Radiation Chemistry: The Basis for an Inherently Green Process

Chapter 12

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Radiation Chemistry: The Basis for an Inherently Green Process Technology Anthony J. Berejka +

Ionicorp , 4 Watch Way, Huntington, NY 11743 (email: [email protected])

In using ionizing radiation generated from electron beam accelerators or in using photoinitiated reactions started by high intensity ultraviolet light, industry has eliminated the need for volatile organic compounds from coatings, inks, and adhesives. Such processes have also been found to be energy efficient and to minimize wastes, conserving both energy and materials. Large-scale process studies have indicated that ionizing radiation can also be used to precipitate sulfur dioxide and nitrous oxides from stack gases and to dehydrohalogenate toxic halocarbons found in wastewater and in soils. While recognized for its environmental benefits by organizations such as the International Atomic Energy Agency, the United States Environmental Protection Agency, and the National Science Foundation, industrial acceptance of such inherently green processes based on radiation chemistry has been slowed by a tendency in U.S. industry to conserve capital in plants and equipment rather than to make fundamental changes in process technology. Case studies are presented to illustrate the mechanisms involved and the resultant environmental and economic benefits.

© 2002 American Chemical Society

Lankey and Anastas; Advancing Sustainability through Green Chemistry and Engineering ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

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Introduction Radiation chemistry embraces a broad scope of scientific and technical inquiry. However, except for the selected use of gamma emission from C o for medical device sterilization and for its emerging use for food treatment, industry does not use radioactive sources. Radioactive C o , with its 5.3-year half-life, poses concerns over transport, storage, and waste disposal, as well as a continuing loss of activity, even when not in use for its intended purposes. Thus, industrial radiation processing relies primarily on two electrically generated radiation sources: accelerated electrons and photons from high intensity ultraviolet lamps. Accelerated electrons have the ability to penetrate matter, being stopped only by mass. In contrast, high intensity ultraviolet light generates primarily surface effects, as illustrated in Figure 1 (/). As shown in Table I, there are over 1000 high-current electron beam accelerators now in industrial use, ranging in voltage potential from 70 keV up to 10 M e V . With electron penetration being proportional to acceleration voltage, as shown in Figure 2, the lower voltage accelerators find use in surface curing and in the cross-linking of polymeric films. Mid-voltage accelerators are used to cross-link the jacketing on wire and cable, in the manufacture of heat shrink tubing, and to partially cross-link tire components. High voltage 10 M e V accelerators are being used in the cross-linking of matrix materials in carbon fiber composites and are being evaluated for food processing applications and medical device sterilization (2, 3). Given their significantly lower capital costs, there are well in excess of 100,000 high intensity ultraviolet units now in industrial use. Their applications deal mainly with the surface curing of inks, coatings, and adhesives. These units typically operate in the 200 to 450 nm range, with lamp intensities as high as 240 W/cm of lamp length (/). 60


60

Table I. Industrial Use of Electron Beam Accelerators Voltage Range 0.1 to 0.3 M e V 0.5 to 5.0 M e V 5.0 to 15 M e V

Industrial Units 300 700 35

Average Power 100 kW 40 k W 15 k W

A given application area dictates the preference for a specific accelerator voltage. The use of ionizing radiation to cross-link wire and cable jacketing and heat shrinkable tubing remains the dominant market (36%) for industrial



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166 irradiation processing, as illustrated in Figure 3, with 1.5 M e V accelerators being widely used in the wire and cable industry. Heat shrinkable films used for food packaging rely upon lower voltages, such as 300 keV to 800 keV, and account for a significant market end use (23%). These applications, for the most part, depend upon the favorable cross-linking response of polyethylene to irradiation. Because ionizing radiation from an electron accelerator can be tightly controlled, major tire manufacturers use irradiation processing to partially cross-link components to enhance their toughness before being molded into a finished tire. This reduces cord strike-through and displacement during molding operations. While some service centers are used by smaller wire and cable producers, a growing interest in irradiation processing through toll service centers is developing for medical device sterilization and, on the horizon, for food disinfection. These application areas demand high beam penetration and the higher voltage 10 M e V accelerators. The fastest growing market segment (25%) has been that of low-voltage (70 to 300 keV) self-shielded accelerators for the curing of inks, coatings, and adhesives. Radiation chemistry is used in situ to polymerize liquid-applied materials containing near-zero volatile organic compounds (VOCs) into functionally cured materials and products.

Green Chemistry for Inks and Coatings V O C Elimination Plus Energy Efficiency The increased industrial acceptance of high-intensity ultraviolet light processing and the use of low voltage electron beams (EB) has been stimulated by the Clean Air Act Amendments of 1990. Historically, formulations for inks, coatings and adhesives have relied on the use of polymeric resins dissolved in volatile organic solvents to reduce the viscosity needed for application. Systems with comparable finished properties have been developed based on compositions of non-volatile monomers and oligomers, typically 99.9% removal of CC1 =CHC1 2

2

Stack Gas Treatment Countries dependent on coal as their primary fuel source, such as Poland, have investigated the use of electron beam treatment of stack gases to eliminate S 0 and N O emissions from power plants. When irradiated in the presence of a small amount of ammonia, these undesirable flue gases form a white precipitate that can be removed from the gas stream and collected for other uses, such as fertilizer, as shown in Figure 5. A production facility has been constructed in Poland that is capable of treating 270,000 m /h of gas emissions, which is half the stack gas output of a medium-sized 60 M W coal-fueled power plant. A twostage process vessel has been constructed that uses two 700 keV, 300 k W accelerators in tandem in each zone. Table V I presents data indicating the effectiveness of this irradiation process for removing undesirable air pollutants that contribute to the formation of acid rain. In excess of $20 million in funding for this project was facilitated by the International Atomic Energy Agency (//). 2

x

3



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Figure 5. Stack gas irradiation facility.


174 Table VI. Irradiation Elimination of Stack Gas Contaminants 3

System: 135,000 m /rf~ S 0 at 1.1 g/m + N O at 0.7 g/m 9 kGy = 90% removal S 0 = 70% removal N O 3

2

3

x

2


x

Summary Radiation chemistry has formed the basis for a number of environmentally friendly or "green" industrial process technologies. Commercial success has been found in the elimination of volatile organic compounds for printing and coating processes. In these areas, high intensity ultraviolet light and low voltage electron beam curing and processing have proven to be point-of-source methods of pollution prevention processes, enabling companies to eliminate V O C s and meet E P A standards so as to comply with the Clean A i r Act Amendments of 1990. This is complemented by significant improvements in overall process efficiency and energy savings. Manufacturers of diverse products, such as fiber optic cables, electronic circuit boards, adhesive coated materials, wood, and other coated products have adopted this mode of irradiation processing and its underlying chemistry. While the technical feasibility has been demonstrated for using radiation chemistry in water, wastewater, and soil remediation, the implementation of these proven processes remains a challenge. However, scale up is underway involving the irradiation treatment of stack gases at a full-size coal-burning power plant in Europe. Within the chemical industry, it has long been known that irradiation initiated synthesis can proceed at rapid rates with minimal need for catalysts. This can help to eliminate the problems of catalyst removal and disposal. Yet, this venue remains largely underexplored and has not been addressed by engineers familiar with chemical processes and reactor design. Not only does the societal apprehension of the term "radiation" thwart some of these developments, but also a lack of inclusion of this form of energy transfer in most academic regimes and curricula hinders this even more. In the mid-1990s, a survey was conducted of some 51 universities that were considered to have an interest in radiation science and technology. This survey found that only six institutions had electron beam facilities that could even be considered for use in these environmental-type projects. Only a few more had industrially suited high-intensity ultraviolet light curing equipment. There existed but a few structured graduate programs involving photochemistry and irradiation science and technology. While outstanding work was being



175 conducted through specific grants, it was found that there was neither a core curriculum nor a core text in this enabling area of technology. There was little to no provision for teaching radiation science and technology to undergraduate students (12). In some instances, there has been an enlightened convergence of public support, mainly through state-based programs, for industrial implementation of environmentally friendly irradiation processing technologies, combined with public desires for pollution prevention and energy conservation. More such programs, with their supportive means to assist industry with capital conversion to irradiation processing, are needed. Radiation chemistry will only prosper when there is greater public understanding of the benefits of this benign and environmentally friendly, "green" process. Radiation is, after all, as natural as sunlight itself.

References 1. 2. 3.

4. 5. 6. 7. 8. 9.

Rechel, C. J., Ed. UV/EB Curing Primer; RadTech International North America: Bethesda, M D , 1991. Bly, J. Electron Beam Processing; International Information Associates: Yardley, PA, 1988. Berejka, A . J. Description and Use of High Current Industrial Electron Accelerators; Enhancement of Wastewater and Sludge Treatment by Ionizing Radiation (NSF Grant BES95-2059); University of Miami: Coral Gables, F L , 1997, pp 133-138. Larsen, L . S.; Berejka, A . J. A Clean Sweep—UV Curing of Small Wood Products. The RadTech Report 1999, (May/June), 20-23. Berejka, A . J. Irradiation Processing in the '90's. Radiation Physics and Chemistry 1995, 46 (4-6), 429-437. Berejka, A . J. Reengineering P S A Manufacture for V O C Reduction and Energy Savings. Adhesives Age 1997, (July), 30-36. Berejka, A . J. Reengineering P S A Manufacture for V O C Reduction and Energy Savings. Adhesives Age 1997, (Sept), 28-30. Cooper, W. J.; Curry, R. D.; O'Shea, Κ. E., Eds. Environmental Applications of Ionizing Radiation; John Wiley & Sons: New York, 1998. Nickelsen, M . G.; Kajdi, D. C.; Cooper, W. J.; Kurucz, C. N.; Waite, T. D.; Gensel, F.; Lorenzl, H . ; Sparka, U . Field Application of a Mobile 20-kW Electron-Beam Treatment System on Contaminated Groundwater and Industrial Wastes. In Environmental Applications of Ionizing Radiation; Cooper, W. J., Curry, R. D., O'Shea, Κ. E., Eds.; John Wiley & Sons: New York, 1998, pp 451-466.



176 10. Schuetz, M . N.; Vroom, D . A . The Use of High-Power, Low-Energy Electron Beams for Environmental Remediation. In Environmental Applications of Ionizing Radiation; Cooper, W. J., Curry, R. D., O'Shea, K . E., Eds.; John Wiley & Sons: New York, 1998, pp 63-82. 11. Chmielewski, A. G.; Tyminski, B . ; Iller, E.; Zimek, Z . ; Licki, J. ElectronBeam Flue-Gas Treatment Process Upscaling. In Environmental Applications of Ionizing Radiation; Cooper, W. J., Curry, R. D., O'Shea, K . E., Eds.; John Wiley & Sons: New York, 1998, pp 197-216. 12. Berejka, A . J. Unpublished report to the Board of Directors of The RadTech Foundation, Ionicorp : Huntington, N Y , January, 1996. +


Radiation Chemistry: The Basis for an Inherently Green Process

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