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Engineering design to protect the environment: teaching and research in chemical engineering at the Univerisyt of Alberta.

Recent controversies over pulp mill and sour gas developments have focused public attention on two aspects of industrial development: the impact of emissions on the environment, and the selection of technology to minimize release of undesirable compounds into the air and water. An integral part of the discipline of chemical engineering is to minimize the impact of industry on the environment. At the University of Alberta, this commitment toward responsible development permeates both the teaching and the research activity in chemical engineering.

A major component of the engineering curriculum is design; teaching the students to bring fundamental concepts to bear on specific practical problems. An important measure of a successful design for a chemical process is production of a useful product, with minimal environmental impact. Chemical engineering students are encouraged to develop innovative and effective designs for waste disposal, recycling of resources and pollution control. A measure of this commitment was the establishment of the course, Process Design for Pollution Control by Fred Otto, FCIC. This course, taught since 1973 with assistance from Alberta Environment, was one of the first in Canada to stress ecological concerns in chemical engineering practice.

Over the past 30 years, the research activity in the department has supported Alberta's economic development, and at the same time, yielded innovations to reduce the impact of developement on the environment. The following are specific examples, both of past successes and current research activity.

Sulphur Recovery from Sour Natural Gas

Natural gas is a highly desirable fuel: it bums cleanly and produces less carbon dioxide than any other fuel. With the current concern over the greenhouse effect and acid rain, natural gas is the best fuel now available. Alberta produces most of Canada's natural gas, but the largest fields contain large amounts of hydrogen sulphide. This toxic and very noxious gas must be removed. Hydrogen sulphide is also produced as a byproduct of refining of crude oil and bitumen.

The modified-claus process converts up to 98% of the hydrogen sulphide into non-toxic elemental sulfur, a bright yellow solid, thereby converting a toxic compound into a valuable asset for Alberta. Over the past 15 years, solid sulphur has been in high demand, and the elemental sulphur from Alberta's natural gas, crude oil, and bitumen has come to dominate the world market. The research work of Ivo Dalla Lana, FCIC, since 1965 has made Important contributions to this technology. A better understanding of the limits to conversion, and how the catalyst in the process behaves, has contributed to a steady reduction in sulphur dioxide emissions from sour gas plants. Dalla Lana's work has lead to improved aluminum oxide catalysts, which have been tested under industrial conditions and are being examined in more detail by a Canadian firm. Research on the kinetics of the reactions of hydrogen sulphide has contributed to improved designs for industrial reactors. His current work concentrates on the conversion of carbonyl sulphide and carbon disulphide. These compounds form as byproducts in the Claus process, and limit the overall sulphur recovery.

The other challenge in treating natural gas streams is to remove the hydrogen sulphide down to safe levels. Because hydrogen sulphide is toxic at low concentrations, the treated gas can only contain a few parts per million of sulphur compounds. This removal is accomplished by treating the gas with amine solvents. The design and operation of these treating processes has been improved by the research of Otto and Alan Mather, MCIC. Their measurements of absorption of hydrogen sulphide and carbon dioxide into treating solvents have laid the basis for the modem engineering design of amine-treating processes for sour gas. Their work continues with the aim of improving treating efficiency still further, by reducing the amount of amine solvent required. New treating solvents are more efficient at removing the hydrogen sulphide, and reduce energy consumption. Research on mixed treating solvents is aimed at recovery of carbon dioxide for enhanced oil recovery.

Catalysts for Air Pollution Control

Calalysts have the ability to promote a chemical reaction which would otherwise occur only very slowly. we are surrounded by pollution-control catalysts; all North American cars have been equipped with catalytic converters since the early 1980s. These converters are a ceramic matrix of alumina coated with microscopic particles of a noble metal such as rhodium, platinum, or palladium. The use of catalytic converters has greatly reduced the harmful emissions from automobiles, one of the main causes of air pollution prior to the mid-1970s. Sieg Wanke, MCIC, has been involved with research related to emission-control catalysts since he joined the department in 1970. David Lynch, MCIC joined this effort in 1978, and their research has resulted in an understanding of processes which occur during the oxidation of pollutants such as carbon monoxide and oxides of nitrogen.

Wanke and Lynch have also investigated the deactivation of exhaust catalysts, which limits the effective lifetime of a catalyic converter. One important result is a model for atomic migration of metals on the catalyst surface, which is in excellent agreement with the observed deactivation and regeneration of catalyst activity. Oxidation of pollutants such as carbon monoxide can give rise to oscillation in performance; Lynch and Wanke unravelled the complex oxidation kinetics. The insight they gained into the interactions between metals, ceramic supports, and reacting gases will allow the development of more effective pollution control catalysts.

Water-resistant Catalysts for Air and Water Clean-up

Nitrogen oxides are a major contributor to acid rain and to urban smog. These compounds are formed by a variety of high temperature chemical processes, including the manufacture of nitric acid. Karl Chuang, MCIC, brought his long experience with water-resistant catalysts to bear, and found that the nitrogen oxides in off-gases could be selectively reduced to form harmless nitrogen gas. This process reacts the off gases with hydrogen over a hydrophobic catalyst, at lower cost than competing processes for converting nitrogen oxides. The special catalyst resists deactivation due to water vapour in the gases, promotes the reaction of hydrogen with the nitrogen compounds at low temperatures, and minimizes the reaction of hydrogen with oxygen to form water. Pilot plant testing at the Cominco Fertilizer Plant (Calgary) has shown catalyst activity for over one year. Two full-scale systems based on this process are under design for Cominco and C-I-L plants (Now ICI Canada) in Canada and the United States. A major chemical production problem is the treatment of dilute solutions of pollutants in water. An ideal process is to oxidize the compounds at low temperatures to form carbon dioxide and water. Chuang is applying wetproofed catalysts to this water treatment challenge, with a grant from the institute for Chemical Science and Technology (ICST). The solution of pollutants is trickled through a catalyst bed, along with air. The organic contaminants pass into the air, then react with oxygen on the surface of the catalyst. most organic pollutants, such as aldehydes, benzene, and phenol can be oxidized to carbon dioxide and water at temperatures below 1700C.

Bioreactors for Waste Treatment

Biological treatment of sewage in simple open reactors has been practiced for many years. Treatment of industrial waste is more challenging, because chemicals in the waste can inhibit the growth of microorganisms. Research by Murray Gray, MCIC, in collaboration with P.M. Fedorak of the Microbiology Department and S.E. Hrudey of the Faculty of medicine, has dealt with the specific problem of phenolic wastes produced from refineries and chemicals manufacture. in an oxygen-free environment, bacteria can convert the pollutants into methane gas, thus converting a liability into a useful fuel. The novel reactor developed at University of Alberta uses activated carbon as an initial support. The carbon adsorbs high-toxic chemicals, and allows the bacteria to establish active methane formation. Under controlled flow conditions, the bacteria form a thick blanket of particles above the activated carbon, providing efficient removal of pollutants. This novel concept has the potential to improve both process conversion and stability of operation, and the resulting technology would be marketable in Canada and worldwide.

Control of pollution and protection of the environment require that we go to the source of the problem and deal with it. The most effective strategies are to design protection into both our industries and our personal habits, by conserving raw materials and energy, minimizing the wastes and byproducts, and recycling useful materials. Environmental protection has always been a challenge of engineering design, to combine fundamental principles with innovative ideas. At the same time, the impact of human activity on our ecosystem is far reaching, and requires multi-disciplinary research over fields ranging from engineering to physics to biology and medicine. Chemical engineers have the design skills, and will continue to work towards solutions to our ecological problems.
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Author:Gray, Murray R.
Publication:Canadian Chemical News
Date:Jan 1, 1992
Previous Article:Chemical engineering - a path to future innovations.
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