Calcium Chloride Supported on Purified Spent Bleaching Earth as Potential Adsorptive Material for Air Dehumidification Application
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Date
2013-03-22
Authors
Mathaga, Kihara John
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Abstract
Thecosmic limitation of high humid environment in tropic regions spurs a lot of interest to the
developmentof low cost desiccants. Calcium chloride has been indicated as the oldest adsorbent
desiccant among chemicals and gas dehydration industries. However, calcium chloride
dissolution behaviour makes it difficult to be utilized well as desiccant. The first attempt to
suppressdeliquescence behavior for dehumidification purpose was in 1976 where silt loam was
usedas the host material. Further work has been presented to achieve the same goal using pure
clay.The pollution effect of the spent bleaching earth (SBE) necessitated an investigation to
determinewhether SHE could be used to eradicate the deliquescence behaviour of calcium
chloride.The spent bleaching earth was purified to remove the entrained hydrocarbons through
three steps; solvent extraction using hexane, oxidation of the hexane residues using 30%
hydrogenperoxide and thermal oxidation. The ratio of 1 gram spent bleaching earth to 5 ml
hexane and reactivation temperature of 550 DC in thermal oxidation were established as the
optimalconditions for reactivation of spent bleaching earth. Hexane was found to remove about
25% of the entrained hydrocarbons mainly oil which was characterized. The results for the
characterization indicated that the oil recovered could be utilized in non-food applications such
as bio-lubricant, detergents, soap and other oleochemicals. Hydrogen peroxide removed about
10%of the remaining hydrocarbons after hexane extraction and thermal treatment about 5% after
the two preceding steps. Laboratory studies were conducted to assess the mixing ratio of the
inorganic salt, auxiliary binder and purified spent bleaching earth in the development of the
composite adsorbent. Samples with different ratios were subjected to a humid environment of
88%relative humidity, by preparing a saturated solution of potassium chromate in a sealed
beaker.The samples which recorded.minirnum surface wetting, spalling and cracking as well as
high water uptake were further subjected to multiple sorption cycle tests. For all the tests
performed, sample ratio of 3 :1 :0.25 of PSBE :CaCb :starch recorded the best results and was
furthertested for its sorption properties at different relative humidity's. Sorption properties were
carried out in a humidity chamber at 11.3, 32.78, 43.16, 52.89, 75.5 and 93.58% relative
humidity where the sorption capacity recorded 14.88, 17.60, 20.95, 24.40, 33.40 and 45.55%
water uptake respectively. The desiccant developed was found to be effective in high moisture
content and thus viable in tropic regions where such environs are common. The sorption data
obtained were subjected to the Langmuir, Freundlich and Brunaeur-Emmett- Teller (BET)
adsorption models in order to determine the type of adsorption isotherm that best interpreted
. water sorption by the material. Results indicated that, water adsorption onto adsorbent
developed followed BET and Langmuir type III isotherm which indicated the formation of
multilayer. The sorption capacity of the adsorbent matrix developed recorded 40 to 45% water
uptake which cohered with commercially available desiccant such as silica gel. Since the SBE is
normally disposed on potential land and limitations for this method of disposal is enormous, it is
recommended that, oil manufacturing industries should emphasis on regenerating and re-using
this waste in making products such as desiccants which they can use to preserve their products as
well as sell to other consumers.