Description
Perlite for Filtration
The physical character of expanded perlite bubbles lends itself
to a variety of special purposes – including use as a filter aid
separating small solid particles from liquids.
Lightweight expanded perlite bubble structures are milled and
classified using strictly defined processes to produce perlite
filter aids with specific flow characteristics. The various grades
utilize the jagged interlocking structures (see image right) to
create billions of microscopic channels between the filter aid
particles to produce optimum flow rates and clarification abilities
for a wide variety of applications.
The Benefits of Perlite as a filter aid
Perlite filter aids are lightweight, inert, impart no taste or odor
to liquids being filtered, and are virtually insoluble in mineral
and organic acids at all temperatures. Solubility in strong
alkaline solutions varies depending on temperature and contact
time.
Without using a filter aid the solid particles in the liquid will
soon accumulate on filtering surfaces and block them.
A perlite filter aid makes a filtering layer (cake) that transfers
the actual filtering from the septum to the whole mass of filter
aid. Filtration occurs in the tiny pores formed by the fine
particles of filter aid.
Volume-Based Pre-coat Filtration
Perlite filter aids provide users with a lightweight material
choice. Perlite filter aid grades provide the user with a density
advantage from *0 to *0% over other types of filter aids. Perlite
filter aid dry density ranges from **0 to **0 kg/m3 (6 to *2
lb/ft3), and the filter cake density range is **0 to **0 kg/m3 (7
to *7 lb/ft3). In contrast, other filtration materials produce
equal performance filter cakes in the range of **0 to **0 kg/m3 (*5
to *5 lb/ft3).
Expanded perlite provides larger volumes with low bulk density
compared to other filter aids. Experience in a variety of
applications has shown that most filter aid users can economically
switch to perlite from other pre-coat filter aids without
sacrificing performance.
Usable With Standard Equipment
Perlite filter aids can be used with either pressure or vacuum
filtration equipment. Perlite generally replaces other filter aids
on a one-to-one volume basis - for example; a cubic measure of
perlite will replace the same volume of other filter aids.
Selection of the optimum grade and dosage may require plant or
laboratory filtration tests.
Flow Rates of Grades
Perlite filter aid grades from various manufacturers range from 0.2
– 6 Darcies. (The Darcy is a common unit of flow rate for filter
aids.) A material with a permeability of one Darcy passes 1
milliliter per second per square centimeter of a liquid of 1
centipoise viscosity (approximately that of water) through a cake 1
centimeter thick at a differential pressure of 1 atmosphere.
The higher flow grades are especially applicable to use with highly
viscous liquids such as syrup, resins or gelatinous slurries.
Productivity, clarity and flow rates may be increased through the
use of perlite filter aid grades. These traits are accomplished
during the liquid's path through the channels created by the
jagged, interlocking particles.
Easy Cake Release
Additional benefits of perlite filter aids come at the end of the
filter cycle. Perlite filter cakes remain porous and do not
compact. Filter cakes built up under pressure release easier when
perlite is used. This release facilitates cleaning, potentially
reduces manpower requirements, and increases productivity. The
lower weight of perlite filter cakes may also reduce disposal
costs.
