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Green chemistry and process safety
Green chemistry and process safety Process Safety
T
he US Environmental Protection Agency (EPA) announced the recipients of the 2015 Presidential Green Chemistry Challenge Awards on July13.1 These awards have been presented since 1996, and in many cases the materials, chemistry, and processes receiving the award also represent potentially inherently safer technology as well. The 2015 ‘‘Greener Reaction Conditions Award’’ was presented to Soltex (Synthetic Oils and Lubricants of Texas), Houston, TX, for a process to manufacture polyisobutylene using a solid state catalyst system in place Lewis acid catalysts such as boron trifluoride (BF3). Replacing the corrosive and toxic BF3 gas (boiling point = 100 8C) with an alcoholBF3 complex on a solid alumina support directly reduces the hazard of handling the toxic gas. Also, because the catalyst is not mixed with the isobutylene monomer, the process eliminates the need for extensive post-reaction treatment to remove BF3 from the product. The environmental benefits of elimination of water washes and other product cleanup operations are clear. There is also a safety benefit to elimination of process steps to clean up product contaminated with catalysts, chemical byproducts, or other impurities. These process steps require additional equipment, which increases the complexity of the process. The equipment for these treatment steps provides additional opportunities for loss of containment from leaks or other failures. Additional equipment and piping also increases the inprocess inventory of hazardous material which could be released. As often stated by Trevor Kletz, any equipment that you can eliminate from a process costs you nothing to purchase, operate, and maintain, and it can never leak or otherwise release hazardous materials. The ideal chemical process uses a highly selective chemical reaction which generates no by-products, and the reactor effluent contains no contaminants and needs no further treatment or purification. The effluent from the reactor can be put into shipping containers and sent directly to your customers. While a green process or material often is also safer, and a fire or explosion would certainly never be considered ‘‘green’’, there are no guarantees. A green chemistry may be more
energetic, increasing the potential for an uncontrolled chemical reaction. A substitute material may be environmentally friendly in some ways, but may also introduce new hazards or increase the magnitude of other existing hazards. Refrigerants are a classic example. Chlorofluorocarbon refrigerants have low acute toxicity and are not flammable, but in the 1970s were discovered to have important upper atmospheric ozone depletion impact. Because of this environmental impact, many of these materials have been phased out. In some cases they have been replaced with refrigerants such as ammonia (flammable and toxic) and light hydrocarbon mixtures (flammable). I remember reading a newspaper story in 1994 about the Lillehammer, Norway Winter Olympics, describing the refrigeration systems for some of the facilities which used ‘‘safe’’ ammonia instead of CFC coolant. Our plants used a lot of ammonia, but all of our ammonia was flammable and toxic! One of our engineers wanted to find out where we could get some of that ‘‘safe’’ ammonia. Of course, the newspaper story meant ‘‘environmentally safer’’ with respect to ozone depletion. We certainly can, and do, design and operate safe refrigeration systems using materials such as ammonia or hydrocarbons, but the hazards of these materials are present in those systems and must be managed by good design and operation. The key to selecting the best overall technology for any purpose is to identify all of the hazards associated with the different technology choices and to determine the optimum overall strategies for managing all of those hazards. This includes not only safety hazards such as fires, explosions, and acute toxicity, but also health and environmental hazards. Some hazards will be best managed with inherently safer designs, eliminating or greatly reducing the hazards. Others may require some combination of design and operating safeguards. Acceptable safety, health, and environmental performance of our technology are required, but there are many ways to achieve this performance. The art of engineering and technology selection is defining which alternative gives the best balance of inherent and engineered management of safety, health, and environmental management for a specific facility in a specific environment.
1
Ritter, S. K. ‘‘Green in 2015.’’ Chem Eng News 93 (33), August 24, 2015, pp. 32–35.
1871-5532 http://dx.doi.org/10.1016/j.jchas.2015.10.010
ß Division of Chemical Health and Safety of the American Chemical Society Elsevier Inc. All rights reserved.
39
T
he US Environmental Protection Agency (EPA) announced the recipients of the 2015 Presidential Green Chemistry Challenge Awards on July13.1 These awards have been presented since 1996, and in many cases the materials, chemistry, and processes receiving the award also represent potentially inherently safer technology as well. The 2015 ‘‘Greener Reaction Conditions Award’’ was presented to Soltex (Synthetic Oils and Lubricants of Texas), Houston, TX, for a process to manufacture polyisobutylene using a solid state catalyst system in place Lewis acid catalysts such as boron trifluoride (BF3). Replacing the corrosive and toxic BF3 gas (boiling point = 100 8C) with an alcoholBF3 complex on a solid alumina support directly reduces the hazard of handling the toxic gas. Also, because the catalyst is not mixed with the isobutylene monomer, the process eliminates the need for extensive post-reaction treatment to remove BF3 from the product. The environmental benefits of elimination of water washes and other product cleanup operations are clear. There is also a safety benefit to elimination of process steps to clean up product contaminated with catalysts, chemical byproducts, or other impurities. These process steps require additional equipment, which increases the complexity of the process. The equipment for these treatment steps provides additional opportunities for loss of containment from leaks or other failures. Additional equipment and piping also increases the inprocess inventory of hazardous material which could be released. As often stated by Trevor Kletz, any equipment that you can eliminate from a process costs you nothing to purchase, operate, and maintain, and it can never leak or otherwise release hazardous materials. The ideal chemical process uses a highly selective chemical reaction which generates no by-products, and the reactor effluent contains no contaminants and needs no further treatment or purification. The effluent from the reactor can be put into shipping containers and sent directly to your customers. While a green process or material often is also safer, and a fire or explosion would certainly never be considered ‘‘green’’, there are no guarantees. A green chemistry may be more
energetic, increasing the potential for an uncontrolled chemical reaction. A substitute material may be environmentally friendly in some ways, but may also introduce new hazards or increase the magnitude of other existing hazards. Refrigerants are a classic example. Chlorofluorocarbon refrigerants have low acute toxicity and are not flammable, but in the 1970s were discovered to have important upper atmospheric ozone depletion impact. Because of this environmental impact, many of these materials have been phased out. In some cases they have been replaced with refrigerants such as ammonia (flammable and toxic) and light hydrocarbon mixtures (flammable). I remember reading a newspaper story in 1994 about the Lillehammer, Norway Winter Olympics, describing the refrigeration systems for some of the facilities which used ‘‘safe’’ ammonia instead of CFC coolant. Our plants used a lot of ammonia, but all of our ammonia was flammable and toxic! One of our engineers wanted to find out where we could get some of that ‘‘safe’’ ammonia. Of course, the newspaper story meant ‘‘environmentally safer’’ with respect to ozone depletion. We certainly can, and do, design and operate safe refrigeration systems using materials such as ammonia or hydrocarbons, but the hazards of these materials are present in those systems and must be managed by good design and operation. The key to selecting the best overall technology for any purpose is to identify all of the hazards associated with the different technology choices and to determine the optimum overall strategies for managing all of those hazards. This includes not only safety hazards such as fires, explosions, and acute toxicity, but also health and environmental hazards. Some hazards will be best managed with inherently safer designs, eliminating or greatly reducing the hazards. Others may require some combination of design and operating safeguards. Acceptable safety, health, and environmental performance of our technology are required, but there are many ways to achieve this performance. The art of engineering and technology selection is defining which alternative gives the best balance of inherent and engineered management of safety, health, and environmental management for a specific facility in a specific environment.
1
Ritter, S. K. ‘‘Green in 2015.’’ Chem Eng News 93 (33), August 24, 2015, pp. 32–35.
1871-5532 http://dx.doi.org/10.1016/j.jchas.2015.10.010
ß Division of Chemical Health and Safety of the American Chemical Society Elsevier Inc. All rights reserved.
39