Production of aromatic amines via catalytic co-pyrolysis of lignin and phenol-formaldehyde resins with ammonia over commercial HZSM-5 zeolites

An Overview of Recycling Phenolic Resin

Over a century ago, phenolic formaldehyde (PF) resin was developed and continues to increase in yield due to its diverse applications. However, PF resin is a thermosetting plastic lacking fluidity and moldability, which are nondegradable in natural environments, leading to severe threats to fossil resources as well as global environmental crises. As a result, recycling PF resin is extremely important. In this review, we provide the recent advances in the recycling of PF resin, which includes mechanical recycling, chemical recycling, and utilization of carbon-based materials. The advantages and disadvantages of each strategy are evaluated from a green chemistry perspective. This article aims to attract interest in PF resin design, synthesizing, application and recycling, offering useful suggestions.

Multifunctional catalyst-assisted sustainable reformation of lignocellulosic biomass into environmentally friendly biofuel and value-added chemicals

Rapid urbanization is increasing the world's energy demand, making it necessary to develop alternative energy sources. These growing energy needs can be met by the efficient energy conversion of biomass, which can be done by various means. The use of effective catalysts to transform different types of biomasses will be a paradigm change on the road to the worldwide goal of economic sustainability and environmental protection. The development of alternative energy from biomass is not easy, due to the uneven and complex components present in lignocellulose; accordingly, the majority of biomass is currently processed as waste. The problems may be overcome by the design of multifunctional catalysts, offering adequate control over product selectivity and substrate activation. Hence, this review describes recent developments involving various catalysts such as metallic oxides, supported metal or composite metal oxides, char-based and carbon-based substances, metal carbides and zeolites, with reference to the catalytic conversion of biomass including cellulose, hemicellulose, biomass tar, lignin and their derivative compounds into useful products, including bio-oil, gases, hydrocarbons, and fuels. The main aim is to provide an overview of the latest work on the use of catalysts for successful conversion of biomass. The review ends with conclusions and suggestions for future research, which will assist researchers in utilizing these catalysts for the safe conversion of biomass into valuable chemicals and other products.

A review on lignin pyrolysis: pyrolytic behavior, mechanism, and relevant upgrading for improving process efficiency

Lignin is a promising alternative to traditional fossil resources for producing biofuels due to its aromaticity and renewability. Pyrolysis is an efficient technology to convert lignin to valuable chemicals, which is beneficial for improving lignin valorization. In this review, pyrolytic behaviors of various lignin were included, as well as the pyrolytic mechanism consisting of initial, primary, and charring stages were also introduced. Several parallel reactions, such as demethoxylation, demethylation, decarboxylation, and decarbonylation of lignin side chains to form light gases, major lignin structure decomposition to generate phenolic compounds, and polymerization of active lignin intermediates to yield char, can be observed through the whole pyrolysis process. Several parameters, such as pyrolytic temperature, time, lignin type, and functional groups (hydroxyl, methoxy), were also investigated to figure out their effects on lignin pyrolysis. On the other hand, zeolite-driven lignin catalytic pyrolysis and lignin co-pyrolysis with other hydrogen-rich co-feedings were also introduced for improving process efficiency to produce more aromatic hydrocarbons (AHs). During the pyrolysis process, phenolic compounds and/or AHs can be produced, showing promising applications in biochemical intermediates and biofuel additives. Finally, some challenges and future perspectives for lignin pyrolysis have been discussed.

Endophytes in Lignin Valorization: A Novel Approach

Lignin, one of the essential components of lignocellulosic biomass, comprises an abundant renewable aromatic resource on the planet earth. Although 15%––40% of lignocellulose pertains to lignin, its annual valorization rate is less than 2% which raises the concern to harness and/or develop effective technologies for its valorization. The basic hindrance lies in the structural heterogeneity, complexity, and stability of lignin that collectively makes it difficult to depolymerize and yield common products. Recently, microbial delignification, an eco-friendly and cheaper technique, has attracted the attention due to the diverse metabolisms of microbes that can channelize multiple lignin-based products into specific target compounds. Also, endophytes, a fascinating group of microbes residing asymptomatically within the plant tissues, exhibit marvellous lignin deconstruction potential. Apart from novel sources for potent and stable ligninases, endophytes share immense ability of depolymerizing lignin into desired valuable products. Despite their efficacy, ligninolytic studies on endophytes are meagre with incomplete understanding of the pathways involved at the molecular level. In the recent years, improvement of thermochemical methods has received much attention, however, we lagged in exploring the novel microbial groups for their delignification efficiency and optimization of this ability. This review summarizes the currently available knowledge about endophytic delignification potential with special emphasis on underlying mechanism of biological funnelling for the production of valuable products. It also highlights the recent advancements in developing the most intriguing methods to depolymerize lignin. Comparative account of thermochemical and biological techniques is accentuated with special emphasis on biological/microbial degradation. Exploring potent biological agents for delignification and focussing on the basic challenges in enhancing lignin valorization and overcoming them could make this renewable resource a promising tool to accomplish Sustainable Development Goals (SDG’s) which are supposed to be achieved by 2030.

Fast hydropyrolysis of biomass Conversion: A comparative review

Recent studies show that fast hydropyrolysis (i.e., pyrolysis under hydrogen atmosphere operating at a rapid heating rate) is a promising technology for the conversion of biomass into liquid fuels (e.g., bio-oil and C₄₊ hydrocarbons). This pyrolysis approach is reported to be more effective than conventional fast pyrolysis in producing aromatic hydrocarbons and also lowering the oxygen content of the bio-oil obtained compared to hydrodeoxygenation (a common bio-oil upgrading method). Based on current literature, various non-catalytic and catalytic fast hydropyrolysis processes are reviewed and discussed. Efforts to combine fast hydropyrolysis and hydrotreatment process are also highlighted. Points to be considered for future research into fast hydropyrolysis and pending challenges are also discussed.

A critical review on metal-based catalysts used in the pyrolysis of lignocellulosic biomass materials

This review discusses the technical aspects of improving the efficiency of the pyrolysis of lignocellulosic materials to increase the yield of the main products, which are bio-oil, biochar, and syngas. The latest aspects of catalyst development in the biomass pyrolysis process are presented focusing on the various catalyst structures, the physical and chemical performance of the catalysts, and the mode of the catalytic reaction. In bio-oil upgrading, atmospheric catalytic cracking is shown to be more economical than catalytic hydrotreating. Catalysts help in the upgrading process by facilitating several reaction pathways such as polymerization, aromatization, and alkyl condensation. However, the grade of bio-oil must be similar to that of diesel fuel. Hence, the properties of the pyrolysis liquid such as viscosity, kinematic viscosity, density, and boiling point are important and have been highlighted. Switching between types of catalysts has a significant influence on the final product yields and exhibits different levels of durability. Various catalysts have been shown to enhance gas yield at the expense of the yields of bio-oil and biochar that shift the overall purpose of pyrolysis. Therefore, the catalytic activity as a function of temperature, pressure, and catalyst biomass ratio is discussed in detail. These operational parameters are crucial because they determine the overall yield as well as the ratio of the oil, char, and gas products. Although significant progress has been made in catalytic pyrolysis, the economic feasibility of the process and the catalyst cost remain the major obstacles. This review concludes that the catalytic process would be feasible when the fuel selling price is reduced to less than US $ 4 per gallon of gasoline-equivalent, and when the selectivity of catalysts is further enhanced.

Pyrolysis of soybean soapstock for hydrocarbon bio-oil over a microwave-responsive catalyst in a series microwave system

A novel Silicon carbide (SiC) foam ceramic based ZSM-5/SiC nanowires microwave-responsive catalyst was developed to upgrade the pyrolysis volatiles in a microwave-assisted series system (both the pyrolysis and catalytic systems were heated by microwave). The growth of SiC nanowires was helpful for the ZSM-5 growth on the SiC foam ceramic. Because the specific surface area of SiC foam ceramic was improved. The dielectric properties of the composite catalyst were improved due to the growth of SiC nanowires. Bio-oil composition analysis showed that area percentage of hydrocarbons and aromatic hydrocarbons could reach 80.89% and 40.48% at catalytic temperature of 450 ℃and 500 ℃, respectively. The microwave-responsive composite catalyst had good aromatization performance in microwave-assisted series system due to high dielectric properties and specific surface area. The composite catalyst performed well after five-cycle regeneration, and the hydrocarbon content could still reach 76.40%, which is 80.89% for the original catalyst.

Advances in Circular Bioeconomy Technologies: From Agricultural Wastewater to Value-Added Resources

This review systematically outlines the recent advances in the application of circular bioeconomy technologies for converting agricultural wastewater to value-added resources. The properties and applications of the value-added products from agricultural wastewater are first summarized. Various types of agricultural wastewater, such as piggery wastewater and digestate from anaerobic digestion, are focused on. Next, different types of circular technologies for recovery of humic substances (e.g., humin, humic acids and fulvic acids) and nutrients (e.g., nitrogen and phosphorus) from agricultural wastewater are reviewed and discussed. Advanced technologies, such as chemical precipitation, membrane separation and electrokinetic separation, are evaluated. The environmental benefits of the circular technologies compared to conventional wastewater treatment processes are also addressed. Lastly, the perspectives and prospects of the circular technologies for agricultural wastewater are provided.

Coked Ni/Al2O3 from the catalytic reforming of volatiles from co-pyrolysis of lignin and polyethylene: preparation, identification and application as a potential adsorbent

Preparation of novel C–Ni/Al₂O₃ composite from the catalytic reforming of volatiles from co-pyrolysis of lignin and polyethylene and its adsorption application.