In the Laboratory
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Recovery and Reutilization of Waste Matter from Coffee Preparation An Experiment for Environmental Science Courses
Santino Orecchio Dipartimento di Chimica Inorganica, Università di Palermo, Parco D’Orleans 2, 90100 Palermo, Italy;
[email protected] This work is designed as an experience for organic and analytical chemistry laboratories involved in environmental science courses. It achieves the following goals: 1. It shows that environmental samples are not homogeneous (1 ).
Analysis of the Extracted Oil To evaluate the chemical and physical characteristics of oil extracted from the grounds, the following determinations are carried out: 1. free fatty acid content
2. It is possible to build up students’ confidence in manipulating everyday matter when they are beginning to study scientific subjects and to introduce some methods of sample preparation in analytical chemistry.
2. saponification number
3. It demonstrates some fundamental analytical principles (acid–base and redox analysis, solid–liquid and liquid– liquid extraction, etc.).
5. unsaponifiable residue
4. It shows the importance of instrumental analysis, such as gas chromatography, atomic absorption spectroscopy and elemental analysis; knowledge of these techniques of quantitative analysis is necessary for many course programs in chemistry, biology, environmental sciences, etc., so that students may appreciate “real and final” applications. 5. It produces an interesting experiment pertinent to scientific professionals that is inexpensive, does not require advanced techniques, and produces minimal waste.
The choice of coffee grounds is based on the fact that they are a fine example of a waste product, they are a material with which students are familiar, and they are readily available. This experiment requires one night to remove water from the sample and 5–6 laboratory periods. To save time it is advisable to divide the students into groups of 3–4. Soap is prepared from the extracted fat fraction. All products (oil, soap, and degreased residue) are analyzed to evaluate some of their potential uses. Experimental Procedure
Sampling To obtain statistically valid results, all samples must be prepared by mixing the coffee grounds collected in several cafeterias. Alternatively, to evaluate sample variability at the end of the experiment, student groups may use different samples of coffee grounds. After their collection, the samples must be dried overnight at 80 °C. Oil Extraction The solvent method is the traditional and most efficient method of extracting the sample. Several reviews (2–4) highlight developments in theory, applications, and instrumentation on supercritical fluid extraction. An example of determination of fat in food products is reported by Snow (5).
3. peroxide value 4. iodine value 6. fatty acid composition
Hydrolysis of Fat (Saponification) The soap-making procedure involves the basic hydrolysis of the oil (6 ). O R R R
C
O
C H2
CO
O
CH
C
O
C H2
+
3NaOH
O
fat
lye O 3
R
C
O
soap
O − Na+
+
HO
C H2
HO
CH
HO
C H2
glycerol
Fat Lye Soap Glycerol The soap obtained is analyzed for the properties color, pH, and foam number, as the physical characteristics are derived from its fat sources. The analysis of the soap is carried out by using the methods reported in literature (7–9). Degreased Residual Analysis To evaluate the possibility of utilizing residues of beverage preparation in the agricultural field, the degreased residue is analyzed for organic, nitrogen, phosphorus, and heavy metal content. Carbon, hydrogen, and nitrogen can be determined with a CHN analyzer. Alternatively, if a CHN analyzer is not available in the laboratory, total nitrogen can be determined by the Kjeldahl method (8, 9). Microwave decomposition provides us with a vehicle for a more rapid Kjeldahl analysis. It is possible to perform the Kjeldahl decomposition step using an open-vessel microwave method in less than 100 minutes, a considerable improvement over the usual 3–4 hours. Organic carbon can be determined by dry combustion in an electric furnace and measurement of the carbon dioxide evolved, but this method presents some analytical difficulty for the students.
JChemEd.chem.wisc.edu • Vol. 78 No. 12 December 2001 • Journal of Chemical Education
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In the Laboratory
Potassium, sodium, and heavy metals in the residue can be determined by burning the coffee ground residual. The solid obtained must be dissolved in HNO3 and diluted. Potassium and sodium are determined by using a flame atomic emission spectrometer. Heavy metal content may be determined using graphite furnace atomization. Students are required to prepare calibration standards by serial dilution of pre-prepared stock solutions. Phosphorus may be analyzed spectrophotometrically using the molybdenum blue method according to the following reaction: H3PO4 + 3NH4 + 12MoO4 + 12H2O → (NH4)3PO4⭈12MoO3 + 24OH᎑ +
2᎑
Mo(VI) + ascorbic acid → Mo(V) The absorbances of the calibration and sample solution were measured using a UV–vis spectrophotometer. Alternatively, to facilitate rapid analysis of solutions containing phosphate, an FIA system can be used (10).
Table 1. Characteristics of Coffee Oil and Palm Oil Coffee Oila
Parameter
Palm Oil
Color
brown
yellow
sp gr/(g cm ᎑3 )
0.922
0.897–0.900
mp/°C
27
38–50
Saturated acids % (relative)
67
45–50
33
50–55
Unsaturated acids % (relative) Acid value/(mg KOH g ᎑1)
11.2
1–7.5
Saponification value/(mg KOH g ᎑1)
215
197–202
Peroxide value/(mg O2 g ᎑1)
7.1
—
Acetyl value
107
—
9
0.2–0.5
74
44–88
Unsaponifiable matter (%) Iodine value aFrom
grounds.
Table 2. Fatty Acid Composition of Coffee Oil and Palm Oil Coffee Oil (%)
Palm Oil (%)
Hazards
Fatty Acid
Many of the commonly used solvents are toxic and flammable and should be used in well-ventilated areas only, away from all flames. Many of the reagents (hydrochloric, nitric, acetic, and sulfuric acids, bases, etc.) are corrosive and very dangerous. This experiment must be done in a chemistry laboratory with all appropriate safety precautions and careful supervision by an instructor.W
Lauric (C12:0)
0.2
—
Trace
Myristic (C14:0)
0.2
—
1–2.5
The extraction of the anhydrous residue of the coffee drink yields about 10% oil. Some properties of the oil are reported in Table 1. The saponification number is very high but is lower than that for coconut oil, whereas the free fatty acid concentration and the iodine value are similar to the values for other oils of industrial interest. The content of unsaponifiable matter is greater than that of oils and greases utilized for food. The latter value is explained by the fact that coffee oil, in addition to triglycerides (about 75%), contains remarkable quantities of other fat components (6 ). Comparison of the fatty acid profile of coffee oil (from the grounds) with those of common oils reveals similarities between coffee oil and palm oil. Palmitic acid is predominant. Table 2 summarizes the percentages of fatty acids of coffee and palm oil. Because of these results, we hydrolyzed the coffee oil with soda and obtained a soap that showed good detergent and foaming properties (Fig. 1) similar to those of olive oil soap and commercial products. In the detergent industry, coffee oil may be employed as an antifoam and in the composition of shoe creme. The excessive use of inorganic fertilizers in agriculture has resulted in the progressive depletion of organic matter from the soil. The high content of organic matter in the degreased coffee grounds (Table 3) permits their utilization to improve the fertility of such soils poor in organic matter,
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Palmitic (C16:0) Palmitoleic (C16:1)
0.2
—
49.8 0.2
—
32.9
32–48
—
0–1.2
Stearic (C18:0)
11.6
7.6
1.9
Oleic (C18:1)
11.8
9.4
40–53
Linoleic (C18:2)
14.2
44.9
Linolenic (C18:3)
0.1
1.2
—
Arachidic (C20:0)
4.9
3.0
—
2–11
Gadoleic (C20:1)
0.8
0.3
—
Arachidonic (C20:2)
0.1
0.6
—
Behenic(C22:0)
1.1
Erucic (C22:1)
0.8
Lignoceric (C24:0)
0.2
0.6 — 0.2
3
2
1
0
laboratory use soap
olive oil soap
cake soap
Soap Type Figure 1. Foam number for some soaps.
Journal of Chemical Education • Vol. 78 No. 12 December 2001 • JChemEd.chem.wisc.edu
— —
4
Foam Number
Discussion
Myristoleic (C14:1)
From Grounds From Coffee
coffee oil soap
—
In the Laboratory
Table 3. Composition of Degreased Residue Parameter
Value
Carbon
48.9%
Hydrogen
6.6%
Nitrogen (N)
2.9%
C/N Phosphate (P2O5)
16.9 0.68%
Ash
2.2%
Potassium (K2O)
1.2%
Lead
Trace
Chromium
Trace
Nickel Zinc
Trace 8 mg kg ᎑1
without increasing levels of heavy metals. The heavy metal content of the residue is practically zero, meeting the standards set by the laws in force for compost. The total nitrogen content of the residue is higher than that of many composts (11) and is similar to the nitrogen content of some commercial products employed for house plants. Degreased coffee grounds may be added directly to the soil, avoiding, in such case, the preliminary preparation of the compost. It is evident that the potential uses of coffee grounds make a good example of how economical, technical, and
environmental advantages can derive from the recovery of some by-products of foods and beverages. W
Supplemental Material
Detailed instructions for the analyses are available in this issue of JCE Online. Literature Cited 1. Guy, R. D.; Ramaley, L.; Wentzell, P. D. J. Chem. Educ. 1998, 75, 1028–1033. 2. McNally, M. E. Anal. Chem. 1995, 67, 308A. 3. Taylor, L. T. Anal. Chem. 1995, 67, 364A. 4. Hawthorne, S. B. Anal. Chem. 1989, 62, 633A. 5. Snow, N. H.; Dunn M.; Patel, S. J. Chem. Educ. 1997, 74, 1108–1111. 6. Phanstiel, O.; Dueno, E.; Wang, Q. X. J. Chem. Educ. 1998, 75, 612–614. 7. Longman, G. F. The Analysis of Detergents and Detergent Products; Wiley: New York, 1975. 8. Official Methods of Analysis, Vol. 2, 15th ed.; Helrich, K., Ed.; Association of Official Analytical Chemists: Arlington, VA, 1990. 9. Welcher, F. J. Standard Methods of Chemical Analysis, Vol. 2, 6th ed.; Van Nostrand: New York, 1963; Part B, p 2308. 10. Guy, R. D.; Ramaley, L.; Wentzell, P. D. J. Chem Educ. 1998, 75, 1028–1033. 11. Bargagli, R.; De Luca E.; Devoto, F.; Martella, L.; Massari, G. Biol. Ital. 1997, 27, 23–29.
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