| 摘要 |
<p>The parent patent relates to the heat treatment of a mixt. of finely-divided solids (I) and gases (II) by introducing opt. preheated (II) into the lower part of a vessel with rotational symmetry, adding (I) to (II) at the latest after entering the vessel, bringing the mixt. to a certain temp. with the vessel mantle and discharging in the upper part of the vessel. The mixt. is passed upwards in at least 2 largely closed, level overlying rings and transported from one to the next in a concentric inner zone of the rings. The improvement comprises the use of (I) consisting of 80-100 wt. % homo-, graft- or co-polymer of min. 50, pref. min. 85 wt. % CH2:CHCl and treatment in the presence of Cl2. (I), esp. polymers produced by the bulk process, can be subjected to intensive heat treatment to remove residual monomer without intense discolouration. The equipment is relatively simple, robust and space-saving and allows classification of the particles. (II) pref. contains 10-10,000, esp. 20-200 mg Cl2/m3. In an example, treatment of PVC (K value 57, average particle size 100 um; residual CH2-CHCl content 7 ppm) at 90 degrees C using gas contg. 59 mg Cl2/m3 reduced the CH2:CHCl content to under 5. Discoloration was reduced if the Cl2 content was increased, e.g. to 156 mg/m3.</p> |
