Clblll classroom AN OPEN-ENDED PROBLEM IN CHEMICAL REACTION ENGINEERING PHILLIP E . SAVAGE University of Michigan the students to develop problem-solving and life-long Ann Arbor, MI 48109-2136 learning skills, to think creatively and innovatively, and to exercise engineering judgment. HE HOMEWORK AND examination problems that This paper describes my experience in implement­ Tstudents encounter in a traditional chemical en­ ing an open-ended problem in our junior-level chemi­ gineering class typically have unique correct solu­ cal reaction engineering class. The problem, which in­ tions. Such problems certainly provide necessary volves evaluating and designing a reactor for destroy­ practice in applying the fundamental course concepts, ing organic compounds in an aqueous waste stream, but if they are used exclusively students might be­ is one that could be easily and profitably used at other lieve improperly, that all engineering problems are universities. simil~rly structured. Worse yet, an exclusive diet of well-defined, single-right-answer problems might PROBLEM DESCRIPTION leave students unprepared for the more open-ended The open-ended problem placed the students in the problems they will face in industry or in graduate re­ chemical reaction engineering group of a multi­ search. While it is true that students are generally national chemical processing corporation. Their com­ exposed to a measure of open-ended problem solving pany generated aqueous waste streams that needed in the capstone design course, such exposure is com­ to be treated before being discharged into the environ­ paratively brief and it occurs late in the curriculum. ment. Incineration was presently being used. On De­ Recognizing the importance of open-ended prob­ cember 7, 1988, the CEO of the company read a short lems in engineering and their under-representation in article in the New York Times (Figure 1) about an the traditional engineering curriculum, the chemical alternative method of treating wastewater streams engineering department at the University of Michigan that involved reacting the organic constituents with set a departmental goal of increasing our under­ oxygen at elevated temperatures and pressures. He graduates' ability to solve open-ended problems. To wanted to know if this technology, termed wet oxida­ achieve this goal we assign at least one open-ended tion, was something his company should be using. problem in each of our required undergraduate class­ After trickling down through a few levels of manage­ es. The structure of the open-ended problems is such ment, the assignment eventually reached the reaction that they are major, semester-long projects in which engineering group (i .e., the students). The groups' students work together in groups of three to five. The stated mission was to evaluate the wet-oxidation open-ended problems offer natural opportunities for technology, make a recommendation about its techni­ cal feasibility, and finally, to size a reactor (or process) and specify its operating conditions. The students received no information other than Phillip Savage is an assistant professor of chemical the scenario above and a copy of the New York Times engineering at the University of Michigan. He received his BS from Penn State and his MChE and PhD article. There were no restrictions on their use of out­ degrees from the University of Delaware. His research side sources of information (e.g., the library, industry, interests are in reaction pathways, kinetics, and mecha­ government agencies, personal contacts, etc.) so prog­ nisms. His current projects incude studies of reactions in supercritical fluids, au/oxidation reactions, and hy­ ress down this avenue was limited only by their imagi­ drocarbon pyrolysis. nation and initiative. Another available pathway to 0 Copyright ChE Division ASEE 1990 information was their corporation's Technical Service 148 CHEMICAL ENGINEERING EDUCATION This paper describes my experience in implementing a n open-ended problem in our junior-level chemical reaction engineering class. [It] involves evaluating and designing a reactor for destroying organic compounds in an aqueous waste stream, ... [and] could be easily and profitably used at other universities. THE NEW YORK T I MES, WEDNESDAY, DECEMBER 7, 1988 hazardous waste problem. Rather, the goal was to de­ velop an open-ended problem in chemical reaction en­ gineering of sufficient complexity to challenge the stu­ Treating Waste Oxygen dents without simultaneously overwhelming them. 5, 000 Feet D own i If a wet waste material, like THE SOLUTION PROCESS sewage sludge, is mixed with oxygen and placed under high Background Information pressure, it undergoes a process that chemists call wet oxidation. The sludge, whose The students' initial activity involved gathering in­ disposal is bec oming a burden to more and more municipal formation about wet oxidation in general, and the sewage plants, is converr.cd to relatively clean water and Oxidyne process mentioned in the New York Times sterile ash . article in particular. Several groups called or wrote to Such processes, when carried out on the earth's Oxidyne to learn more about their process technology surface, require elaborate vessels under high pressure, and its applicability to their particular waste stream. special pumps and ample acreage for buildings and Other groups resorted to the library in search of back­ equipment. But a Dallas ground information on wet oxidation and vertical, un­ company, the Oxidync Group Inc., has developed a system derground wet oxidation reactors. Although the liter­ that moves the process to the bollom of a well 5,000 feet ature provides limited descriptions of underground underground, where i t is carried out in a scaled reactor oxidation reactors [1,2), it is rich in general descrip­ vessel. tions of wet oxidation processes [3-8). Of course, the In the process, sludge is pumped to the bolt om r,f the presence of this information in the literature did not well. Because of the weight of the sludge coming down the mean that the students, who apparently had little pipe, pressures at the bouom of the well can exceed 2,000 training in performing literature searches, would find pounds per square inch. Oxygen is sent down through it. Indeed, very few groups were adept at locating the another pipe and the wet relevant papers and patents. oxidation begins. Reaction Raw sludge is constantly Zone pumped into the system and treated water and ash rome SP£Clf1CTIONS The Search for Data out. Wet oxidation produces About 5,000 feet considerable heat, some of 2.000psi All of the groups realized that they needed much which can be usP.d to drive the 550 degrees Fahrenheit process. more data than they initially received in the problem statement. In memos to the Technical Service Direc­ tor, they requested essential data such as the flow Copyright OJ988 by The New York Ti mes Company. rate, density, temperature, and composition of the Reprinted by permission. aqueous waste stream and the concentrations of the FIGURE 1 various components. I played the role of the Technical Services Director, but this assignment could also be delegated to a teaching assistant if desired. For this Department. This department would conduct experi­ problem, I specified a wastewater stream at ambient mental work for them, but the students had to define temperature flowing at 30 liters/minute. The stream clearly the precise experiments they wanted done and contained 1% each of phenol, chlorophenol, and acetic the data they desired to be reported. Additionally, acid. The precise composition of the stream is, of the Technical Services Department conducted experi­ course, arbitrary, but it is for these three compounds ments only in response to written memos directed to that the literature [5, 9-14) provides the most kinetics the Technical Services Director. data for the wet oxidation reactions. One perceptive Note that the scenario described above was not group realized that the component concentrations in a intended to represent the way a real corporation oper­ real process could exhibit fluctuations even though the ates. Likewise, the data used in this problem (pre­ process was nominally at a steady state. They sent a sented in the next section) were not necessarily in­ memo asking whether such variations occurred and if tended to mimic those associated with a genuine so, what their magnitude was. To avoid introducing SUMMER 1990 149 unnecessary complexity into the problem I told them groups encountered was that they requested data that that the variations in concentration were sufficiently were not as useful as they had envisioned. For exam­ small that they could be safely neglected. ple, one group requested that the Technical Services Another piece of information that the students Department run a wet oxidation reaction in an isother­ needed was the maximum permissible concentrations mal CSTR, sample the liquid phase at specified times, of the organics in the reactor effluent. Different and identify and determine the concentrations of the groups took different approaches to obtaining this in­ different components. They were planning to use the formation. Nearly every group did some library re­ concentration vs. time data to derive the reaction rate search in an attempt to find environmentally accept­ laws. Of course, concentrations do not change with able discharge levels for phenol, chlorophenol, and time in a steady-state CSTR; thus the reply memo acetic acid. Most groups, however, found an apparent from the Technical Services Director showed that the lack of readily available, specific guidelines. Some component concentrations in the effluent stream, groups contacted the State of Michigan Department though lower than those in the feed stream, remained of Natural Resources for state regulations, others con­ time invariant. Upon examining the reply memo, the tacted the EPA for Federal regulations, still other group eventually realized its mistake. The next memo groups contacted environmental engineers in local in­ requested experiments in a batch reactor wherein con­ dustries (i.