Diano Antenucci

First experimental evidence of alluaudite-like phosphates with high Li-content: the (Na1-xLix)MnFe2(PO4)3 series (x = 0 to 1)

Members of the Na 1-x Li x MnFe 2 (PO 4 ) 3 series, with the alluaudite structure type, were synthesized by solid-state reaction in air. The crystal structure refinement of the NaMnFe 2 (PO 4 ) 3 end-member (space group C2/ c, Z = 4, a = 12.018(2), b = 12.565(3), c = 6.415(1) A, β = 114.33(3)°), a synthetic compound with a chemical composition corresponding to the idealized composition of the Buranga alluaudite, was carried out to R 1 = 0.026. The following cationic distribution was observed: Na + + □ in A(1) and A(2)′ (□ denotes lattice vacancies), Mn 2+ in M(1), Fe 3+ + Fe 2+ in M(2). The A(2)′ site exhibits a distorted gable disphenoid morphology and is found at the (0, y, ¼) (y ≈ 0) position in channel 2 of the alluaudite structure. The crystal structure of Na 0.5 Li 0.5 MnFe 2 (PO 4 ) 3 (space group C2/ c, Z = 4, a = 11.988(2), b = 12.500(3), c = 6.392(1) A, β = 114.67(3)°), refined to R 1 = 0.034, leads to the cationic distribution: Li + + Na + + □ in A(2)′, Na + + □in A(1), Mn 2+ in M(1), Fe 3+ + Fe 2+ in M(2). Thus, the substitution mechanism involved in the replacement of Na by Li in the Na 1-x Li x MnFe 2 (PO 4 ) 3 alluaudite-like compounds corresponds to □ + Na □ Li + □, with x ranging from 0.00 to 0.90.

Carbon stable isotope analysis as a tool for tracing temperature during the El Tremedal underground coal gasification at great depth

Abstract The new opportunity given by the underground gasifier developed at Alcorisa in Spain (Province of Teruel) in the framework of an European experiment has promoted a better understanding of gasification in a natural reactor. The thermodynamical equilibria of gasification reactions and the repartition of the stable isotopes of carbon (13C/12C) in the produced gases have been used to monitor the process. An estimation of the temperatures inside the gasifier and at the exhaust has been performed. As shown by the isotopic balances, the tar formation is negligible or null and the pyrolysis zone spreads continuously. The study has confirmed the reality of the 13C isotopic abundance measurements for the system CO/CO2 as an indicator of the temperature inside the gasifier. During the gasifier expansion, the temperature at the exhaust decreases whereas the temperature inside the gasifier is practically constant showing a slight increasing trend. As pointed out by the data, the oxygen enrichment of the gasifying agent plays an important role on the estimated temperatures.

Acidic degradation of zeolite catalysts in the course of aromatic chlorination using sulfuryl chloride

Abstract The structural changes of two faujasite-type zeolites in the course of aromatic chlorinations by sulfuryl chloride, SO 2 Cl 2 , were investigated by X-ray powder diffraction. Both catalysts examined, the NaX zeolite, which promotes catenary side-chain chlorination, and the ZF520 zeolite, which promotes nuclear electrophilic chlorination, are strongly altered in the acidic reaction medium (hydrochloric acid and sulfur dioxide are evolved continually as the reaction proceeds). In the presence of residual humidity, progressive dealumination of the ZF520 catalyst occurs without destruction of the zeolite framework. It gives rise to the formation of an alum type structure, for which the molecular formula (H 3 O)Al(SO 4 ) 2 · 12H 2 O has been suggested. Rapid degradation of the NaX zeolite is accompanied by the formation of sodium chloride and of the sodium aluminium sulfate hexahydrate, NaAI(SO 4 ) 2 · 6H 2 O. These compounds indeed catalyze the side-chain chlorination of toluene by SO 2 Cl 2 . Under water exclusion, structural degradation of both zeolites is slowed down and formation of hydrated sulfates is prevented; however, the efficiency of the catalysts is also reduced.

A Gas Chromatographic Separation for the H and C Stable Isotope Ratio Determination of Coal Compounds

A new, completely automated gas chromatography technique has been developed to separate the different gaseous compounds produced during underground coal gasification for their (13)C/(12)C and D/H isotope ratio measurements. The technique was designed for separation and collection of H(2), CO, CO(2), H(2)O, H(2)S, CH(4), and heavier hydrocarbons. These gaseous compounds are perfectly separated by the gas-phase chromatograph and quantitatively sent to seven combustion and collection lines. H(2), CO, CH(4), and heavier hydrocarbons are quantitatively oxidized to CO(2) and/or H(2)O. The isotopic analyses are performed by the sealed-tube method. The zinc method is used for reduction of both water and H(2)S to hydrogen for D/H analysis. Including all preparation steps, the reproducibility of isotope abundance values, for a quantity higher than or equal to 0.1 mL of individual components in a mixture (5 mL of gases being initially injected in the gas chromatograph), is ±0.1‰ for δ(13)C(PDB) and ±6‰ for δD(SMOW).