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Cellulose Industry

Preparation of Cellulose and Cellulose Derivatives

Applications

Product Reference


Preparation of Cellulose and Cellulose Ether

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 with the 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 CMC-powders.

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Fine Grinding with the Precision Knife Mill

The 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 types.

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. 

The 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.

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Precutting of Moist Cellulose Ether 

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.

Press 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 into a 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.

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Fine-Grinding of Dry Cellulose Ether

After the drying process the cellulose ether is too coarse, and it needs to be ground much finer for other necessary applications. For this fine-grinding the 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.

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Simultaneous Drying/Grinding of Moist Cellulose Ether

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 190C. 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 () and it is secured by means of an explosion barrier.

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2009 PALLMANN Industries, Inc.
PALLMANN Industries, Inc.
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