There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Recent discoveries of nonradical oxidation in aqueous-phase advanced oxidation processes (AOPs) have induced tremendous interest in environmental remediation of wastewater, whereas different findings from a variety of investigations have also raised severe controversies in the occurrence and mechanism of the nonradical reaction. Hence, critical understandings of the nonradical reaction will significantly advance the knowledge and its application for catalytic oxidation and wastewater treatment. In this review, we would like to present state-of-the-art research on nonradical pathways in persulfate-based AOPs, with emphases on the controversial methodologies for identifying the oxygen reactive species (ROS), ambiguous reaction mechanisms, intrinsic impacts of metal/carbon catalysts and organic substrates in the nonradical-based catalytic oxidation reactions. Moreover, further research directions on mechanistic investigation of the nonradical pathway with rational experimental design and advanced strategies, as well as the potential applications of the nonradical system are proposed.

Nonradical reactions in environmental remediation processes: Uncertainty and challenges

Increasing demand for sustainable chemicals and fuels has pushed academia and industry to search for alternative feedstocks replacing crude oil in traditional refineries. As a result, an immense academic attention has focused on the valorisation of biomass (components) and derived intermediates to generate valuable platform chemicals and fuels. Zeolite catalysis plays a distinct role in many of these biomass conversion routes. This contribution emphasizes the progress and potential in zeolite catalysed biomass conversions and relates these to concepts established in existing petrochemical processes. The application of zeolites, equipped with a variety of active sites, in Bronsted acid, Lewis acid, or multifunctional catalysed reactions is discussed and generalised to provide a comprehensive overview. In addition, the feedstock shift from crude oil to biomass involves new challenges in developing fields, like mesoporosity and pore interconnectivity of zeolites and stability of zeolites in liquid phase. Finally, the future challenges and perspectives of zeolites in the processing of biomass conversion are discussed.

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Potential and challenges of zeolite chemistry in the catalytic conversion of biomass

The continuous increase in the generation of waste plastics together with the need for developing more sustainable waste management policies have promoted a great research effort dealing with their valorization routes. In this review, the main thermochemical routes are analyzed for the valorization of waste polyolefins to produce chemicals and fuels. Amongst the different strategies, pyrolysis has received greater attention, but most studies are of preliminary character. Likewise, the studies pursuing the incorporation of waste plastics into refinery units (mainly fluid catalytic cracking and hydrocracking) have been carried out in batch laboratory-scale units. Other promising alternative to which great attention is being paid is the process based on two steps: pyrolysis and in-line intensification for olefin production by means of catalytic cracking or thermal cracking at high temperatures.

Thermochemical routes for the valorization of waste polyolefinic plastics to produce fuels and chemicals. A review

Pyrolysis converts lignocellulosic biomass to bio-oil that can be a precursor to fuel and chemicals for industries. The bio-oil contains high oxygenates fractions that deteriorate the bio-oil fuel properties. Catalysts acted to upgrade the bio-oil through selected bond cleavage reactions such as deoxygenation, cracking, decarbonylation and others reactions. Bulk and supported acid or base catalysts in biomass pyrolysis tailored the production of high-grade bio-oil. The catalytic biomass pyrolysis is an approach that is reliable for producing quality renewable fuel and chemical precursors. This paper elucidated recent studies on catalytic pyrolysis of lignocellulose biomass to renewable fuel grade bio-oil and chemicals. The review discussed the various principal activities on biomass characteristics and their potentials in pyrolysis process to produce the high-grade biofuel precursor. The possible processes used in perpetuating the pyrolysis devolatilisation of biomass are also appraised along with catalysts type, and their catalytic activities in the production of renewable bio-oil and bio-chemicals. Therefore, catalyst development for the upgrade of bio-oils from pyrolysis of biomass to renewable fuel and chemicals precursor remains a topical issue.

Recent progress on catalytic pyrolysis of lignocellulosic biomass to high-grade bio-oil and bio-chemicals

This study investigated the effects of desilication of ZSM-5 zeolite on its catalytic properties in catalytic fast pyrolysis (CFP) of lignocellulosic biomass. A series of mesoporous ZSM-5 zeolites were prepared by desilication of a conventional microporous ZSM-5 zeolite with NaOH solutions of varying concentrations (0.1–0.5 M). The creation of mesopores improved the diffusion property of the desilicated ZSM-5 zeolites and their catalytic activity for cracking bulky oxygenates (e.g., syringols derived from the lignin component of biomass). Consequently, the desilicated zeolites produced more aromatic hydrocarbons (carbon yields of 26.2–30.2%) and less coke (39.9–41.2%) in CFP of beech wood than the parent microporous ZSM-5 (23.2% aromatics and 44.4% coke). The highest aromatic yield (30.2%) and lowest coke yield (39.9%) were obtained in CFP of beech wood with mildly desilicated zeolite treated with 0.3 M NaOH solution. However, desilication with a greater concentration, 0.5 M NaOH, decreased the aromatic yield to 26.2% due to a considerable loss of microporosity in the severely desilicated zeolite. The results indicate that carefully controlled desilication of zeolite can improve the conversion of lignocellulose to valuable aromatic hydrocarbons and decrease the formation of undesired coke, thus improving the product distribution in CFP of lignocellulose.

Catalytic fast pyrolysis of biomass with mesoporous ZSM-5 zeolites prepared by desilication with NaOH solutions

Extraction optimization, characterization and antioxidant activity in vitro of polysaccharides from mulberry (Morus alba L.) leaves.

Box-Behnken design for extraction optimization, characterization and in vitro antioxidant activity of Cicer arietinum L. hull polysaccharides.

A series of gallium-containing MFI zeolites were prepared via impregnation of conventional aluminosilicate ZSM-5 with Ga (Ga/ZSM-5) or hydrothermal synthesis of galloaluminosilicate (Ga–Al–Si) and gallosilicate (Ga–Si) MFI zeolites. These Ga-containing zeolites were then tested as the catalysts for co-feed catalytic fast pyrolysis (CFP) of pine wood and low-density polyethylene (LDPE) mixtures. Compared with conventional ZSM-5 zeolites, the Ga-containing MFI zeolites considerably increased the yields of valuable petrochemicals (monoaromatic hydrocarbons and olefins) and decreased the yields of undesired polyaromatic hydrocarbons and low-value alkanes from the co-feed CFP. In addition, Ga–Al–Si and Ga–Si zeolites generally produced both higher yields and selectivities for valuable petrochemicals (e.g., p -xylene and olefins) than Ga/ZSM-5 in the co-feed CFP. The results indicate that Ga-containing zeolites may be used to improve petrochemical production in co-feed CFP of biomass and plastics, and direct hydrothermal synthesis of Ga–Al–Si and Ga–Si MFI zeolites may provide a more convenient and better alternative to post modification of ZSM-5 with Ga to prepare Ga-containing zeolites for co-feed CFP.

Maximizing carbon efficiency of petrochemical production from catalytic co-pyrolysis of biomass and plastics using gallium-containing MFI zeolites

This study investigated the effects of ZSM-5 impregnation with boron on its catalytic properties in catalytic fast pyrolysis (CFP) of cellulose, low-density polyethylene (LDPE), and their mixtures. A series of boron-modified ZSM-5 zeolites were prepared by impregnating a conventional ZSM-5 with different boron loadings (0.5–3 wt.%). Due to boron deposition, the acidity and pore size of ZSM-5 decreased with increasing the boron loading. When impregnated with 1 wt.% boron, ZSM-5 preserved sufficient catalytic activity for the production of valuable monoaromatic hydrocarbons and decreased the formation of undesired polyaromatic hydrocarbons in CFP of cellulose. In addition, the pore narrowing of ZSM-5 by boron deposition greatly enhanced p -xylene production over m - and o -xylenes in CFP. This result indicates that slightly decreasing the pore size of ZSM-5 can improve aromatic distribution toward more valuable products in CFP. Co-feeding of cellulose with LDPE in CFP further improved the product distribution. As a result of boron modification and co-feeding, the monoaromatic yield increased from 20.0 C% for CFP of cellulose alone with the parent ZSM-5 to 24.6 C% for co-feed CFP of cellulose and LDPE mixture (mixing ratio of 4:1) with the boron-modified ZSM-5, while the polyaromatic yield decreased from 11.3 C% to 6.0 C%. The yield for p -xylene also increased from 2.23 C% to 5.57 C% while the selectivity increased from 47.9% to 75.2%. The results indicate that ZSM-5 modification with boron and co-feeding of plastics have a beneficial effect for improving aromatic product distribution in CFP of biomass.

Optimizing the distribution of aromatic products from catalytic fast pyrolysis of cellulose by ZSM-5 modification with boron and co-feeding of low-density polyethylene

Wei Wang

Papers

Catalytic fast pyrolysis of biomass with mesoporous ZSM-5 zeolites prepared by desilication with NaOH solutions

Extraction optimization, characterization and antioxidant activity in vitro of polysaccharides from mulberry (Morus alba L.) leaves.

Box-Behnken design for extraction optimization, characterization and in vitro antioxidant activity of Cicer arietinum L. hull polysaccharides.

Maximizing carbon efficiency of petrochemical production from catalytic co-pyrolysis of biomass and plastics using gallium-containing MFI zeolites

Optimizing the distribution of aromatic products from catalytic fast pyrolysis of cellulose by ZSM-5 modification with boron and co-feeding of low-density polyethylene