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CHAPTER 1
Principles of Green Chemistry and White Biotechnology
BERNARDO DIAS RIBEIRO, MARIA ALICE Z. COELHO, AND ALINE MACHADO DE CASTRO
1.1 Green Chemistry: Could Chemistry be Greener?
Since the Second World War, world industrialization has been accelerated without caring about its effects on the environment, and peoples' safety and health. This has led to increased global warming, depletion of the ozone protective layer which protects against harmful UV radiation, contamination of land and waterways due to the release of toxic chemicals by industry, and the reduction of nonrenewable resources such as petroleum. Nevertheless, there is a growing awareness amongst end-users of the risks that chemicals are often associated with, and of the need to dissociate themselves from any chemical in their supply chain that is recognized as being hazardous.
In the 1990s, the idea of developing new or improving existing chemical products and processes to make them less hazardous to human health and the environment had already been contemplated. Initially, in 1991, the Office of Pollution Prevention and Toxics (OPPT) of the United States launched a research grant program named "Alternative Synthetic Pathways for Pollution Prevention". In 1993, the program was expanded to include other topics, such as greener solvents and safer chemicals, and was renamed "Green Chemistry".
Nowadays, green chemistry has as main objective the promotion of innovative chemical technologies that reduce or eliminate the use or generation of hazardous substances in the design, manufacture, and use of chemical products, meaning the use of more environmentally acceptable chemical processes and products.
In 1998, Paul Anastas and Warner announced a set of 12 principles as a useful guide for designing environmentally benign products and processes or to evaluate already existing processes, and in 2003, this promulgated another 12 principles on Green Engineering, which correlates Chemical Engineering with Green Chemistry, aiming to achieve sustainability (in the three dimensions: ecological, economic and social), maximize efficiency, minimize waste and increase profitability, as shown in Table 1.1.
To achieve greener chemical processes, besides the more intensive use of renewable feedstocks, several technologies have been developed, some old and some new, which are becoming proven clean technologies, such as the use of alternative solvents (supercritical fluids, ionic liquids, fluorous liquids), non-thermal energetic sources (microwaves, ultrasounds, electrical fields, solar energy), environmentally-friendly separation processes such as membranes (ultrafiltration, nanofiltration and pervaporation), and biological catalysts, such as micro-organisms and enzymes, allowing the creation of more energy-efficient processes.
1.2 White Biotechnology
Biotechnology is a very broad area which embraces five main sectors:
Blue Biotechnology – Also known as Marine and Fresh-water Biotechnology, this sector includes bioprospecting in marine environments and the use of molecular biology and microbial ecology tools in marine organisms.
Green Biotechnology – Is the biotechnology for agricultural applications. As input, plants are genetically modified to have resistance to insects or diseases, and as outputs, plants present improved agronomic behavior (yield, withstanding environmental stress) and can be used as green factories.
Red Biotechnology – Is the area that focuses on humans and is used to develop alternative solutions to medical problems and issues from diagnosis to therapy. Also named Pharmaceutical Biotechnology.
White Biotechnology – Related to the use of living cells (yeasts, molds, bacteria, plants) and enzymes to synthesize products at industrial scale. Also known as Industrial Biotechnology.
Yellow Biotechnology – Also known as Insect Biotechnology, this emerging field in applied entomology covers the use of insects in drug discovery, their study for plant defense, and the use of insects as a source of enzymes and cells for biotransformations and as a source of biosensors for online detection of compounds at industrial scale. Therefore, this area interacts with White and Green Biotechnology areas.
Enzymes are classified into 6 classes (as described below) and they receive a classification number, based on their class, subclass and the specific chemical groups participating in the reaction.
1. Oxidoreductases: All enzymes catalyzing oxidoreduction reactions belong to this class. The substrate that is oxidized is regarded as a hydrogen donor.
2. Transferases: Transferases are enzymes which catalyze the transfer of a group, e.g. a methyl group or a glycosyl group, from one compound (generally regarded as a donor) to another compound (generally regarded as an acceptor).
3. Hydrolases: These enzymes catalyze the hydrolytic cleavage of C–O, C–N, C–C and some other bonds, including phosphoric anhydride bonds.
4. Lyases: Enzymes catalyzing the cleavage of C–C, C–O, C–N, and other bonds by elimination, leaving double bonds or rings, or conversely adding groups to double bonds.
5. Isomerases: These enzymes catalyze geometric or structural changes within one molecule.
6. Ligases: Enzymes that catalyze the linkage of two molecules, coupled with the hydrolysis of a diphosphate bond in ATP or a similar triphosphate.
White biotechnology is a continuously growing sector, with an average annual growth in the period 2007–2012 of 10.4%. The industry embraces the large-scale production of molecules for several sectors, such as: fertilisers and gases, organic chemicals, polymers and fibers, agrochemicals, adhesives and sealants, paints and coatings, food additives, detergents, cosmetics, active pharma ingredients, as well as the enzymes involved in the production of final molecules, such as in textiles processing, beverages, foods, biofuels and pulp and paper.
The worldwide market for white biotechnology involved transactions on the order of &8364;92 billion in 2010. In late 2011, it was estimated that sales would increase to around &8364;228 billion in 2015 and to around &8364;515 billion in 2020. Specifically, in the field of enzyme catalysis, the global estimated market size of enzymes in 2010 was USD2.82 billion, with food and feed being the major end-user market (USD1.19 billion) and textiles the fastest growing end-user market (4.99%). In 2010, carbohydrases (hydrolases acting on carbohydrates) were the fastest growing product segment (7.6%), and proteases alone accounted for 48% (USD1.35 billion) of the total enzyme market. Additionally, lipases, a group of enzymes of paramount importance in green processes, have also shown growth in their market, which increased from USD235 million in 2001 to USD429 million in 2010, mainly focused on the production of pharmaceuticals, foods and beverages and cleaning products. The projected global market for lipases in 2015 is USD634 million.
Enzyme-catalyzed reactions are indicated to be very promising to meet green chemistry criteria. In the context of the principles of green chemistry, catalysts as a whole provide not only a solution for the problem of waste, but additionally create more energy efficient and less raw material consuming processes. Biocatalysts, specifically, present some positive points: they can act as non-toxic catalysts; they generally operate with high selectivity, yielding high product purity; they operate under moderate reaction conditions at near ambient temperature, pressure and pH, thus resulting in reduced energy consumption; the reaction medium is commonly aqueous, which per se is considered non-toxic; biocatalysts have the potential to prevent high consumption of metals and organic solvents; as natural catalysts, enzymes can be considered as renewable catalysts. It should be highlighted, however, that even for biocatalytic processes, each procedure must be evaluated for its environmental friendliness and economic feasibility. Some important remarks on the use of biocatalysts in industrial processes are given in Table 1.2.
1.3 Concluding Remarks
With the above considerations, the interaction between green chemistry and white biotechnology will have a relevant role in the construction of a new industrial concept based on technologies (described herein in this book) that, in the near future, will become the basis of a new paradigm. Some examples of the development of sustainable production processes based on such principles can be seen nowadays all over the world. They can help to save energy and the environment.
Especially concerning to Brazil, it is generally recognized that the country has competitive advantages related to: the available area and favorable climate; the efficient production of biomass (sugar cane, eucalyptus, soy, etc.); the pioneering production of biofuels on a large scale; the productivity of agriculture which grew at twice the global average from 2001 to 2009, and it is the country with the highest biodiversity in the world, through the multiplicity of species and habitats.
Nevertheless, improvement in bioprocess efficiency needs considerable effort before bioprocesses can be considered a serious alternative to petrochemical industrial processes. Challenges related to the conversion of sugars contained in biomass into the required compounds as effectively as possible will lead to new biocatalyst characteristics, as well as novel operation strategies.
CHAPTER 2
Sustainability, Green Chemistry and White Biotechnology
ROGER A. SHELDON
2.1 Introduction to Green Chemistry and Sustainability
The roots of industrial organic synthesis can be traced back to the preparation of the first synthetic dye, mauveine (aniline purple) by Perkin in 1856. This serendipitous discovery (Perkin's goal was the synthesis of the anti-malarial drug, quinine) marked the advent of the synthetic dyestuffs industry based on coal tar, a waste product from steel manufacture. The modern pharmaceutical and allied fine chemical industries evolved as spin-offs of this industry. The target molecules were initially relatively simple, but in the ensuing decades they became increasingly complicated, as exemplified by the introduction of semi-synthetic beta-lactam antibiotics and steroid hormones in the 1940s and 1950s. To meet this and subsequent challenges, synthetic organic chemists have developed increasingly sophisticated methodologies. However, many of these time-honoured and widely applied synthetic methodologies were developed at a time when the toxic properties of many reagents and solvents were not known and waste minimisation and sustainability were not significant issues.
The publication of Rachel Carson's "Silent Spring" in 1962 and Barry Commoner's "The Closing Circle" in 1971 focused the attention of the general public on the problem of the negative side effects of the products of the chemical industry on our natural environment. This formed the basis for the environmental movement. Chemistry was perceived to be the source of the problem rather than as the means to a solution to it. However, the solution to the environmental problem is not a world without chemistry, but one with new and better chemistry that produces environmentally friendly products without the use or generation of hazardous and/or toxic substances. Another watershed was the publication in 1987 of the report "Our Common Future" by the World Commission on Environment and Development, otherwise known as the Brundtland report. This report recognised that industrial and societal development were necessary to provide a growing global population with a satisfactory quality of life, but that such development must also be sustainable over time. In the following decades, the concept of sustainability became the focus of considerable attention both in industry and in society as a whole. There is even a sustainability index (http://www.djindexes. com/sustainability/) that ranks companies on the basis of their sustainability performance. For example, the 2012 supersector leader for Chemicals in the Dow Jones Sustainability Index is Akzo Nobel (Netherlands). Furthermore, 2005–2014 was declared by the United Nations as the "Decade of Education for Sustainable Development".
Sustainable development is defined as development that meets the needs of the present generation without compromising the needs of future generations to meet their own needs. As Graedel has pointed out, it is based on two central tenets: (i) using natural resources at rates that do not unacceptably deplete supplies over the long term and (ii) generating and dissipating residues at rates no higher than can be assimilated readily by the natural environment. Sustainability consists of three components: societal, ecological and economic, otherwise referred to as the three Ps: people, planet and profit. One important issue from the viewpoint of the chemical and allied industries is the sustainable use of chemical feedstocks. It is abundantly clear that a society based on non-renewable fossil resources – oil, coal and natural gas – is not sustainable over the longer term. However, it is worth pointing out that 97% of crude oil is processed to fuels and only ca. 3% serves as a feedstock for chemicals manufacture.
At roughly the same time that the concept of sustainable development was emerging, in the mid-1980s, there was mounting concern regarding the copious amount of waste being generated by many industrial chemical processes, particularly in the fine chemicals and pharmaceuticals industries. An illustrative example is provided by the manufacture of phloroglucinol, a reprographic chemical and pharmaceutical intermediate. Up until the mid-1980s, it was produced mainly from 2,4,6-trinitrotoluene (TNT) by the process shown in Figure 2.1, a perfect example of vintage nineteenth century organic chemistry.
The phloroglucinol product is obtained in >90% overall yield over the three reaction steps and, according to classical concepts of selectivity and reaction efficiency, would generally be considered to be a selective and efficient process. However, for every kilogram of phloroglucinol produced, ca. 40 kg of solid waste, containing Cr2(SO4)3, NH4Cl, FeCl2 and KHSO4 are formed. This process was eventually discontinued because of the prohibitive costs associated with the disposal of the chromium-containing waste. It is immediately clear, from an examination of the reaction stoichiometry, that this largely inorganic waste is a consequence of the use of inorganic reagents in stoichiometric amounts. The reaction stoichiometry predicts the formation of ca. 20 kg of waste per kilogram of phloroglucinol, assuming 100% chemical yield and exactly stoichiometric quantities of the various reagents. The observed formation of 40 kg of waste in practice is a direct consequence of the use of an excess of the oxidant and reductant and a large excess of sulfuric acid, which has to be subsequently neutralised with base, and an isolated yield of phloroglucinol of less than 100%.
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