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加拿大Chemical Engineering专业essay:绿色化学原理The principles of Green

论文价格: 免费 时间:2019-06-27 14:41:22 来源:www.ukassignment.org 作者:留学作业网
目前的原油产量无法满足日益增长的全球石油需求(Pfaltzgraff&Clark,2014年)。绿色化学通过使用清洁技术、替代产品和再生材料来生成化学物质、材料和燃料,提供替代品(2014年,第3页)。与常规化学程序相比,绿色化学采用了更环保的生产技术(Savage,2013年)。Savage(2013年,第125-127页)指出,绿色化学工艺必须适用于工业应用,且性能优于当前的化学工艺。邓恩(2012,第1452页)指出,近年来,社会对绿色、可持续和可再生化学程序的发展有着重要的期望,而且这种趋势在未来也会越来越受到欢迎。本文介绍了绿色化学的三个基本原理及其应用,并评价了这些原理对人类社会的重要性。
绿色化学的三个原理如下:Current crude oil production fails to meet increasing global oil demand (Pfaltzgraff & Clark, 2014). Green chemistry offers alternatives through the use of clean techniques, substitute products, and recycled materials to generate chemical substances, materials, and fuels (2014, p.3). In contrast to routine chemical procedures, green chemistry adopts more ecofriendly production techniques (Savage, 2013). Savage (2013, pp. 125-127) states that the processes of green chemistry must be suitable for industrial application and perform better than current chemical processes. Dunn (2012, p.1452) points out that recent years have seen significant social expectation for the development of greener, sustainable, and renewable chemical procedures, and it appears this tendency will gain greater popularity in the future as well. This article describes three fundamental principles of green chemistry and how they can be applied, and evaluates the importance of these principles to human society.
绿色化学涉及与减少或消除使用有毒材料的化学物质和程序有关的创新(Anastas和Warner,1998年)。绿色化学,作为一个概念,由Paul T.Anastas和J.C.Warner于1998年首次提出(Pfaltzgraff和Clark,2014年)。尽管绿色化学过程并非完全无害,但绿色化学的目标是利用危害较小的溶剂或更安全的合成技术,以减少废物产生和利用回收材料或发明节能方法(Savage,2013年)。该领域在过去十年中获得了综合利润,因为它有能力利用化学改革同步实现环境和财务目标(Anastas&Eghbali,2010年)。
Green chemistry involves innovation pertaining to chemical substances and procedures that decrease or eliminate the use of toxic materials (Anastas & Warner, 1998). Green chemistry, as a concept, was first introduced by Paul T. Anastas and J.C. Warner in 1998 (Pfaltzgraff & Clark, 2014). Although processes of green chemistry are not entirely harmless, the objective of green chemistry is to harness less harmful solvents or safer techniques of synthesis to generate less waste and to utilize recycled materials or invent energy-conserving methods (Savage, 2013). This domain has garnered comprehensive profits in the past decade as it has the capacity to use chemical reformation to achieve environmental and financial aims synchronously (Anastas & Eghbali, 2010).
The three principles of green chemistry are as follows:
Firstly, using the maximum amount of renewable materials in production (Mason, Cintas, Clark, & Macquarrie, 2002). If conditions permit, processes and materials used should be sustainable instead of wasteful (Gilbertson, Zimmerman, Plata, Hutchison, & Anastas, 2015). ‘Sustainable’ denotes environmental-friendly materials rather than fossil fuel-based carbon materials (Gilbertsonet al., 2015).
Secondly, using and generating non-toxic substances (Mason et al., 2002).Ahluwalia and Kidwai (2004) mention that avoiding or minimizing the production of toxic substances is the most significant principle of green chemistry. Uyguner-Demirel and Bekbolet (2012, p.3) describe this principle specifically indicates that waste cannot be produced if the situation is conducive, and the amount of waste should be minimized. Methods to attain this aim can not only use elementary approaches, such as decreasing loss of solvent because of evaporation, but also utilize complicated approaches, such as devising new reactions to produce products with least wastage as their most important goal (Uyguner-Demirel & Bekbolet, 2012, pp. 3-4). Guaranteeing that the maximum amount of raw substances is taken up in the target product is the best way to prevent waste generation (2012, p.4). If the toxic materials are inadvertently produced, workers should resort to protective measures, such as use of a mask and isolation gown (Ahluwalia & Kidwai, 2004).
Thirdly, using safer and more energy-efficient procedures (Ahluwalia & Kidwai, 2004). Anastas and Eghbali (2010) propose that decreasing harm throughout the processes in the product life cycle is one of the goals of green chemistry that has been illustrated to be economically beneficial. Hazard is explained as the capacity to cause damage to people and their surroundings (Anastas & Eghbali, 2010). Inherent harmfulness of a chemical material or procedure can be designed to be minimal at any stage during manufacturing, specifically pertaining to toxicity, mechanical hazards (e.g., detonation and combustibility), or global dangers such as the loss of the ozone layer (2010). Toxicity may be generated during chemical changes in the processing of raw substrates and production of target products (2010). An elaborate design will decrease or remove the risks associated with chemical materials and their manufacturing (2010). When synthesizing chemical substances, it is important to minimize energy requirements (Ahluwalia & Kidwai, 2004). In exothermic processes, massive cooling is sometimes necessary and could increase the overall cost of production (2004). If the product obtained is not pure, it has to be refined by additional procedures, which would use more energy (2004). Therefore, redesigning the manufacturing process, for example, to eliminate the need for purification, could lead to minimization of target energy needs (2004).
Three examples of the applications of three important principles of green chemistry are elucidated further. These examples comprise practices from various fields and demonstrate that principles of green chemistry can be applied in actuality.
To begin with, green chemistry has been applied with regard to solvents. Plenty of volatile and noxious menstruums are utilized in chemical procedures, which leads to environmental and safety issues (Wu & Han, 2013). In recent years, using environment-friendly menstruums has emerged as an important part of green chemistry (2013). Supercritical carbon dioxide (scCO₂) is one such ecofriendly solvent, and comprises carbon dioxide maintained above its critical temperature (31.1°C) and critical pressure (7.4 MPa) (Zhang, Heinonen, & Levänen, 2014). In contrast to scCO₂, supercritical water occurs at temperatures beyond 374°Cand pressures above 22.1 MPa, which would need more energy (Komarneni, 2003). Numerous chemical processes are operated in scCO₂ (Wu & Han, 2013), which greatly influences green procedures. Carbon dioxide is inactive, noncombustible, innocuous, cheap, and easily obtained from secondary products of several industrial procedures, so supercritical CO₂ has been regarded as an innocuous and an environment-friendly green mestruum that could substitute for several solvents such as carbon tetrachloride (CCl4) and benzene that are utilized in conventional manufacturing processes (Zhang et al.,  2014). Both CCl4 and benzene are volatile, toxic, and carcinogenic while also being detrimental to the environment (2014). Although CO₂ is a “greenhouse” gas, the CO₂ utilized in supercritical CO₂ procedure can be obtained from other industrial chemical manufacturing processes that will neither generate additional CO₂ nor increase the amount of this greenhouse gas (2014). Moreover, the utilization of CO₂ is sustainable and the use of scCO₂ provides a method to deal with industrial emissions (2014). Procedures for the use of scCO₂ are energy saving due to the easily attainable critical temperature and pressure (2014). Supercritical CO₂ has been broadly utilized in food manufacturing, such as for caffeine removal from caffeine-containing materials or extracting hops (2014). Furthermore, scCO₂ is utilized in cleaning and drying organic waste (2014).
Next, green chemistry is applied to biological fuels. There is increasing widespread interest in converting recycled materials into biological fuels to replace conventional fuels, given the depletion of fossil fuel resources (Sanna & Rahman, 2015). Furthermore, establishments are motivated to invest in renewable fuels due to the rising requirements of energy and fuel, and the adverse effects of fossil oil use, such as global warming (2015). Microalgae are arousing significant interest as a substitute and sustainable source for energy production (2015). Microalgae contain considerable quantities of oil, so they can be used to generate various types of biological fuels such as jet fuels and biodiesel using traditional techniques (2015). Microalgae are regarded as one of the most significant raw materials for biological fuels (Wijffels & Barbosa, 2010). Photosynthetic microorganisms only need 1 or 2 steps to convert CO₂ into carbon-rich greases, which is much faster than processes where lipids are generated from agricultural oily crops. In addition, photosynthetic microorganisms do not use arable lands (2010). Microalgae that contain large amount of greases could generate biological oils (Chisti, 2007). Microalgae can be cultivated using various methods, including phototrophic (growing in light without extra nourishment), heterotrophic (growing in dark with extra nourishment), and mixotrophic (growing in either dark or light with extra nourishment) processes (Sawangkeaw & Ngamprasertsith, 2013). A conducive growth environment with light intensity, nutrient production (nitrogen and organic carbon), pH, and temperature could affect microalgal growth rate and lipid content (Sanna & Rahman, 2015).#p#分页标题#e#
Furthermore, biodegradable plastics are another area of application for green chemistry. Exploration of substitutes is necessary to decrease dependence on nonrenewable energy resources because of depleting fossil fuels, high costs of fossil oils, and environmental influences related to their byproducts (Giin-Yu, Chia-Lung, Ling, Liya, & Lin, 2014). Plastic substances that originate from petroleum chemicals have a harmful influence on the environment due to their non-biodegradable character (Getachew & Woldesenbet, 2016). Most plastic substances that are presently utilized in daily life are non-biodegradable polymers that are produced from fossil fuels (Dahman & Ugwu, 2014). Non-biodegradable plastics have an adverse impact on the environment, so different types of biodegradable plastics are being researched (2014). An alternative method to prevent plastic pollution generated through conventional fossil fuel-based plastics is the use of biodegradable plastics (Getachew & Woldesenbet, 2016). Poly(-β-hydroxybutyrate) (PHB) is an important biodegradable natural polymer that can be generated through zymosis procedures using various bacterial species, the majority of which have been proven to use PHB in their cells as the source of carbon and energy (Dahman & Ugwu, 2014). This makes PHB an ideal green biological material that can be produced from recycled low-cost materials using fermentative procedures (2014).
These principles of green chemistry have been used successfully in several aspects worldwide. Numerous consumers worry about their carbon footprint through the commodities they purchase, therefore, companies are regarding green chemistry as a tool to improve their market presence (Savage, 2013). However, there are plenty of barriers to green chemistry: for example, the entire green chemistry usage in the science group meets with remarkable difficulties that comprise economic, financial, regulatory, technical, organizational, and cultural barriers (Roschangar, Sheldon & Senanayake, 2015). Several companies have a serious resistance to the application of green chemistry due to a misconception that the development of green procedures is merely motivated by environment-friendly beliefs (Meyer, Gonzalez, Marteel‐Parrish, & Abraham, 2014). The main problem that engineers and chemists encounter is with regard to helping chemical industries increase their reliance on green chemistry (Meyer et al., 2014). An effective method would be to make stakeholders, such as investors and manufacturers, realize the advantages of using green chemistry in industries (2014). Looking to the future, the replacement of traditional chemical technologies by greener catalytic substitutes and the displacement of the noxious and/or harmful menstruums will continue to be significant, but needs to be supported by 2 more elements toward sustainability (Sheldon, 2017). First, the transition from a fossil fuel-based to a recycled biological-based processing of current chemical products and invention of new substances that are biological degradable (2017). Second, a shift from a discontinuous linear economy to a cyclical economy that devises substances and procedures with protection of resources and waste removal (2017). William Ford Jr pointed out that a good company produces wonderful services and products; however, a great company succeeds in all these things and makes an effort to develop a better world (2017).
In conclusion, the purpose of green chemistry is improving reaction design to minimize waste production, which has positive effects on the environment, the society, and the domain of chemical engineering. The principles of green chemistry give the chances to use eco-friendly methods and recycled materials to generate substances. There are many applications of the principles of green chemistry, such as green solvents, biological fuels and biodegradable plastics. Green chemistry has multiple advantages: firstly, safer processes can decrease the costs of toxic waste disposal. Secondly, green chemistry has advantages for workers and consumers, because it reduces exposure to harmful materials. However, there are some limitations to green chemistry: for instance, green menstruums are not always more useful than commonly used menstruums, so chemists and engineers try to find the solutions to decrease the limitations. In the future, green chemistry will still be a significant valuable part in manufacturing, as the loss of natural resources and the increasing serious environmental pollution. Green chemistry helps to develop the innovation of renewable energy, providing alternatives to fossil fuels and to a more economical use of resources.
Green chemistry is a new strategy for sustainable development of the chemical industry. The green carbon concept is the Foundation of science and as a new frontier science, it will become one of the mainstreams of chemical technology development in the 21st century. For the future development of green chemistry technology, the following aspects in researching and development should be paid attention.
(1) The direct conversion technology should be emphasised on and "atom-economy" for the synthetic steps should be improved. From a green point of view, many of the traditional organic synthesis requires two steps, or even three steps. It will reduce into one step as an atom-economic reaction and complete to direct conversion technology. This is the eternal theme for scientific workers. Such as the production of the propylene oxide, the traditionally method is by a two step reaction of chlorine by alcohol. With the development of titanium silicalite molecular sieve, you can achieve Catalysis oxidation of propylene to propylene oxide by atom-economy new method. Of course, to achieve the atom-economy with a single reaction is still very difficult, or even impossible, you can make full use of the relevant integration of chemical reactions, that is, the waste from a reaction as the raw material for another, so as to achieve the closed loop, realize the zero-emission of chemical production.
(2) Pay more attention to the input of the energy and energy management in the process. And develope technologies which will be with minimum energy consumption during the process cycle. Develop new processes and technologies for energy saving, instead of the traditional technologies with high energy consumption and carbon dioxide emissions. Rational use of solar energy, hydrogen energy and thermal energy to reduce carbon emissions in the process.
(3) The concentration conversion technologies of carbon dioxide in the output end is also paid  attention to. Through the development of efficient catalytic material to address efficient activation and directional conversion of carbon dioxide and other key scientific issues. Also, it can promotion applications of renewable energy technologies with photocatalytic electrochemical methods in carbon dioxide, in pursuit of the minimum carbon dioxide emissions from the system.
In short, new developments, new requirements and new challenges in the chemical industry need to largely develop the green chemistry which is with low energy consumption, low carbon during the life cycle. To believe, with the improving of China chemical science and technology, the green and efficient chemical process will be gradually used in industria. The green chemistry will play a crucial role for the sustainable development of Chinese energy chemical industry and the environmental protection.
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