Final Solid Products Research Articles

Isothermal and non-isothermal decomposition of zinc malonate dihydrate in different atmospheres

Thermal decomposition of zinc malonate dihydrate was studied using isothermal gas accumulatory method under vacuum. Non-isothermal measurements were also used to study the same reaction under different dynamic gas atmospheres (i.e. N 2, air or H 2). It was found that the isothermal kinetic data were best fitted to the contracting cube equation [1 − (1 − α) 1/3] = kt, between 0.10 < α < 0.87 (where α is the fractional decomposition). The decomposition of the present reactant (using both the isothermal and non-isothermal techniques) was found to be sensitive to the pre-dehydration and to the mass of the reactant sample together with the prevailing gas atmosphere. NMR and IR analyses of the partially decomposed salt have indicated the formation of zinc acetate as a reaction intermediate. X-ray diffraction has characterized ZnO as the final solid product from the decomposition under vacuum or under any dynamic gas atmosphere. CO 2 together with traces (≈1.6%) of CO were the permanent gaseous products detected in the isothermal measurements. In addition, gas chromatography has identified CO 2 and acetone as the main volatile gaseous products together with traces of CO, especially at the beginning of the decomposition. Kinetic parameters, e.g. the activation energy ( E a) and the frequency factor (ln A) were calculated together with the enthalpy (Δ H) of the dehydration and the decomposition processes under different gas atmospheres.

TG/DTA/MS/IR study on decomposition of cadmium malonate hydrates in inert and oxidative atmosphere

Thermal decomposition of cadmium malonate hydrates was studied in dynamic helium and air atmospheres. It was found that content of hydration water in the initial sample strongly influences the way of decomposition reaction. The dehydration of cadmium malonate hydrate takes place in the temperature range 80–170 °C. The anhydrous cadmium malonate decomposes at about 250 °C. It was stated that the primary solid product of cadmium malonate decomposition is metallic cadmium. The gaseous products of cadmium malonate decomposition are CO 2, acetone, isobutylene and propyne and traces of water, acetic acid and oxygen. In helium majority of cadmium evaporates and the residue consists of small amount of elementary carbon formed in result of pyrolysis of malonate. The residue after decomposition of cadmium malonate with low amount of crystallization water molecules contains additionally CdO. The secondary reactions between decomposition products occur: oxidation of cadmium by oxygen in statu nascendi and formation of CdCO 3 in reaction between cadmium oxide and CO 2. In air cadmium instantaneously oxidizes and the final solid product of decomposition is CdO.

IR laser-induced co-decomposition of dimethyl selenide and trisilane: Gas-phase formation of SiSe and chemical vapor deposition of nanostructured H/Si/Se/C polymers

Chemical changes in IR laser irradiated gaseous mixtures of dimethyl selenide and trisilane have been diagnosed by laser-induced fluorescence (LIF) of transient species and by FTIR, Raman, photoelectron spectroscopy and electron microscopy of the final solid products deposited from the gas phase. It is revealed that decomposition of both compounds leads to gas-phase formation of SiSe and deposition of solid nanostructured polymeric materials. We present indirect evidence on the presence of Si Se bonds in these polymers by revealing that these polymers undergo hydrolysis in air to H 2Se and CH 3SeH, which converts them to solid silicone-based films containing elemental selenium. Plausible reactions taking place in the gas phase and upon exposure of solids to air are suggested.

Characterization of the thermal decomposition products of ammonium phosphomolybdate hydrate

In this study, the thermal decomposition mechanism of ammonium phosphomolybdate hydrate in air and inert gas atmospheres was determined and the intermediate and final products formed during the thermal decomposition were characterized using TGA, DTA, FTIR, XRD, EDS and EGA methods. In the first decomposition step, in both atmospheres, ammonium phosphomolybdate hydrate lost only its crystal water. At the following decomposition steps, ammonium phosphomolybdate hydrate acted differently in air and inert gas atmospheres. In air, in the second decomposition step, stoichiometric phosphomolybdenum oxide was formed as the final solid product. The ammonia gas evolved was oxidized with the oxygen present in air to form nitrogen and water. In inert gas atmosphere, in the second decomposition step, a portion of the ammonia gas evolved reduced the stoichiometric oxide formed (phosphorus hydrogen molybdenum oxide) to produce the nonstoichiometric oxide (phosphorus hydrogen molybdenum suboxide). The rest of the ammonia gas was released from the system partly undissociated and partly dissociated as nitrogen and hydrogen. In inert gas atmosphere, in the third decomposition step, the phosphorus hydrogen molybdenum suboxide formed lost its water to produce the phosphomolybdenum suboxide. It was also observed that phosphomolybdenum suboxide had good semiconductive property. The activation energies for the first and second decomposition steps of ammonium phosphomolybdate hydrate were determined in nonisothermal conditions.

The solid state reaction between lanthanum oxide and strontium carbonate

The reaction between lanthanum oxide and strontium carbonate was studied non-isothermally between 350 and 1150 °C at different heating rates, intermediates and the final solid product were characterized by X-ray diffractometry (XRD). The reaction proceeds through formation of lanthanum oxycarbonate La 2O(CO 3) 2, lanthanum dioxycarbonate La 2O 2CO 3, and non-stoichiometric strontium lanthanum oxide La 2SrO x ( x = 4 + δ). La 4SrO 7 was found to be the final product which begins to form at ∼700 °C. Li + doping enhances the formation of the final product as well as commencement of the reactions at lower temperatures.

A study on synthesis and thermal, spectral and biological properties of carboxylato-Mg(II) and carboxylato-Cu(II) complexes with bioactive ligands

Synthesis, elemental (CHN), spectral (FTIR), thermogravimetry (TG), differential thermal analysis (DTA) and complexometric titration have been applied to the investigation of the thermal behavior and structure of the complexes: Mg(ac)2(mpc)3·3H2O(I), Mg(Clac)2(mpc)2·3H2O(II), Mg(Cl2ac)2(mpc)2·3H2O(III), Mg(Cl3ac)2(mpc)2·3H2O(IV) and [Cu(ac)2(mpc)]2·3H2O(V) (ac=CH3COO-, Clac=ClCH2COO-, Cl2ac=Cl2CHCOO-, Cl3ac=Cl3CCOO- and mpc=methyl-3-pyridyl carbamate). Thermal decomposition of these complexes is a multi-stage processes. The composition of the complexes and the solid state intermediate and resultant products of thermolysis had been identified by means of elemental analysis and complexometric titration. The possible scheme of decomposition of the complexes is suggested. Heating the complexes first resulted in a release of water molecules. The TG results show that the loss of the volatile ligand (mpc) occurs in one step for complexes II, IV and V, and in two steps for complexes I and III. The final solid product of thermal decomposition was MgO or CuO. The thermal stability of the complexes can be ordered in the sequence: I=II<IV<III<V. Mpc was coordinated to Mg(II) or Cu(II) through the nitrogen atom of its heterocyclic ring. IR data suggest to a unidentate coordination of carboxylates to magnesium or copper n complexes I-V. The preliminary studies have shown that the complexes do have antimicrobial activities against bacteria, yeasts and/or fungi. The highest antimicrobial activities were manifested by the complex V.

Thermochemical investigations of natural phosphate with ammonium sulfate additive

The free energy of the acidic ammonium sulfate is a good precondition it’s use as an additive or reagent for decomposition of natural phosphates on the way to obtain NPS or NPKS complex fertilizers. During our previous studies it was confirmed that as a result of thermo-mechanical treatment new solid phases are formed as a result of the phosphates decomposition. The aim of this study is to find out appropriate conditions for thermal treatment of Tunisia phosphorite with ammonium sulfate where the content of P2O5 soluble forms has its maximum. The process was investigated under dynamic thermal conditions. Structure and phase transformations of the mixtures to intermediate and final solid products are confirmed by different techniques. X-ray powder diffraction, infrared spectroscopy and electron microscopy have been applied successfully and relationship found between phase structure and thermal treatment applied. As a result of the complex studies optimal temperatures are determined. The solid products under optimal conditions contain phosphorous in soluble forms available for plants in the soil. As a final it is concluded that the final products could be used as complex mineral fertilizers.

Separation and Purification of p-Xylene from the Mixture of m-Xylene and p-Xylene by Distillative Freezing

A new separation technique, called distillative freezing (DF), is described in detail. Basically, the DF process is operated at triple point condition, in which the liquid mixture is simultaneously vaporized and solidified due to the three-phase equilibrium. It results in the formation of pure solid, and liquid phase and vapor phase of mixtures. The process is continued until the liquid phase is completely eliminated and only the pure solid crystals remain in the feed. As the DF process is conducted under an adiabatic condition, the latent heat released in forming the solid crystals is mostly removed by vaporizing portions of liquid mixtures. The DF process is applied in this work to separate and produce solid p-xylene (PX) crystals from liquid mixtures of m-xylene (MX) and PX. The experimental results show that, for a liquid mixture of 100 g comprising10% MX and 90% PX, a final solid PX product of about 51.5 g is obtained when the final operation is at T = − 25.4 °C and P = 30.792 Pa by the proposed DF process. The final purity of solid products analyzed by gas chromatography can reach 99.1% PX.

Reactivity of hydrogen peroxide towards Fe 3O 4, Fe 2CoO 4 and Fe 2NiO 4

The kinetics of CRUD oxidation by H 2O 2 has been studied using aqueous suspensions of metal oxide powder. Fe 3O 4, Fe 2CoO 4 and Fe 2NiO 4 were used as model compounds for CRUD. In addition, the activation energies for the reaction between H 2O 2 and the three CRUD models were determined. The rate constants at room temperature were determined to 6.6 (±0.4) × 10 −9, 3.4 (±0.4) × 10 −8 and 1.6 × 10 −10 m min −1 for Fe 3O 4, Fe 2CoO 4 and Fe 2NiO 4, respectively. The corresponding activation energies are 52 ± 4, 44 ± 5 and 57 ± 7 kJ mol −1, respectively. The mechanism of the reaction is briefly discussed indicating that the final solid product in all three cases is Fe 2O 3. In addition to the experimental studies, the theoretical grounds for kinetics of reactions in particle suspensions are discussed. The theoretical discussion is also used to explain the somewhat unexpected trends in reactivity observed experimentally.

Development of Processes for Environmental Protection Based on Self‐Propagating Reactions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Physicochemical characterization of the decomposition course of hydrated ytterbium nitrate: thermoanalytical studies

Yb(NO 3) 3·6H 2O was used as a parent compound for the formation of Yb 2O 3 at up to 800 °C in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG), and the gaseous decomposition products were identified by mass spectrometry (GC–MS). The intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that, Yb(NO 3) 3·6H 2O decomposes completely through 11 endothermic mass loss processes. The dehydration occurs through the first six steps at 95, 145, 165, 175 and 200 °C, forming crystalline nitrate Yb(NO 3) 3, which decomposes to YbO 0.5(NO 3) 2 at 250 °C. The latter, decomposes to non-stoichiometric unstable intermediate YbO 0.75(NO 3) 1.5 at 335 °C, which decompose immediately to a stable and crystalline YbONO 3 at 365 °C, then to a non-stoichiometric unstable intermediate Yb(O) 1.25(NO 3) 0.5 at 470 °C. Finally, Yb 2O 3 was formed at 510 °C. The decomposition course and surface morphology were supported and followed by SEM and textural studies ( S BET).The final product Yb 2O 3 at 600 °C has a large irregular sheet shaped particles containing a large pores, voids and cracks and has S BET=45 m 2/g. The gaseous decomposition products are water vapor, nitric acid and nitrogen oxides (NO, NO 2 and N 2O 5). The activation energy (Δ E in kJ/mol) was calculated non-isothermally for each thermal processes.

Highly active disordered extra large pore titanium silicate

A new disordered microporous silica and its titanium silicate analog have been synthesized using a bola-amphiphile surfactant 1,12-diamino dodecane (DADD) as a structure directing agent (SDA). Powder X-ray diffraction, N 2 sorption, 29Si MAS NMR, UV–visible diffuse reflectance, FT-IR spectroscopic tools, and TEM and SEM–EDS were used to characterize this material. Only low angle peak was observed in the XRD for all the samples. TEM images indicated a wormhole-like structure in this material similar to that observed for mesoporous silica HMS, MSU-1, MSU-X, etc. or microporous Si-TMS7. Pore diameter of the micropore estimated from N 2 adsorption isotherms was ≈11.2 Å. Spectroscopic data indicated the incorporation of titanium in the tetrahedral silica network in this material. Three microporous type, Ti-DMS1 titanium silicate samples were synthesized with Si/Ti mole ratios of 24.5, 46.5 and 68.0 in the final solid products. After the removal of the template through calcination this microporous titanium silicate showed an excellent catalytic activity in the ammoximation of bulky ketones using dilute aqueous hydrogen peroxide and aqueous ammonia.

Complexes of dicamba with cadmium(II), copper(II), mercury(II), lead(II) and zinc(II)

New solid complexes of a herbicide known as dicamba (3,6-dichloro-2-methoxybenzoic acid) with Pb(II), Cd(II), Cu(II) and Hg(II) of the general formula M(dicamba)2·xH2O (M=metal, x=0-2) and Zn2(OH)(dicamba)3·2H2O have been prepared and studied. The complexes have different crystal structures. The carboxylate groups in the lead, cadmium and copper complexes are bidentate, chelating, symmetrical, in Hg(dicamba)2·2H2O - unidentate, and in the zinc salt - bidentate, bridging, symmetrical. The anhydrous compounds decompose in three stages, except for the lead salt whose decomposition proceeds in four stages. The main gaseous decomposition products are CO2, CH3OH, HCl and H2O. Trace amounts of compounds containing an aromatic ring were also detected. The final solid decomposition products are oxychlorides of metals and CuO.

Development of processes for environmental protection based on self-propagating reactions

The possibility of exploiting self-propagating reactions for environmental protection is discussed in this paper. In particular, results obtained at the laboratory scale and related to the fixation and consolidation of high level radioactive wastes, the recycling of silicon sludge and aluminum dross produced by semiconductor industries and aluminum foundries, the treating and recycling of a highly toxic solid waste from electrolytic zinc plants, and the degradation of chlorinated aromatics, are examined with particular emphasis on the latter case. Specifically, the self-propagating destruction of hexachlorobenzene and 2-(2-4-dichlorophenoxy)-propanoic acid with calcium hydride as reductive substrate is demonstrated. In fact, the heat liberated by the reactions involved is large enough to guarantee the self-sustaining character of the process within a wide range of reactants compositions. Moreover, no residual chlorinated organic compounds were found in the final solid product. Some reactor engineering aspects, as well as other significant future scientific and technological issues, are also addressed in view of large-scale applicability of processes based on self-propagating reactions. To date, the batch reactor technology seems to be more easily applicable, although the use of continuous reactors is not excluded in the next future.

Refining of crude lecithin using dense carbon dioxide as anti-solvent

Gas anti-solvent crystallization (GASC) has been utilized for refining of crude lecithin (L) from its solution in hexane (H) with dense carbon dioxide as the anti-solvent, leaving behind its oil in the solution. The performance of the process has been evaluated in terms of the lecithin content and its recovery in the final solid product. The effects of various process parameters have been analyzed at temperatures in the range of 283–313 K, pressures in the range of 15–80 bar, initial oil in crude lecithin in the range of 20–60 wt.% and hexane in the feed solution in the range of 80–95 wt.%. The crystallization of lecithin is facilitated by a drastic reduction of its solubility in hexane solution due to CO 2 dissolution which varied in the range of 40–75 wt.% CO 2 at temperatures in the range of 283–313 K. However, any phase separation of oil was avoided which occurred with more than 63 wt.% CO 2 in the solution. The highest value of selectivity of lecithin (defined as the ratio of the wt.% ratios of lecithin and oil in the product to that in the feed solution) was observed at 298 K and 65 bar for a complete (100%) recovery lecithin, and the selectivity decreased on lowering the temperature to 283 K. At any temperature, crystallization of lecithin occurred over a range of pressure or a range of CO 2 dissolution, allowing different combinations of enrichment and recovery of lecithin from the feed solution. The highest enrichment in the product was 98.6 wt.% lecithin with 78% recovery and this could be obtained at 298 K and 58 bar, starting from the crude lecithin feed having 60 wt.% oil. For a lower initial oil content, even a lower pressure was required to obtain a final solid product having the same lecithin content. Also, the lecithin content in the final product increased with an increase in the hexane-to-feed ratio, as oil remained miscible in the excess hexane.

Phenoxyalkanoic acid complexes. Part I. Complexes of lead(II), cadmium(II) and copper(II) with 4-chloro-2-methylphenoxyacetic acid (MCPA)

New solid heavy metal complexes with 4-chloro-2-methylphenoxyacetic acid (MCPA) of the general formulae: Pb(MCPA) 2·H 2O and Cd(MCPA) 2·2H 2O have been prepared. Diffractometric, IR spectroscopic and thermal analyses of these complexes and the previously described Cu(MCPA) 2 have been performed. The complexes have different structures, a low level of crystallinity and exhibit a tendency to form polymers. An attempt has been made to explain the mode of the ligand molecule coordination on the basis of the position of the bands of the characteristic ν asym and ν sym vibrations of the carboxylate group. The course of the TG, DTG and DTA curves indicates that the compounds decompose in two (the copper salt) or three stages. The decomposition of the cadmium complex is preceded by dehydration. The basic gaseous products of decomposition are H 2O and CO 2. HCOOH, HOCH 2COOH, HCl and trace amounts of compounds containing an aromatic ring were also detected. The final solid decomposition product is a metal oxide.

Solid products and rate-limiting step in the thermal half decomposition of natural dolomite in a CO 2 (g) atmosphere

Natural dolomite powders obtained from caves which give unusual high resistance building materials, have been decomposed in a Knudsen cell at high CO 2 pressures in the temperature range of 913–973 K. XRD traces for the final solid products, after the first half thermal decomposition, have shown, that beside the XRD patterns for the calcite and MgO, the existence of a new structure with major peaks at 2 θ equal to 38.5 and 65°. This finding has been ascribed to a solid solution of MgO in calcite. The kinetic analysis of the TG curves yield a total apparent enthalpy (Δ H ∗) for the decomposition equal to 440±10 kJ mol −1 for a range of fraction decomposed ( α) varying between 0.2 and 0.7. This value is much closer to the theoretical expected at 950 K value Δ H=486 kJ mol −1 for the dolomite decomposition in CO 2 environment, where CaO, MgO and oxides of solid solution can be the solid reaction products. The rate determining step is the transport of CO 2 across the reacting interface through an high activated thermal process due to solid state diffusion of CO 3 2− in the bulk and/or the grain boundaries phases of CaCO 3 and/or of the solid solution. The microstructure evolution of the solid products follows a shear-transformation mechanism. At temperatures below 943 K, porous product particles are characterized by a monomodal narrow pore size distribution around 0.05 μm. At higher temperatures, a critical level of tensions inside the particles is reached and a bimodal pore size distribution around 1 and 0.05 μm is formed.

Biological and physicochemical study of zinc(II) propionate complexes with N-donor heterocyclic ligands

New zinc(II) propionate complexes (CH3CH2COO)2Zn·Ln·xH2O, where n=1-2, x=0 or 2, were prepared by reaction of zinc(II) propionate with heterocyclic ligands (L=theophylline, nicotinamide, methyl-3-pyridyl carbamate) and their thermal properties were studied. The prepared complex compounds were characterized by elemental analysis and IR spectra. TG/DTG and DTA measurements of the prepared compounds were performed in the air atmosphere under dynamic conditions. The thermal decomposition can be characterized as a multi-step process. The first step is attributed to the elimination of water or N-donor ligand molecules. It is followed by the decomposition of propionate anion when diethyl ketone and carbon dioxide were released. Zinc oxide was found as a final product of the thermal decomposition of the complex compounds under study. The volatile intermediate products of the thermal decomposition of zinc(II) propionate complexes were identified by IR-spectroscopy, qualitative chemical analyses and final solid product by X-ray powder diffraction method. Moreover, IR spectra suggest monodentate coordination of propionate anion to zinc. The complexes were tested against bacteria and filamentous fungi and show both antimicrobial activity and fungistatic effect towards pathogens as well as probiotic activity towards Lactobacillus paracasei.

Formation and characterization of samarium oxide generated from different precursors

Sm(NO 3) 3·6H 2O and Sm 2(C 2O 4) 3·10H 2O were used as precursors for the formation of Sm 2O 3. Thermal processes involved in the decomposition course of both salts up to 800 °C in air were monitored by nonisothermal gravimetry and differential thermal analysis. Intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction and scanning electron microscopy. The results showed that Sm(NO 3) 3·6H 2O decomposes completely through nine endothermic mass loss processes. The dehydration occurs through the first four steps at 90, 125, 195, and 240 °C, culminating in a crystalline nitrate monohydrate, which subsequently decomposes to Sm(OH)(NO 3) 2 at 355 °C. The latter decomposes rapidly to form a stable and crystalline SmO(NO 3) at 460 °C, through nonstoichoimetric unstable intermediates. Finally Sm 2O 3 forms at 520 °C. For the oxalate, the dehydration occurs in five steps: the anhydrous oxalate is thermally unstable and immediately decomposes to Sm 2O 3 at 645 °C through two unstable intermediates. The crystalline oxide obtained from the nitrate contains larger pores than the oxide obtained from the oxalate, as indicated from scanning electron microscopy (SEM) results.

Precipitation of K-V(V)-Oxide from V(IV) Sulfate Solution by Ozonation

The oxidative precipitation of vanadium(IV) from its sulfate solutions with ozone has been investigated. During the ozonation, the solution pH was maintained constant by consuming the liberated hydrogen ion with drops of KOH solution. Chemical analysis of the precipitates showed that the values of x and y for the final solid product, KxV2Oy are from 0.30-0.47 (depending on pH) and 5.0, respectively. X-ray diffraction revealed that these potassium-incorporating vanadium(V) oxides have the basic structure of V2O5. The progress of oxidation of vanadium(IV) and precipitation of vanadium(V) were monitored by determining the concentrations of vanadium(IV) and vanadium(V) remaining in the solution and by ORP measurement. The rate of ozonation of vanadium(IV) increases with increasing pH, while the precipitation of vanadium(V) proceeds favourably at pH 1.5 at 25 °C and at pH 2.0 at 70 °C. A rise in temperature accelerates the oxidative precipitation of vanadium(IV) to make recovery of vanadium ion effective.