ABSTRACT
Biomass tar restricts the wide application and development of biomass gasification technology. In the present paper, palygorskite, a natural magnesium-containing clay mineral, was investigated for catalytic pyrolysis of rape straw in situ and compared with the dolomite researched widely. The two types of natural minerals were characterized with XRD and BET. The results showed that combustible gas derived from the pyrolysis increased with an increase in gasification temperature. The H(conversion) and C(conversion) increased to 44.7% and 31% for the addition of palygorskite and increased to 41.3% and 31.3% for the addition of dolomite at the gasification temperature of 800°C, compared with 15.1% and 5.6% without addition of the two types of material. It indicated that more biomass was converted into combustible gases implying the decrease in biomass tar under the function of palygorskite or dolomite and palygorskite had a slightly better efficiency than that of dolomite in the experimental conditions.
Subject(s)
Aluminum Silicates/chemistry , Brassica napus/chemistry , Calcium Carbonate/chemistry , Gases/chemistry , Magnesium Compounds/chemistry , Magnesium/chemistry , Silicon Compounds/chemistry , Biomass , Catalysis , Clay , Tars/chemistry , Temperature , Waste ProductsABSTRACT
Palygorskite has a fibrous like morphology with a distinctive layered appearance. The simplified formula of palygorskite (Mg(5)Si(8)O(20)(OH)(2)(OH(2))(4)·nH(2)O) indicates that two different types of water are present. The dehydration and rehydration of palygorskite have been studied using thermogravimetry and H(2)O-temperature programmed desorption. X-ray diffractograms, NH(3) adsorption profiles, and NH(3) desorption profiles were obtained for thermally treated palygorskite as a function of temperature. The results proved water molecules were mainly derived from Si-OH units. In addition, five kinds of acid sites were found for palygorskite. The number of acid sites of external surfaces was larger than that of the internal surfaces. Bonding on the internal surface acid sites was stronger than the bonding of the external surfaces. Rehydration restored the folded structure of palygorskite when thermal treatment temperature was lower than 300 °C.
Subject(s)
Magnesium Compounds/chemistry , Silicon Compounds/chemistry , Temperature , Molecular Structure , Surface PropertiesABSTRACT
Goethite and Al-substituted goethite were synthesized from the reaction between ferric nitrate and/or aluminum nitrate and potassium hydroxide. XRF, XRD, TEM with EDS were used to characterize the chemical composition, phase and lattice parameters, and morphology of the synthesized products. The results show that d(020) decreases from 4.953 to 4.949Å and the b dimension decreases from 9.951Å to 9.906Å when the aging time increases from 6 days to 42 days for 9.09 mol% Al-substituted goethite. A sample with 9.09 mol% Al substitution in Al-substituted goethite was prepared by a rapid co-precipitation method. In the sample, 13.45 mol%, 12.31 mol% and 5.85 mol% Al substitution with a crystal size of 163, 131, and 45 nm are observed as shown in the TEM images and EDS. The crystal size of goethite is positively related to the degree of Al substitution according to the TEM images and EDS results. Thus, this methodology is proved to be effective to distinguish the morphology of goethite and Al substituted goethite.
