Chemical and Biological Engineering ETDs

Publication Date

1970

Abstract

There have been several methods commonly used for measuring particle size distribution of particulate systems in the subsieve region, i.e., less than 45 microns. Of the many indirect procedures of particle size analysis, sedimentation methods are among the most satisfactory and most widely used. - The value and appeal of sedimentation techniques are twofold: (1) the equipment required is simple and (2) a wide range of sizes may be measured readily with considerable accuracy and reproducibility. These techniques utilize the dependence of the falling velocities of particles on their size.

This study widely encompasses the various factors involved in the size distribution analysis of particulate systems, in particular carbon black. First, it was decided that acetone dispersed carbon black satisfactorily without a dispersing agent. Photomicrography was employed to ensure there was no agglomeration. A simple sedimentation pipette, invented by Andreason, was used and from the data obtained, a characteristic curve for the carbon particles was plotted. From the curve the percentage by weight of any sample in a given size range could be obtained.

The size range investigated in this study was between 38.4 and 1.5 microns. From theory it was found that this constituted the ideal size range for gravitational sedimentation analysis, by the pipette method. Arithmetic cumulative distribution and size frequency plots (histograms) showed that the particles tend to become finer with increasing temperature of their formation (about 2100°F). Thus, the coarsest particles resulted at the lowest formation temperature in a carbon black pilot plant (run 1, 1900°F) and the finest at the highest temperature (run 4, 2200°F). It was of interest to know whether the size distribution of carbon black followed a certain mathematical function or not. For this purpose, log-probability plots for the four runs were drawn. It was found that the resulting plots were asymptotic curves, showing that the distribution was not a simple log-normal type. A modified log-normal distribution was proposed whereby a straight line was obtained when (MMoo/Moo -M), rather than M, was plotted against the percent undersize, where M = size of particles Moo= maximum size of particles formed.

It was concluded that the sedimentation method for particle size distribution analysis is a versatile method, whenever rapid size determinations are required in the laboratory. Although many weighings were involved, the method was accurate and suitable for occasional analyses. The common criticism that sedimentation techniques are valid for spherical particles under restricted conditions, is not vindicated because due consideration is usually given to the convenience of reporting size rather than settling velocities. Thus particulate matter may be represented by a rate of sedimentation distribution in a specific medium, and the distribution reported will be free of theoretical assumptions. The main disadvantages of the pipette method (sampling, volume change and solution turbulence errors) are probably too small to be of consequence in routine work, but corrections must be applied for accurate analysis.

A verification of this method was done by a visual microscopic technique. It was found that the two results were in good agreement.

Document Type

Thesis

Language

English

Degree Name

Chemical Engineering

Level of Degree

Masters

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

James H. Turner

Second Committee Member

Thomas T. Castonguay

Third Committee Member

Kenneth Edward Cox

Fourth Committee Member

George Heinz Quentin

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