Interaction between coal and liquefaction catalysts studied by high temperature electron spin resonance

The high temperature electron spin resonance technique has been used to obtain in situ information on the behaviour of liquefaction catalysts during coal pyrolysis. The spin concentration in coal was induced in the presence of a catalyst at the pyrolysis temperature. ZnCl₂ drastically increased the spin concentration of coal. The order of activity of the catalysts with respect to the increase in spin concentration was: ZnCl₂ (impregnated) ?ZnCl₂ (dispersed) >ZnCl₂/KCl>SnCl₂ > SbCl₃≈AlCl₃ ≈CaCl₂ > coal alone.     

Conversion of solvent-refined coal to liquid products in the presence of Lewis acids

The formation of liquid products from a solvent-refined coal (SRC) was studied using Lewis acid catalysts in the presence of either benzene or cyclohexane as an extracting solvent. The soluble products were characterized by elemental analysis, ¹H-n.m.r., and, in some experiments, by gel permeation chromatography. Only ZnCl₂ and SnCl₂, the weakest Lewis acids examined, enhanced the dissolution of SRC over that observed in the absence of a catalyst. Increases in solubility were accompanied by increases in $\text{H}\text{C}$ and aliphatic character and by decreases in average molecular weight. These changes are ascribed to the ability of ZnCl₂ and SnCl₂ to promote depolymerization and hydrogenation of the SRC. Alkylation with isopropanol was also found to enhance the solubility of SRC in benzene and cyclohexane.     

High temperature and high pressure H n.m.r. and e.s.r. studies on coal liquefaction reactions

Changes in chemical reactions during coal liquefaction of Yallourn brown coal and Akabira bituminous coal were monitored by using high temperature and high pressure ¹H n.m.r. A simple high temperature and high pressure e.s.r. cell was constructed and the variation in concentration of free radicals during coal liquefaction reactions was monitored under the same experimental conditions as for n.m.r. With the liquefaction and coking reaction, typical spectra of n.m.r. and e.s.r. were obtained and could distinguish the reaction steps: swelling; liquefaction; coking. The combination of high temperature and high pressure n.m.r. and e.s.r. is promising to the chemistry of coal liquefaction reactions.     

Effects of Lewis acid catalysts on the hydrogenation and cracking of three-ring aromatic and hydroaromatic structures related to coal

Little is known about the hydrogenation and cracking of fused aromatic nuclei during the liquefaction of coal under the influence of Lewis acid catalysts. This study was conducted to establish the effects of catalyst acidity on the activity and selectivity of Lewis acid catalysts, the sources of hydrogen involved in hydrogenation and cracking, and the relationships between reactant structure and reactivity. Three-ring aromatic and hydroaromatic compounds were used to simulate some of the structural units present in coal. The catalysts examined were ZnCl₂ and AlCl₃. It has been established that the rates of both processes are strongly influenced by the Brönsted acidity of the active catalyst, e.g. H⁺ (MX_nY)^?, and the Brönsted basicity of the aromatic portions of the reactant. The source of the hydrogen used for hydrogenation depends on the choice of catalyst. In the presence of AlCl₃, Scholl condensation of aromatic nuclei serves as the principal source of hydrogen. Molecular hydrogen is used exclusively, however, when hydrogenation is catalysed by ZnCl₂. The formation of reaction products and the trends in reactant reactivity are discussed on the basis of cationic mechanisms. The results of this study contribute to an understanding of the processes which occur during the liquefaction of coal using ZnCl₂ or AlCl₃.     

Effectiveness of both ZnCl2- and SnCl2-containing molten salt catalysts for hydrogenation of Big Ben coal in the absence of a solvent

Hydrogenation of Big Ben coal (Australian bituminous coal) with 9.8 MPa H₂ for 3h at 400 °C has been carried out using a batch autoclave system in the presence of a molten salt catalyst such as ZnCl₂, SnCl₂, ZnCl₂-KCl-NaCl (3:1:1 mol ratio) and SnCl₂-KCl (3:2). The hexane-soluble (HS) yield decreases in the order: SnCl₂-KCl, SnCl₂, ZnCl₂-KCl-NaCl, ZnCl₂. The use of SnCl₂-containing melt is characterized by higher yields of both HS and benzene-soluble (BS) fractions and the suppression of gas yield compared with the use of ZnCl₂. The average aromatic unit and the molecular weight of HS increase in the order: ZnCl₂, ZnCl₂-KCl-NaCl, SnCl₂, SnCl₂-KCl. Chromatographic separation of HS fractions indicates that the saturate content is lowest and polar-material content is highest with the SnCl₂-KCl melt: this fact coupled with the structural parameters suggests that HS material with SnCl₂-KCl melt has, on average, a reasonably-high-molecular-weight skeleton which has more alkyl chains and heteroatoms. Micrographs of resulting benzene-insoluble (Bl) materials clearly indicated that the Bl particles were larger when ZnCl₂ was used than when the other melts were used, the Bl particles in these cases being of similar size. Lewis acidity and the viscosity of the molten salt appear to be related, in part, to the size of the Bl particles.     

Mechanochemical effects in coal conversion. 1. Coal hydrogenation in gaseous hydrogen aided by mechanical energy

Hydrogenation experiments with a Pennsylvania anthracite coal were carried out in H₂ under the following conditions: with simultaneous grinding; with grinding and the addition of 1% tin; without simultaneous grinding; and without grinding but with the addition of SnCl₂ (1% Sn). Temperature was maintained at 442 °C and pressure at ≈6.8 MPa gauge (1000 psig). By eliminating or minimizing the effects of heating that were due to grinding, and of size and mass transfer, the net effects on hydrogenation of the above conditions were examined. SnCl₂, as expected, increased the light products, both gaseous and liquid. Grinding substantially increased the heavy oil products (MW ≈ 280), but not the light fractions. The effect of grinding in combination with the addition of tin was very similar to the effect of SnCl₂. A simple mechanistic scheme is postulated to represent these effects. Rationale of the mechanochemical effects is presented. Some preliminary results of the e.s.r. measurements regarding these effects are also included.     

Supported platinum/tin complexes as catalysts for hydroformylation of 1-hexene in supercritical carbon dioxide

Platinum–phosphine complexes anchored on silica and on mesoporous MCM-41 supports were synthesized. Hydroformylation of 1-hexene was performed at 100 °C in supercritical carbon dioxide (pressure=2700 psi) using these supported platinum catalysts with SnCl₂ · 2H₂O (Sn:Pt=3.5:1) as co-catalyst. No hydrogenation was observed and high regioselectivity to heptanal was obtained.     

Effects of Lewis acid catalysts on the hydrogenation and cracking of two-ring aromatic and hydroaromatic structures related to coal

Little is known about the hydrogenation of fused aromatic nuclei during the liquefaction of coal under the influence of Lewis acid catalysts. This study was conducted to establish the effects of catalyst acidity on the activity and selectivity of Lewis acid catalysts, the sources of hydrogen involved in hydrogenation and cracking, and the relations between reactant structure and reactivity. Two-ring aromatic and hydroaromatic compounds were used to simulate some of the structural units present in coal. The catalysts examined were ZnCl₂ and AlCl₃. ZnCl₂ is less active than AlCl₃ for both hydrogenation and cracking but it does not promote the formation of tars via Scholl condensation: Methyl or hydroxyl substitution of the reactants greatly enhances their reactivity towards hydrogenation and cracking. The source of hydrogen consumed during hydrogenation depends on the choice of catalyst. In the presence of AlCl₃, Scholl condensation of aromatic nuclei serves as the principal source of hydrogen. Molecular hydrogen is used exclusively, though, when hydrogenation is catalysed by ZnCl₂. The formation of reaction products and the trends in reactant reactivity can be interpreted on the basis of carbonium ion mechanisms. The results of this study provide a basis for assessing the extent of hydrogenation occurring during the liquefaction of coal using ZnCl₂ or AlCl₃.     

Novel Esterification of Glycerol Catalysed by Tin Chloride (II): A Recyclable and Less Corrosive Process for Production of Bio-Additives

Abstract  

In this work, a novel process based on use of a SnCl₂·2H₂O catalyst which is less corrosive, inexpensive, and a water tolerant Lewis acid was employed for synthesis of fuel bio-additives from glycerol. High yields and selectivities were achieved for glycerol esterification with acetic acid under mild reaction conditions. The SnCl₂ catalyst showed to be as active as p-toluene sulfonic and sulfuric acid, catalysts commonly used in acid-catalysed esterification reactions. However, its use has significant advantages in comparison to these Br?nsted acid catalysts, including lower reactor corrosion and unnecessary neutralization at the end reaction. The SnCl₂ catalyst can also be recovered and reused without loss of catalytic activity. Additionally, effects of reaction temperature, HOAc:glycerol molar ratio and catalyst concentration on both selectivity and yield of glycerol acetates were also investigated. The lower corrosiveness, facilitated handling, as well as potential for reuse without activity loss after simple recycle protocols are positive aspects of SnCl₂ catalysts.     

Highly selective synthesis of dimethyl carbonate from urea and methanol catalyzed by ionic liquids

Direct synthesis of dimethyl carbonate from methanol and urea using ionic liquids, such as Et₃NHCl–FeCl₃, Et₃NHCl–ZnCl₂, Et₃NHCl–CuCl₂, Et₃NHCl–SnCl₂ and emimBr–ZnCl₂, as catalysts were investigated. Among the ionic liquids, Et₃NHCl–ZnCl₂ or emimBr–ZnCl₂ exhibited higher activity for the synthetic reaction and surprisingly high selectivity to DMC. The effects of the various reaction conditions, i.e. reaction temperature, molar ratio of methanol to urea, and amount and composition of catalysts, on the synthesis of DMC were discussed in a systematic way. The reaction mechanism and the reasons why raised activity and high selectivity of the catalyst are maintained were explored.     

Homogenous catalysis in the reactions of olefinic substances. V. Hydrogenation of soybean oil methyl ester with triphenylphosphine and triphenylarsine palladium catalysts

Some palladium complexes containing coordinated triphenylphosphine or arsine have been found to be effective and selective catalysts in the homogeneous hydrogenation of soybean oil methyl ester. The characteristic features of the catalysis are 1) isomerization ofcis double bonds totrans double bonds, 2) migration of isolated double bonds to form conjugated dienes, 3) selective hydrogenation of poly olefines to mono olefines without hydrogenation of mono olefine, 4) ester exchange of methyl ester to butyl ester, 5) effective hydrogenation and isomerization by methanol in the absence of elemental hydrogen. The catalytic activity of a variety of palladium complexes decreases in the following order: (ϕ₃P)₂PdCl₂+SnCl₂·2H₂O>(ϕ₃P)₂PdCl₂+GeCl₂>(ϕ₃P)₂Pd(CN)₂> (ϕ₃As)₂Pd(CN)₂>(ϕ₃P)₂PdCl₂≫(ϕ₃As)₂PdCl₂. However, neither K₂PdCl₄ with SnCl₂·2H₂O nor (ϕ₃P)₂Pd(SCN)₂ was effective for hydrogenation. The hydrogenation and isomerization of soybean oil methyl ester have been examined under various conditions using a mixture of (ϕ₃P)₂PdCl₂ and SnCl₂·2H₂O. Under nitrogen pressure, in benzene and methanol as a solvent, both isomerization and hydrogenation of soybean oil methyl ester proceeded less effectively than under hydrogen pressure. This work was done under contract with the USDA. Earlier articles in the series are: I, Inorg. Chem.4, 1618 (1965): II, Proceedings of the Symposium on Coordination Chemistry (Tihany, Hungary, 1964), Edited by M. T. Beck, Budapest, 1965; III, JAOCS43, 337 (1966); IV, Advances in Chemistry Series, American Chemical Society, in press.     

D.s.c., electrical conductivity,and n.m.r. studies of salt precipitation effects in PPO complexes

Differential scanning calorimetry (d.s.c.) and electrical conductivity measurements of poly(propylene oxide), PPO, complexed with the salts NaI and KSCN are reported. In addition, ²³Na n.m.r. measurements on PPO-NaI (x = 8), both at ambient and elevated pressure (2 kbar), have been performed. The d.s.c. data clearly indicate that the salt precipitates out of the complexes at about 85°C for NaI and 60°C for KSCN. These effects are manifested by a dramatic departure of the conductivity from Vogel-Tammann-Fulcher (VTF) behaviour, and a relatively sharp drop in mobile Na⁺ concentration, as deduced from n.m.r. measurements, above about 80°C. High pressure n.m.r. linewidth measurements are consistent with a pressure-induced increase in glass transition temperature.     

Polyborane-derived metal borides. 1. Hydrodesulphurization catalysts with potential for coal liquefaction

A new class of metal borides prepared at elevated temperatures and under hydrogen pressure from borane anions and cobalt or nickel salts catalyse the hydrodesulphurization of thiophene at 400 °C to butane and H₂S. The most active catalysts are prepared from the anions NaB₅H₈ and NaB₁₀H₁₃. These borides have unusually high boron levels (12–17%) and exhibit high sulphidation resistances. Using these catalysts, 88–99% conversion of thiophene is observed. With less active catalyst systems or at lower temperatures, butene and tetrahydrothiophene are also produced. Under similar reaction conditions, the nickel-pentaborane derived catalyst promotes 93% hydrogenolysis of furan. The boride catalysts do not promote hydrogenation of non-heterocyclic aromatics such as toluene and ethylbenzene. The potential of these new boride systems in processes related to coal liquefaction is discussed.     

Solubility increase of coal by alkylation with various alcohols

A vitrinite concentrate of Taiheyio coat has been reacted with various alcohols using ZnCl₂ as a catalyst under nitrogen pressure. The reaction conditions such as the reaction time, reaction temperature, initial nitrogen pressure and the effect of other Lewis acids as catalysts have been examined using methanol. The product from the reaction with methanol at 400 °C is fully soluble in pyridine, 57% in benzene and 26% in straight-chain hexane. This result is similar to that obtained when coal is hydrogenated under 10 MPa hydrogen pressure. Higher temperature, higher initial nitrogen pressure and longer reaction times give increased solubility. ZnCl₂ and FeCl₃ are the best catalysts. Of the various alcohols, branched alcohols give better results.     

Relaxation spectrometry of polyethylene in urea-polyethylene complex by BL n.m.r. and e.s.r. measurements

The molecular motions of polyethylene in urea-polyethylene complexes have been studied by e.s.r. and BL n.m.r. The e.s.r. spectra of alkyl free radicals located along the polymer chains were recorded and the temperature dependences of hyperfine splitting widths due to the β-protons (ΔH_β1, ΔH_β2) and linewidths were estimated. A decrease in (ΔH_β1 ? ΔH_β2) and narrowing (which appears over a wide temperature region) was found. The motional narrowing of line widths in the _BL n.m.r. spectra were also found. Correlation times for the molecular motion of polyethylene molecules were calculated from this magnetic resonance data, taking into account the distribution of relaxation times according to Miyake's equation. It was concluded that the molecular motions studied by e.s.r. and n.m.r. were the same. Relaxation time spectra indicated higher activation energies (10 kcal) than those calculated for a system with a single correlation time.     

The selective homogeneous hydrogenation of soybean methyl esters

Soybean methyl esters are homogeneously, selectively hydrogenated in the presence of a variety of catalysts, of which [Pt(Pph₃)₂Cl₂]+SnCl₂·2H₂O and [MoCl₂(CO)₃(Pph₃)₂]+SnCl₂·2H₂O are typical. Many variations can be made in these catalysts without destroying their selectivity. All of the catalysts bring about isomerization of the substrate molecules. The role of the solvent and the mechanism of the reaction are discussed. One of 10 papers to be published from the Symposium “Hydrogenation”, presented at the AOCS Meeting, New Orleans, April 1970.     

E.s.r. study of free radicals in poly(vinyl carbazole)

Poly(N-vinylcarbazole) was γ-irradiated at 77 K. The analysis of e.s.r. spectra showed that cation radicals centred at N were produced in the system. Hyperfine splitting constants are: a^N=0.57 mT and a^H_β=0.68 mT. The dependence of the rate constant of free radical decay on pressure (1–800 MPa) was studied at various temperatures (90–170°C). Activation volumes were determined for two characteristic pressure and temperature ranges. The results of e.s.r. measurements are compared with those obtained from dynamic-mechanical measurements.     

The application of the f.m.r. technique to coal characterization studies

The mineral magnetite has been detected in a sample of Pittsburgh No. 8 coal by the ferromagnetic resonance technique. The magnetite particles contained in a ground sample were < 0.07 μm diameter and have a chemical composition between Fe_2.98804O₄ and Fe_2.99704O₄. The results of acid treatment indicated that the magnetite is not embedded in the organic coal material, but is readily removed. The use of the f.m.r. technique as exemplified in the present work has important potential in the study of ferro-and ferrimagnetic minerals in raw coal and their interactions with paramagnetic organic free radicals during coal conversion processes.     

In situ d electron density of Pt particles on supports by XANES

The dependency of d electron density of Pt in Pt/SiO₂ catalysts on the particle size was investigated by means of in situ X-ray absorption near-edge structure (in situ XANES) spectroscopy. The d electron density of Pt particles was measured under vacuum, H₂ and ethene, to gain information about ethene hydrogenation on Pt/SiO₂. The intensities of the white lines at L_III and L_II edges in XANES spectra, which are regarded to reflect the unoccupied density of state, varied with the change of particle size under both vacuum and reaction gas atmospheres. The interaction between Pt particle and adsorbates was weak with small particles below 1.5 nm. A new peak induced by Pt-H bonding in the XANES spectra under H₂ was observed for the samples with Pt particle size 1.5 nm. This is related to the change of the turnover frequency and activation energy for ethene hydrogenation by Pt particle size.     

Measurement of anisotropic development in a low-rank coal using e.s.r. spectroscopy and optical texture

Anisotropic development in a low-rank coal (Cerrejón coal) has been induced using natural heavy oil or anthracene oil as additives in a cocarbonization system at 500 °C. The heavy oil showed better modifying activity. To monitor the anisotropic development optical microscopy and e.s.r. spectroscopy have been used. The concentration of stabilized free radicals, measured at room temperature (trapped free radicals) increased with anisotropic development. The concentration of stabilized free radicals allows interaction in the carbonization system to be followed even when the microcrystallinity of the anisotropic phase is too small to be observed under the microscope.