting in the enrichment of C component in solid products.

Co-pyrolysis behavior of fermentation residues with woody sawdust by thermogravimetric analysis and a vacuum reactor

This study aimed at cost-effective utilization of fermentation residues (FR) from biogas project for bio-energy via co-pyrolysis of FR and woody sawdust (WS). In this study, a vacuum reactor was used to study the pyrolysis behaviors of individual and blend samples of FR and WS. Obvious synergistic effects were observed, resulting in a lower char yield but a higher gas yield. The presence of woody sawdust promoted the devolatilization of FR, and improved the syngas (H₂ and CO) content in the gaseous products. Compared to those of the char from pyrolysis of individual feedstock, co-pyrolysis of FR and WS in the vacuum reactor promoted the cracking reactions of large aromatic rings, enlarged the surface area and reduced the oxygenated groups of the resulted char.

Effect of iron(III) ion on moso bamboo pyrolysis under microwave irradiation

The effect of iron(III) ion on microwave pyrolysis of moso bamboo was investigated. Hydrofluoric acid washing was used as a pilot process to demineralize moso bamboo in order to eliminate the influences of the other inorganics contained in moso bamboo itself. The results indicated that the addition of iron(III) ion increased the maximal reaction temperatures under microwave condition dependent on the amount of the added iron(III) ion. The production of the non-condensable gases was promoted by the addition of iron(III) ion mainly at the expense of liquid products. Iron(III) ion exhibited the positive effect for syngas production and inhibited the formation of CO₂ and CH₄. The formation of Fe₂O₃ and Fe₃O₄ was found during microwave pyrolysis and the mechanism of the two metallic oxides formation was described in this work.

Synergistic dye adsorption by biochar from co-pyrolysis of spent mushroom substrate and Saccharina japonica

The potential of activating terrestrial biomass (spent mushroom substrate, SMS) with ash-laden marine biomass [kelp seaweed, KE] via co-pyrolysis in the field of adsorption was first investigated. KE biochar (KBC), SMS biochar (SMSBC), biochar (SK10BC) from 10%-KE added SMS, and biochar (ESBC) from KE-extract added SMS were used for the adsorption of cationic dye crystal violet (CV). ESBC had highest fixed carbon content (70.60%) and biochar yield (31.6%). SK10BC exhibited high ash content, abundant functional groups, coarser surface morphology and Langmuir maximum adsorptive capacity (610.1mg/g), which is 2.2 times higher than that of SMSBC (282.9mg/g). Biochar activated by a small amount of high ash-containing biomass such as seaweed via co-pyrolysis can serve as viable alternative adsorbent for cationic dye removal.

Enhanced levofloxacin removal from water using zirconium (IV) loaded corn bracts

The presence of antibiotics in the environment has attracted considerable attention due to their toxicity. In this study, agricultural waste corn bracts (CBs) modified by zirconium cations were utilized to remove levofloxacin (LEV) from wastewater. Zr-modified CBs exhibited a strong adsorption capacity (Q_max = 73 mg/g), and their desorption rate could reach 89% by simply adjusting the pH to 11. FTIR and XPS analyses indicated that the mechanism of LEV adsorption included the complexation between the ketone/carboxyl groups of LEV and the Zr atoms and the π-π electron-donor-acceptor interaction. Zr-modified CBs are economic, effective and nontoxic adsorbents. This material not only removes antibiotics from wastewater but also enables recycling and reuse of agricultural waste.

Effect of torrefaction on the properties of rice straw high temperature pyrolysis char: Pore structure, aromaticity and gasification activity

The influence of torrefaction on the physicochemical characteristics of char during raw and water washed rice straw pyrolysis at 800-1200°C is investigated. Pore structure, aromaticity and gasification activity of pyrolysis chars are compared between raw and torrefied samples. For raw straw, BET specific surface area decreases with the increased torrefaction temperature at the same pyrolysis temperature and it approximately increases linearly with weight loss during pyrolysis. The different pore structure evolutions relate to the different volatile matters and pore structures between raw and torrefied straw. Torrefaction at higher temperature would bring about a lower graphitization degree of char during pyrolysis of raw straw. Pore structure and carbon crystalline structure evolutions of raw and torrefied water washed straw are different from these of raw straw during pyrolysis. For both raw and water washed straw, CO₂ gasification activities of pyrolysis chars are different between raw and torrefied samples.

Effect of Potassium on the Mechanisms of Biomass Pyrolysis Studied using Complementary Analytical Techniques

Complementary analytical methods have been used to study the effect of potassium on the pyrolysis mechanisms of cellulose and lignocellulosic biomasses. Thermogravimetry, calorimetry, high-temperature (1) H NMR spectroscopy (in situ and real-time analysis of the fluid phase formed during pyrolysis), and water extraction of quenched char followed by size-exclusion chromatography coupled with mass spectrometry have been combined. Potassium impregnated in cellulose suppresses the formation of anhydrosugars, reduces the formation of mobile protons, and gives rise to a mainly exothermic signal. The evolution of mobile protons formed from K-impregnated cellulose has a very similar pattern to the evolution of the mass loss rate. This methodology has been also applied to analyze miscanthus, demineralized miscanthus, miscanthus re-impregnated with potassium after demineralization, raw oak, and Douglas fir. Hydrogen mobility and transfer are of high importance in the mechanisms of biomass pyrolysis.

Effects of four types of dilute acid washing on moso bamboo pyrolysis using Py-GC/MS

The influences of four types of dilute acid washing (H2SO4, HCl, HF, HNO3) on moso bamboo pyrolysis were investigated via pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The effects of acid washings on the inorganics contents and the chemical structure were also analyzed. The results indicated that all the acid washings could effectively remove a large portion of inorganics and disrupt the chemical structure to a certain extent. HCl-washing behaved the best in removing inorganics and had the most marked disruption effect on bamboo structure. Acid washings promoted the bamboo pyrolysis and increased the contents of both phenols and sugars. HCl-washing had the most significant promotion effect on the levoglucosan formation with the absolute peak area increasing from 8.12×10(8) to 1.92×10(9). The absolute peak areas of 2,3-dihydrobenzofuran decreased more or less after acid washings. All the acid washings except H2SO4-washing could significantly increase the absolute peak area of methoxyeugenol.

Catalytic conversion of cellulosic biomass to ethylene glycol: Effects of inorganic impurities in biomass

The effects of typical inorganic impurities on the catalytic conversion of cellulose to ethylene glycol (EG) were investigated, and the mechanism of catalyst deactivation by certain impurities were clarified. It was found that most impurities did not affect the EG yield, but some non-neutral impurities or Ca and Fe ions greatly decreased the EG yield. Conditional experiments and catalyst characterization showed that some impurities changed the pH of the reaction solution and affected the cellulose hydrolysis rate; Ca and Fe cations reacted with tungstate ions and suppressed the retro-aldol condensation. To obtain a high EG yield, the pH of the reaction solution and the concentration of tungstate ions should be respectively adjusted to 5.0-6.0 and higher than 187ppm. For raw biomass conversion, negative effects were eliminated by suitable pretreatments, and high EG yields comparable to those from pure cellulose were obtained.