Gasification of coals treated with non-aqueous solvents. 6. Catalytic steam gasification at atmospheric pressure

Nickel-catalysed steam gasification was examined for two Japanese and three German coals which had been pretreated with liquid ammonia. Reaction temperatures range from 923 to 1123 K. The greatest enhancement in reactivity by ammonia treatment and 1 wt % nickel loading was observed for Leopold coal. With this treatment, the temperature could be lowered by about 55 K to achieve the same conversion level as the original coal. The apparent activation energy decreased from 220 to 140 J/mol. The crucible swelling number decreased from $\text{1}\text{1}\text{2}$to 0. The surface of the char after gasification was examined by a scanning electron microscope. The role of the catalyst and the interaction of nickel with sulphur are discussed.     

Gasification of coals treated with non-aqueous solvents. 5. Properties of coals treated with liquid ammonia

Five coals of various ranks were treated with liquid ammonia at 373 K and 10 MPa, and some properties were examined. Although the equilibrium pore volume accessible to carbon dioxide was not affected, the rate of adsorption increased remarkably upon treatment. The pore volume determined by a larger molecule, say hexane, also increased greatly. When a nickel salt was impregnated among the coal surfaces, more satisfactory results were obtained on the treated coal. The treated coals were more easily comminuted than the parent coals. The relation between the change of these properties and the gasification reactivity is discussed.     

Gasification of coals treated with non-aqueous solvents. 4. Reactivity of coals treated with liquid ammonia

Gasification rates of twelve coals treated with liquid ammonia and impregnated with nickel were measured in hydrogen and in steam, and the effects of the ammonia treatment were compared. The treatment was found to promote gasification of most bituminous coals, especially the higher-caking coals. The increases in reactivity relative to untreated specimens were larger for gasification with hydrogen at 1273 K than for those with steam at 1125 K, but the trends with coal rank were similar. From a correlation found between the reactivities and the degree of degradation of the coal particles caused by the ammonia treatment, it was inferred that the treatment affected their pore structure.     

Gasification of coals treated with non-aqueous solvents. 1. Liquid ammonia treatment of a bituminous coal

A Japanese bituminous coal was treated with liquid ammonia at temperatures up to 120 °C. Extract was separated from the treated coal by washing with benzene-ethanol mixture. The amount of extract was about 2% in a single treatment at 120 °C and some additional extract was obtained by successive treatments. Particles of the residue had cracks and showed an increase in surface area. The ammonia-treated coal was found highly reactive toward gasification with hydrogen at high temperature when catalysed by nickel.     

Gasification of coals treated with non-aqueous solvents. 3. Swelling behaviour of a single coal particle

The swelling behaviour of a single coal particle was examined photographically under rapid heating up to 870 K in an atmosphere of nitrogen or hydrogen, to test how treatment with liquid ammonia affected the swelling property of a Japanese bituminous coal. It was found that the treated particle began to swell at higher temperature than the untreated one in either atmosphere, and that the impregnation of the treated coal with a nickel salt appreciably suppressed the swelling of coal particles especially those of smaller particle size.     

Effect of pressure on gasification reactivity of three Chinese coals with different ranks

The gasification reactivities of three kinds of different coal ranks (Huolinhe lignite, Shenmu bituminous coal, and Jincheng anthracite) with CO₂ and H₂O was carried out on a self-made pressurized fixed-bed reactor at increased pressures (up to 1.0 MPa). The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), and BET surface area. Results show that the char gasification reactivity increases with increasing partial pressure. The gasification reaction is controlled by pore diffusion, the rate decreases with increasing total system pressure, and under chemical kinetic control there is no pressure dependence. In general, gasification rates decrease for coals of progressively higher rank. The experimental results could be well described by the shrinking core model for three chars during steam and CO₂ gasification. The values of reaction order n with steam were 0.49, 0.46, 0.43, respectively. Meanwhile, the values of reaction order n with CO₂ were 0.31, 0.28, 0.26, respectively. With the coal rank increasing, the pressure order m is higher, the activation energies increase slightly with steam, and the activation energy with CO₂ increases noticeably. As the carbon conversion increases, the degree of graphitization is enhanced. The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40% of char gasification.     

Effect of the nature of solvents on the swelling of coals

The degrees of swelling of coals in n-alkylamines, 4-alkylanilines, and n-alcohols and the rates of their penetration into the structure of coals are inversely proportional to the molar volumes of homologs.     

Solvolytic liquefaction of coals with a series of solvents

Solvolytic liquefaction of coals of different rank was studied with a variety of solvents at 370–390 °C under nitrogen in order to elucidate the role of solvent in coal liquefaction of this kind and to find a suitable solvent for the highest yields of liquefaction. The yield was found to depend strongly upon the nature of the coal as well as the solvent under these conditions. Pyrene and a SRC-BS pitch were excellent solvents for Miike coal, which was fusible with high fluidity at these temperatures. However, the former was less efficient for Itmann and Taiheiyō coals which were fusible at a higher temperature and non-fusible, respectively. The mechanism of solvolytic liquefaction is discussed, including nature of coal and solvent at reaction temperatures, in order to understand the properties required for high yields with non-fusible coals in solvolytic liquefaction. It is found that for liquefaction with a high yield if the coal is non-fusible, solvolytic reaction should take place between solvent and coal, so giving a liquid phase of low viscosity at the reaction temperature. The solvolytic reaction may be one of hydrogen transfer when SRC-BS is used as the solvent.     

Effect of the properties of solvents on the yields of extracts from coals

It was found that data on the amounts of extracts obtained in a Soxhlet apparatus from Indian and Japanese coals depend on their chemical composition, and they can be related to the physicochemical properties of extractants by means of multiparameter equations.     

The action of solvents on coal at low temperatures: 2. Medium- and high-rank coals

The dissolution behaviour of three medium-rank and three high-rank coals in various solvents has been studied. Aqueous KOH is a non-solvent up to 180 °C. Dissolution of medium-rank coals into aliphatic amines and pyridine is not influenced by mass transfer effects in the 120–180 °C temperature range-although it is at room temperature-and does not involve the breaking of chemical bonds. This sets them apart from low-rank coals, where ester bonds have to be broken before dissolution can take place. An extraction limit of ≈50% seems to exist. Of the solvents studied, nonoethanolamine is the best for low-rank bituminous coals but rather poor for higher-rank coals, while the reverse is true of pyridine. Extract yields in hexylamine and ethylenediamine remain approximately constant in the medium-rank range. Low-volatile bituminous coals and semi-anthracites still contain some soluble matter, the extraction of which is diffusion-limited, at least up to 180 °C. From the results a hypothesis concerning the basic physical constitution of coal is derived and a model of the coalification process rationalizing the conjectured changes in constitution with rank is suggested.     

Reaction of ketohexoses with acid in certain non-aqueous sugar solvents

Ketohexoses or potential ketohexoses react rapidly with acids at high temperatures in non-aqueous solvents (containing the grouping R·O·C·C·OH in their structures¹) to produce 5-hydroxymethyl-furfural (HMF). HMF reacts further to give the solvent ether (e.g., II, III or IV ) in a slow reaction. Several of these ethers have been reduced partially to mono-ethers of 2,5-di(hydroxymethyl)furan ( V, VI or VII ) and fully to mono-ethers of 2,5-di(hydroxymethyl)tetrahydrofuran ( VIII, IX or X ).     

Thermal stabilization of poly(vinyl chloride) treated with organoaluminium compounds: 2. Effect of solvents

Poly(vinyl chloride) was treated with organoaluminium compounds in various solvents. The strong Lewis acids, alkyl-aluminium chlorides, predominantly cause the decomposition of PVC rather than the alkylation of the polymer regardless of solvents. In non-polar hydrocarbons, the treatment of PVC with trialkylaluminiums leads to increased heat sensitivity. In 1,2-dichloroethane solution and in benzene slurry, the trialkylaluminium-treated PVC exhibits significant improvement in thermal stability over unmodified PVC due to the exchange of the labile chlorines inherent in the polymer for relatively more stable alkyl groups. The apparent activation energy of the reaction of PVC with triethylaluminium in benzene slurry is the same as that in 1,2-dichloroethane solution, but the initial rate of alkylation of the polymer in benzene is about 10 times faster than that of the polymer in 1,2-dichloroethane. The aluminium concentration in the PVC particles is about twice that calculated from the swelling ratio of the PVC particles in benzene, suggesting that triethylaluminium not only penetrates into the swollen particles but is also adsorbed on the surface of the PVC particles to cause the increase in the aluminium concentration around the labile chlorines in the polymer chain. The alkylated PVC, compounded with only small amounts of zinc soap including an epoxidized oil and a chelating compound, shows excellent initial stabilization and long-term stability superior to the starting polymer even when this is compounded with 3 parts organotin stabilizers.     

非水溶剂预处理木质纤维原料研究进展

木质纤维素是目前中国最丰富的可再生资源,但由于其交织的复杂结构阻碍了内部纤维素和半纤维素的后续转化,这促使研究者们去寻求有效的预处理方法以解决目前的困境。近年来,随着预处理溶剂不断被发现和新型溶剂的快速涌现,非水溶剂预处理作为一种新兴的预处理方式在木质纤维素生物炼制中展现出良好的效果和应用前景。本文在系统介绍了各种非水溶剂理化性质和特点的基础上,综述了各种非水溶剂对木质纤维素预处理的作用原理、半纤维素和木质素的去除效果以及对纤维素酶解性能的影响,同时总结归纳了不同非水溶剂预处理的主要优缺点,并对非水溶剂预处理面临的挑战和未来的发展方向进行了展望,以期对未来绿色、低廉、高效的预处理方法提供借鉴和指导。     

Effect of mechanochemical treatment on petroleum coke-CO2 gasification

The effect of mechanochemical treatment during the grinding of petroleum coke on its gasification by CO₂ was studied. An additive derived by drying the black liquor in papermaking industry is adopted in grinding process. Results show that the gasification reactivity of petroleum coke is effectively improved by grinding, and the activation by wet grinding is more noticeable than that by dry grinding. Besides, by wet grinding petroleum coke and additive together, the active metal species in additive are not easily volatilized in gasification, and retain a high catalytic reactivity to the coke-CO₂ reaction throughout most of the conversion range. Changes in crystal structure of the petroleum coke induced by mechanochemical treatment is related to its gasification reactivity. In general, the crystalline-amorphous phase transition is the tendency of long time mechanical grinding, while a crystal structure re-formation stage is observed after wet grinding of petroleum coke with and without additive for some time. Similar phenomenon has also been found in the reported data, but not given attention. Some discussion is made in the paper, and more work should be undertaken to disclose the mechanism.     

Gasification of silicone fluids under external thermal radiation. Part I. Gasification rate and global heat of gasification

Transient gasification rates and fluid temperatures were measured for polydimethylsiloxane fluids ranging in viscosity from 0.65 cS to 60 000 cS in a nitrogen atmosphere at external radiant fluxes from 20 kW/m² to 70 kW/m². A detailed energy balance for each fluid sample was conducted to determine its global heat of vaporization. Two major energy loss corrections were identified and quantified. The absorption of incident radiation by the volatile products from short chain oligomers was measured and found to substantially reduce the incident flux to the sample surface; the energy loss due to re-radiation was determined to be a substantial factor in reducing the net heat flux to the sample for long chain length fluids. Other energy losses, e.g. heat loss to the substrate, were observed but were less significant. The average gasification rate for each fluid increased linearly with increasing external radiant flux. The global heat of gasification increases with an increase in the chain length (molecular weight) for the siloxane oligomers. These agreed well with calculated values. The global heat of gasification for 50 cS fluid is about 1200 kJ/kg and its value remains nearly constant for all higher molecular weight dimethylsiloxanes. Pyrolysis rates for siloxane fluids are very sensitive to trace catalysts. Measurements of the global heat of gasification for ultra-clean polymers resulted in significantly higher values (3000 kJ/kg). The gasification of siloxanes occurs via two modes or combinations thereof: (1) volatilization of molecular species native to the polymer, and (2) volatilization of thermal degradation products. The former process dominates for low molecular weight siloxanes (η<10 cS) and the latter process dominates for high molecular weight siloxanes (η>1000 cS). For the intermediate molecular weight siloxanes, both volatilization and degradation processes occur. © 1998 John Wiley & Sons, Ltd.     

Action of solvents on coal at low temperatures: 1. Low-rank coals

The dissolution behaviour of brown coals (67–75% C, daf) in pyridine, primary amines and aqueous KOH has been studied. The solubility in the last two solvents greatly depends on temperature, but in the first it is relatively temperature-independent. Pretreatment of the brown coals with aqueous HCl or with sodium ethanolate in ethanol leads to enhanced solubility. It is concluded that ester-bond breaking is necessary before extensive dissolution can take place. The solubility of brown coals in amines and aqueous KOH is found to increase with increasing carboxylic-acid group concentration in the coal. The solubility of Morwell brown coal in n-alkylamines at 180 °C increases with increasing length of the alkylchain in the solvent. The class of good solvents for brown coals is restricted to strong bases, because: 1. ester bonds have to be broken, 2. the acidic coal fragments have to be solubilized. Because of their capacity to break ester bonds these are so-called reactive solvents. Complete solvent recovery is impossible in the case of amines.     

Effect of the mineral components of brown coals on the properties of organic matter in the interaction with solvents

The cation-exchange forms of a considerable portion of metals that occur in brown coals from various deposits were identified. Based on swelling data, the interaction of the organic matter of coals with solvents was studied depending on the concentrations of mineral components. It was found that natural brown coals exhibit a densely crosslinked supramolecular structure with the predominance of molecular-size pores. In the course of decationization, the organic matter underwent partial depolymerization; the rate of diffusion and the accessibility of fragments to solvents with relatively bulky molecules dramatically increased.     

Study on the structure and gasification characteristics of selected South African bituminous coals in fluidised bed gasification

The gasification characteristics of three South African bituminous coals were investigated in a bubbling fluidised bed reactor. The three coals are similar in rank, but two are inertinite-rich coals and the third has a high vitrinite content. The microstructural characteristics of the parent coals and their resultant chars were determined using XRD, FT-IR, Raman and petrographic analysis. The microstructural changes that occurred in the organic (maceral) and the inorganic (mineral) fractions of the selected coals were evaluated. The change in the carbon structure was correlated to the proportions of inertinite and vitrinite macerals in the coals. High vitrinite content resulted in an increase in the order of the disordered carbon structure after gasification and this leads to greater graphitised ordered carbon structures. While a high inertinite content resulted in low or no structural transformation of the chemical structure. The transformation of inorganic mineral constituents of the coal was correlated to the amount of inertinite present in the selected coals. Higher proportions of inertinite macerals and inertinitic chars resulted in higher proportions of melted minerals. Char samples with low proportions of organic matter resulted in higher proportion of melted minerals covering the char surface.     

The process of activation of carbons by gasification with CO2-I. Gasification of pure polyfurfuryl alcohol carbon

Adsorption measurements, of nitrogen at 77°K, and mercury density measurements have been used to elucidate the detailed changes in microporosity of an 850°C polyfurfuryl alcohol carbon resulting from gasification with CO₂. The role of closed pores is emphasised and a model of the activation process is developed which enables the closed pore volume of the carbon to be determined without assuming a value for the density of the carbon in the pore walls. It is shown that all the closed porosity is opened to adsorbate and hence reacting gas in the initial stages of gasification. The model is also applied to the results of other workers.     

Hydrothermal dewatering of lower rank coals. 3. High-concentration slurries from hydrothermally treated lower rank coals

A novel method of producing a product of low intra-particle porosity (<1 μm pore radius) from highly porous Latrobe Valley raw brown coals uses a combination of hydrothermal and evaporative drying. Low porosity coal was made in three different batch autoclave systems at 320 °C for residence times as low as 10 min. Higher temperatures (up to 350 °C) increased porosity slightly but the water vapour pressure and the loss of organic material were significantly increased. Although the low and high porosity products differed dramatically in appearance and hardness, other chemical and spectroscopic properties were similar with the exception of pyrolysis-gas chromatography-mass spectrometry patterns.The relationship between intra-particle porosity and the maximum wt% dry solids concentration of aqueous slurries (for a viscosity of less than 1000 mPa s), ?_max, established by earlier workers for hydrothermally treated brown coals was found to hold for the new products and was extended to a wider range of porosities and a range of mean particle sizes (mps) (20-100 μm). A range of surfactants (anionic, cationic and neutral), which led to an increase of up to 7% in ?_max for a bituminous, Blair Athol coal, increased ?_max for products of hydrothermal or the new treatment by only 2-4%. This small increase resulted, however, in the formation of slurries of the low porosity products with ?_max's of up to 64%, similar to those obtained with high rank coals, and considered to be of commercial interest.