Preparation of Cellulose
and Cellulose Derivatives
Preparation of Cellulose and
Cellulose derivatives, such
as MC, CMC, HEC, HPMC, MHEC etc, depending on the
application, are contained as additives in many products
in order to influence their characteristics.
In the construction
industry, they control the water binding ability of
cement, gypsum and fillers. As wallpaper paste, CMC is
possibly the most well known product. As additives in
washing detergents, the derivatives prevent graying and
discoloration. Cellulose derivatives are also
thickeners, and when used in foodstuffs, they enhance
composition, form, structure and consistency. In the
pharmaceutical industry, CMC contained in tablets define
active ingredient release and serve as binding agents.
Cellulose powders ground
Precision Knife Mill, type PSC have big surfaces,
thus improving the reaction and the filling weight in
the reactor. Cellulose ether is washed and granulated
and the still moist product is ground and homogenized by
means of knife mills or double stream mills; this
results in a product where drying may be carried out
easier and with better results. Afterwards the cellulose
ether is ground to a fineness of less than 0.5 mm, or
pulverized to less than 0.18 mm in a
Turbofiner mill, type PLM, or a
Contra-Selector mill, type PPSR, depending on the
requirement. Simultaneous grinding and drying is
possible on these mills by hot air induction, thereby
significantly simplifying the process. In the
pharmaceutical industry, cryogenic grinding systems with
counter rotating pin mills produce the finest
original materials for the production of cellulose ether
are hard wood, coniferous wood, or cotton linters
cellulose. Cellulose comes in the form of sheet, roll,
or loose material, such as pre-cut cotton bales, and the
Precision Knife mill can grind each of these cellulose
Conveyor belts are utilized
to feed loose materials, and a metal protector prevents
any metallic contaminations. Cellulose sheets or
cellulose rolls are fed into the grinding chamber via an
integrated draw-in device. The produced fine cellulose
powders, of high bulk density, improve the reaction and
the filling weight in the reactor.
Precision Knife Mill, Type PSC has been designed
especially for the production of these powders. The
upper part of the housing can be opened hydraulically
which enables easy access to the grinding chamber, and
easy cleaning and maintenance.
After washing and
granulating, the cellulose ether moisture may be up to
60% and is in a form of press cake or irregular lumps.
For the subsequent drying, or for the chemical recovery
of alcohol, from stripped alcohol ethers, homogenous
granules are desired.
cakes are ground by means of
Knife Mills, Type PS, between rotating and fixed
knives. The fineness is determined by the size of the
screen holes. Gas tight mills are available for
processes where the addition of nitrogen is necessary.
Lumps can be fed directly
Double Stream mill Type PSKM. The lumps are ground
by impacting and cutting on a combination of grinding
tracks and screening rings. The obtained homogenous
particles simplify the feeding into the dryer and
improve the drying process.
Each mill can be delivered
in stainless steel design.
After the drying process the
cellulose ether is too coarse, and it needs to be ground
much finer for other necessary applications. For this
Turbofiner Type PLM is used. The material is ground
in a high-turbulent air flow between the fast rotating
beater plates and the stationary grinding zone.
The material is fed by
vibratory feeder, dosing screw or rotary air lock either
through a cyclone separator or directly into a filter.
Then, it is separated on a screening machine according
to its fineness. Coarse particles are recycled back into
the grinding process.
After the reactor, the
cellulose ether is of elastic to plastic consistency. A
fine and dry powder is necessary for further use of the
cellulose ether. The
Turbofiner Type PLM allows the product-gentle
pulverizing and simultaneous drying of moist cellulose
ethers with starting moisture of 60% of weight.
Ambient air is sucked in and
cleaned by an air filter, and then an air heater heats
the air up to 190°C. Moist feed material is transported
via a rotary valve into the hot air stream and into the
mill which pulverizes the material in a high activity
rotational field by means of micro whirls. The
pulverized product is pneumatically transported and
dried further on the way from the mill to the filter.
The filter separates the ground material from the
conveying, respectively the drying air, and then it
discharges it via a discharging device from the filter.
The retention time of the material in the mill as well
as the degree of drying is determined by the air flow.
Afterwards the ether is screened, mixed and ensiled. The
pulverizing system is designed for an explosive pressure
of 10 bar (ü) and it is secured by means of an explosion