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•Iron nanoparticles-based biochar catalyst was used to produce phenols firstly.•High yields and selectivities of phenols were achieved in the process.•Deactivation mechanism of ...catalyst was illustrated in detail.
Selective production of phenols via ex-situ catalytic pyrolysis of lignocellulosic biomass is a promising route in biomass conversion. Therefore, developing a low-cost and effective catalyst for this process has emerged as an important topic. Here, the iron nanoparticles-based carbonaceous catalysts were prepared via combining hydrothermal carbonization and pyrolysis approach and first used in the catalytic microwave-assisted pyrolysis of torrefied corn cob for phenols production. The effects of catalyst types, catalytic temperature, and catalyst to feedstock ratio on the production of phenolic compounds were studied. The total selectivity of phenols can reach 91.07 area% with the total yield of 18706.6 µg/ml bio-oil using the FeHC@ hydrochar catalyst (prepared by hydrothermal carbonization in the Fe(NO3)3 solution and pyrolysis) at the catalytic temperature of 450 °C and catalyst to feedstock ratio of 5:10. After using seven times, partial loss of catalytic activity of FeHC@hydrochar was found. This study also presented unique insights into the deactivation of carbonaceous catalysts, showing that sintering, oxidation of α-Fe and Fe3C phases, active site coverage, and pore blockage were the causes of the reduction of catalytic performance. Regeneration experiments showed that it is impracticable to calcine deactivated catalyst at an inert atmosphere and more advanced techniques needed to be developed to solve this problem. Overall, this study can provide a reference for realistic scale-up production of renewable phenols.
Increasing fossil fuel consumption and global warming has been driving the worldwide revolution towards renewable energy. Biomass is abundant and low-cost resource whereas it requires environmentally ...friendly and cost-effective conversion technique. Pyrolysis of biomass into valuable bio-oil has attracted much attention in the past decades due to its feasibility and huge commercial outlook. However, the complex chemical compositions and high water content in bio-oil greatly hinder the large-scale application and commercialization. Therefore, catalytic pyrolysis of biomass for selective production of specific chemicals will stand out as a unique pathway. This review aims to improve the understanding for the process by illustrating the chemistry of non-catalytic and catalytic pyrolysis of biomass at the temperatures ranging from 400 to 650 °C. The focus is to introduce recent progress about producing value-added hydrocarbons, phenols, anhydrosugars, and nitrogen-containing compounds from catalytic pyrolysis of biomass over zeolites, metal oxides, etc. via different reaction pathways including cracking, Diels-Alder/aromatization, ketonization/aldol condensation, and ammoniation. The potential challenges and future directions for this technique are discussed in deep.
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•Properties of lignocellulosic biomass and its pyrolysis chemistry are extensively reviewed.•Catalytic pyrolysis of lignocellulosic biomass for selective production of valuable chemicals is outlined.•Different catalytic reforming pathways are summarized.•Future research directions and technological challenges are proposed.
Renewable fuels or chemicals from lignocellulosic biomass have the potential to be a substitute for fossil fuels, thereby reducing greenhouse gas emissions and diversifying energy supplies. ...Integrating torrefaction and pyrolysis is a feasible and promising technology that converts biomass into fuels or chemicals. Understanding of the relevant process designs and mechanisms is favorable to the cohesion and optimization of these two processes and the innovation of reactors for commercial-scale biorefineries. First, biomass properties and their corresponding pyrolysis behaviors have been discussed in consideration of the challenge presented by complex biomass structures that limit the in-depth research on torrefaction or pyrolysis. Second, torrefaction fundamentals are illustrated in detail, and many kinetic models with comprehensive mechanism schemes, such as pseudo-mechanistic model and one-, two-, or multi-step models, are summarized. The effect of torrefaction on biomass characteristics and subsequent pyrolysis is reviewed to further elucidate the integrated process. The novel integration of torrefaction and up-to-date pyrolysis techniques is also outlined to improve product quality. Finally, future directions and technological challenges associated with the integrated process are proposed and its economic potential is also evaluated.
•Different torrefaction kinetic models have been developed to guide the reactor design and optimize the parameters.•Torrefaction significantly affects characteristics of biomass feedstock and improves the pyrolysis behavior.•Integrating torrefaction and developing pyrolysis techniques is promising to utilize the biomass energy effectively.•Pyproduct reuse and r heat recovery can enhance the economic competitiveness of the integrated process.•The self-catalysis mechanism of light organic acid and economic evaluation need to be studied further.
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•The most suitable method (OFW method) for activation energy calculation was found.•The most suitable methods (KAS and DAEM methods) for pre-exponential factor calculation were ...found.•The optimal torrefaction condition of corncob (240 °C) was determined.•Torrefaction enhanced the aromaticity of corncob.
The effects of torrefaction pretreatment on corncobs properties and its pyrolysis kinetic parameters were investigated in this study. Proximate and ultimate analyses indicated that torrefaction increased the H/Ceff ratio and higher heating value of corncobs, and reduced its oxygen content. Although the mass yield was also reduced, the corresponding energy yield was relatively higher. The crystallinity index of biomass showed a first upward and then downward trend with the torrefaction temperature. Kinetic parameters obtained from three models indicated that both the activation energy and the pre-exponential factor increased with the elevated torrefaction temperature and it's better to calculate the activation energy by the OFW method and to use the KAS and DAEM methods to calculate the pre-exponential factor. In addition, it was found that the optimum pretreatment temperature of corncobs was 240 °C.
The catalytic properties of different catalytic materials on the pyrolysis of plastics have been extensively investigated. In order to better understand the relevant mechanism of catalytic pyrolysis ...of plastic waste, the effect of different acidity and pore size of catalytic material on its pyrolysis kinetic parameters and the distribution of pyrolysis products needs to be studied to provide a stronger theoretical basis for its resource utilization. This study aims to study the effects of HZSM-5, Hβ, HY and MCM-41 on the thermodynamic properties, kinetic parameters and pyrolysis characteristics of low-density polyethylene (LDPE), analyze the relationship between the specific catalytic pyrolysis products and the properties of the catalyst. Among the four catalysts, HZSM-5 obtained the most concentrated product distribution and the highest yield of monocyclic aromatic hydrocarbons, and it was found that the cracking of LDPE mainly occurred in its pores. Due to the large pore size and low concentration of acid sites, the main product type obtained by MCM-41 was olefins. In addition, it was found that HY reduced the pyrolysis temperature of LDPE and the activation energy of the reaction to the greatest extent. The different catalytic effects were mainly caused by different pore structures and acid site concentration. Moreover, it was found that the addition of catalyst changed the cracking mechanism of LDPE. Under the comprehensive consideration with the goal of producing monocyclic aromatic hydrocarbons, HZSM-5 is the most suitable catalyst among them.
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•The catalytic effects of HZSM-5, Hβ, HY and MCM-41 were studied.•HZSM-5 is the most suitable catalyst for the production of MAHs from LDPE.•Different pore structures and acid sites cause the changes of catalytic effects.•Partial LDPE scission sites changed from random-chain to end-chain due to catalysis.•The cracking reaction of LDPE occurs in the pores of HZSM-5.
•A newly developed continuous fast microwave-assisted pyrolysis system was used.•It is the first time to pyrolysis Camellia oleifera shell with microwave.•The effects of temperature and feed rate on ...pyrolysis were studied.
In this study, a continuous fast microwave-assisted pyrolysis system was developed to produce bio-oil, gas, and biochar from rice straw and Camellia oleifera shell. The effects of different pyrolysis temperatures (400 °C, 500 °C, and 600 °C) and feed rates (rice straw: 25, 45, and 66 g/min; C. oleifera shell: 100, 200, and 400 g/min) on bio-oil production were investigated. Experimental results showed that the yields of bio-oil (31.86 wt%) and gas (54.49 wt%) produced by the microwave-assisted pyrolysis of rice straw increased with increasing temperature. By contrast, the yields of bio-oil (27.45 wt%) and biochar (35.47 wt%) produced by the pyrolysis of C. oleifera shell decreased with increasing temperature. The contents of phenols, aldehydes, and alcohols in bio-oil produced from the shell were higher than those in bio-oil derived from rice straw.
•Fe modified bio-char catalyst was prepared from low-cost rich husk.•The yields and selectivities of phenol and cresol in bio-oil were significantly increased.•Catalyst deactivation and regenation ...tests were conducted to evaluate the lifetime of the catalyst.
Microwave-assisted catalytic pyrolysis of torrefied corn cob into phenol-rich bio-oil on Fe modified bio-char catalyst was investigated in this study. The well-developed surface pore was confirmed by scanning electronic microscope (SEM) images and nitrogen adsorption/desorption isotherms, indicating that the porous structure of bio-char depended on the Fe modification to a large extent. Temperature-programmed desorption of NH3 (NH3-TPD) analysis showed that the Fe modified bio-char catalyst mainly presented strong acid sites. The use of bio-char catalyst can decrease the bio-oil yield and increase the gas yield but the biochar did not experience any significant change because of the ex-situ catalysis mode. Catalytic pyrolysis of torrefied corn cob using Fe modified bio-char catalyst was able to produce the higher yields and selectivities of phenol and cresol, where the catalytic performance of the bio-char catalyst was superior to commercial activated carbon. In addition, the catalyst deactivation and regenation tests were also conducted to evaluate the service life of the catalyst.
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•Microwave-driven HZSM-5@SiC ceramic foam was prepared and characterized.•The deactivation characteristics of HZSM-5@SiC ceramic foam were studied.•Process of microwave catalytic ...pyrolysis of soapstock for aromatic oil was studied.
In view of the poor selectivity of aromatic hydrocarbons in bio-oil from biomass pyrolysis and the high pressure drop and rapid coking and deactivation of catalyst in industrial scale, a microwave-driven HZSM-5@SiC ceramic foam has been constructed, and applied to the ex-situ catalytic fast pyrolysis of soapstock to improve the content of aromatic hydrocarbons in bio-oil. The effects of different catalysts and heating modes and mass ratios of HZSM-5@SiC ceramic foam to soapstock on the distribution of pyrolysis products have been investigated. In addition, combined with the comparison of microwave and electric heating, the deactivation characteristics of HZSM-5@SiC ceramic foam have been studied. Finally, the process of preparing aromatic oil by microwave-driven catalytic pyrolysis of soapstock was discussed. Experimental results indicate that compared with HZSM-5, HZSM-5@SiC ceramic foam has a higher yield of bio-oil and higher aromatization activity. Under microwave heating, the relative content of aromatic hydrocarbons increases from 25.18% to 100% when the mass ratio of HZSM-5@SiC ceramic foam to soapstock increases from 0:1 to 1:1. Compared with electric heating catalysis, HZSM-5@SiC ceramic foam has the lowest yield of coke under microwave heating. After five consecutive uses, it still maintains more than 90% catalytic activity and has higher stability, which provides a scientific basis for the pilot scale experiments of soapstock catalytic pyrolysis.
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•The synergistic effect of K and Ca during pyrolysis was studied.•The addition of K2CO3 promoted the decomposition and condensation of lignin.•The addition of Ca(OH)2 and K2CO3 ...promoted the uniform distribution of each other.•The inorganic components play an important role in evenly distributing the catalyst.
The effects of K and Ca on the pyrolysis of rice straw were studied. The results showed that impregnating a certain amount of Ca is beneficial to the uniform distribution of K, and mixing a certain amount of K is also beneficial to the uniform distribution of Ca. Ca and K would combine with the silicon-aluminum compound in the sample during the pyrolysis and become invalid. Ca can effectively reduce the invalid K, but cannot completely protect K from combining with the silicon-aluminum compound. The binary metal carbonates K2Ca(CO3)2 and K2Ca2(CO3)3 were produced during the pyrolysis of the samples, which have a limited effect for the uniform distribution of the catalysts. In addition, acid-leaching removed most of the inorganic components in rice straw, which made it difficult for the catalyst to be evenly distributed, indicating that the inorganic components play an important role in evenly distributing the catalyst.
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•Choerospondias axillaris seeds were used as a precursor of biochar catalyst firstly.•Fe-modified biochar catalyst has obvious promotion effect on phenolic compounds.•The selectivity ...of furfural was the highest by Fe0.2@biochar.•Fe0.4@biochar have the highest selectivity to phenol.•The Fe-modified biochar catalyst has catalytic activity after 5 consecutive uses.
In order to develop a more economical and easy-to-recover catalyst, this study prepared Fe-modified biochar catalyst by microwave pyrolysis carbonization and impregnation, and applied it to microwave catalysis pyrolysis of corn cobs to prepare phenol-rich bio-oil. The results showed that H3PO4 can greatly increase the specific surface area of the biochar catalyst. The Fe-modified biochar catalyst promoted the conversion of aldehydes and ketones in corn cobs bio-oil, thereby greatly increasing the content of phenolic compounds. Among them, Fe0.4@biochar had the best selectivity to phenol, approximately 16.45 area%. Fe0.2@biochar had the best selectivity to furfural, which was 10.68 area%. After repeated use for 5 times, the catalytic effect was still selective to phenolic compounds.
