Processing and treatment of polymers, plastiques and other chemical products
Gentle processing technology of high-value products
We define chemical products as materials with a defined composition of various components which are not listed separately. This can be pure materials as well as mixtures. This definition is not clear-cut and may have different meaning depending on the context. Chemical products can be differentiated terminologically regarding to their different degree of purity. Chemicals with a high purity are termed fine chemicals while the term technical chemicals names materials with a lower purity.
Chemical products e.g. are natural rubber, paint, cosmetics, pharmaceuticals, synthetic fertilizer, adhesives, building protective agents, cleaning agents and pyrotechnics. In processing of these substances chemical conversion is not a necessarily step but mostly physico-chemical procedures like mixing, milling, screening, extraction or emulsifying are used.
The first chemicals employed in industrial processes were sulphuric acid, soda, chlorinated lime, synthetic fertilizer, plastics and colorants. These were followed by pharmaceutical agents like acetylsalicylic acid, chloral hydrate and ether.
In addition to these classical screening applications, we are also capable of sieving MOFs (Metal Organic Frameworks). We recommend RHEWUM MDS screens, because of their unbeatable selectivity. The machine sieves MOFs gentle and without unnecessary product waste.
MOFs are made of microporous crystalline, which consist of metallic crystal structures, known as SBUs (secondary building units), and organic molecules can be constructed (linkers) as connecting elements between the nodes. The resulting pores in the lattice structure will be filled in use with other substances. Application areas are for example the storage of gas, but also the selective separation of gases and possibly liquids. The extremely large internal surface is brought into use, which may be greater than, for example that of activated carbon and the precisely defined lattice structure.
For materials of this class there are - besides the abbreviation MOF - a variety of other abbreviations such as IRMOF, HKUST, ZIF, COF, or MFU but also BAF (=University Bergakademie Freiberg.
For the gentle treatment of this high grade chemical products in separation processes basically a screening process has to be chosen which processes the granulates resp. powders carefully without producing additional dust.
RHEWUM: preparation processesing technology for polymers
In the production of synthetic granules the polymerised pellets become screened to defined lenghts. Conventional particle size of these “On-size” pellets is between 1.6 mma nd 6.0 mm. For cooling and hardening the granues become extruded in a water quench. Afterwards the water is separated from the solids and the geranules are screenid to the defined sizes. Often the screening machines are made of stainless steel and the pellets are screened on punched plates. Sometimes the screening takes part under exclusion of oxygene. In this cases the screening machines are executed gas tight and flooded with an inert gas, e.g. nitrogen. In some cases the surface of the machines is polished.
Another task in the area of polymers is the optical sorting of charges which are contaminated in terms of colour. In case of an unwanted mixing of granules with different colours they become separated by optical sorting.
Polymers are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polytetrafluorethylene (PTFE), polymethylmethaacrylate (PMMA), polyamide (PA), polyester , polycarbonate (PC) and polyethylenterephtalat (PET). In the polymerisation process these polymers are generated from monomers by polymerisation, polycondensation or polyaddition. Furthermore thermoplastics, duroplastics and elastomers are differentiated regarding to their physical characteristics.
Soda Ash, Sodium Carbonate – a very fine sieving
Soda Ash, Sodium Carbonate is an important additive in glass production as well as in the production of detergents and whiteners. In the glass production process soda ash is mixed with glass and melted on. The soda ash is acting as flux melting agent which reduces the melting point of the quartz powder (to approx. 850°C). When bleaching with soda the soda is dissolved after drying and screening. In the last step of neutralisation in bleaching of cotton the acid carry-over is absorbed by soda solution. In modern detergents soda is contained only indirectly as regulator for foam formation (curd soaps).
Typically the screening task is to remove dust from the final soda product. The screening process mostly proceeds in a grain size range between 0.1 mm and 1.15 mm. The feed rates change between 5 t/h and 75 t/h per screening machine. Besides the product screening protection screening before packaging of the final sales products is part of the process. The possibly generated soda agglomerates are removed reliably by screening between 1 mm and 4 mm.