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Title: Cationic polyelectrolytes in coal water mixture formulations.
Author: Stephens, Brian Paul.
ISNI:       0000 0001 3480 2974
Awarding Body: Polytechnic, Huddersfield,
Current Institution: University of Huddersfield
Date of Award: 1991
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A novel range of cationic polyelectrolytes was assessed as potential 'additives for coal-water mixtures (CWMs). The anionic polyelectrolytes Lomar D and Borresperse NH were obtained to provide a comparison with the cationic compounds. Several typical UK coals were selected f~r CWM preparation giving variation in coal type and particle size distribution (PSD). The polyDADMAC (diallyl dimethyl ammonium chloride)-containing cationic polyelectrolytes were very good dispersants of powdered coal. An app~ratus was designed and assembled for the preparation of CWMs by the dry blending of coal and polyelectrolyte/water solution. In general CWMs containing cationic polyelectrolytes were more viscous and more stable than those containing anionic polyelectrolytes. In addition CWMs containing cationic polyelectrolytes did not have yield stresses. The most stable and less compacted CWMs contained either polyDADMAC (1) or polyDADMAC (P) (a peroxide treated polyDADMAC homopolymer). Adsorption studies of these cationic polyelectrolytes and the anionic polyelectrolytes on coal indicated that approximately twice more anionic than cationic polyelectrolyte was adsorbed at the plateau of the adsorption isotherms for these systems. The adsorption layer of the anionic polyelectrolytes probably lies flat on the coal surface forming a more complete monolayer. This leads to reduced CWM viscosity and rapid coal particle settlement. In contrast ~he cationic polyelectrolytes probably adsorb only partially with a large proportion of the polymer chains protruding into the aqueous phase. This leads to higher CWM viscosity and greater resistance to coal particle settlement. The rheological classification of CWMs used in this study was, in general, dilatant. It was found that CWM viscosity increased with dose level of polyelectrolyte. Throughout the rheological measurements, viscosity measurements and stability tests the cationic polyelectrolytes polyDADMAC (1) and polyDADMAC (P) performed better than either of the anionic polyelectrolytes as a single CWM additive. CWMs containing these polyDADMAC polymers were compared to two commercial CWMs. The fact that only one of the commercial samples contained a yield stress indicated that a yield stress is not essential for a commercial product. The commercial samples were pseudoplastic and contained a large percentage of coal particles < 20 ~m. In spite of this CWMs containing polyDADMAC (1) and polyDADMAC (P) performed quite well in comparison with the commercial samples. Several properties of CWMs have been elucidated which indicate that cationic polyelectrolytes, in particular polyDADMAC (1) and polyDADMAC (P), have potential in CWM formulations. A further study could investigate the atomisation and combustion properties of CWMs containing cationic polyelectrolytes, in particular polyDADMAC (1) and polyDADMAC (P).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemical engineering