San Antonio, Texas
June 10, 2012
June 10, 2012
June 13, 2012
25.853.1 - 25.853.13
Introductory Adsorption Laboratory ExperimentAbstract: It is always exciting to bring nonengineering or first year engineering studentsinto the laboratory – they can learn a lot about engineering by working in the space, butthe experiment needs to be safe and accessible. This paper describes an adsorptionexperiment with safe and simple data collection. The analysis can be simple (graphingdisappearance of a dye as a function of time) or complex (calculating equilibria, rateexpressions and thermodynamic quantities). Groups of students can collect data underdifferent conditions and tell a more complete story about the adsorption process.Background: Students may have a basic understanding of adsorption or absorption, butnot necessarily understand the difference. Both processes are commonly used withproducts familiar to students. Applications of adsorption include wastewater treatment,odor removal, food product decolorization and fabric dyeing. Students who understandbasic principles of adsorption will have a better understanding of some environmentaland chemical processes.Two undergraduate students helped develop an adsorption laboratory experiment andanalysis to teach nonengineering students and first year engineering students about theprocess. The experiment will be used in an “Engineering for Everyone” course as well asan Introduction to Engineering course for first year engineering students (using slightlydifferent mathematical presentations in the two courses). Assessment results will beavailable in May 2012.Theory: Adsorption is usually modeled using isotherms, a word which may scare manystudents from even trying the experiment. However, only an understanding of algebra,logarithms and linear regression is necessary to model the process using a Freundlichisotherm. After drawing the adsorption process and defining phrases such as“equilibrium”, “adsorbate” and “bulk fluid”, the students have a picture of the adsorptionprocess. Next, the Freundlich isotherm is introduced as an empirical model (equation(1)) where qe represents the amount of dye adsorbed at equilibrium, and c represents theconcentration of dye in the bulk fluid. 1 qe = k c n (1)The equation can be linearized and the temperature dependent constants k and 1/n foundby linear regression: € 1 lnqe =ln k + lnc (2) nStudents can prepare the graphs and perform the regression in Excel with little problem. €Modeling the adsorption kinetics is more complicated, and requires a differentialequation. However, if a simplified process is described to the students, they canunderstand the model at some level. Equation (3) is a pseudo first order model, where qtrepresents the amount of dye adsorbed at time t and k1 is the rate constant. dqt = k1 (qe −qt ) (3) dtSolving equation (3) with the initial condition that qt = 0 at t = 0 yields € ln(qe −qt )=lnqe − k1 t (4)Again, students are able to graph the data and use regression in Excel to obtain estimatesof the rate constant and equilibrium adsorption. This value can be compared to theexperimental value.€Procedure: Students read an introductory article describing adsorption [ref], followed bya short presentation in class. They answered qualitative questions [provided in anappendix], displaying their understanding of adsorption and its vocabulary.In the laboratory, they completed the adsorption experiment: white fabric is immersed ina beaker filled with KoolAid, and liquid samples are removed every minute until thewater is clear (and the fabric is colored). The amount of dye in each liquid sample ismeasured with a spectrophotometer. [Provide a detailed procedure in the appendix ifnecessary]The students then moved to the computer lab and completed the data analysis as a group.Because the students performed the experiments under different conditions (adsorbateconcentration and temperature), the data can be combined to tell the full story. Thestudents then wrote a laboratory report, which was analyzed to measure understanding ofadsorption and see if it improved after the experiment [provide rubric].Results: Graphs from the experiments will include typical data (graph of dye adsorbed asa function of time), Freundlich isotherm and first order model fit. Data will also bepresented on the effectiveness of the laboratory experience on helping studentsunderstand the process of adsorption, comparing student understanding of adsorptionbefore and after the laboratory.Conclusions: The experiment is safe, simple and, because of the color, interesting to awide range of students. The analysis requires only a basic familiarity with Excel.Students are able to see how temperature and concentration affect the total amount of dyeadsorbed. The students’ understanding of the adsorption process increased. Thelaboratory experiment is safe, simple and visual. It can be modified and used as anoutreach experience for younger students.References:Chairat, M., Rattanaphani, S., Bremer, J.B., Rattanaphani, V., An adsorption and kineticstudy of lac dyeing on silk. Dyes and Pigments 2005 (64): 231 – 41.Seader, J.D., Henley, E.J., Separation Process Principles, 2nd Edition, Wiley, 2006, pages548 – 613.Wallitsch, E. “Kinetics of Dyeing” Undergraduate Poster Presentation, 9/15/2011.I would prefer to have this paper in a poster session, although I will accept whateverworks.
Piergiovanni, P. R. (2012, June), Introductory Adsorption Laboratory Experiment Paper presented at 2012 ASEE Annual Conference & Exposition, San Antonio, Texas. 10.18260/1-2--21610
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