Size Reduction and Sieve Analysis PDF

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Experiment 4 Size Reduction and Screening: Sieve Analysis Bryle Kristann C. Camarote, Nimrod B. Romelo, & Sarah Jane I. Valdon University of the Philippines Visayas, School of Technology, UPV, Miagao, Iloilo I. Theory Many natural and manufactured materials occur in dispersed form, which means t...

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Experiment 4 Size Reduction and Screening: Sieve Analysis Bryle Kristann C. Camarote, Nimrod B. Romelo, & Sarah Jane I. Valdon University of the Philippines Visayas, School of Technology, UPV, Miagao, Iloilo I.

Theory

Many natural and manufactured materials occur in dispersed form, which means that they consist of differently shaped and sized particles. The particle size distribution, i.e. the number of particles of different sizes, is responsible for important physical and chemical properties such as: (a) mechanical bulk behavior, (b) surface reaction, (c) taste, (d) miscibility, (e) filtration properties and (f) conductivity. These properties highlight the importance of having knowledge about the particle size distribution, particularly within the context of quality assurance in the production of bulk goods. If the particle distribution changes during the manufacturing process, then the quality of the finished product also changes (Retsch Gmbh & Co., 2004). In some processes, solid materials usually occur in size which are too large to be operated. These solids are reduced in size to subdivide larger solid particles into smaller ones. Solids may be reduced in size by a number of methods such as crushing, grinding, rubbing, and cutting (Geankoplis, 2003). Size reduction process is also termed as comminution or pulverization. Normally, size reduction may be achieved by two methods, namely precipitation or mechanical process. In the precipitation method, the substance is dissolved in an appropriate solvent. This method is suitable for the production of raw materials. In the mechanical process, the substance is subjected to mechanical forces using grinding equipment. Particles subjected to size reduction can now be examined to determine its particle size distribution. Several methods are used in determining the particle size distribution. Choosing a particular method depends primarily on dispersion status, i.e. on the degree of “fineness” of sample. The oldest and best known method is particle size determination by sieve analysis. Sieving is the separation of a fine material from a coarse material by means of a meshed or perforated vessel. The aperture of a sieve may be regarded as a series of gauges which reject or pass particles as they are introduced to the aperture. This theory was actually in practice during the early Egyptian era as grains were sized with 'sieves' of woven reeds and grasses (Allen, 1981). A series of sieves usually in 21/n series, each screen having larger openings than the one below, are used to characterize particles into size ranges (Foust et al., 1980). An example of sieve apparatus is shown in Figure 1 below.

Figure 1. Sieving apparatus (Forney LP, 2015) 1

During sieving, a known weight of the sample is subjected to horizontal or vertical movement in accordance with the chosen method. It is placed upon the top of a group of nested sieves (the top sieve has the largest screen openings and the screen opening sizes decrease with each sieve down to the bottom sieve which has the smallest opening size screen for the type of material specified) and shaken by mechanical means for a period of time, as shown in Figure 2 below. This causes a relative movement between the particles and the sieve; depending on their size, the individual particles either pass through the sieve mesh or are retained on the sieve surface. The likelihood of a particle passing through the sieve mesh is determined by the ratio of the particle size to the sieve openings, the orientation of the particle and the number of encounters between the particle and the mesh openings (Retsch Gmbh & Co., 2004).

Figure 2. Schematic diagram of sieve analysis (Gupty, 2003) The products of size reduction process are defined in terms of the particle-size distribution. Particle size distribution curves are generated by plotting cumulative percent passing versus particle size and by plotting percent mass retained versus particle size. For calculations and most comparisons, complete particle-size analysis is necessary (Geankoplis, 2003). Particle size determination has become a critical application in chemicals, food, paints, cosmetics, coatings, materials, and many other industries. Particle size, shape, density, and distribution affect the physical properties and chemical behaviors of all the products. For example, sieving is typically used when the drug substance is close to the particle size specification, and it can be met by removing the oversized particles. Sieving can also be used to break agglomerates. A sieve or screener is an essential part of every pharmaceutical production process, particularly as product quality and integrity are so important. The use of a sieve gets rid of oversized contamination to ensure that ingredients and finished products are quality assured during production and before use or dispatch (Walker, 2014).

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II.

Objectives

This experiment aimed to determine the particle size distribution of the ground macaroni pasta using sieve analysis. Specifically, it aims to: i. Determine the percent passing of particles in each sieve with mesh numbers 10, 25, 35, 45, 120, 140, and 200; ii. Obtain a particle distribution curve by plotting particle size versus mass retained iii. Obtain a cumulative %passing curve by plotting cumulative %passing vs particle size

III.

Scope and Limitations

The experiment was done at the School of Technology, University of the Philippines Visayas Miagao, using the available sieving set-up. The particle size distribution of other materials other than the macaroni pasta were not included in the experiment. Utilizing different materials will put into account the difference in the structural lattice of the samples which in turn will affect the particle size distribution using the same size reducing equipment. The size reducing equipment used was a size reducer located in Lecture Room 4. Furthermore, other parameters of the sample that can affect the particle size distribution such as moisture content, brand of pasta, and ingredients, were not taken into consideration. The presence of moisture will lower the grinding and sieving efficiency, and different brands and ingredients could mean variation in the mechanical structure and rigidity of the sample, thereby affecting the resulting particle size distribution.

IV.

Methodology 

A. Materials  Macaroni pasta sample  Spatula  Size Reducer  Aluminum foil  (2) 500-mL Beaker  Oven dryer  Desiccator

   

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Sieving set-up with mesh numbers 10, 25, 35, 45, 120, 140, and 200 Brush for cleaning the sieve trays Mechanical shaker Analytical Balance PPE (e.g. lab gowns, mask, gloves)

B. Methods Prior to the experiment, the Material Safety Data Sheet of the macaroni pasta sample was reviewed and proper Personal Protective Equipment attire was observed. The laboratory materials such as spatula and 500-mL beakers were borrowed from the lab technician. Permission to use the oven dryer, desiccator, sieving set-up with the specified mesh numbers, mechanical sieve shaker, and analytical balance was done in order to ensure usage of the stated apparatus and equipment. The sieve trays were cleaned using brush to free the mesh screens from foreign contaminants. Using a beaker, 230 grams of macaroni pasta sample was weighed in an analytical balance. To obtain a mixture of fine and coarse particles, the weighed sample was grinded for one minute via size reducer located in Lecture Room 4. Consequently, the ground sample was transferred to an aluminum foil and dried in an oven at 103⁰C for one hour. The dried sample was then stored in a desiccator for five minutes to prevent moisture absorption from the surroundings. Simultaneously, the initial weight of the eight trays with mesh numbers 10, 35, 45, 60, 80, 120, 140, and 200 as well as the bottom pan were obtained and recorded. The sieve trays were stacked accordingly trays in order of increasing mesh number from top to bottom and was securely placed on the mechanical shaker. Furthermore, the dried sample from the desiccator was weighed and the obtained weight was used as the basis for analysis. The sample was transferred to the top sieve with the Figure 3. Schematic shaker set to run for five minutes. Figure 5 displays the diagram of sieve analysis schematic diagram of sieve analysis. After which, the shaker was turned off and the final masses of the sieve trays were recorded in order to determine the amount of sample retained in the pan and each of the trays. The laboratory materials were then clean and the borrowed equipment were returned to the lab technician.

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V.

Results and Discussion Table 1. Grinding Efficiency of the Size Reducer Mass of macaroni pasta before grinding 400 grams Mass of macaroni pasta after grinding 407.25 grams Efficiency 101.81%

In this experiment, macaroni pasta was used as a sample. Before the sieve analysis, macaroni pasta was ground into powder using the size reducer equipment in the unit operations laboratory. 400 grams of sample was fed into the size reducer equipment and 407.25 grams of powdered sample was recovered, resulting to a 101.81% efficiency. Based from the results shown in Table 1 above, more than a 100% efficiency was obtained for the size reducer equipment; which is scientifically impossible. This inaccuracy in the results was due to the stuck powdered samples in the equipment from previous experiments. Due to the large size of macaroni pasta, the stuck particles in the equipment were pushed out during the grinding process and was mixed with the powdered macaroni pasta. This resulted to obtaining a powdered sample greater than 400 grams. In other words, the sample used in the sieve analysis was a mixture of ground macaroni pasta and other particles.

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% Mass retained

50 40 30 20 10 0 0

500

1000

1500

2000

Particle Size (µm)

Figure 4. Percent Mass Retained vs Particle Size

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2500

Cumulative Percent Passing (wt%)

120 100 80

60 40 20 0 0

500

1000

1500

2000

2500

Particle Size (µm)

Figure 5. Particle Size Distribution: Cumulative Percent Passing vs Particle Size The ground macaroni pasta was initially weighed and 230.30 grams of it were used in the sieve analysis. The top sieve with a mesh size of 2000 µm retained 25.56 g dried particles which accounts for 11.14% of the total sample. As what can be observed in Table 2 of the Appendices, several particles were retained on the sieve which have sizes greater than 2000 µm. This implies that the sample was not ground intensively and uniformly. On the other hand, most of the powdered dry sample was retained at the second sieve with a mesh size of 707 µm, amounting to 49.17% of the total sample. The percent mass retained sample versus the particle size is shown in Figure 5 above. As observed in the figure, indeed most of the sample was retained at this sieve. This means that most of the particles of the sample have a particle size smaller than 2000 µm but larger than 707 µm. All sieves with mesh sizes 500 µm, 355 µm, 125 µm, 106 µm and 75 µm, including the bottom pan have found to retain certain amount of samples. These results showed that particle sizes smaller than the 7th sieve with a mesh size of 75 µm, were present in the powdered macaroni pasta sample. The percent mass retained in each of the sieve including the bottom pan were found to be 14.04%, 9.99%, 10.50%, 2.52%, 1.86% and 0.76%, respectively. Through sieve analysis, particle size distribution of a specific sample can be obtained. It provides the information on which particles are either too large or too small. It also allows one to obtain an evenly distributed sample which is very important in the industry especially in food analyses. Shown in Figure 6 above is the particle distribution curve obtained by plotting cumulative percent passing versus particle size based from the data calculated. This graph coincides with the graph from Perry’s Chemical Engineering Handbook (2008) for particle size distribution curves. As what can be seen in the graph, it has an increasing trend indicating that lesser particles pass through the sieve as the particle size decreases. There is a greater percentage of particles that pass through the sieves having larger mesh sizes. From the results of the experiment, the mass of the powdered sample before the sieve analysis was 230.30 grams which only had 229.41 grams after being put into the mechanical shaker for 5 minutes and weighed. There was a loss of about 0.89 grams in the sample which was maybe because some particles were spilled out of the sieve during weighing of the individual sieves.

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VI. Conclusion The size reducer equipment was not so accurate in grinding the sample. Some powdered samples can get stuck on it and removal of these require tedious methods. On the other hand, through sieve analysis, the particle size distribution of the ground macaroni pasta sample was obtained. The cumulative percentage passing at mesh numbers 10, 25, 35, 120, 140 and 200 were 100%, 88.86%, 39.68%, 25.65%, 15.66%, 5.16% and 2.64%, respectively. The percent mass retained and the cumulative percentage passing were plotted versus the mesh size of the sieve. The generated graph coincides with the particle size distribution curve found on the Perry’s Chemical Engineering Handbook.

VII. Recommendation For a more evenly distributed powdered sample, a high-grade blender is recommended. Although limited only to softer food samples unlike macaroni pasta, it is easier to use and requires lesser time in reducing the particle size. Also, the operation time of the mechanical shaker can be lengthened and observe how it affects the results.

VIII. References Allen, T. (1981). Particle Size Measurement. New York: Chapman and Hall. 124-131. Forney LP. (2015). Sieve Kit – Soil Particle Size Analysis Set. Retrieved 3 March 2017 from http://www.forneyonline.com/index.php/sieves/soils-particle-size-analysis-kit-sievestack-kit-4.html Foust, A., Wenzel, L., Clump, C., Maus, L., & Andersen, L. (1980). Principles of unit operations (2nd ed.). John Wiley & Sons (Asia) Pte Ltd. 153-159. Geankoplis, C. (2003). Transport process and unit operations. Singapore: Prentice Hall. 840-849. Gupty, C. K. (2003). Chemical Metallurgy. Wiley-VCH Verlag. 138-142. Retsch Gmbh & Co. (2004). The Basic Principles of Sieve Analysis, 1–8. Retrieved March 3 from http://www.ninolab.se/fileadmin/Ninolab/pdf/retsch/documents/af_sieving_basics_2004_en. pdf Walker, G. (2014). “Sieve Analysis”. Retrieved 3 March 2017 from http://www.innopharmalabs.com/tech/applications-and-processes/sieve-analysis.

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IX. Appendices

A. Raw Data

Table 2. Weight of the Sieve Trays Before and After Sieving Mesh No.

Mesh size

10 25 35 45 120 140 200 Pan

2000 707 500 355 125 106 75 0

TOTAL

mass of empty sieve, g 453.31 410.59 376.42 363.08 523.1 343.41 341.44 367.47 3178.82

mass of sieve & particles, g

mass of particles, g

478.87 523.4 408.62 386 547.18 349.2 345.7 369.26 3408.23

25.56 112.81 32.2 22.92 24.08 5.79 4.26 1.79 229.41

X 100 100 100 100 100 100 100 100 100

% mass retained

cumulative weight passing, g

Cumulative % passing

11.14 49.17 14.04 9.99 10.50 2.52 1.86 0.78 100

229.41 203.85 91.04 58.84 35.92 11.84 6.05 1.79

100.00 88.86 39.68 25.65 15.66 5.16 2.64 0.78

B. Sample Calculation For Mesh No 10 and 25 Mass of particles = Mass of sieve & particles – mass of empty sieve = 478.87g – 453.31g = 25.56 g

%mass retained =

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Cumulative weight passing = Total mass passed – mass retained = 229.41g – 25.56g = 203.85g Cumulative % passing = % passing – %mass retained = 100% - 11.14% = 88.86%

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C. Photos

Figure 6. Unground Macaroni pasta sample

Figure 9. Weighing of the ground macaroni sample in an analytical balance

Figure 7. Feeding of Macaroni sample into the size reducer

Figure 10. Feeding of the ground macaroni into the sieve tray

Figure 8. The size reducer with the ground sample 9

Figure 11. Operating the mechanical sieve shaker

Figure 12. Weighing of the sieved macaroni samples

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