Metrics of Green Chemistry and Sustainability: Past, Present, and Future

The first green chemistry metrics - the E factor (kgs waste/kg product) and atom economy (mol wt of product/sum of mol wts of starting materials) - were introduced in the early 1990s and were actually green chemistry avant la lettre. In the last two decades, these two metrics have been adopted worldwide by both academia and industry. The E factor has been refined to distinguish between simple and complete E factors, for example, and to define the system boundaries. Other mass-based metrics such as process mass intensity (PMI) and reaction mass efficiency (RME) have been proposed. However, mass-based metrics need to be augmented by metrics which measure the environmental impact of waste, such as life cycle assessment (LCA), and metrics for assessing the economic viability of products and processes. The application of such metrics in measuring the sustainability of processes for the manufacture of pharmaceuticals and other fine chemicals is discussed in detail. Mass-based metrics alone are not sufficient to measure the greenness and sustainability of processes for the conversion of renewable biomass vs fossil-based feedstocks. Various metrics for use in assessing sustainability of the manufacture of basic chemicals from renewable biomass are discussed. The development of a sustainable biobased production of chemicals meshes well with the concept of a circular economy, based on resource efficiency and waste minimization by design, to replace traditional linear, take-make-use-dispose economies.Accepted Author ManuscriptBT/Biocatalysi

Biocatalysis in ionic liquids: State-of-the-union

This perspective reviews the current status and prospects of biocatalysis in ionic liquids. Although they are not strictly speaking ionic liquids, deep eutectic solvents are included because of the close similarities of their properties and potential applications with those of ionic liquids. One consequence of the ongoing transition from an economy based on fossil resources to a circular economy based on renewable biomass is the burgeoning interest in the use of biocatalysis for the selective conversion of carbohydrates and triglycerides to liquid fuels and chemicals in biorefineries. The use of inexpensive, environmentally attractive ionic liquids as solvents, in the pre-treatment and subsequent biocatalytic conversions, for example, is expected to play an important enabling role in this process.Accepted Author ManuscriptBT/Biocatalysi

E Factors, Green Chemistry and Catalysis: Records of the Travelling Chemist

Applied Science

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.BT/Biocatalysi

Chemicals from renewable biomass: A renaissance in carbohydrate chemistry

The conversion of sugars, derived from waste polysaccharide biomass, to commodity chemicals by fermentation or catalytic hydrogenation, oxidation or dehydration or combinations thereof are reviewed.Accepted Author ManuscriptBT/Biocatalysi

Cross-linked enzyme aggregates (CLEAs): Stable and recyclable biocatalysts

The key to obtaining an optimum performance of an enzyme is often a question of devising an effective method for its immobilization. In the present review, we describe a novel, versatile and effective methodology for enzyme immobilization as CLEAs (cross-linked enzyme aggregates). The method is exquisitely simple (involving precipitation of the enzyme from aqueous buffer followed by cross-linking of the resulting physical aggregates of enzyme molecules) and amenable to rapid optimization. We have shown it to be applicable to a wide variety of enzymes, including, in addition to a wide variety of hydrolases, lyases, e.g. nitrile hydratases and oxynitrilases, and oxidoreductases such as laccase and galactose oxidase. CLEAs are stable, recyclable catalysts exhibiting high catalyst productivities. Because the methodology is essentially a combination of purification and immobilization into one step, the enzyme does not need to be of high purity. The technique is also applicable to the preparation of combi-CLEAs, containing two or more enzymes, for use in one-pot, multistep syntheses, e.g. an oxynitrilase/nitrilase combi-CLEA for the one-pot conversion of benzaldehyde into (S)-mandelic acid, in high yield and enantiomeric purity.BiotechnologyApplied Science

The Road to Biorenewables: Carbohydrates to Commodity Chemicals

The pressing need for climate change mitigation has focused attention on reducing global emissions of carbon dioxide by effectuating the transition from fossil-based chemicals manufacture to a carbon neutral alternative based on lignocellulosic waste. The first step involves fractionation of the lignocellulose into cellulose, hemicellulose, and lignin. Subsequently, a cellulase enzyme cocktail is used to catalyze the hydrolysis of the polysaccharides into their constituent sugars. This is followed by selective conversion of the carbohydrates into commodity chemicals using a variety of sustainable bio- and chemocatalytic methodologies. These include, inter alia, fermentative production of alcohols, diols, and carboxylic acids and a variety of chemocatalytic reductions and oxidations. Hence, the transition from fossil feedstocks to lignocellulose represents a switch from hydrocarbons to carbohydrates as the primary basic chemicals. To compare these renewable biomass-based routes with their petrochemical equivalents, it is necessary to develop reliable sustainability metrics.Accepted Author ManuscriptBT/Biocatalysi

Biocatalysis and biomass conversion: Enabling a circular economy

Two of the grand societal and technological challenges of the twenty first century are the 'greening' of chemicals manufacture and the ongoing transition to a bio-based economy: that is a sustainable, carbon-neutral economy based on renewable biomass as the raw material. These challenges are motivated by the need to eliminate environmental degradation and mitigate climate change. Waste minimisation and waste valorisation in a circular economy constitute a point of overlap of these grand challenges. In a bio-based economy, ideally waste biomass, particularly agricultural and forestry residues and food supply chain waste, are converted to liquid fuels, commodity chemicals, and biopolymers by employing clean, catalytic processes.Biocatalysis has the right credentials to achieve this goal. Enzymes are biocompatible (sometimes even edible), biodegradable and essentially non-hazardous. Additionally, they are derived from inexpensive renewable resources which are readily available and not subject to the large price fluctuations which undermine the long term commercial viability of catalysts derived from scarce precious metals. Moreover, thanks to spectacular advances in molecular biology the landscape of biocatalysis has dramatically changed in the last two decades. Developments in (meta)genomics in combination with 'big data' analysis have revolutionised new enzyme discovery and developments in protein engineering by directed evolution have enabled dramatic improvements in their performance. These developments have their confluence in the bio-based circular economy.BT/Biocatalysi

The E factor at 30: a passion for pollution prevention

The introduction of the E Factor in 1992 focussed attention on the problem of waste generation, defined as everything but the desired product, in chemicals manufacture and gave rise to a paradigm shift in our concept of efficiency in chemical processes, from one based solely on chemical yield to one that assigns value to eliminating waste. Thirty years later, it has become clear that waste is the underlying cause of the major global environmental problems, from climate change to plastic pollution and that the solution to this ubiquitous waste problem is pollution prevention at source enabled by green and sustainable chemistry. The role played by (bio)catalysis, alternative solvents, the emergence of a carbon neutral circular economy based on renewable resources and the electrification of chemicals manufacture based on renewable energy in the drive towards pollution prevention and sustainable industries is delineated.BT/Biocatalysi

Cleas, combi-cleas and ‘smart’ magnetic cleas: Biocatalysis in a bio-based economy

Biocatalysis has emerged in the last decade as a pre-eminent technology for enabling the envisaged transition to a more sustainable bio-based economy. For industrial viability it is essential that enzymes can be readily recovered and recycled by immobilization as solid, recyclable catalysts. One method to achieve this is via carrier-free immobilization as cross-linked enzyme aggregates (CLEAs). This methodology proved to be very effective with a broad selection of enzymes, in particular carbohydrate-converting enzymes. Methods for optimizing CLEA preparations by, for example, adding proteic feeders to promote cross-linking, and strategies for making the pores accessible for macromolecular substrates are critically reviewed and compared. Co-immobilization of two or more enzymes in combi-CLEAs enables the cost-effective use of multiple enzymes in biocatalytic cascade processes and the use of “smart” magnetic CLEAs to separate the immobilized enzyme from other solids has raised the CLEA technology to a new level of industrial and environmental relevance. Magnetic-CLEAs of polysaccharide-converting enzymes, for example, are eminently suitable for use in the conversion of first and second generation biomass.BT/Biocatalysi