2.2. Preparation

P(SS-co-AA-co-DMDAAC) was synthesized by convenient free radical polymerization technology, which is beneficial for large-scale production. The typical synthesis process is described as follows. SS, NaHSO₃ and deionized water were added to a flask under stirring. After SS was dissolved thoroughly, the mixture was warmed to 80°C. Then, AA, DMDAAC and (NH₄)₂S₂O₈ aqueous solutions were simultaneously dripped into the flask within 1.5 h and the mixture was allowed to react for another 2 h. After polymerization, the product was cooled to room temperature. The pH value of the solution was adjusted to 7–8 by using 1 M NaOH solution. The crude product solution was concentrated, and further purified through precipitation in an excess of ethyl alcohol. Finally, P(SS-co-AA-co-DMDAAC) was obtained as a faint yellow powder.

To reliably evaluate the performances of P(SS-co-AA-co-DMDAAC) for used as a dispersant in CWS, two types of coal from Yili (Xinjiang Province, China) and Yulin (Shaanxi Province, China) were adopted for the preparation of CWS, respectively. The proximate and ultimate analyses of the coal are listed in table 1. The coal was pulverized by a FM-3 pulverizer (Shanghai Ke Heng Industrial Co., Ltd., China). The coal particles with different particle size distribution were mixed based on the following ratio: 25 wt% of 124–420 µm, and 75 wt% of less than 74 µm coal particles [22,23]. The coal was mixed with a calculated amount of dispersant and water. After stirring for 10 min at 600 r.p.m., CWS was obtained and subjected to further measurements.

Proximate and ultimate analysis.