Particle Size Reduction & Separation Kausar Ahmad Kulliyyah of Pharmacy http://staff.iium.edu.my/akausar PHM3133 Dosage Design 1 2011/12

Contents Particle size reduction Fluid energy mill or jet mill Air classifier mill Others Crusher Grinder Particle size separation Cyclone Others Sieves Classifiers Membrane filtration PHM3133 Dosage Design 1 2011/12

Equipment & mechanism Knife - cutting E.g. carrot slicer ( 5 mm) Crusher – compression E.g. crushing rolls (5 mm) Grinder – impact and attrition E.g. hammer/ball millls, bowl grinder (100 m) Ultra-fine grinder – attrition E.g. fluid-energy mills (5 m) Knife - cutting E.g. carrot slicer ( 5 mm) PHM3133 Dosage Design 1 2011/12

Choosing the equipment 5 mm & 100 m size of feed particles 100 to 5 m size-reduction ratio Mohr’s scale: talc=1,diamond=10 hardness of feed 600 kg/hr processing rate abrasive, soft type of material PHM3133 Dosage Design 1 2011/12

Step-by-step size reduction Feed material 10 cm Crusher : 10x Feed 1 cm Grinder: 100x Feed 100 m Fluid energy mill: 20x Product ca. 5 m HOW MANY TIMES REDUCTION? PHM3133 Dosage Design 1 2011/12

Attrition mills - principle attrition - the act of wearing or grinding down by friction hit the particles with high velocity air to fracture them increasing the impact velocity or the energy (increase temperature), produces smaller particles generate a greater amount of fines What types of materials can be processed using the attrition methods? ….and what types…. cannot…? PHM3133 Dosage Design 1 2011/12

Types of attrition mills Fluid energy mill High pressure steam, high T Compressed air, high T Air classifier mill Air FEED into slightly negative pressure compartment! Q. But why? PHM3133 Dosage Design 1 2011/12

Classifier Equipment that is used to narrow down the size distribution of product Normally built-in design i.e. comes together with the mill Classifying ability depends on Design and operation condition Feed throughput Air velocity PHM3133 Dosage Design 1 2011/12

Air classifier mill Consists of: Hammer mill Hammer mill reduces the size Classifier Classifier determines the size distribution Size and distribution depends on Design of mill and classifier Operation conditions Their speed of rotation Feed throughput PHM3133 Dosage Design 1 2011/12

Air classifier mill (ACM) PRODUCT ca. 100 m (to Fluid Energy Mill) ROTATE CLASSIFIER FEED ROTATE If the particle is TOO BIG when it enters the classifier compartment, the particle will fall down into the mill Further size reduction occurs until the particle can escape the classifier Thus the maximum size that goes out of classifier is controlled Minimum size depends on mill design e.g. height of pin ATMOSPHERIC AIR PHM3133 Dosage Design 1 2011/12

Fluid Energy Mill (FEM) FEED (from ACM) Area enlarged Superheated compressed Air/steam PHM3133 Dosage Design 1 2011/12

FEM: Design & Operation Size and distribution depends on Design Air nozzles Feed inlets Grinding chamber Operation conditions Air/steam at high pressure and temperature is introduced into the chamber and reduces the size of particles Feed throughput PHM3133 Dosage Design 1 2011/12

FEM After size reduction Air/steam at high P, T PHM3133 Dosage Design 1 2011/12

? Size reduction & separation FEED into FEM injector CYCLONE CYCLONE PRODUCT HIGH VELOCITY HOT AIR/STEAM PRODUCT PHM3133 Dosage Design 1 2011/12

Cyclone Equipment for separation To separate product from air and/or fines Based on centrifugal force Heavy particles settle down Fine particles escape PHM3133 Dosage Design 1 2011/12

Cyclone FINES OUTLET FROM FEM INLET PRODUCT PHM3133 Dosage Design 1 2011/12

Factors affecting extent of separation Design of cyclone Diameter Height Operation of cyclone Feed throughput Velocity at inlet PHM3133 Dosage Design 1 2011/12

Feed properties Need to know size distribution of the feed stream. may lead to significant cost-reduction methods such as pre-classifying the material to remove fines before milling. Thus, use air classifier mill first, followed by fluid energy mill. PHM3133 Dosage Design 1 2011/12

Controlling feed/throughput feeding the material into a mill, and handling the product discharging from it, can pose a significant problem e.g. FEM back-flow feed at a controlled rate is critical to optimizing the performance of mills. PHM3133 Dosage Design 1 2011/12

Problems with poor feed-control waste overfilling the milling zone Fail QC, waste retards exit of properly sized particles & fail QC, waste subjecting them to further size reduction and excessive generation of fines maintenance accelerate equipment wear PHM3133 Dosage Design 1 2011/12

Example of equipment wear Internal piping CONSTRUCTION MATERIAL + FEED FEM milling area PHM3133 Dosage Design 1 2011/12

Problems with FINE products Highly charged, static May produce sparks Possible explosion Need to earth equipment Very cohesive Stick to silos Form agglomerates Poor flow Add (pyrogenic) silica to allow free flow Health hazard…………….. De-duster PHM3133 Dosage Design 1 2011/12

Dust Filter http://www.pharmaceuticalonline.com/nl/347748/1849996 PHM3133 Dosage Design 1 2011/12

Exercise What do you do with so much air/steam in your milled products? What is the difference between a fluid energy mill and a fluidised bed dryer? Function? Operating principle? PHM3133 Dosage Design 1 2011/12

References Levin, M. (2002). Pharmaceutical process scale-up. New York: Marcel Dekker. p 71, 120, 205, 224, 322, 417, 501, 503 PHM3133 Dosage Design 1 2011/12