Green chemistry, catalysis and valorization of waste biomass

Scaling-up green chemistry: bridging innovation and industrial applications

This Feature Article reviews recent advances in green chemistry, with a focus on scaling up both conceptually and industrially. We particularly discuss the contributions to circular economy principles through solvent replacement, non-conventional activation technologies, and the valorization of waste and biomass. The article also outlines strategies to transition lab-scale innovations into widespread and impactful industrial applications, highlighting opportunities and challenges associated with this transition.

From 3D to 4D printing of lignin towards green materials and sustainable manufacturing

Lignin is the second most abundant renewable and sustainable biomass resource. Developing advanced manufacturing to process lignin/lignocellulose into functional materials could reduce the consumption of petroleum-based materials. 3D printing provides a promising strategy to realize complex and customized geometries of lignin materials. The heterogeneity and complexity of lignin hinder its processing via additive manufacturing, but the recent advancement in lignin modification and polymerization provides new opportunities. Here, we summarize the recent state-of-the-art 3D printing of lignin materials, including the selection and formulation of lignin materials based on different printing techniques, the chemical modification of lignin for enhanced printability, and the related application fields. Additionally, we highlight the significant role of the 3D printing of lignocellulose biomass materials, such as wood powder and agricultural wastes. It was concluded that the most challenging part is to enhance the printability of lignin materials through modification and pretreatment of lignin while keeping the whole process green and sustainable. Beyond 3D printing, we further discuss the development of smart lignin materials and their potential for 4D printing. Ultimately, we discuss the current challenges and potential opportunities for the additive manufacturing of lignin materials. We believe this review can raise awareness among researchers about the potential of lignin materials as whole materials for constructing blocks and can promote the development of 3D/4D printing of lignin towards sustainability.

Harnessing light without photocatalysts: advances in photocatalyst-free C-N bond formation

The present feature article focuses on recent developments in the realm of photocatalyst-free C-N bond formations, highlighting the innovative approaches that leverage light without relying on traditional photocatalysts. Exploring alternative methodologies underscores the advancements in synthetic strategies, enabling efficient and sustainable C-N bond formation reactions. The abstracted review emphasizes the significant progress made in this field, shedding light on the potential for novel and environmentally friendly pathways for chemical synthesis.

Biomass Valorization via Paired Electrocatalysis

Electrochemical valorization of biomass represents an emerging research frontier, capitalizing on renewable feedstocks to mitigate carbon emissions. Traditional electrochemical approaches often suffer from energy inefficiencies due to the requirement of a second electrochemical conversion at the counter electrode which might generate non-value-added byproducts. This review article presents the advancement of paired electrocatalysis as an alternative strategy, wherein both half-reactions in an electrochemical cell are harnessed to concurrently produce value-added chemicals from biomass-derived feedstocks, potentially doubling the Faradaic efficiency of the whole process. The operational principles and advantages of different cell configurations, including 1-compartment undivided cells, H-type cells, and flow cells, in the context of paired electrolysis are introduced and compared, followed by the analysis of various catalytic strategies, from catalyst-free systems to sophisticated homogeneous and heterogeneous electrocatalysts, tailored for optimized performance. Key substrates, such as CO2, 5-hydroxymethylfurfural (HMF), furfural, glycerol, and lignin are highlighted to demonstrate the versatility and efficacy of paired electrocatalysis. This work aims to provide a clear understanding of why and how both cathode and anode reactions can be effectively utilized in electrocatalytic biomass valorization leading to innovative industrial scalability.

Functional characterization of two AA10 lytic polysaccharide monooxygenases from Cellulomonas gelida

Lytic polysaccharide monooxygenases (LPMOs) are redox enzymes targeting the crystalline region of recalcitrant polysaccharides such as cellulose and chitin. Functional characterization of two LPMOs from the cellulose-degrading soil bacterium Cellulomonas gelida, CgLPMO10A and CgLPMO10B, showed expected activities on cellulose but also revealed novel features of AA10 LPMOs. While clustering together with strictly C1-oxidizing and strictly cellulose-active AA10 LPMOs, CgLPMO10A exhibits activity on both cellulose and chitin, oxidizing the C1 carbon of both substrates. This combination of substrate and oxidative specificity has not been previously observed for family 10 LPMOs and may be due to a conspicuous divergence in two hydrophobic residues on the substrate-binding surface. CgLPMO10B oxidizes cellulose at both the C1 and C4 positions and is also active on chitin, in line with predictions based on phylogeny. Interestingly, while coming from the same organism and both acting on cellulose, the two enzymes have markedly different redox properties with CgLPMO10B displaying the lowest redox potential and the highest oxidase activity observed for an AA10 LPMO so far. These results provide insight into the LPMO machinery of C. gelida and expand the known catalytic repertoire of bacterial LPMOs.

Surface Acidic Species-Driven Reductive Amination of Furfural with Ru/T-ZrO2

Catalyst development for upgrading bio-based chemicals towards primary amines has increasingly attracted owing to their applications in the pharmaceutical and polymer industries. The surface acidic sites in metal oxide-based catalysts play a key role in the reductive amination of aldehydes/ketones involving H2 and NH3; however, the crucial role of the type of surface acidic species and their strength remains unclear. Herein, this study exhibits the catalytic reductive amination of furfural (FUR) to furfurylamine (FUA) with Ru supported on tetragonal (Ru/T-ZrO2) and monoclinic (Ru/M-ZrO2) ZrO2. Ru/T-ZrO2 exhibited an 11.8-fold higher rate of reductive amination than Ru/M-ZrO2, giving a quantitative yield of FUA (99 %) at 80 °C in 2.5 h and is recyclable up to four runs. Catalyst surface investigation using spectroscopic techniques, like X-ray photoelectron, electron paramagnetic resonance, and Raman, confirm higher oxygen vacancy sites (1.6 times) on the surface of Ru/T-ZrO2 compared to Ru/M-ZrO2. Moreover, in-situ NH3-diffuse reflectance infrared Fourier transform spectroscopy studies display that Ru/T-ZrO2 has more moderate Bronsted acidic sites (surface H-bonded hydroxyl groups) than Ru/M-ZrO2. Further, the controlled experiments and poisoning studies with KSCN and 2,6-lutidine suggest the crucial role of Ov sites (Lewis acidic sites) and surface hydroxyl groups (Bronsted acidic sites) for selective FUA formation.

Oxidation of cellulose fibers using LPMOs with varying allomorphic substrate preferences, oxidative regioselectivities, and domain structures

Lytic polysaccharide monooxygenases (LPMOs) are excellent candidates for enzymatic functionalization of natural polysaccharides, such as cellulose or chitin, and are gaining relevance in the search for renewable biomaterials. Here, we assessed the cellulose fiber modification potential and catalytic performance of eleven cellulose-active fungal AA9-type LPMOs, including C1-, C4-, and C1/C4-oxidizing LPMOs with and without CBM1 carbohydrate-binding modules, on cellulosic substrates with different degrees of crystallinity and polymer chain arrangement, namely, Cellulose I, Cellulose II, and amorphous cellulose. The potential of LPMOs for cellulose fiber modification varied among the LPMOs and depended primarily on operational stability and substrate binding, and, to some extent, also on regioselectivity and domain structure. While all tested LPMOs were active on natural Cellulose I-type fibers, activity on the Cellulose II allomorph was almost exclusively detected for LPMOs containing a CBM1 and LPMOs with activity on soluble hemicelluloses and cello-oligosaccharides, for example NcAA9C from Neurospora crassa. The single-domain variant of NcAA9C oxidized the cellulose fibers to a higher extent than its CBM-containing natural variant and released less soluble products, indicating a more dispersed oxidation pattern without a CBM. Our findings reveal great functional variation among cellulose-active LPMOs, laying the groundwork for further LPMO-based cellulose engineering.

Impact of Porous Silica Nanosphere Architectures on the Catalytic Performance of Supported Sulphonic Acid Sites for Fructose Dehydration to 5-Hydroxymethylfurfural

5-hydroxymethylfurfural represents a key chemical in the drive towards a sustainable circular economy within the chemical industry. The final step in 5-hydroxymethylfurfural production is the acid catalysed dehydration of fructose, for which supported organoacids are excellent potential catalyst candidates. Here we report a range of solid acid catalysis based on sulphonic acid grafted onto different porous silica nanosphere architectures, as confirmed by TEM, N2 porosimetry, XPS and ATR-IR. All four catalysts display enhanced active site normalised activity and productivity, relative to alternative silica supported equivalent systems in the literature, with in-pore diffusion of both substrate and product key to both performance and humin formation pathway. An increase in-pore diffusion coefficient of 5-hydroxymethylfurfural within wormlike and stellate structures results in optimal productivity. In contrast, poor diffusion within a raspberry-like morphology decreases rates of 5-hydroxymethylfurfural production and increases its consumption within humin formation.

The effect of linker conformation on performance and stability of a two-domain lytic polysaccharide monooxygenase

A considerable number of lytic polysaccharide monooxygenases (LPMOs) and other carbohydrate-active enzymes are modular, with catalytic domains being tethered to additional domains, such as carbohydrate-binding modules, by flexible linkers. While such linkers may affect the structure, function, and stability of the enzyme, their roles remain largely enigmatic, as do the reasons for natural variation in length and sequence. Here, we have explored linker functionality using the two-domain cellulose-active ScLPMO10C from Streptomyces coelicolor as a model system. In addition to investigating the WT enzyme, we engineered three linker variants to address the impact of both length and sequence and characterized these using small-angle X-ray scattering, NMR, molecular dynamics simulations, and functional assays. The resulting data revealed that, in the case of ScLPMO10C, linker length is the main determinant of linker conformation and enzyme performance. Both the WT and a serine-rich variant, which have the same linker length, demonstrated better performance compared with those with either a shorter linker or a longer linker. A highlight of our findings was the substantial thermostability observed in the serine-rich variant. Importantly, the linker affects thermal unfolding behavior and enzyme stability. In particular, unfolding studies show that the two domains unfold independently when mixed, whereas the full-length enzyme shows one cooperative unfolding transition, meaning that the impact of linkers in biomass-processing enzymes is more complex than mere structural tethering.

Progress in Development of Magadiite to Produce Multifunctional Lamellar Materials

The attractive properties of magadiite, a lamellar and crystalline material, could give rise to new industrial processes due to its unique and modulating intrinsic properties. In this context, the high degree of expansion of its lamellae, a key factor for its potential use in several areas of scientific research, has attracted the attention of several researchers. The aim of this review is to provide a historical overview of the hypothetical models developed to explain the magadiite crystalline structure. Furthermore, different synthesis strategies for the preparation of magadiites as sodic, protonic, and hybrid (inorganic-inorganic and inorganic-organic) materials are discussed along with several routes for obtaining modified magadiites. Also, the use of magadiite in catalytic reactions, notably in ethanol dehydration and fructose conversion reactions, is a growing area of research. Other potential applications include the adsorption and absorption of environmental pollutants (e.g., phenol and methylene blue in wastewater), use as a photocatalyst in the oxidation of toluene, and use in medicine (e.g., as a drug delivery or antibacterial/antifungal agent). This highlights the many opportunities for the development of new synthesis methods to obtain multifunctional materials in the search for new applications.

In situ study of the evolution of NiFe nanocatalysts in reductive and oxidative environments upon thermal treatments

The conversion of biomass as a sustainable path to access valuable chemicals and fuels is very attractive for the chemical industry, but catalytic conversions still often rely on the use of noble metals. Sustainability constraints require developing alternative catalysts from abundant and low-cost metals. In this context, NiFe nanoparticles are interesting candidates. In their reduced and supported form, they have been reported to be more active and selective than monometallic Ni in the hydrogenation of the polar functions of organic molecules, and the two metals are very abundant. However, unlike noble metals, Ni and Fe are easily oxidized in ambient conditions, and understanding their transformation in both oxidative and reductive atmospheres is an important though seldom investigated issue to be addressed before their application in catalysis. Three types of NiFe nanoparticles were prepared by an organometallic approach to ensure the formation of ultrasmall nanoparticles (<3.5 nm) with a narrow size distribution, controlled composition and chemical order, while working in mild conditions: Ni2Fe1 and Ni1Fe1, both with a Ni rich core and Fe rich surface, and an alloy with a Ni1Fe9 composition. Supported systems were obtained by the impregnation of silica with a colloidal solution of the preformed nanoparticles. Using advanced characterization techniques, such as wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) in in situ conditions, this study reports on the evolution of the chemical order and of the oxidation state of the metals upon exposure to air, hydrogen, and/or increasing temperature, all factors that may affect their degree of reduction and subsequent performance in catalysis. We show that if oxidation readily occurs upon exposure to air, the metals can revert to their initial state upon heating in the presence of H₂ but with a change in structure and chemical ordering.

Towards efficient and greener processes for furfural production from biomass: A review of the recent trends

As mentioned in several recent reviews, biomass-based furfural is attracting increasing interest as a feasible alternative for the synthesis of a wide range of non-petroleum-derived compounds. However, the lack of environmentally friendly, cost-effective, and sustainable industrial procedures is still evident. This review describes the chemical and biological routes for furfural production. The mechanisms proposed for the chemical transformation of xylose to furfural are detailed, as are the current advances in the manufacture of furfural from biomass. The main goal is to overview the different ways of improving the furfural synthesis process. A pretreatment process, particularly chemical and physico-chemical, enhances the digestibility of biomass, leading to the production of >70 % of available sugars for the production of valuable products. The combination of heterogeneous (zeolite and polymeric solid) catalyst and biphasic solvent system (water/GVL and water/CPME) is regarded as an attractive approach, affording >75 % furfural yield for over 80 % of selectivity with the possibility of catalyst reuse. Microwave heating as an activation technique reduces reaction time at least tenfold, making the process more sustainable. The state of the art in industrial processes is also discussed. It shows that, when sulfuric acid is used, the furfural yields do not exceed 55 % for temperatures close to 180 °C. However, the MTC process recently achieved an 83 % yield by continuously removing furfural from the liquid phase. Finally, the CIMV process, using a formic acid/acetic acid mixture, has been developed. The economic aspects of furfural production are then addressed. Future research will be needed to investigate scaling-up and biological techniques that produce acceptable yields and productivities to become commercially viable and competitive in furfural production from biomass.

Soya bean derived activated carbon as an efficient adsorbent for capture of valuable heavy metals from waste aqueous solution

The removal of hazardous metal ions from liquid waste effluents is very important for water as well as environmental safety. In this regard, this article discusses in detail the U(VI) uptake from aquatic environment using biomass-based Soya Bean activated carbon (labeled as AC-SB). XRD, SEM, FTIR, Raman, and BET analysis were used to characterize the synthesized AC-SB sorbent. Batch-type experiments were used to investigate the effect of various parameters on adsorption efficiency, including pH, metal-ion concentration, temperature, and contact time. The sorption experimental data have been described well with pseudo-second-order kinetic mathematical equations. The equilibrium state of the uptake reaction was 120 min. The Langmuir isotherm model accurately described the equilibrium process which declares that the uranium sorption is a monolayer and homogeneous process. The sorption capacity of the prepared AC was 32.7 mg g−1. Thermodynamic analysis explore that the U(VI) uptake process is endothermic, feasible and spontenous process. The displayed results demonstrate that the prepared AC-SB sorbent could be used as the proper material for uranium sorption from real matrix samples.

Hydrogenolysis of Lignin and C–O Linkages Containing Lignin-Related Compounds over an Amorphous CoRuP/SiO2 Catalyst

Efficient depolymerization of C–O linkages is essential for converting lignin into fuels and higher value-added chemicals. In this work, CoRuP/SiO2, an amorphous Ru-Co phosphide composite, was fabricated for the efficient hydrogenolysis of ether linkages. The 4–O–5 and α–O–4 linkages containing lignin-related compounds, such as diphenyl ether, benzyl phenyl ether, 3-methyl diphenyl ether, and dibenzyl ether, are selected as representatives of linkages in lignin. Under mild conditions, Ru-containing metallic phosphides have high-performance for the catalytic depolymerization of C–O linkages. Compared with other catalysts, CoRuP/SiO2 shows an outstanding selectivity for benzene and excellent efficiency in depolymerizing diphenyl ethers, yielding only a small amount of by-products. Furthermore, the total acidity shows a linear relationship with the hydrogenolysis reactivity in cleaving aromatic ether bonds. The mechanisms for the catalytic hydrogenolysis of 4–O–5 and α–O–4 bonds over CoRuP/SiO2 are proposed. Moreover, two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance spectroscopic analysis demonstrates that CoRuP/SiO2 could effectively depolymerize C–O bonds of lignin. These dominant hydrogenolysis products from lignin have excellent potential in the production of high value-added drugs or pharmaceutical intermediates. The hydrogenolysis of lignin can be a highly efficient alternative to the existing method of lignin utilization.

Closing the Carbon Loop in the Circular Plastics Economy

Today, plastics are ubiquitous in everyday life, problem solvers of modern technologies, and crucial for sustainable development. Yet the surge in global demand for plastics of the growing world population has triggered a tidal wave of plastic debris in the environment. Moving from a linear to a zero-waste and carbon-neutral circular plastic economy is vital for the future of the planet. Taming the plastic waste flood requires closing the carbon loop through plastic reuse, mechanical and molecular recycling, carbon capture, and use of the greenhouse gas carbon dioxide. In the quest for eco-friendly products, plastics do not need to be reinvented but tuned for reuse and recycling. Their full potential must be exploited regarding energy, resource, and eco efficiency, waste prevention, circular economy, climate change mitigation, and lowering environmental pollution. Biodegradation holds promise for composting and bio-feedstock recovery, but it is neither the Holy Grail of circular plastics economy nor a panacea for plastic littering. As an alternative to mechanical downcycling, molecular recycling enables both closed-loop recovery of virgin plastics and open-loop valorization, producing hydrogen, fuels, refinery feeds, lubricants, chemicals, and carbonaceous materials. Closing the carbon loop does not create a Perpetuum Mobile and requires renewable energy to achieve sustainability. This article is protected by copyright. All rights reserved.

Digital technologies and circular economy in supply chain management: in the era of COVID-19 pandemic

This empirical study aims to identify the importance of Digital Technologies (DT) as an enabler in the Circular Economy (C.E.) based business model, especially during Covid-19. The concept of 'circular economy' has now been advocated as a methodology to stimulate economic growth in line with the environmental sustainability. Hence, the practices of recycling, reduction, reuse/re-manufacture, and repairing (4R's) are deemed to be the core of a circular economy. Recently, the advent of the pandemic Covid-19 has forced the nations of the world to resort to alternate resource use in their manufacturing and trading of goods and services as the supply chains have almost remained disrupted since Covid-19 appeared. We investigate the impacts of Covid-19 upon the use of technological innovation (T.I.), circular economy practices (CEP), and organizational performance (ORP) incorporating the Structural Equation Modeling (SEM). Our results show that Covid-19 significantly impacted the adoption of technological innovation, circular economy, which leads toward organizational performance. Moreover, the practices and operations under the circular economy framework also appear to influence organizational performance significantly. Our study findings bring forward meaningful insights into improving CEF-cum-technology based practices in developing and emerging markets in Asia, and convey significant implications for the business community, policymakers, and researchers.

Sustainable Sorbitol Dehydration to Isosorbide using Solid Acid Catalysts: Transition from Batch Reactor to Continuous-Flow System

Isosorbide is one of the most interesting cellulosic-derived molecules with great potential to be implemented in wide range of products that shaping our daily life. This Review describes the recent developments in the production of isosorbide from sorbitol in batch and continuous-flow systems under hydrothermal conditions using solid acid catalysts. Moreover, the current hurdles and challenges regarding the synthesis of isosorbide from cellulosic biomass in continuous-flow process using solid acid catalysts are summarized, as well as the scaling-up of this process into pilot level, which will lead to an established industrial process with high sustainability metrics.

Valorization of agro-industrial biowaste to green nanomaterials for wastewater treatment: Approaching green chemistry and circular economy principles

Water pollution is one of the most critical issues worldwide and is a priority in all scientific agendas. Green nanotechnology presents a plethora of promising avenues for wastewater treatment. This review discusses the current trends in the valorization of zero-cost, biodegradable, and readily available agro-industrial biowaste to produce green bio-nanocatalysts and bio-nanosorbents for wastewater treatment. The promising roles of green bio-nanocatalysts and bio-nanosorbents in removing organic and inorganic water contaminants are discussed. The potent antimicrobial activity of bio-derived nanodisinfectants against water-borne pathogenic microbes is reviewed. The bioactive molecules involved in the chelation and tailoring of green synthesized nanomaterials are highlighted along with the mechanisms involved. Furthermore, this review emphasizes how the valorization of agro-industrial biowaste to green nanomaterials for wastewater treatment adheres to the fundamental principles of green chemistry, circular economy, nexus thinking, and zero-waste manufacturing. The potential economic, environmental, and health impacts of valorizing agro-industrial biowaste to green nanomaterials are highlighted. The challenges and future outlooks for the management of agro-industrial biowaste and safe application of green nanomaterials for wastewater treatment are summarized.

N-Doped Carbon Dot Hydrogels from Brewing Waste for Photocatalytic Wastewater Treatment

The brewery industry annually produces huge amounts of byproducts that represent an underutilized, yet valuable, source of biobased compounds. In this contribution, the two major beer wastes, that is, spent grains and spent yeasts, have been transformed into carbon dots (CDs) by a simple, scalable, and ecofriendly hydrothermal approach. The prepared CDs have been characterized from the chemical, morphological, and optical points of view, highlighting a high level of N-doping, because of the chemical composition of the starting material rich in proteins, photoluminescence emission centered at 420 nm, and lifetime in the range of 5.5-7.5 ns. With the aim of producing a reusable catalytic system for wastewater treatment, CDs have been entrapped into a polyvinyl alcohol matrix and tested for their dye removal ability. The results demonstrate that methylene blue can be efficiently adsorbed from water solutions into the composite hydrogel and subsequently fully degraded by UV irradiation.

Catalytic Pyrolysis of Lignin Model Compound (Ferulic Acid) over Alumina: Surface Complexes, Kinetics, and Mechanisms

Studies of the thermochemical properties of the important model compound of lignin-ferulic acid (FA) and its surface complexes are substantial for developing technologies for catalytic pyrolysis of renewable biomass into biofuels and lignin-derived chemicals as well as for bio-oil upgrading. In this work, the catalytic pyrolysis of ferulic acid over alumina was studied by temperature-programmed desorption mass spectrometry (TPD MS), in situ FT-IR spectroscopy, thermogravimetric analysis, and DFT calculations. We established that both the carboxyl group and the active groups (HO and CH3O) of the aromatic ring interact with the alumina surface. We calculated the kinetic parameters of formation of the main products of catalytic pyrolysis: 4-vinylguaiacol, guaiacol, hydroxybenzene, benzene, toluene, cresol, naphthalene, and PACs. Possible methods of their forming from the related surface complexes of FA are suggested.

Use of glycerol waste in lactic acid bacteria metabolism for the production of lactic acid: State of the art in Poland

Lactic acid is a naturally existing organic acid, which may be used in many different branches of industrial application. It can be made in the sugar fermentation process from renewable raw lactic acid, which is an indispensable raw material, including in the agricultural, food, and pharmaceutical industries. It is an ecological product that has enjoyed great popularity in recent years. In 2010, the US Department of Energy published a report about lactic acid to be a potential building element for future technology, whose demand grows year by year. The lactic acid molecule naturally exists in plants, microorganisms, and animals and can also be produced by carbohydrate fermentation or chemical synthesis from coal, petroleum products, and natural gas. In industry, lactic acid can be produced by chemical synthesis or fermentation. Although racemic lactic acid is always produced chemically from petrochemical sources, the optically pure L(+) – or D(−) – lactic acid forms can be obtained by microbial fermentation of renewable resources when an appropriate microorganism is selected. Depending on the application, one form of optically pure LA is preferred over the other. Additionally, microbial fermentation offers benefits including cheap renewable substrates, low production temperatures, and low energy consumption. Due to these advantages, the most commonly used biotechnological production process with the use of biocatalysts, i.e., lactic acid bacteria. The cost of raw materials is one of the major factors in the economic production of lactic acid. As substrate costs cannot be reduced by scaling up the process, extensive research is currently underway to find new substrates for the production of LA. These searches include starch raw materials, lignocellulosic biomass, as well as waste from the food and refining industries. Here, the greatest attention is still drawn to molasses and whey as the largest sources of lactose, vitamins, and carbohydrates, as well as glycerol – a by-product of the biodiesel component production process. Focusing on the importance of lactic acid and its subsequent use as a product, but also a valuable raw material for polymerization (exactly to PLA), this review summarizes information about the properties and applications of lactic acid, as well as about its production and purification processes. An industrial installation for the production of lactic acid is only planned to be launched in Poland. As of today, there is no commercial-scale production of this bio-raw material. Thus, there is great potential for the application of the lactic acid production technology and research should be carried out on its development.

Structure and Applications of Pectin in Food, Biomedical, and Pharmaceutical Industry: A Review

Pectin is a biocompatible polysaccharide with intrinsic biological activity, which may exhibit different structures depending on its source or extraction method. The extraction of pectin from various industrial by-products presents itself as a green option for the valorization of agro-industrial residues by producing a high commercial value product. Pectin is susceptible to physical, chemical, and/or enzymatic changes. The numerous functional groups present in its structure can stimulate different functionalities, and certain modifications can enable pectin for countless applications in food, agriculture, drugs, and biomedicine. It is currently a trend to use pectin to produce edible coating to protect foodstuff, antimicrobial bio-based films, nanoparticles, healing agents, and cancer treatment. Advances in methodology, use of different sources of extraction, and knowledge about structural modification have significantly expanded the properties, yields, and applications of this polysaccharide. Recently, structurally modified pectin has shown better functional properties and bioactivities than the native one. In addition, pectin can be used in conjunction with a wide variety of biopolymers with differentiated properties and specific functionalities. In this context, this review presents the structural characteristics and properties of pectin and information on the modification of this polysaccharide, its respective applications, perspectives, and future challenges.

Bibliographic mapping of post-consumer plastic waste based on hierarchical circular principles across the system perspective

The current dominating production and consumption model is based on the linear economy (LE) model, within which raw materials are extracted-processed-consumed-discarded. A circular economy (CE) constitutes a regenerative systemic approach to economic development which views waste as a valuable resource to be reprocessed back into the economy. In order to understand the circular strategy for a systemic change from an LE to a CE as a means of resolving the issue of plastic waste, this research aims to map current circular strategy trends across the system perspective contained in the literature relating to plastic CE literature. The novelty of the research lies in the mapping and review of the distribution of comprehensive circular strategies within the 9R framework across the entire system perspective (e.g. micro-meso-macro) down to its sub-levels in the literature on a plastic CE. The bibliographic mapping and systematic literature review iindicateed that the majority of the research focused on recycle (R8), followed by refuse (R0), reuse (R3), and reduce (R2). Certain circular strategies are more appropriate to handling certain plastic materials, despite CE's favoring of prevention and recycling over incineration. Recover (R9) is often used to process mixed and contaminated plastic. Recycling (R8) is the most popular circular strategy and the most applicable to plastic material with three recycle trends, namely; mechanical recycling, chemical recycling and DRAM (Distributed-Recycling-and-Additive-Manufacturing). Prolonging the product life through refurbishing (R5) is not applicable to plastic due to its material limitations. Reduce (R2) popularity as circular strategy reflects the preference to reduce consumption, either by launching campaigns to prevent waste or increasing production efficiency. Research on Rethink (R1) has largely focused on rethinking product design, consumer and organization behavior and perceptions of CE. Refuse (R0) strategy is an adoption of bio-based plastics which have a similar function to fossil-based plastics.

Brazilian açaí berry seeds: an abundant waste applied in the synthesis of carbon-based acid catalysts for transesterification of low free fatty acid waste cooking oil

Residues of açaí seeds (Euterpe oleracea Mart.) were a novel source for the synthesis of the acid heterogeneous catalyst applied in the conversion of low free fatty acid waste cooking oil (WCO) to biodiesel. Yield of activated carbon (AC) and catalyst (CAT), as well as density of SO₃H groups and total acidity, was analyzed in an entirely random designed experiment using multiple linear regression, one-way ANOVA, and Tukey's post hoc test. Time, temperature, dosage of KOH, and ratio of H₂SO₄/AC were the predictor variables with 3 levels each, at a significance level of α = .05. A significant yield variation portion of AC was explained by the experimental factors (R² = .891, F (3, 23) = 62.9, p < .0001), as did the yield of CAT (R² = .960, F (3, 23) = 185.7, p < .0001), density of SO₃H (R² = .969, F (3, 23) = 242.2, p < .0001), and total acidity (R² = .973, F (3, 23) = 280.6, p < .0001). Levels of time (p = .001) and KOH dosage (p = .006) were significant to the yield of AC, and temperature levels were not influent on density of SO₃H (p = .731) or total acidity (p = .762). CAT showed a S_BET of 249 m² g^-1, V_pore of 0.104 cm³ g^-1, low crystallinity, high thermal stability, and a mesoporous amorphous structure. Optimized catalytic tests resulted in 89% conversion of WCO and 11 cycles of reuse, better than pure H₂SO₄ or pure KOH (p < .0001) and also better than many biomass-derived catalysts reported in the literature.

The Limonene Biorefinery: From Extractive Technologies to Its Catalytic Upgrading into p-Cymene

Limonene is a renewable cyclic monoterpene that is easily obtainable from citrus peel and it is commonly used as a nutraceutical ingredient, antibacterial, biopesticide and green extraction solvent as well as additive in healthcare, fragrance and food and beverage industries for its characteristic lemon-like smell. Indeed, the lack of toxicity makes limonene a promising bio-alternative for the development of a wide range of effective products in modern biorefineries. As a consequence, industrial demand largely exceeds supply by now. Limonene can be also used as starting substrate for the preparation of building block chemicals, including p-cymene that is an important intermediate in several industrial catalytic processes. In this contribution, after reviewing recent advances in the recovery of limonene from citrus peel and residues with particular attention to benign-by-design extractive processes, we focus on the latest results in its dehydrogenation to p-cymene via heterogeneous catalysis. Indeed, the latest reports evidence that the selective production of p-cymene still remains a scientific and technological challenge since, in order to drive the isomerization and dehydrogenation of limonene, an optimal balance between the catalyst nature/content and the reaction conditions is needed.

Exploiting Nature's Most Abundant Polymers: Developing New Pathways for the Conversion of Cellulose, Hemicellulose, Lignin and Chitin into Platform Molecules (and Beyond)

The four most prominent forms of biomass are cellulose, hemicellulose, lignin and chitin. In efforts to develop sustainable sources of platform molecules there has been an increasing focus on examining how these biopolymers could be exploited as feedstocks that support the chemical supply chain, including in the production of fine chemicals. Many different approaches are possible and some of the ones being developed in the authors' laboratories are emphasised.

Unveiling Modifications of Biomass Polysaccharides during Thermal Treatment in Cholinium Chloride : Lactic Acid Deep Eutectic Solvent

A deep analysis upon the chemical modifications of the cellulose and hemicelluloses fractions that take place during biomass delignification with deep eutectic solvents (DES) is lacking in literature, being this a critical issue given the continued research on DES for this purpose. This work intends to fill this gap by disclosing a comprehensive study on the chemical modifications of cellulose (microcrystalline cellulose and bleached kraft pulp) and hemicelluloses (xylans) during thermal treatment (130 °C) with cholinium chloride/lactic acid ([Ch]Cl/LA) at molar ratio 1 : 10, one of the best reported DES for biomass delignification. The obtained data revealed that [Ch]Cl/LA (1 : 10) has a negative impact on the polysaccharides fractions at prolonged treatments (>4 h), resulting on substantial modifications including the esterification of cellulose with lactic acid, shortening of fibers length, fibers agglomeration and side reactions of the hemicelluloses fraction (e. g., humin formation, lactic acid grafting). Wood delignification trials with [Ch]Cl/LA (1 : 10) at the same conditions also corroborate these findings. Moreover, the DES suffers degradation, including the formation of lactic acid derivatives and its polymerization. Therefore, short time delignification treatments are strongly recommended when using the [Ch]Cl/LA DES, so that a sustainable fractionation of biomass into high quality cellulose fibers, isolated lignin, and xylose/furfural co-production along with solvent recyclability could be achieved.

Covalent organic frameworks as emerging host platforms for enzyme immobilization and robust biocatalysis - A review

In recent years, the synthesis and application of green and sustainable products have become global ecological and societal issues. Based on the principles of green chemistry, the application of different biocatalysts not only produce target products and decreases side effects but also enhances the selectivity and activity. Enzyme-based biocatalysts are very interesting due to their high catalytic performance, eco-friendly reaction systems, and selectivity. Immobilization is demonstrated as a favorable approach to improve the stability and recyclability of enzymes. Among different supports, porous and crystalline materials, covalent organic frameworks (COFs), represent an interesting class of support matrices for the immobilization of different enzymes. Owing to tunable physicochemical characteristics, a high degree of crystallinity, large specific surface area, superior adsorption capacity, pre-designable structure and marked stability, COFs might consider as perfect host materials for improving the desirable properties of enzymes, such as poor stability, low operational range, lack of repeatability, and products/by-products inhibition for large-scale applications. The enzyme-incorporated COFs have emerged as one of the hopeful ways to constitute tailor-made biocatalytic systems, which can be employed in an array of reactions. Highly porous nature of many COFs led to increased process output in contrast to other micro/nanoparticles. The enzymes can be integrated into COFs through different techniques, including physical adsorption and direct covalent attachment between the enzyme molecules and COFs or through a cross-linking agent. Herein, we discuss and highlight the synthesis methods, properties, and functionalization of COFs and the recent literature for the application of these materials in enzymes immobilization. Main approaches for immobilization of enzymes into COFs and the catalytic applications of these materials are also presented. This study offers new avenues to address the limitations of traditional enzyme immobilization supports as well as delivers new possibilities to construct smart biocatalytic systems for diverse biotechnological applications.

Catalytic Oxidations in a Bio-Based Economy

The role of bio- and chemo-catalytic aerobic oxidations in the production of commodity chemicals in a bio-refinery is reviewed. The situation is fundamentally different to that in a petrochemicals refinery where the feedstocks are gaseous or liquid hydrocarbons that are oxidized at elevated temperatures in the vapor or liquid phase under solvent-free conditions. In contrast, the feedstocks in a biorefinery are carbohydrates that are water soluble solids and their conversion will largely involve aerobic oxidations of hydroxyl functional groups in water as the solvent under relatively mild conditions of temperature and pressure. This will require the development and use of cost-effective and environmentally attractive processes using both chemo- and biocatalytic methods for alcohols and polyols.

Tuneable Acidity in Fluorinated Al-SBA-15 Materials for the Esterification of Valeric Acid to Alkyl Valerates

The acidity of Al-SBA-15 materials functionalized by ball milling with several niobium loadings (0. 25-1 wt.%) as well as with several fluorine loadings (by wet impregnation using NH₄F as a precursor) was characterized and materials investigated in the esterification of valeric acid to alkyl valerates. The parent Al-SBA-15 support as well as the modified materials loaded with Nb and/or F have been catalysts synthesized characterized by X-ray diffraction (XRD), N₂ physisorption measurements, and diffuse reflection infrared spectroscopy (DRIFT) among others. A special interest was paid on the acidity of the materials that was investigated by temperature-programmed desorption of pyridine. Interestingly, the characterization results for the materials containing fluorine showed up an increase in the acidity strength despite of a reduction in the number of acid sites. The catalytic performance of the as-prepared catalysts was investigated in the microwave-assisted esterification reaction of valeric acid to valerate esters. Thus, while the materials modified with niobium exhibited a lower catalytic activity as compared with the catalytic support (Al-SBA-15), the materials loaded with fluorine either onto Al-SBA-15 or on Nb1%/Al-SBA-15 materials presented enhanced conversion values of valeric acid. Therefore, it can be said that the new acid sites with enhanced strength formed by the incorporation of fluorine boost the esterification of valeric acid with alcohols to form the respective valerate ester.

Catalytic Pyrolysis of Aliphatic Carboxylic Acids into Symmetric Ketones over Ceria-Based Catalysts: Kinetics, Isotope Effect and Mechanism

Ketonization is a promising way for upgrading bio-derived carboxylic acids from pyrolysis bio-oils, waste oils, and fats to produce high value-added chemicals and biofuels. Therefore, an understanding of its mechanism can help to carry out the catalytic pyrolysis of biomass more efficiently. Here we show that temperature-programmed desorption mass spectrometry (TPD-MS) together with linear free energy relationships (LFERs) can be used to identify catalytic pyrolysis mechanisms. We report the kinetics of the catalytic pyrolysis of deuterated acetic acid and a reaction series of linear and branched fatty acids into symmetric ketones on the surfaces of ceria-based oxides. A structure–reactivity correlation between Taft’s steric substituent constants Es* and activation energies of ketonization indicates that this reaction is the sterically controlled reaction. Surface D3-n-acetates transform into deuterated acetone isotopomers with different yield, rate, E≠, and deuterium kinetic isotope effect (DKIE). The obtained values of inverse DKIE together with the structure–reactivity correlation support a concerted mechanism over ceria-based catalysts. These results demonstrate that analysis of Taft’s correlations and using simple equation for estimation of DKIE from TPD-MS data are promising approaches for the study of catalytic pyrolysis mechanisms on a semi-quantitative level.

Is Green Chemistry a feasible tool for the implementation of a circular economy?

The main goal of this research is to evaluate the contributions of Green Chemistry as a potential tool to drive the transition to circularity. For this, we have carried out a bibliographic study, analyzing those documents, process, or experiences that dealt jointly with the Green Chemistry aspects related to circularity such circular economy, industrial ecology, and closed loop. Findings show that few authors have treated that disciplines together in the last 10 years. Based on an analysis of academic literature, common strategies (design, raw materials, life cycle assessment, processes, normative, new business, and collaboration), specific experiences (catalyst, biobased products or methods, recycling, and reusing), and difficulties to overcome (metrics, transdisciplinary research, unawareness, and competitiveness) have been identified. Finally, different kind of measures, as behind such joint metrics, informal open spaces, closer the industry, education, standards and label are proposed to facilitate the development of Green Chemistry, circular economy, industrial ecology, and closed loop with the ultimate goal of improving sustainable development.From the evidences found, we finally conclude that it is possible to use Green Chemistry and its principles as a tool to drive the transition to circularity, being the development of open spaces for exchange information between different actors from academia, governments and regulatory actors, business and industrial sectors, with the aim of promoting disruptive advances in sustainability.

Preparation and Modification of Biomass-Based Functional Rubbers for Removing Mercury(II) from Aqueous Solution

Biomass-based functional rubber adsorbents were designed and prepared via inverse vulcanization and post-modification. The plant rubber was synthesized with sulfur and renewable cottonseed oil as well as various micromolecular modifiers with nitrogen-containing functional groups. Results showed that types of nitrogen-containing functional groups and dosages of modifiers had a significant impact on the adsorption capacities of the resulting polymers for Hg2+. Notably, when the mass ratio of 2-aminoethyl methacrylate (AEMA) to sulfur was 0.05, the resulting polymer polysulfide-co-cottonseed oil modified by AEMA (SCOA2) showed the highest adsorption capacity (343.3 mg g-1) among all the prepared samples. Furthermore, the Hg2+ removal efficiency of SCOA2 remained over 80% of its original value after five adsorption-desorption cycles. It demonstrated a promising case for utilizing cheap industrial by-products (sulfur) and renewable materials (cottonseed oil). The prepared functional rubber provides alternative approach for mercury removal in waste utilization and sustainable chemistry.

Identifying the roles of acid–base sites in formation pathways of tolualdehydes from acetaldehyde over MgO-based catalysts

Basic (M–O)-type centers convert C₄ intermediates to renewable xylene analogs and proximal acid sites tune isomeric selectivity.