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• Three types of solution with different severities were used to wash rice straw. • One sharp peak was in DTG curves for Raw-RS, but two peaks for HCl-RS and APBO-RS. • Evolution of evolved gases (H 2 O, CH 4 , CO, CO 2 , and C O stretching) was analyzed. • APBO pretreatment showed the highest activation energy for rice straw pyrolysis. • The relative content of levoglucosan was increased because of the removing of AAEMs. Washing pretreatment is a promising method for upgrading biomass by removing alkali metal and alkaline earth metals (AAEMs). In this study, three types of solution with different pretreatment severities (i.e., water (H 2 O), dilute hydrochloric acid (HCl) solution, and aqueous phase bio-oil (APBO)) were used to study the effects of the washing pretreatment on the pyrolysis behaviors and kinetics of rice straw. The pyrolysis experiments of raw and pretreated rice straw (Raw-RS, H 2 O-RS, HCl-RS, and APBO-RS) were carried out using TG-FTIR and Py-GC/MS. Results show that among the three types of washing pretreatment methods, the APBO washing pretreatment has the highest removal efficiency of AAEMs: 99.7% of K, 91.7% of Na, 96.6% of Mg, and 95.2% of Ca. According to TG-FTIR results, only one sharp mass loss peak was present in the DTG curves of Raw-RS and H 2 O-RS, whereas two mass loss peaks (one sharp peak and one shoulder peak) were observed in HCl-RS and APBO-RS. The evolution pattern of the volatile compounds (H 2 O, CH 4 , CO, CO 2 , and C O stretching) was thoroughly investigated, and the absorbance intensity of these components increased with the washing pretreatment of APBO and HCl. The APBO washing pretreatment had the highest activation energy in the conversion rate of 0.2–0.75, followed by HCl and H 2 O washing pretreatment. According to the Py-GC/MS results, the washing pretreatment reduced the relative contents of acids, ketones, furans, and phenols in bio-oil, whereas removing of AAEMs increased the relative contents of anhydrosugars (mainly levoglucosan). Among the three types of washing pretreatments, the APBO washing pretreatment had the most remarkable influence on the property of bio-oil, and this indicates that the APBO washing pretreatment is a promising method for upgrading biomass and its pyrolytic product. [ABSTRACT FROM AUTHOR]

This study presented an approach to upgrade biomass and pyrolysis products using a process based on torrefaction liquid washing combined with torrefaction pretreatment. The torrefaction of cotton stalk was first conducted at 250 °C for 30 min and then the resulting torrefaction liquid products were collected and reused to wash cotton stalk. The pyrolysis of the original and pretreated cotton stalk was performed at 500 °C for 15 min in a fixed-bed reactor. The results indicated that the combined pretreatment obviously reduced the metallic species in cotton stalk, decreased the water and acids contents while promoted phenols in bio-oil, declined the ash content in biochar, as well as improved the heating value of non-condensable gas. Overall, the combined pretreatment did not only allow to reuse the liquid products issued from torrefaction pretreatment but also improved the quality of biomass and the pyrolysis products, making it a novel promising pretreatment method. [ABSTRACT FROM AUTHOR]

Bio-oil is the liquid product of the fast pyrolysis of biomass. Recently, bio-oil has gained increasing attention for its direct use in combustion within boilers and furnaces as well as its use in automobiles and chemical materials after refining. Unfortunately, the composition of bio-oil is very complex. Aging occurs during storage, which leads to obvious changes in the physical and chemical properties of the oil. The poor storage stability of bio-oil restricts its extensive applications as a key renewable energy alternative. Viscosity and average molecular weight, as well as water and solid content can measured to determine changes in bio-oil. In this article, the testing parameters and technologies used for examining bio-oil stability and research progress in the field of bio-oil stability are reviewed. Emphasis is placed on thermal and oxidation stability. Scientific and technical developments towards improving bio-oil stability are also discussed. Furthermore, important aspects for consideration when developing experimental plans for bio-oil upgrades are examined. It also points out challenges to success with bio-oil upgrading in the future. [ABSTRACT FROM AUTHOR]

• Solar torrefaction and solar pyrolysis of cotton stalk were performed. • Deoxygenation was the key for preparing high quality biomass sample. • Torrefaction had a significant effect on the subsequent catalytic pyrolysis. • Selective yield of benzene, toluene, and xylene increased markedly by torrefaction. • Torrefaction pretreatment inhibited the formation of coke deposited on the catalyst. Solar pyrolysis of biomass is a novel method for bio-fuels production. In this study, cotton stalks were first subjected to solar torrefaction at 200–300 °C, and then subjected to solar catalytic pyrolysis at 550 °C. The effects of torrefaction deoxygenation pretreatment and HZSM-5 zeolite on the bio-fuels (gas, biochar, and bio-oil) upgradation was investigated. Results showed that the elements of cotton stalks removed via torrefaction follow the order of deoxygenation > dehydrogenation > decarbonization. Torrefaction pretreatment has a remarkably influence on the subsequent catalytic pyrolysis. The bio-oil and gas yields were considerably reduced while the biochar yield increased with increasing torrefaction temperature. The primary pyrolytic volatiles cracked under the HZSM-5 catalyst, followed by a series of deoxygenation and aromatization reactions to form H 2 O, CO 2 , CO, alkanes, olefins, and aromatic hydrocarbons. Consequently, the oxygen-containing functional groups were removed to generate hydrocarbons that were rich in bio-oil, meanwhile the selective yield of benzene, toluene, and xylene (BTX) increased remarkably. Moreover, the torrefaction pretreatment inhibited the formation of coke deposited on the catalyst and promoted the carbon yield in the biochar. Considering the benefits of electricity savings, the approach proposed herein is a potential way to improve the competitiveness of biomass-derived products. [ABSTRACT FROM AUTHOR]

• Bamboo is treated with a new deashing method using light bio-oil leaching. • Biochar preparation method from co-pyrolysis of heavy bio-oil and bamboo is proposed. • Effect of mass ratio, temperature, and time on the biochar property is investigated. • The synergistic effect of heavy bio-oil and leached bamboo promotes biochar yield. • Best fitting models for yield and HHV of biochar are quadratic regression equations. Light fraction of bio-oil (LB) has high contents of water and organic acids with good liquidity and is a promising leaching agent for deashing of biomass. Heavy fraction of bio-oil (HB) contains more amounts of phenols and pyrolytic lignin, has poor fluidity, and is easy to carbonize when heated. In this study, a novel method for preparation of biochar from co-pyrolysis of HB and LB leached bamboo (LB-bamboo) has been proposed. Effects of three experimental variables, namely, mass ratio (1:0–0:1), pyrolysis temperature (400–700 °C), and residence time (5–30 min), on the mass yield and properties of biochar were investigated, based on response surface methodology. Results showed that co-processing of HB and bamboo by pyrolysis synergistically improved the yield and higher heating value (HHV) of biochar. Under typical co-pyrolysis conditions (mass ratio 1:1, 550 °C, and 17.5 min), the experimentally determined yield (25.97%) and HHV (29.43 MJ/kg) of biochar from co-pyrolysis of HB and raw bamboo were 1.61% and 1.01 MJ/kg higher than the corresponding theoretically predicted values. The ash and metallic species in bamboo were significantly removed by LB leaching pretreatment, leading to a more synergistic effect observed during the subsequent co-pyrolysis. The experimentally determined yield (24.63%) and HHV (30.62 MJ/kg) of biochar from co-pyrolysis of HB and LB-bamboo were 2.40% and 1.57 MJ/kg higher than the corresponding theoretical values. Ultimately, the regression equations between the biochar properties and the three experimental variables were established. The best fitting models for yield and HHV of biochar were quadratic regression equations. [ABSTRACT FROM AUTHOR]

Leaching essentially removes metallic species from biomass and improves the quality of pyrolysis products. However, common acid solutions, such as hydrochloric acid and acetic acid are expensive and difficult to recycle. This paper reports a new leaching pretreatment, using phenol and guaiacol solutions, which are mainly present in liquid by-products from thermal conversion of biomass. The characteristics of releasing of volatiles and upgradation of pyrolytic products of bamboo were investigated. Four key results can be obtained. (i) Phenolic leaching had much higher removal efficiency of metallic species, compared to water leaching. (ii) Pyrolytic behavior of bamboo changed drastically by phenolic leaching. Specifically, it enhanced the release of pyrolytic volatiles, separated the pyrolysis zones of hemicellulose and cellulose, and eliminated pyrolytic peak for extractives. (iii) Phenolic leaching upgraded the three phase pyrolysis products. Specifically, it inhibited the formation of acids, promoted the formation of anhydrosugars in bio-oil, improved the specific surface area of bamboo charcoal, and increased the volume fraction of methane in the gaseous products. (iv) With improved migration of oxygen and carbon from bamboo to bio-oil, the bio-oil replaced bamboo charcoal to become the pyrolysis product with increased energy yield. The above results demonstrated the importance and promise of phenolic-leaching pretreatment in upgradation of products of bamboo pyrolysis. From application perspective, light bamboo vinegar was an alternative for leaching of biomass. The use of bamboo vinegar filtrate containing metallic species had potential benefits for preparation of liquid fertilizer. • Phenolic leaching reduces the catalytic effect of metal species on bamboo pyrolysis. • Phenolic leaching enhances the release of pyrolytic volatiles of bamboo. • Phenolic leaching improves the quality of three phase products of bamboo pyrolysis. • Oxygen and carbon migration from bamboo to bio-oil are promoted by phenolic leaching. • Bio-oil replaces char to become the pyrolysis product that dominates energy yield. [ABSTRACT FROM AUTHOR]

• Solar-driven pyrolysis of biomass was performed using a parabolic-dish solar reactor. • Biomass was pretreated by APBO washing, solar drying, and solar torrefaction. • Fuel quality of biomass was remarkedly improved by the combined pretreatments. • Generation of acids was inhibited while the phenols and anhydrosugars were promoted. • Solar energy has a potential to replace conventional electric or fossil fuel heating. In this study, three types of biomass were first pretreated with an aqueous phase bio-oil instead of traditional acid washing. Then, the washed samples were pretreated with drying (100 ℃, 30 min) and torrefaction (250 ℃, 30 min) using a parabolic-trough solar receiver system. The subsequent pyrolysis was performed at 550 ℃ for 10 min using a parabolic-dish solar receiver system. Results showed that the solar energy can effectively ensure the temperature required for biomass drying, torrefaction, and pyrolysis, having thus a potential to replace the conventional electric heating or fossil fuel heating. Such a strategy combines the advantages of the independent pretreatments, i.e., leaching out of metallic species and reduction of oxygen content. Consequently, the high heating value of bio-oil increased remarkably, the generation of acids was strongly inhibited, whereas the formation of phenols and anhydrosugars was promoted. Therefore, the method proposed herein is promising for upgrading of biomass and bio-oil. [ABSTRACT FROM AUTHOR]

• Removal rate of AAEMs are remarkably improved by using aqueous phase bio-oil. • Furfural, hydroxyacetone, ethylene glycol, phenol and guaiacol are used for leaching. • Acetic acid is the key component in bio-oil to leach AAEMs from biomass. • Synergistic leaching effect occurred between acetic acid and non-acidic components. • Non-acidic compounds in bio-oil play an important role in leaching of AAEMs. In this study, six dominant organic compounds in biomass pyrolyzed bio-oil, composed of acidic compound (acetic acid) and non-acidic compound (furfural, hydroxyacetone, ethylene glycol, phenol, and guaiacol) were used to remove AAEMs from different lignocellulosic biomass (rice husk, cotton stalk, and fir sawdust) by leaching pretreatment. Other four conventional solutions (deionized water, hydrochloric acid solution, aqueous phase bio-oil, and simulated bio-oil) were selected as control eluents. Results showed that the removal rate of AAEMs was highly affected by the types of immersion solutions, pH values, and the species of biomass. Majority of K in biomass could be removed by leaching of acetic acid. Ca was more difficult to be removed by leaching of water and acetic acid, but could be removed by leaching of HCl. In general, the removal rate of K was highest among the four species of AAMEs by using five non-acidic components, followed by Na, Mg, and Ca. The use of five non-acidic solutions was significantly benefit for the remove of K, Mg, and Na, but, was less useful in removal of Ca in rice husk and fir sawdust. However, the removal rates of Ca in cotton stalk by leaching of phenol, guaiacol, and hydroxyacetone were increased to nearly three times than water leaching. A synergistic effect for removing AAEMs occurred between acetic acid and non-acidic components in bio-oil, indicating that the non-acidic compounds also play an important role in leaching of AAEMs. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1. Bio-oil is prepared by co-pyrolyzed of heavy bio-oil and bamboo. • 2. Light bio-oil was used to leach bamboo to remove ash and alkali metals. • 3. Compared to bamboo pyrolysis, co-pyrolysis improved the fuel properties of bio-oil. • 4. Leaching pretreatment of bamboo improved the yield and quality of bio-oil. • 5. The predictive equations for the yield and properties of bio-oil were established. The quality of bio-oil produced by conventional pyrolysis of biomass feedstocks is relatively low. In particular, the bio-oil phase separates into light bio-oil (LB) and heavy bio-oil (HB) that are difficult to use. In this study, light bio-oil was used to leach bamboo to remove ash and alkali metals, and then the leached bamboo was co-pyrolyzed with HB. The response surface methodology was used to evaluate the influences of the different experimental conditions (temperature, residence time, and mass ratio) on the properties of the resulting bio-oil. The results highlight that the mass yield and quality of bio-oil produced with HB and bamboo were improved compared to bio-oil produced with only bamboo alone. Under the optimal co-pyrolysis conditions using an HB/raw bamboo mass ratio of 4:1, 640 °C and 25 min, the highest yield of 61.84% was obtained, and the bio-oil had the lowest water content (15.78%) and a higher heating value (HHV) of 27.75 MJ/kg. The yield and HHV were further increased in the bio-oil prepared by co-pyrolysis of HB and bamboo pretreated by the LB leaching process. Moreover, the relative contents of phenols and hydrocarbons in the bio-oil increased, while that of acids decreased because of the synergistic effects of the combined raw materials on the bio-oils produced by co-pyrolysis. Finally, predictive models for the bio-oil yield and properties were established and gave a foundation for the preparation and utilization of bio-oils. [ABSTRACT FROM AUTHOR]

Acids present in bio-oil are considered to be effective agents to remove alkali and alkaline earth metallic species (AAEMs) from biomass, therefore affecting biomass pyrolysis. This study assessed whether phenols in bio-oil have a similar effect, with the pyrolysis characteristics of leached bamboo investigated using water and two typical phenolic compounds, phenol and guaiacol. Results confirmed that phenols have an important role in the removal of AAEMs, removing 96.4–96.6% of K, 84.6–85.4% of Mg, 77.2–81.9% of Na, and 66.7–69.1% of Ca. TG-FTIR results showed that phenolic leaching enhanced the pyrolytic release of volatile components of bamboo (H 2 O, CO 2 , CO, CH 4 , and carbonyl (C=O)-containing components), increased the temperature of pyrolysis peaks and decreased the activation energy, while increasing separation of the hemicellulose and cellulose pyrolysis zone. The results of Py-GC/MS showed that phenolic leaching reduced the production of acids but promoted the formation of anhydrosugars in bio-oil, indicating that phenolic leaching of AAEMs has a positive effect on the pyrolysis utilization of bamboo. Unlabelled Image • AAEM of bamboo are remarkably removed by using phenol solution and guaiacol solution. • Catalytic effect of metallic species on pyrolysis is reduced by phenolic leaching. • Evolution of volatile components (H 2 O, CH 4 , CO, CO 2 and C O stretching) is analyzed. • Phenolic leaching increases DTG max temperature and decreases the activation energy. • Extractives are removed by leaching, resulting in variation of pyrolysis behavior. [ABSTRACT FROM AUTHOR]

In this study, a two-section pyrolysis reactor was used for the pyrolysis of corn straw at 550°C. The pyrolysis of corn straw was performed in the first section, while a biochar sample (untreated biochar, acid-washed biochar, or biochar loaded with NaCl, KCl, MgCl2, or CaCl2) was placed in the second section. The effects of the biochar and the metal salts it contained on corn straw pyrolysis were researched. The results showed that acid-washing pretreatment removed most of the metal ions (99.1% of K, 95.2% of Ca, 94.3% of Na, and 95.3% of Mg) in biochar. As the amount of acid-washed biochar added raised from 0 to 3 g, the bio-oil yield declined from 51.2% to 45.3%, the gas yield raised from 21.9% to 27.1%, and volume fraction of CO and H2 increased from 33.5% and 10.8% to 35.6% and 13.1% respectively. In addition, the acid-washed biochar promoted the decomposition of acid substances in the pyrolysis volatiles and the formation of phenolic substances. After loading with various metal salts in biochar, the bio-oil yield is further reduced while gas yield is further increased. Among the metal salts, KCl exhibited the strongest effects on the enrichment of phenolics and decomposition of acids. In addition, MgCl2 clearly promoted CO formation. The results in this study confirm that both biochar and its constituent metal ions play important roles in the secondary cracking of pyrolysis volatiles, and thus biochar has potential for application as a catalyst in biomass pyrolysis. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • AAEMs of rice straw are remarkably removed by aqueous phase bio-oil (APBO) washing. • Pyrolysis of washed rice straw with water, HCl and APBO are comparatively studied. • Qualities of biomass and pyrolysis product are improved by all washing pretreatments. • Formation of anhydrosugars in pyrolysis are greatly promoted by HCl and APBO washing. • APBO washing has a better improvement effect on pyrolysis products than acid washing. Abstract 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-pyrolysis polygeneration of heavy bio-oil and pine sawdust is studied. • Light bio-oil is used to leach pine sawdust to remove ash and alkali metals. • Leaching pretreatment of pine sawdust improves the mass yield and quality of bio-oil. • Co-pyrolysis of pine sawdust and heavy bio-oil has obvious synergistic effect. • The sum of energy yield of biochar and bio-oil is more than 80%. The liquid products obtained from pyrolysis of biomass include light bio-oil and heavy bio-oil. The former contains large amounts of water and organic acids, while the latter contains more of pyrolysis lignin and phenolic compounds. Herein, a new method of pine wood co-pyrolysis polygeneration along with bio-oil recycling was proposed for upgradation of pyrolysis products. Light bio-oil was used for leaching of pine sawdust, instead of the traditional acid leaching pretreatment, followed by its co-pyrolysis with heavy bio-oil. The synergistic effect during co-pyrolysis polygeneration was studied. Results showed that leaching pretreatment could effectively remove the alkali metals (95.6 % of K) from pine wood, which improved the quality and energy yield of bio-oil during the subsequent pyrolysis. The maximum increase in mass yield and energy yield of bio-oil were 6.7 % and 7.1 %, respectively. The co-pyrolysis of pine wood and heavy bio-oil had obvious synergistic effect, which increased the mass yield of biochar (maximum increase: 3.3 %) and pyrolysis gas, while reducing the water and relative acids contents of bio-oil and improving the contents of CO and C 2+ gases in the gaseous products. The maximum differences between the experimental and theoretical HHVs of biochar and bio-oil were 1.01 MJ/kg and 1.94 MJ/kg, respectively. Thus, this method provides a potential way to classify and utilize light and heavy components of bio-oil and also provides a basis for biomass pyrolysis polygeneration technology. [ABSTRACT FROM AUTHOR]