Phosphorus catalysis in the pyrolysis behaviour of biomass

Phosphorus is a key plant nutrient and as such, is incorporated into growing biomass in small amounts. This paper examines the influence of phosphorus, present in either acid (H₃PO₄) or salt ((NH₄)₃PO₄) form, on the pyrolysis behaviour of both Miscanthus × giganteus, and its cell wall components, cellulose, hemicellulose (xylan) and lignin (Organosolv). Pyrolysis–gas chromatography–mass spectrometry (PY–GC–MS) is used to examine the pyrolysis products during thermal degradation, and thermogravimetric analysis (TGA) is used to examine the distribution of char and volatiles. Phosphorus salts are seen to catalyse the pyrolysis and modify the yields of products, resulting in a large increase in char yield for all samples, but particularly for cellulose and Miscanthus. The thermal degradation processes of cellulose, xylan and Miscanthus samples occur in one step and the main pyrolysis step is shifted to lower temperature in the presence of phosphorus. A small impact of phosphorus was observed in the case of lignin char yields and the types of pyrolysis decomposition products produced. Levoglucosan is a major component produced in fast pyrolysis of cellulose. Furfural and levoglucosenone become more dominant products upon P-impregnation pointing to new rearrangement and dehydration routes. The P-catalysed xylan decomposition route leads to a much simpler mixture of products, which are dominated by furfural, 3-methyl-2-cyclopenten-1-one and one other unconfirmed product, possibly 3,4-dihydro-2-methoxy-2H-pyran or 4-hydroxy-5,6-dihydro-(2H)-pyran-2-one. Phosphorus-catalysed lignin decomposition also leads to a modified mixture of tar components and desaspidinol as well as other higher molecular weight component become more dominant relative to the methoxyphenyl phenols, dimethoxy phenols and triethoxy benzene. Comparison of the results for Miscanthus lead to the conclusion that the understanding of the fast pyrolysis of biomass can, for the most part, be gained through the study of the individual cell wall components, provided consideration is given to the presence of catalytic components such as phosphorus.     

Elucidation of interaction among cellulose, lignin and xylan during tar and gas evolution in steam gasification

Time profiles of evolution rates of gas and tar in steam gasification of model biomass samples were examined using a continuous cross-flow moving bed type differential reactor to elucidate the interaction of the major biomass components (cellulose, xylan, lignin) during gas and tar evolution. Two types of model biomass samples (sample A: mixture of cellulose (65 wt%) and lignin (35 wt%); sample B: mixture of cellulose (50 wt%), xylan (23 wt%), and lignin (27 wt%)) were used for the experiment. In steam gasification of sample A, the evolutions of water-soluble tar and gaseous products (CO, H₂, CH₄ and C₂H₄) are significantly suppressed by the interaction between cellulose and lignin. The primary (initial) decomposition of lignin is hindered by the interaction with pyrolysate of cellulose. Then, the CO₂ evolution appreciably enhanced and the evolution of water-soluble tar delays. These results may imply that the volatilization of water-soluble tar derived from cellulose is suppressed by lignin and then the decomposition of char derived from polymerized saccharides and lignin takes place, emitting mainly CO₂. From the results using sample B, it was found that the addition of xylan greatly enhances the evolutions of gases (CO₂, CO, CH₄ and H₂) and accelerates the evolution of water-soluble tar and CO₂, implying that the enhancement of decomposition of water-soluble tar into gases and/or xylan decomposes into gases without significant interaction with cellulose or lignin. In addition, yields of the major tar components (levoglucosan, furfural and 5-methylfurfural) were measured using HPLC. It was observed that the interaction among cellulose, xylan and lignin suppresses the evolution of levoglucosan and significantly increases the evolution rate of 5-methylfurfural. There is an insignificant influence of interaction among cellulose, xylan and lignin for furfural evolution.     

DSC investigation of the thermal behaviour of (NH4)2SO4, NH4HSO4 and NH4NH2SO3

Gaseous products evolved from (NH₄)₂SO₄, NH₄HSO₄ and NH₄NH₂SO₃ during successive heating and cooling cycles were flushed with inert gas into analyzer Dräger tubes hooked tightly to the terminal port of the DSC cell base. This simple procedure allowed the starting temperature of the decomposition to be determined and the amount of the individual gases in the mixture to be identified and even estimated. NH₄NH₂SO₃ at 523 K in humid air produced HNH₂SO₃ initially and, on further cycling, (NH₄)₂SO₄ and NH₄HSO₄ also appeared. The ΔH_f values for NH₄HSO₄ were (kJ mole^?1): in an airtight sample holder 12.67, in a dry argon atmosphere 11.93, and in a static air atmosphere 10.92. Endothermic peaks for (NH₄)₂SO₄ and 498 and 411 K represented the incongruent melting point and the polymorphic transition of (NH₄)₂SO₄·NH₄HSO₄. After the first heating in air to 530 K, (NH₄)₂SO₄ and NH₄HSO₄ exhibited closely similar cyclic DSC curves. The endothermic peaks at about 393–420 K may be assigned to different combinations of (NH₄)₂SO₄ and NH₄HSO₄.     

Stabilization of ammonium dinitramide in the liquid phase

The kinetics of accumulation of the main products of thermal decomposition of ammonium dinitramide in the melt was investigated. The isotope composition of nitrogen-containing gases evolved by the decomposition of ¹⁵NH₄N(NO₂)₂ and NH₄ ¹⁵N(NO₂)₂ was found. Easily oxidized salts, amines, amides, iodides, and other compounds soluble in the melt interfere with the liquid-phase decomposition of ammonium dinitramide.     

Thermal decomposition behavior of the rare-earth ammonium sulfate R2(SO4)3·(NH4)2SO4

Rare-earth ammonium sulfate octahydrates of R₂(SO₄)₃·(NH₄)₂SO₄·8H₂O (R=Pr, Nd, Sm, and Eu) were synthesized by a wet process, and the stable temperature region for the anhydrous R₂(SO₄)₃·(NH₄)₂SO₄ form was clarified by thermogravimetry/differential thermal analysis, infrared, Raman, and electrical conductivity measurements. Detailed characterization of these double salts demonstrated that the thermal stability of anhydrous R₂(SO₄)₃·(NH₄)₂SO₄ is different between the Pr, Nd salts and the Sm, Eu salts, and the thermal decomposition behavior of these salts was quite different from the previous reports.     

Thermodynamics of aqueous solutions of poly ethylene glycol di-methyl ethers in the presence or absence of ammonium phosphate salts

Precise measurements of density and sound velocity at different temperatures ranging from 283.15 to 308.15 K for solutions of PEGDME250, PEGDME500 and PEGDME2000 in water and of PEGDME500 in aqueous solutions of 0.500 mol kg⁻¹ ammonium di-hydrogen phosphate ((NH₄)H₂PO₄) and di-ammonium hydrogen phosphate ((NH₄)₂HPO₄), binodal curves at temperature ranges 293.15-318.15 K for the aqueous PEGDME500 + (NH₄)₂HPO₄, PEGDME500 + (NH₄)₃PO₄, PEGDME2000 + (NH₄)H₂PO₄, PEGDME2000 + (NH₄)₂HPO₄, PEGDME2000 + (NH₄)₃PO₄ and PPG400 + (NH₄)₂HPO₄ two-phase systems, and liquid-liquid equilibrium data at temperature ranges 298.15-318.15 K for the aqueous PEGDME500 + (NH₄)₂HPO₄ and PEGDME2000 + (NH₄)₂HPO₄ two-phase systems have been taken. From the experimental density and sound velocity data, the apparent specific volume, excess specific volume, isentropic compressibility and isentropic compressibility deviation values have been determined and the effect of temperature, charge on the anion of electrolytes and molar mass of PEGDME on the volumetric and compressibility properties of the investigated polymer solutions as well as on the salting-out effect of PEGDMEs produced by ammonium phosphate salts has been studied.     

Crystal structures and physicochemical properties of mixed salts of ammonium nitrate and sulfate

Mixed salts (NH₄)₂SO₄·2NH₄NO₃ (1) and (NH₄)₂SO₄·3NH₄NO₃ (2) were synthesized and studied by X-ray diffraction analysis. The unit cell parameters of these salts were determined and their crystal structures were solved. The thermal stability of the salts was studied by differential scanning calorimetry and thermogravimetric analysis. The temperatures and enthalpies of incongruent melting of compounds 1 and 2 were determined. The enthalpies of formation from the constituent salts were estimated.     

The application of solid sorbents for the purification of aluminum contaminated chemicals used as modifiers in electrothermal atomic absorption spectrometry

Various microcolumns with solid sorbents (ion exchange resins, functionalised cellulose sorbents, chelating resins) have been tested with respect to their ability for the purification of aluminum contaminated chemicals used as modifiers in electrothermal atomic absorption spectrometry. The purification of NaNO₃, Mg(NO₃)₂, K₂SO₄ and (NH₄)₂HPO₄ has been the most effective with an almost 100% efficiency, when Spheron-Oxine was used as chelating resin. The sorption of aluminum from KOH solution has been found to be very high (around 90%) for all investigated sorbents. However, the best results have been obtained with anion-exchange resins. It has been difficult to purify concentrated mineral acids (HCl, H₂SO₄). A retention of aluminum above 80% has been achieved only when Cellex P, Chelex 100 or Amberlite XAD-2 have been used.     

Hydrolysis of magnesium hydride in the presence of ammonium salts

The influence of the nature of ammonium salts (NH₄Cl, (NH₄)₂SO₄, (NH₄)HSO₄, [(CH₃)NH₃]Cl) and their concentration in aqueous solutions on the hydrolysis of magnesium hydride has been studied. The highest degree and fastest rate of hydrolysis are observed at an ammonium salt concentration of ～7.5%. The most efficient activator among the ammonium salts under consideration is (NH₄)HSO₄.     

Effects of melamine phosphate on the thermal decomposition and combustion behavior of reconstituted tobacco sheet

In this paper, first the MP-modified reconstituted tobacco sheet (RTS) was prepared by a paper-making process. Thermogravimetric analysis coupled to Fourier transform infrared spectrometer (TG-FTIR) had been used to investigate the influences of melamine phosphate (MP) on the thermal decomposition and the formation of evolved volatile products of RTS. TG-FTIR results illustrated that the incorporation of MP into RTS could retard the thermal decomposition of the major components of RTS and meanwhile lead to the formation of more thermally stable char. Moreover, the main gases released during the pyrolysis of RTS and MP-modified RTS were H₂O, CO₂, CO, NH₃, carbonyl compounds, alcohols, phenols, alkanes, and alkenes. The presence of MP changed the formation of evolved volatile products of RTS obviously. The effects of MP on the combustion behavior of RTS were studied by micro-scale combustion calorimetry and cone calorimetry. Results demonstrated that the formation of combustible gases was mainly determined by the thermal decomposition stage occurred in the temperature range of 150–600 °C. The incorporation of MP into RTS influenced the release of fuel gases and the char formation in the process of the thermal decomposition of RTS, and eventually retarded the flammability and combustibility of RTS.     

Analysis of (NH4)2SO4/(NH4)H2PO4 mixtures by thermogravimetry and X-ray diffraction

(NH₄)₂SO₄ and (NH₄)H₂PO₄ are the principal components in the powder material used in fire extinguishers. In this paper the mutual influence in their thermal decomposition is investigated by thermogravimetry. Two methods for the quantification of both salts in mixtures (NH₄)₂SO₄/(NH₄)H₂PO₄ are proposed. The first employs thermogravimetry and is based on the measurement of the mass fraction in the 500-550 °C interval, once (NH₄)₂SO₄ has totally decomposed to yield gaseous products. The second uses some selected peaks in the X-ray diffractogram.     

Gasification characteristics of coal char under CO2 atmosphere

The char gasification characteristics and the composition of evolved gases in a CO₂ environment have been studied using a thermogravimetric analyzer (TG) coupled with a mass spectrometer. Three types of coal char were studied: lignite (TXL), sub-bituminous (PRB), and bituminous (KYB). TG results showed that the reactivities of TXL and PRB were higher than that of KYB, and the reactivity of TXL was higher than that of PRB. The characterization of the chars implied that the mineral content in the char plays an important role in the reactivity and that the surface area and pore volume may accelerate the reactivity of chars. The evolved gases from three chars were mainly CO and SO₂. SO₂ was slightly delayed by CO during gasification of TXL and PRB chars, but for KYB, SO₂ and CO formed in the same temperature range, but at higher temperatures compared with TXL and PRB. The CO production of KYB was the best, 0.98 mg mg^?1; and SO₂ was the least, 0.031 mg mg^?1. PRB and TXL chars had similar CO production, but SO₂ in TXL was higher.     

Enzyme-polyelectrolyte complex: Salt effects on the reaction of urease with polyallylamine

The effects of inorganic mono- and divalent salts of different types on how the cation polyelectrolyte polyallylamine hydrochloride (PAA) binds with the oligomer enzyme urease were studied. It was shown that in solutions of the monovalent salts NaCl, KCl, and NH₄Cl, polyelectrolyte-protein complexes formed by electrostatic interactions, which decreased monotonically as the salt concentrations increased according to the classic law of statistical physics, correlating the Debye radius with the ionic strength of the solution. In solutions of the divalent salts Na₂SO₄ and (NH₄)2_SO₄, the efficiency of the formation of the polyelectrolyte-protein complexes changed abruptly (the enzyme was drastically activated) at low salt concentrations (∼0.6–0.8 mM), which was not consistent with the classic theory of charge interactions in solutions with different ionic strengths. Turbidimetric titration at different salt concentrations in the given range revealed a high aggregative ability for sulfates and low ability for chlorides. It was concluded that the anomalies in the concentration dependence of the enzyme activity and aggregative ability were related to the formation of stable bonds PAA to the divalent SO₄²⁻ anion, which increased drastically when the ratio of anion concentration to the number of positively charged PAA monomers in solution reached 1: 2.     

IR spectra and thermal decomposition/dehydration of double complex salts of lanthanum(III) sulphate complex anions with several cobalt(III) ammine complex cations

Double complex salts of lanthanum(III) sulphate complex anions with several cobalt(III) ammine complex cations, [Co(NH₃)₆][La(SO₄)₃]·H₂O (1), (NH₄)₃[Co(NH₃)₅ H₂O]-[La(SO₄)₃]₂·2H₂O (2), and (NH₄)₃[Co(NH₃)₄(H₂O)₂][La(SO₄)₃]₂·2H₂O (3), were prepared by the addition of hexaamminecobalt(III), pentaammineaquacobalt(III), and cis- tetra-amminediaquacobalt(III) complexes to the solution containing lanthanum(III) ion and excess ammonium sulphate. The IR spectra of sulphate groups of these double complex salts were much more complicated than those of the almost free sulphate groups such as (NH₄)₂SO₄ and [Co(NH₃)₆]₂(SO₄)₃·5H₂O. Furthermore, values of activation energy in the dehydration process of 1, 2 and 3 were estimated using modified Doyle's and Wiedemann's method. They were 95.6 ± 4.3, 157.1 ± 15.5 and 163.2 ± 20.8 kJ mol^?1, respectively. Here, one molecule water is released per molecule of 1, 2 and 3.     

Investigation of the evolved gases from Sulcis coal during pyrolysis under N2 and H2 atmospheres

The evolution of gases and volatiles during Sulcis coal pyrolysis under different atmospheres (N₂ and H₂) was investigated to obtaining a clean feedstock of combustion/gasification for electric power generation. Raw coal samples were slowly heated in temperature programmed mode up to 800 °C at ambient pressure using a laboratory-scale quartz furnace coupled to a Fourier transform infrared spectrometer (FTIR) for evolved gas analysis. Under both pyrolysis and hydropyrolysis conditions the evolution of gases started at temperature as low as 100 °C and was mainly composed by CO and CO₂ as gaseous products. With increasing temperature SO₂, COS, and light aliphatic gases (CH₄ and C₂H₄) were also released. The release of SO₂ took place up to 300 °C regardless of the pyrolysis atmosphere, whilst the COS emissions were affected by the surrounding environment. Carbon oxide, CO₂, and CH₄ continuously evolved up to 800 °C, showing similar release pathways in both N₂ and H₂ atmospheres. Trace of HCNO was detected at low pyrolysis temperature solely in pure H₂ stream. Finally, the solid residues of pyrolysis (chars) were subjected to reaction with H₂ to produce CH₄ at 800 °C under 5.0 MPa pressure. The chars reactivity was found to be dependent on pyrolysis atmosphere, being the carbon conversions of 36% and 16% for charN₂ and charH₂, respectively.     

THERMAL REACTIONS IN SYNTHETIC APATITE–AMMONIUM SULFATE MIXTURE

The thermal reactions in the mixtures of hydroxylapatite or fluorapatite and (NH₄)₂SO₄up to 500°C were studied with the purpose of elaborating the conditions of obtaining calcium–ammonium cyclophosphate that could be used as fertilizer. Thermal analysis with a simultaneous FTIR analysis of the evolved gases as well as the analyses of chemical and phase composition of solid products were performed. The thermal changes in the mixtures could be divided into three steps: (1) decomposition of (NH₄)₂SO₄and reactions of apatite with these products at 250–420°C, (2) calcium ammonium polyphosphate formation at 290–450°C, and (3) reaction of CaSO₄with CaNH₄P₃O₉at 320–500°C. Higher concentrations of NH₃in the gas phase promote the formation of CaNH₄P₃O₉and increase its stability. Calcination at temperatures above 350°C causes decomposition of CaNH₄P₃O₉with a decrease in the content of water-soluble phosphorus and evolvement of SO₂.     

Solid/liquid- and vapor-phase interactions between cellulose- and lignin-derived pyrolysis products

Solid/liquid- and vapor-phase interactions between cellulose- and lignin (Japanese cedar milled wood lignin)-derived pyrolysis products were studied under the conditions of N₂/600 °C/40–80 s. A dual-space closed ampoule reactor was used to eliminate the solid/liquid-phase interactions, and careful comparison of the resulting data with those of the pyrolysis of the mixed samples gave some insights into the solid/liquid- and vapor-phase interactions separately. With the solid/liquid-phase interactions, the tar yields from both cellulose and lignin increased with the decreasing yields of the char fractions in a short pyrolysis time of 40 s (primary pyrolysis stage). Most of the identified tar components from cellulose and lignin increased in their yields. The vapor-phase interactions were significant at a longer pyrolysis time of 80 s (secondary reaction stage) when the methoxyl groups of the lignin-derived volatiles were cleaved homolytically. The vapor-phase interactions accelerated the gas formation from the cellulose-derived volatiles with suppressing the vapor-phase char formation of the lignin-derived volatiles. The yields of methane and catechols from lignin also increased greatly instead of the formation of o-cresols. Most of these influences are explained with a proposed interaction mechanism, in which the cellulose-derived volatiles act as H-donors while the lignin-derived volatiles (radicals) act as H-acceptors.     

Kinetics of the Formation of Goethite in the Presence of Sulfates and Chlorides of Monovalent Cations

The synthesis of goethite by oxidation of Fe²⁺in presence of metallic iron was undertaken in an aqueous medium containing indifferent salts such as Na₂SO₄, (NH₄)₂SO₄, NaCl, and NH₄Cl. Temperature and bubbling air rate were maintained, respectively, at 70°C and 1 L/min. The influence of anions and cations on the kinetics of each step of the process has been followed distinctly, the iron dissolution rate has been determined by the variation of the medium acidity, and the precipitation of goethite has been determined by gravimetric measurements. With respect to Cl⁻, the SO₄²⁻anion decreases the rate of the two reactions. NH₄⁺acts as an inhibitor when it is present at low concentrations and as an accelerator for higher concentrations; the limit corresponding to the change of NH₄⁺behavior depends on the nature of the counter ion. The reaction product is composed of pure goethite in the presence of sulfate salts, whereas a mixture of goethite and lepidocrocite, respectively, 60–70 and 40–30%, was observed in the presence of chloride salts.     

Testing the retardancy effect of various inorganic chemicals on smoldering combustion of Pinus halepensis needles

The fire retarding performance of 28 different inorganic chemical substances was tested by measuring the relative particle fire hazard properties of Pinus halepensis needles treated with these chemicals. The tests were performed using a new method, based on a specifically designed apparatus for monitoring the forest species temperature, under precisely controlled temperature and static air atmosphere conditions. The relative ignition and smoldering combustion properties determined were: the ignition delay time, the combustion rate, the heat content and the mass residue of forest samples. The key elements for the effectiveness of fire retardants were the delay of ignition and the reduction of heat and combustion rate. The chemicals examined were: Cu, Fe, Al₂O₃, Fe₂O₃, SiO₂·H₂O, NaHCO₃, KI, KBr, KCl, NaCl, CaCO₃, MnSO₄·5H₂O, CuSO₄·5H₂O, MgCl₂·6H₂O, Na₂B₄O₇·10H₂O, Na₂HPO₄, Na₂CO₃, Na₂SiO₃, ZnSO₄·7H₂O, Zn₃(PO₄)₂·2H₂O, NH₄Br, NH₄Cl, NH₄HCO₃, (NH₄)₂CO₃, NH₄H₂PO₄ (MAP), (NH₄)₂SO₄ (AS), (NH₄)₂HPO₄ (DAP) and a commercial retardant containing both DAP and AS. Among them the best performance was exhibited by ammoniac phosphates, followed by ammoniac sulfates and silica.     

Diammonium hydrogen phosphate: a versatile and inexpensive reagent for one-pot synthesis of dihydropyrimidinones, quinazolinones and azalactones under solvent-free conditions

Diammonium hydrogen phosphate, (NH₄)₂HPO₄, efficiently catalyzes the three-component Biginelli reaction between an aldehyde, a β-dicarbonyl compound and urea or thiourea under solvent-free conditions to afford the corresponding dihydropyrimidinones in high yields. Also, the synthesis of 2,3-disubsitituted-(3H)-quinazolin-4-ones is achieved by the one-pot reaction of isatoic anhydride, primary amines and orthoesters in the presence of (NH₄)₂HPO₄. The reaction of hippuric acid with aromatic aldehydes and acetic anhydride resulted in the formation of azalactones using catalytic amounts of (NH₄)₂HPO₄.