The effect of oxygen and volatile combustibles on the sulphation of gaseous KCl

Sulphur/sulphate containing additives, such as elemental sulphur (S) and ammonium sulphate (NH₄)₂SO₄), can be used for sulphation of KCl during biomass combustion. These additives convert KCl to an alkali sulphate and a more efficient sulphation is normally achieved for ammonium sulphate compared to sulphur. The presence of SO₃ is thus of greater importance than that of SO₂. Oxygen and volatile combustibles could also have an effect on the sulphation of gaseous KCl. This paper is based on results obtained during co-combustion of wood chips and straw pellets in a 12 MW circulating fluidised bed (CFB) boiler. Ammonium sulphate was injected at three positions in the boiler i.e. in the upper part of the combustion chamber, in the cyclone inlet, and in the cyclone. The sulphation of KCl was investigated at three air excess ratios (λ = 1.1, 1.2 and 1.4). Several measurement tools were applied including IACM (on-line measurements of gaseous alkali chlorides), deposit probes (chemical composition in deposits collected) and gas analysis. The position for injection of ammonium sulphate had a great impact on the sulphation efficiency for gaseous KCl at the different air excess ratios. There was also an effect of oxygen on the sulphation efficiency when injecting ammonium sulphate in the cyclone. Less gaseous KCl was reduced during air excess ratio λ = 1.1 compared to the higher air excess ratios. The optimal position and conditions for injection of ammonium sulphate were identified by measuring KCl with IACM. A correlation was observed between the sulphation of gaseous KCl and reduced chlorine content in the deposits. The experimental observations were evaluated using a detailed reaction mechanism. It was used to model the effect of volatile combustibles on the sulphation of gaseous KCl by SO₃. The calculations supported the proposition that the presence of combustibles at the position of SO₃ injection (i.e. AS) causes reduction of SO₃ to SO₂.     

Thermal decomposition of (NH4)2SO4 in presence of Mn3O4

The main objective of this work is to develop a hybrid water-splitting cycle that employs the photon component of sunlight for production of H₂ and its thermal (i.e. IR) component for generating oxygen. In this paper, (NH₄)₂SO₄ thermal decomposition in the presence of Mn₃O₄, as an oxygen evolving step, was systematically investigated using thermogravimetric/differential thermal analyses (TG/DTA), temperature programmed desorption (TPD) coupled with a mass spectrometer (MS), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) techniques. Furthermore, thermolysis of ammonium sulfate, (NH₄)₂SO₄, in the presence of Mn₃O₄ was also investigated by conducting flow reactor experiments. The experimental results obtained indicate that at 200-450 °C, (NH₄)₂SO₄ decomposes forming NH₃ and H₂O and sulfur trioxide that in the presence of manganese oxide react to form manganese sulfate, MnSO₄. At still higher temperatures (800∼900 °C), MnSO₄ further decomposed forming SO₂ and O₂.     

Comparison of catalytic hydroliquefaction of Xiaolongtan lignite over FeS, FeS+S and SO4/ZrO2

The catalytic hydroliquefaction of Xiaolongtan lignite (XL, a Chinese lignite) was investigated in a batch autoclave. The effects of reaction temperature, time and initial H₂ pressure on the yields of gaseous and extractable portions (GEPs) were discussed. The catalytic activity of FeS+S was compared with that of FeS and SO₄^2-/ZrO₂, respectively. The results show that FeS+S is more active for XL hydroliquefaction than the other two catalysts and affords the highest gas and oil (G & O) yields in the three catalysts. The highest total yield of GEPs from XL hydroliquefaction gets to 90.0%, while total yield of G & O is 61.1% at 420 °C for 30 min over FeS+S. The assistant catalysis of the added sulfur was discussed. The structural features of asphaltenes and preasphaltenes were examined by elemental and FTIR analyses.     

Isotopic composition of dissolved sulphate and hydrogen sulphide from some thermal springs of Sicily

Samples of some thermal springs from Sicily have been analysed for the isotopic composition of sulphur-bearing species. The values of δ³⁴S(SO₄²⁻ (range: +7.3, +31.7‰), δ³⁴S(H₂S) (range: −12.2, +27.8), δ³⁴S(S°) (range: +1.9, +24.5) and δ¹⁸O(SO₄²⁻) (range: −2.5, +23.9) obtained show such a remarkable variability in data as to hypothesize different genetic processes concerning these species.Furthermore, from the available experimental data, the relationship between the isotopic composition of the sulphur in the dissolved sulphate and in the associated hydrogen sulphide (ΔSO₄²⁻ - H₂S = 25 – 30‰) seems to indicate the bacterial reduction of sulphate ion as one of the processes most significantly influencing the isotopic geochemistry of sulphur.     

H2SO4 stability of PBI-blend membranes for SO2 electrolysis

For hydrogen to become a serious contender for replacing fossil fuels, the manufacturing thereof has to be further investigated. One such process, the membrane based Hybrid Sulfur (HyS) process, where hydrogen is produced from the electrolysis of SO₂, has received considerable interest recently. Since H₂SO₄ is formed during SO₂ electrolysis, H₂SO₄ stability is a prerequisite for any membrane to be used in this process. In this study, pure as well as blended polybenzimidazole (PBI), partially fluorinated poly(arylene ether) (sFS) and nonfluorinated poly(arylene ethersulfone) (sPSU) membranes were investigated in terms of their acid stability as a function of acid concentration. Membranes were characterized using weight change, TGA, GPC, SEM/EDX and IEC. While a general stability was observed at 30 and 60 wt% H₂SO₄, the blended sFS-PBI and sPSU-PBI showed the highest stability throughout. According to the VI curve obtained for the SO₂ electrolysis, the sPSU-PBI blend membrane performed slightly better than Nafion^®117.     

Hydrogen production from solid reactions between MAlH4 and NH4Cl

Solid reactions between alkali aluminum hydrides (MAlH₄, M = Li or Na) and NH₄Cl (at mole ratio 1:1) at 170 °C were investigated quantitatively using temperature programmed reaction (TPR), thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The release of 3 mol of H₂ from per mole of MAlH₄ was measured, corresponding to 5.6 wt.% H₂ capacity for the NaAlH₄/NH₄Cl system and 6.6 wt.% for LiAlH₄/NH₄Cl, respectively. By ball milling of the precursor compounds prior to the mixing, the reaction proceeded fast and NH₃ production as the by-product could be avoided. The quick solid reactions may be attributed to the low melting temperatures of MAlH₄ and the exothermic nature of the reactions. The reaction mechanism was also discussed.     

Synthesis and dehydrogenation of LiCa(NH2)3(BH3)2

We report the synthesis of a new hydrogen storage material with a composition of LiCa(NH₂)₃(BH₃)₂. The theoretical hydrogen capacity of LiCa(NH₂)₃(BH₃)₂ is 9.85 wt.%. It can be prepared by ball milling the mixture of calcium amidoborane (Ca(NH₂BH₃)₂) and lithium amide (LiNH₂) in a molar ratio of 1:1. The experimental results show that this material starts to release hydrogen at a temperature as low as ca. 50 °C, which is ca. 70 °C lower than that of pure Ca(NH₂BH₃)₂ possibly resulting from the active interaction of NH₂⁻ in LiNH₂ with BH₃ in Ca(NH₂BH₃)₂. ca. 4.1 equiv. or 6.8 wt.% hydrogen can be released at 300 °C. The dehydrogenation is a mildly exothermic process forming stable nitride products.     

Vapour/liquid fractionation of rare earths,Y, Na,K, NH4, Cl,HCO3, SO4 and borate in fluids from the Piancastagnaio geothermal field,Italy

Vapour/liquid fractionation of rare earth elements and yttrium (REY), Na⁺, K⁺, NH₄⁺, HCO₃⁻, SO₄²⁻, Cl⁻ and borate in geothermal fluids from the Piancastagnaio geothermal field (Mt. Amiata geothermal area, Tuscany, central Italy) were evaluated based on the chemistry of collected liquids and condensed vapours. Apparent vapour–liquid partitioning factors (^appD^V/L) of REY vary from 0.3 to 0.01. These factors are much higher than those of Na (<0.001) and K (∼0.001). Volatile components are ion pairings such as NH₄HCO₃^o, NH₄Cl^o, NaHCO₃^o, CaSO₄^o and REYO(HCO)₃^o ⇔ REY(OH)CO₃^o. In vapour, REY and NH₄⁺ are negatively correlated. High and low ^appD^V/L(REY) indicate variations of NH₄⁺ concentrations in liquids. The results of this study are relevant to the understanding of element migration and deposition under hydrothermal boiling conditions.     

Synthesis and crystal structure analysis of complex hydride Mg(BH4)(NH2)

Complex hydride Mg(BH₄)(NH₂), which consists of double anion BH₄⁻ and NH₂⁻, was synthesized and the crystal structure was analyzed by synchrotron X-ray diffraction. The mixture sample of Mg(BH₄)₂ + Mg(NH₂)₂ prepared by ball milling was reacted and crystallized to Mg(BH₄)(NH₂) by heating at about 453 K. This crystal phase transforms into amorphous phase above 473 K and subsequently the dehydrogenation begins. The crystal structure of Mg(BH₄)(NH₂) was determined from measurement data at 453 K (chemical formula: Mg_0.94(BH₄)₁(NH₂)_0.88, crystal system: tetragonal, space group: I4₁ (No.80), Z = 8, lattice constants: a = 5.814(1), c = 20.450(4) Å at 453 K). Mg(BH₄)(NH₂) is ionic crystal which the cation (Mg²⁺) and the anions (BH₄⁻ and NH₂⁻) are stacking alternately along the c-axis direction. Two BH₄⁻ and two NH₂⁻ tetrahedrally coordinate around Mg²⁺ ion.     

Behaviors of SO2 absorption in [BMIm][OAc] as an absorbent to recover SO2 in thermochemical processes to produce hydrogen

The solubility behavior of SO₂ in 1-butyl-3-methylimidazolium acetate ([BMIm][OAc]) was investigated. The solubility of SO₂ in [BMIm][OAc] was measured to be 0.6 in mole fraction at 50 °C in a stream of SO₂ gas. The desorption of SO₂ from [BMIm][OAc] was never completed, until the temperature was raised to 170 °C in a stream of N₂, indicating that the absorption of SO₂ is irreversible at the experimental condition. An in-situ IR study showed that acetate anion in [BMIm][OAc] transformed into acetic acid during the SO₂ absorption. After removing acetic acid at 170 °C by evacuation, the bands at 1210, 1045 and 850 cm⁻¹ appeared in IR spectra. The bands at 1210 and 1047 cm⁻¹ were assigned to S–O stretching mode of HOSO₂⁻ (an isomer of HSO₃⁻) and the band at 885 cm⁻¹ was assigned to the symmetric stretching mode of HO–S. FT-IR study suggested that acetic acid and most plausibly [BMIm][HOSO₂] were generated from the interactions of [BMIm][OAc] with SO₂ and adventitious water in feed gas and/or [BMIm][OAc] during absorption–desorption process. [BMIm][HOSO₂] recovered after removing acetic acid was found to be a new and reversible SO₂ absorbent with the SO₂ absorption capacity of 0.55 in mole fraction.     

Optimization of alternative options for SO2 emissions control in the Mexican electrical sector

This article develops a least-cost optimization model in terms of the projected SO₂ abatement costs of nine selected options for SO₂ emissions control in the 10 most polluting power plants of the Mexican electrical sector (MES)—including SO₂ scrubbing technologies, fuel oil hydrotreating desulphurization and fuel substitutions. The model not only finds the optimal combination of SO₂ control options and generating units at 10% reduction intervals referred to the total SO₂ emissions but also meets the restriction imposed in the NOM-085-ECOL-1994 (Mexican Official Norm) for allowable emission levels within critical zones. Similarly, two schemes are studied and analysed in this model: the first case considers the economical benefits derived from the substitution of fuel oil by imported low sulphur content coal in the Petacalco power plant and; the second case does not considered such economical benefits. Finally, results are obtained for these two cases in terms of the corresponding costs—investment, O&M, fuel—, abatement costs and the SO₂ emissions reduction.     

The effect of Pt loading amount on SO2 oxidation reaction in an SO2-depolarized electrolyzer used in the hybrid sulfur (HyS) process

The effect of Pt loading amount on SO₂ oxidation reaction in an SO₂-depolarized electrolyzer used in the hybrid sulfur (HyS) process for hydrogen generation was investigated by using transmission electron microscopy (TEM), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). From the analysis of the CVs, it was found that the electrochemical active surface area increased as the Pt loading amount increased, while Pt utilization decreased. The CVs obtained in the SO₂-free and SO₂-saturated 50 wt.% H₂SO₄ solutions indicated that the chemical transformation of the adsorbed species to PtO at a higher potential creates passivation layers which partially cover the electrode surface and inhibit SO₂ oxidation reaction. The LSVs revealed that the increase in Pt loading amount resulted in a considerable improvement of SO₂ oxidation kinetics in a low potential region as compared with that in a high potential region. However, the area-specific activity for SO₂ oxidation reaction decreased due to the reduction of Pt utilization.     

Experimental analysis of SO2 effects on Molten Carbonate Fuel Cells

The aim of this work is to investigate how SO₂ can affect MCFC performance and to discover the possible mechanisms involved in cathode sulphur poisoning, specifically considering the possible use of MCFCs in CCS (Carbon Capture and Storage) application. The different contributions of cathodic, anodic and electrolyte reactions have been considered to get a complete picture of the evolution of performance degradation. Experimental tests have been performed at the Fuel Cell Centre laboratories of Korea Institute of Science and Technology (KIST) thanks to 100 cm² single cell facilities and comparing results using both an optimized gas for laboratory conditions and a gas composition that simulates MCFCs when running in a Natural Gas Combined Cycle (NGCC) power plant. Polarisation curves, endurance tests, impedance measurements and gas analyses have been carried out to support the investigation.     

Synthesis and thermal decomposition properties of a novel dual-cation/anion complex hydride Li2Mg(BH4)2(NH2)2

A novel dual-cation/anion complex hydride (Li₂Mg(BH₄)₂(NH₂)₂), which contains a theoretical hydrogen capacity of 12.1 wt%, is successfully synthesized for the first time by ball milling a mixture consisting of MgBH₄NH₂ and Li₂BH₄NH₂. The prepared Li₂Mg(BH₄)₂(NH₂)₂ crystallizes in a triclinic structure, and the [NH₂] and [BH₄] groups remain intact within the structure. Upon heating, the prepared Li₂Mg(BH₄)₂(NH₂)₂ decomposes to release approximately 8.7 wt% hydrogen in a three-step reaction at 100–450 °C. In addition, a small amount of ammonia is evolved during the first and second thermal decomposition steps as a side product. This ammonia is responsible for the lower experimental dehydrogenation amount compared to the theoretical hydrogen capacity. The XRD and FTIR results reveal that Li₂Mg(BH₄)₂(NH₂)₂ first decomposes to LiMgBN₂, LiBH₄, BN, LiH and MgBNH₈ at 100–250 °C, and then, the newly formed MgBNH₈ reacts with LiH to form Mg, LiBH₄ and BN at 250–340 °C. Finally, the decomposition of LiBH₄ releases hydrogen and generates LiH and B at 340–450 °C.     

Dehydrogenation reactions of mechanically activated alkali metal hydrides with CO2 at room temperature

Reactions between alkali metal hydrides MH (M = Li, Na, or K) and carbon dioxide (CO₂) at room temperature were systematically investigated for the first time. It was found that the raw alkali metal hydrides did not react with CO₂ under static-pressure conditions at room temperature, but the mechanically activated alkali metal hydrides reacted with CO₂ and released large amounts of hydrogen (H₂). Under the same ball-milling conditions, the order of reactivity of the alkali metal hydrides with CO₂ was KH > NaH > LiH. The particle size of the activated alkali metal hydrides had a large influence on the reactivity of the alkali metal hydrides with CO₂. During the reactions, CO₂ was reduced by alkali metal hydrides, generating elemental carbon, alkali metal oxides and H₂, and it was consumed by alkali metal oxides, forming carbonates.     

Synthesis,structural characterization,and hydrolysis of Ammonia Borane (NH3BH3) as a hydrogen storage carrier

In the present study, synthesis, structural characterization, and hydrolysis of the promising hydrogen storage carrier ammonia borane (NH₃BH₃), were investigated. NH₃BH₃ was prepared by one-pot chemical reaction between sodium borohydride (NaBH₄) and different ammonia salts [NH₄X, X: SO₄, CO₃, Cl] in the presence of solvent, tetrahydrofurane (THF). Synthesizes with different temperatures (20–40 °C), reaction times (30–130 min), amount of added THF volume (50–200 ml) and NaBH₄/(NH₄)₂SO₄ input molar ratios (0.47–0.75) were performed in order to find the optimum reaction conditions for obtaining maximum product yield. The characterization of NH₃BH₃ products was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), elemental analysis (C, H, N, O) and NMR spectroscopy. Characterization results indicated that NH₃BH₃ as a crystalline powder at 98% purity was achieved with 92.18% production yield. Additionally, hydrolysis of product NH₃BH₃ in the presence of amorphous Co–B catalyst at 22–80 °C under magnetic stirring (700 rpm) was performed. The maximum hydrogen generation rate was 5447.80 ml min⁻¹ g cat⁻¹ and the hydrolysis reaction kinetics were clarified based on zero-order, first-order and Langmuir–Hinshelwood kinetic models.     

Comparison of ionically and ionical-covalently cross-linked polyaromatic membranes for SO2 electrolysis

It has been shown that hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) process. During the HyS electrolysis step, SO₂ and H₂O are converted to H₂ and H₂SO₄, which implies that membranes to be used for this process should have both a high proton conductivity and acid stability. In this study ionic and ionic-covalently cross-linked polybenzimidazole (PBI) blended membranes were investigated and compared with Nafion^®212 in terms of their acid stability. Characterization of the membranes, which included monitoring the change in weight, swelling, SEM/EDX, TEM, TGA-MS, FTIR and IEC before and after H₂SO₄ treatment showed that all tested membranes were stable in 80 wt% H₂SO₄ at 80 °C for 120 h. Subsequent HyS electrolysis showed that the blend membranes performed better than Nafion^®115 at current densities below 0.3 A/cm², while performing similar above 0.3 A/cm².     

SO2 permeability and proton conductivity of sPEEK membranes for SO2-depolarized electrolyzer

The SO₂ transport properties of Nafion^® and sPEEK membranes were measured using an electrochemical reaction cell to investigate their application in the electrochemical hybrid sulfur process. The permeability of SO₂ in the membranes was determined from a combined theory based on Faraday's law and Fick's law where the electrochemical reaction rate of SO₂ in the downstream membrane is the same as its diffusion flux through the membrane. Both Nafion^® and sPEEK membranes show higher SO₂ diffusion coefficients at higher temperatures. For sPEEK membranes, increasing the degree of sulfonation resulted in increasing permeability, as more water was imbibed in the membranes with higher degrees of sulfonation. Activation energy was extracted from the temperature-dependence of the diffusion coefficients for both membranes. The sPEEK membranes exhibited similar diffusion coefficients to those of Nafion^®, even at high sulfonation degrees of 70%. Besides SO₂ permeability, proton conductivity and mechanical properties were measured for comparison between the 2 polymer membranes. Although the proton conductivity of the sPEEK was slightly lower than the Nafion^® membrane, it was very competitive considering its higher mechanical strength and much lower cost.