Behavior of Alkali Metals

As already stated, low-rank coals are classified as salty coals if the Na20 content in the ash exceeds 4wt% or 0.5 wt% of the dry coal. These coals show a special devolatilization behavior, which also occurs in gasification systems with lower operation temperature such as moving-bed or fluid-bed systems. 

Alkali metals occur in salty coals typically as chlorides, humates, sulfates, and carbonates. The reducing atmosphere in the gasifier favors the continuous liberation of volatile minerals, resulting in steadily changing eutectics causing transitions of the ash fusion behavior, which are nearly unpredictable. 

The devolatilization of the salty compounds starts in average at 650 °C and is finished around 1200 °C. The highest vapor pressures occur for alkaline chlorides and sulfates becoming remarkable at 400-800 °C. The volatility of chlorides is strongly enhanced in the presence of steam yielding hydrochloric acid as shown in the following equations. 

The formed HCl can be a main source of corrosion in combination with steam. However, investigations revealed that the presence of kaohnite (Al203-2Si02-2H20) can significantiy suppress progression of Equations (3.47) and (3.48) [15]. 

If sulfur is present in the coal, Na2S can also be formed. Although sulfates are composed from alkaline and earth alkaline oxides reacting with liberated SO3 at temperatures below 1030 °C, a decomposition to hydroxides occurs again at higher temperatures as shown in the following equation  

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Figure 1. A/A0 as a function of C1/2. A comparison of the behavior of alkali metals in amine solvents with the behavior of salts in aqueous and nonaqueous systems. KNOz in H20 and in NHZ (48) sodium in NHz (15) potassium in NH2CH2CHzNH2 (11) lithium in CHzNH2 (3).

Ikeda, T., Nakahara, J., Sasaki, M., and Yasunaga, T. (1984). Kinetic behavior of alkali metal ion on zeolite 4A surface using the stopped-flow method. J. Colloid Interface Sci. 97, 278-283. 

Solutions of metals in ammonia. One of the striking differences between water and ammonia is the behavior of alkali metals toward these solvents. With water, these metals react rapidly to liberate hydrogen ... 

K. Kubota, J. Matsumoto, Chem. Lett. 2011, 40, 1105-1106. Melting and crystaUization behaviors of alkali metal (fluorosulfonyl)(trifluoromethylsulfonyl)amides. 

Kubota, K Matsumoto, H., Melting and Crystallization Behaviors of Alkali Metal (Fluorosulfonyl)(trifluoromethylsulfonyl)amides, Chem. Lett., 2011,40,1105-1106. 

Sando, lon-chromatographic behavior of alkali metal cations and ammonium ion on zirconium-adsorbing silica gel,/. Chromatogr. A, 884,123, 2000. 

BEHAVIOR OF ALKALI METAL-NONALKALI METAL COMBINATIONS... 

The thermal decomposition of alkali metal oxyfluoroniobates is also not a trivial process. MNbOF4 compounds (where M = alkali metal) with a chain-type structure are relatively stable up to temperatures in the range of 500-600°C. Fig. 90 presents mass loss dependences on temperature of several MNbOF4 compounds. As can be seen, among the compounds presented, only CsNbOF4 exhibits significantly different behavior, beginning its thermal decomposition at a lower temperature of about 400°C. 

Calculations of alkali metal allyl derivatives involving all alkali metals (Li-Cs) indicate a preferred geometry with the metal symmetrically bound in a predominantly electrostatic manner to all three carbon atoms.143 Solution studies of allyllithium in ether indicate the compounds to be highly aggregated in THF complex dynamic behavior is observed. 

Measurements of the magnetic properties based on a selection of alkali metal rich and alkali metal poor amalgams show a different behavior at higher temperatures. 

Then, contrary to our previous hypothesis, the reaction proceeds via a Bai2 displacement of aniline on DMC. The product, mono-A -methyl aniline (PhNHMe), plausibly adsorbs into the zeohte in a different way with respect to anihne, because different H-bonds (N H — O-zeolite) take place with the solid. As recently reported by Su et al., A-methyl amines also may interact with NaY by H-bonding between the protons of the methyl group and the oxygen atoms of the zeolite this probably forces the molecule a bit far from the catalytic surface in a fashion less apt to meet DMC and react with it. This behavior can account for the mono-A-methyl selectivity observed, which is specific to the use of DMC in the presence of alkali metal exchanged faujasites in fact, the bis-A-methylation of primary aromatic amines occurs easily with conventional methylating agents (i.e., dimethyl sulfate). ... 

The broader subject of the interaction of stable carbenes with main-group compounds has recently been reviewed. Accordingly, the following discussion focuses on metallic elements of the s and p blocks. Dimeric NHC-alkali adducts have been characterized for lithium, sodium, and potassium. For imidazolin-2-ylidenes, alkoxy-bridged lithium dimer 20 and a lithium-cyclopentadienyl derivative 21 have been reported. For tetrahydropyrimid-2-ylidenes, amido-bridged dimers 22 have been characterized for lithium, sodium, and potassium. Since one of the synthetic approaches to stable NHCs involves the deprotonation of imidazolium cations with alkali metal bases, the interactions of alkali metal cations with NHCs are considered to be important for understanding the solution behavior of NHCs. 

Hanawalt and Richey observed that additions of alkali-metal alkoxides to diaUtylmag-nesium led in some reactions to behavior resembling that of trialkylmagnesates. This includes enhanced reactivities in addition to pyridine leading to 4- or 2-aIkyl-substituted... 

Sulfamic acid and its salts retard the precipitation of barium sulfate and prevent precipitation of silver and mercury salts by alkali. It has been suggested that salts of the type AgNHSO,K [15293-60-1] form with elemental metals or salts of mercury, gold, and silver (19). Upon heating such solutions, the metal deposits slowly in mirror form on the wall of a glass container. Studies of chemical and electrochemical behavior of various metals in sulfamic acid solutions are described in Reference 20. 

The electrochemical oxidation of aromatic aldehydes (1) must be studied in strongly alkaline media. Acidity functions for strongly alkaline aqueous solutions of alkali metal and quaternary ammonium hydroxides, corresponding to dissociation of proton (H ), are well established (2, 3). Substituted anilines and diphenylamines (4,5) and indoles (6) were used as acid-base indicators for establishment of such scales, but whether an acidity scale based on one type of indicator can be rigorously applied to acid-base equilibria involving structurally different acidic groups for reactions in strongly alkaline media remains questionable. For substituted anilines, behavior both parallel (7) and nonparallel (8) to the H scale based on indole derivatives has been reported. The limited solubility of anilines in aqueous solutions of alkali metal hydroxides, the reactions of the aniline derivative with more than one hydroxide ion, irreversible substitution reactions (9), and the possibility of hydroxide ion addition rather than... 

Polyborates and pH Behavior. Whereas boric acid is essentially monomeric in dilute aqueous solutions, polymeric species may form at concentrations above 0.1 M. The conjugate base of boric acid in aqueous systems is the tetrahydroxyborate [15390-83-7] anion sometimes called the metaborate anion, B(OH) 4. This species is also the principal anion in solutions of alkali metal (1 1) borates such as sodium metaborate,... 

If a small piece uf an alkali metal is dropped into a Dewar task containing liquefied ammonia, the solution immediately assumes an intense deep blue color. If more alkali metal is dissolved in the ammonia, eventually a point is reached where. 1 bronze-colored phase separates and floats on the blue solution.- Further addition of alkali metal results in the gradual conversion of blue solution to bronze solution until the former disappears. Evaporation of the ammonia from the bronze solution allows one to recover the alkali metal unchanged.) This unusual behavior has fascinated chemists since its discovery in 1864. Complete agreement on the theoretical interpretation of experimental observations made on these solutions has not been achieved. 

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