Study On The Preparation And Property Of Starch Based Briquette Binders

Recent years, smog in Jing-Jin-Ji is serious. Coal combustion pollution is one of the main reasons. Promotion of clean briquette is an effective way to reduce the pollution of coal burning.In this thesis, corn starch was subjected to gelatinization, oxidization modification and crosslinking modification to obtain pure starch briquette binder, oxidized starch briquette binder, and cross-linked starch briquette binder, which are characterized by cold compressive strength and re-dry strength. The factors which could affect the cold compressive strength and re-dry strength were investigated systematically. According to the results, the reaction conditions of different starch based briquette binders were optimized, and the relationship between starch based briquette binders and cold compressive strength and re-dry strength was studied. Main results were summarized as follows:1. Study on the preparation condition of pure starch briquette binder. During the process, the main reaction conditions which were expected to affect cold compressive strength and re-dry strength were investigated systematically, including gelatinization times, gelatinization temperatures and starch dosages. By orthogonal test, the optimal reaction conditions are obtained: starch dosage is 1.50%(for coal), gelatinization temperature is 95 oC, and gelatinization time is 60 min. The cold compressive strength of briquette in this condition could reach 492N/A, which could conform to the local standard of clean briquette in Hebei province. However, re-dry strength of this briquette could not be measured due to its poor water resistance.2. Study on the preparation condition of oxidized starch briquette binder. Potassium permanganate was used to modify starch. Comparing viscosity, carboxyl content and infrared spectra(FTIR) of oxidized starch, and cold compressive strength and re-dry strength of briquette, the effect of preparation conditions(pH, temperature, oxidant dosage and starch dosage) on the properties of starch could be obtained. According to orthogonal tests, the best preparation conditions are oxidized starch dosage 1.00%(for coal), potassium permanganate dosage 3%(for starch), oxidation temperature 35 oC, and activation of alkalinity pH = 11. In this condition, the cold compressive strength of briquette could reach 485N/A, which complies with the local standard in Hebei Province. However, after oxidation modification, the hydrophilicity of oxidized starch briquette binder is improved, which lead to bad water-resisting property for briquette. Re-dry strength after immersion could not be measured according to the Determination of Compressive Strength of Industrial Briquette after Soaking and Re-drying.3. Study on the preparation condition of cross-linked starch briquette binder. Borax was used to modify starch. Comparing sediment volume and infrared spectra(FTIR) of cross-linked starch, and cold compressive strength and re-dry strength of briquette, the effect of preparation conditions(cross-linker concentration, crosslinking time, crosslinking temperature and cross-linked starch dosage) on the properties of starch could be obtained. According to orthogonal tests, the best preparation condition is cross-linked starch dosage 1.50%(for coal), crosslinking time 30 min, crosslinking temperature 45 oC, and cross-linker concentration 0.50%. In this conditions, the cold compressive strength of briquette could reach 511N/A, which complies with the local standard in Hebei Province. The briquette in this conditions also has certain water resistance ability, and re-dry strength after immersion could reach 388N/A.4. According to FTIR analysis of three starch based briquette binders, a positive correlation between the number of oxygen-containing functional groups in binders and briquettes and cold compressive strength for briquettes, and a negative correlation between the number of oxygen-containing functional groups in binders and briquettes and the water resistance for briquettes could be found. According to mercury porosimeter analysis of different briquettes, it was found that the macroporous structure of briquettes is one of the key factors affecting cold compressive strength of briquette. The more developed macroporous structures are, the lower cold compressive strength is. According to SEM photos of different starches, it could be concluded that the more severe the crystal shell on the surface of starch granule is damaged, the lower the viscosity of the starch binder is, and the better the bonding property of the starch binder is. According to SEM photos of different briquettes, briquette with higher internal compaction has higher cold compressive strength.