CHAPTER 1: Principles of Green Chemistry and White Biotechnology
-
Published:30 Nov 2015
-
Series: Green Chemistry Series
B. D. Ribeiro, M. A. Z. Coelho, and A. Machado de Castro, in White Biotechnology for Sustainable Chemistry, ed. M. A. Coelho and B. D. Ribeiro, The Royal Society of Chemistry, 2015, pp. 1-8.
Download citation file:
White Biotechnology can be regarded as Applied Biocatalysis, with enzymes and microorganisms, aiming at industrial production from bulk and fine chemicals to food and animal feed additives. In your turn, Biocatalysis has many attractive features in the context of Green Chemistry: mild reaction conditions (physiological pH and temperature), environmentally compatible catalysts and solvent (often water) combined with high activities and chemo-, regio- and stereoselectivities in multifunctional molecules. This affords processes which are shorter, generate less waste and are, therefore, both environmentally and economically more attractive than conventional routes. The objective of this chapter is to comprise a brief introduction of the classification of biotechnology areas, including white biotechnology, as well as present enzyme classification and markets, and green chemistry principles, which are the basis of this book.
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.1,2
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”.3
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.1,4,5
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,4 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,5,6 as shown in Table 1.1.
Comparative framework of principles of Green Chemistry and Green Engineering
Green Chemistry . | Green Engineering . | |
---|---|---|
1. Prevention: It is better to prevent waste than to treat or clean up waste after it has been created | 1. Inherent rather than circumstantial: Designers need to strive to ensure that all materials and energy inputs and outputs are as inherently nonhazardous as possible | |
2. Atom economy: Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product | 2. Prevention instead of treatment: It is better to prevent waste than to treat or clean up waste after it is formed | |
3. Less hazardous chemical syntheses: Wherever practicable, synthetic methods should be designed to use and generate substances that present low or no toxicity to human health and the environment | 3. Design for separation: Separation and purification operations should be designed to minimize energy consumption and materials use | |
4. Designing safer chemicals: Chemical products should be designed to effect their desired function while minimizing their toxicity | 4. Maximize efficiency: Products, processes, and systems should be designed to maximize mass, energy, space, and time efficiency | |
5. Safer solvents and auxiliaries: The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary whenever possible and should be innocuous when used | 5. Output-pulled versus input-pushed: Products, processes, and systems should be “output pulled” rather than “input pushed” through the use of energy and materials | |
6. Design for energy efficiency: Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure | 6. Conserve complexity: Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse, or beneficial disposition | |
7. Use of renewable feedstocks: A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable | 7. Durability rather than immortality: Targeted durability, not immortality, should be a design goal | |
8. Reduce derivatives: Unnecessary derivatization (use of blocking groups, protection/deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste | 8. Meet need, minimize excess: Design for unnecessary capacity or capability (e.g., “one size fits all”) solutions should be considered a design flaw | |
9. Catalysis: Catalytic reagents (as selective as possible) are superior to stoichiometric reagents | 9. Minimize material diversity: Material diversity in multicomponent products should be minimized to promote disassembly and value retention | |
10. Design for degradation: Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment | 10. Integrate material and energy flows: Design of products, processes, and systems must include integration and interconnectivity with available energy and materials flows | |
11. Real-time analysis for pollution prevention: Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances | 11. Design for commercial “afterlife”: Products, processes, and systems should be designed for performance in a commercial “afterlife” | |
12. Inherently safer chemistry for accident prevention: Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires | 12. Renewable rather than depleting: Material and energy inputs should be renewable rather than depleting |
Green Chemistry . | Green Engineering . | |
---|---|---|
1. Prevention: It is better to prevent waste than to treat or clean up waste after it has been created | 1. Inherent rather than circumstantial: Designers need to strive to ensure that all materials and energy inputs and outputs are as inherently nonhazardous as possible | |
2. Atom economy: Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product | 2. Prevention instead of treatment: It is better to prevent waste than to treat or clean up waste after it is formed | |
3. Less hazardous chemical syntheses: Wherever practicable, synthetic methods should be designed to use and generate substances that present low or no toxicity to human health and the environment | 3. Design for separation: Separation and purification operations should be designed to minimize energy consumption and materials use | |
4. Designing safer chemicals: Chemical products should be designed to effect their desired function while minimizing their toxicity | 4. Maximize efficiency: Products, processes, and systems should be designed to maximize mass, energy, space, and time efficiency | |
5. Safer solvents and auxiliaries: The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary whenever possible and should be innocuous when used | 5. Output-pulled versus input-pushed: Products, processes, and systems should be “output pulled” rather than “input pushed” through the use of energy and materials | |
6. Design for energy efficiency: Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure | 6. Conserve complexity: Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse, or beneficial disposition | |
7. Use of renewable feedstocks: A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable | 7. Durability rather than immortality: Targeted durability, not immortality, should be a design goal | |
8. Reduce derivatives: Unnecessary derivatization (use of blocking groups, protection/deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste | 8. Meet need, minimize excess: Design for unnecessary capacity or capability (e.g., “one size fits all”) solutions should be considered a design flaw | |
9. Catalysis: Catalytic reagents (as selective as possible) are superior to stoichiometric reagents | 9. Minimize material diversity: Material diversity in multicomponent products should be minimized to promote disassembly and value retention | |
10. Design for degradation: Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment | 10. Integrate material and energy flows: Design of products, processes, and systems must include integration and interconnectivity with available energy and materials flows | |
11. Real-time analysis for pollution prevention: Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances | 11. Design for commercial “afterlife”: Products, processes, and systems should be designed for performance in a commercial “afterlife” | |
12. Inherently safer chemistry for accident prevention: Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires | 12. Renewable rather than depleting: Material and energy inputs should be renewable rather than depleting |
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.2,4,7
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,8 this sector includes bioprospecting in marine environments and the use of molecular biology and microbial ecology tools in marine organisms.9
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.10
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.11 Also named Pharmaceutical Biotechnology.12
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.13
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.14
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.15
Oxidoreductases: All enzymes catalyzing oxidoreduction reactions belong to this class. The substrate that is oxidized is regarded as a hydrogen donor.
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).
Hydrolases: These enzymes catalyze the hydrolytic cleavage of C–O, C–N, C–C and some other bonds, including phosphoric anhydride bonds.
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.
Isomerases: These enzymes catalyze geometric or structural changes within one molecule.
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%.16 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,17 as well as the enzymes involved in the production of final molecules, such as in textiles processing,18 beverages, foods, biofuels19 and pulp and paper.20
The worldwide market for white biotechnology involved transactions on the order of €92 billion in 2010. In late 2011, it was estimated that sales would increase to around €228 billion in 2015 and to around €515 billion in 2020.17 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%).20 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.20 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 2010,20 mainly focused on the production of pharmaceuticals, foods and beverages and cleaning products.21 The projected global market for lipases in 2015 is USD634 million.20
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.22 It should be highlighted, however, that even for biocatalytic processes, each procedure must be evaluated for its environmental friendliness and economic feasibility.23 Some important remarks on the use of biocatalysts in industrial processes are given in Table 1.2.
Important remarks about biocatalysis in green chemistry (adapted from ref. 23)
Remarks . | Critical analysis . |
---|---|
1. Use of water as green solvent | Some organic compounds present low solubility in water; downstream processing of aqueous solutions often demands extraction with organic solvents |
2. Enzyme engineering | Promising field which, however, requires a long time for development from the idea to implementation at an industrial scale; new high throughput methods can accelerate development |
3. Productivity | Considering that a minimum volumetric productivity of 0.1 g L−1 h−1 and a minimum final product concentration of 1 g L−1 is acceptable for implementation at an industrial scale, process optimization in terms of the increase of the substrate concentration and its feeding form and the stability of the biocatalyst is required |
4. Low substrate concentration | Due to enzyme inhibition problems, low substrate concentrations are commonly adopted, resulting in oversized reactors and inefficient downstream processing |
5. Potential as an alternative process | Although biocatalytic processes are often greener than chemical ones, for industry, ecological reasons are not the only subjects to be addressed for the replacement of an existing process. On the other hand, sometimes there are no chemical alternatives to a biotechnological pathway |
6. Pharmaceutical development | The combination of chemical and biocatalytic steps is the most promising path for specific and functionalized products; for the obtainment of chiral molecules, if the separation of racemates is complex and not reliable, enantioselective biotransformations should be used |
7. Price of the catalyst | The cost contribution of the biocatalyst is strongly related to the value of the products. They may vary from USD 0.05 kg−1product (bulk chemicals) to up to USD 10 kg−1product (pharma products)24 |
8. Downstream processing | Aqueous solutions, commonly used in biotransformations, require a significant amount of solvent for product isolation; strategies such as in situ product removal and engineering of solvent-tolerant enzymes could overcome this issue |
9. Use of ionic liquids | Functional fluids often improve substrate solubility, but incur additional expense in downstream processing; more information about their toxicity is needed |
10. Substrate spectrum for biocatalysis | Although specificity is claimed to be one advantage of enzymes over chemical catalysts, some biocatalysts, such as lipases, present substrate versatility and diverse catalytic function |
Remarks . | Critical analysis . |
---|---|
1. Use of water as green solvent | Some organic compounds present low solubility in water; downstream processing of aqueous solutions often demands extraction with organic solvents |
2. Enzyme engineering | Promising field which, however, requires a long time for development from the idea to implementation at an industrial scale; new high throughput methods can accelerate development |
3. Productivity | Considering that a minimum volumetric productivity of 0.1 g L−1 h−1 and a minimum final product concentration of 1 g L−1 is acceptable for implementation at an industrial scale, process optimization in terms of the increase of the substrate concentration and its feeding form and the stability of the biocatalyst is required |
4. Low substrate concentration | Due to enzyme inhibition problems, low substrate concentrations are commonly adopted, resulting in oversized reactors and inefficient downstream processing |
5. Potential as an alternative process | Although biocatalytic processes are often greener than chemical ones, for industry, ecological reasons are not the only subjects to be addressed for the replacement of an existing process. On the other hand, sometimes there are no chemical alternatives to a biotechnological pathway |
6. Pharmaceutical development | The combination of chemical and biocatalytic steps is the most promising path for specific and functionalized products; for the obtainment of chiral molecules, if the separation of racemates is complex and not reliable, enantioselective biotransformations should be used |
7. Price of the catalyst | The cost contribution of the biocatalyst is strongly related to the value of the products. They may vary from USD 0.05 kg−1product (bulk chemicals) to up to USD 10 kg−1product (pharma products)24 |
8. Downstream processing | Aqueous solutions, commonly used in biotransformations, require a significant amount of solvent for product isolation; strategies such as in situ product removal and engineering of solvent-tolerant enzymes could overcome this issue |
9. Use of ionic liquids | Functional fluids often improve substrate solubility, but incur additional expense in downstream processing; more information about their toxicity is needed |
10. Substrate spectrum for biocatalysis | Although specificity is claimed to be one advantage of enzymes over chemical catalysts, some biocatalysts, such as lipases, present substrate versatility and diverse catalytic function |
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.