Enhancement of benzene-methanol extraction (low molecular weight products) of coal in depolymerization reactions

Depolymerization of coals is an important reaction for the study of coal structure. Coal is depolymerized by using p-toluenesulphonic acid in phenol. Depolymerization takes place mainly through the cleavage of C-C and C = bonds and subsequent phenolation, whereas C-O-C linkages of coal are not affected by this treatment. In the present work, reactions, such as, reduction of coal through Li in ethylene-diamine, alkaline-degradation and dry HCl gas, which are known to cleave C-O-C linkages in coal selectively, have been coupled (as a pre-treatment) with depolymerization reactions. This could enhance the yields of low molecular weight products from coal as revealed by the enhancement in the benzene-methanol (7/3 vol/vol) extractability of depolymerized coals. The use of Ce(IV) salt, benzoyl peroxide, lead tetra-acetate and potassium persulphate, promotes the depolymerization reaction to low molecular weight products. These studies help in understanding the mechanism of generation of asphaltenes and, thereby, might help in the studies of liquefaction of coal.     

Oxygen electroreduction on carbon-supported platinum catalysts. Particle-size effect on the tolerance to methanol competition

The kinetics of oxygen reduction in methanol-containing acid electrolyte was investigated at platinum-based electrodes using the porous rotating disk electrodes (RDE) technique. Utilization of commercial-grade (E-TEK) carbon-supported Pt particles with narrow size distribution provided evidences for a particle size effect on the tolerance of oxygen reduction electrocatalysts to methanol competition. In methanol-containing perchloric acid electrolyte, the mass activity (MA, A g⁻¹ Pt) for oxygen reduction increases continuously with a decrease in particle size from d=4.6 to 2.3 nm, whereas in methanol-free electrolyte MA is roughly independent of the size, when d≤3.5 nm. Effects of addition of a second metal to Pt were also investigated. Based on particle size considerations Pt:Cr-C appears to be a more active catalyst than Pt-C for oxygen reduction in methanol-containing electrolyte.     

Depolymerization of Turkish lignites. 2. Effect of phenol concentration in a closed system

A lignite (C, 66.9 wt%) was depolymerized, using sulphuric acid as a catalyst, in a closed system in which the phenol/coal ratio was varied from 1.5 to 10. The products were separated by solvent extraction and silica gel chromatography. The i.r. and n.m.r. spectra, and the molecular weight of the products were measured. In the experiments with a phenol/coal ration of 10, complete depolymerization of the coal was seen provided the temperature of depolymerization was at least 210 °C. The products generally contained disubstituted aromatic structures connected by methylene bridges, it was found that as the phenol/coal ratio was increased there was a decrease in the number of methylene bridges connecting the aromatic structures. The molecular weights of the straight-chain pentane and benzene-soluble material were lower than the molecular weights of similar fractions in depolymerization experiments carried out in open systems. A method for the structural analysis of straight-chain pentane and benzene-soluble material based on i.r., ¹H n.m.r. and molecular weight measurements is suggested.     

Kinetic study of the depolymerization of Bruceton coal

The depolymerization of coals using phenol and p-toluenesulphonic acid, was studied.In this reaction the acid ‘catalyst’ is destroyed, its rate of destruction being different for different coals. A kinetic study of the depolymerization of Bruceton coal under conditions of gradually declining acid concentration has been carried out. Parameters which were monitored include the weight increase of the products, the solubility of the products in benzene-ethanol, the extractability of the products into pyridine, the amount of colloidal material present in the pyridine-extractables, and the molecular weight distribution of the pyridine-soluble products. Under the conditions used, the reaction produces primarily polymeric products from coal. The molecular weight distribution of the pyridine-soluble material seems to undergo no major changes with reaction time.     

Solvolytic extraction of coal through acylation and amidomethylation

Carboxylic acids, acid anhydrides and N-hydroxy methylamides were used to acylate Assam coal under Friedel—Crafts reaction conditions. This reaction resulted in the enhancement of the extractability of coal in benzene—methanol (7:3 vol./vol.) and quinoline after acylation with carboxylic acids and acid anhydrides. The effect of catalyst (AlCl₃) concentration on reaction was also investigated. l.r. spectra of reaction products indicated the introduction of acyl groups in the coal structure. Phthalimidomethylation could render about 50% coal extractable in quinoline.     

Mechanism of coal hydrogenation—liquefaction; Effect of temperature and coal particle size

The effect of coal particle size, hydrogen pressure and temperature on the extent of coal conversion in an entrained flow reactor is presented. Coal hydrogenation is done by feeding dry coal with ZnCl₂ catalyst into a continuous stream of hydrogen. The hydrogen-coal stream enters a long, small internal-diameter reactor (coiled tube reactor) controlled at about 500°C and 12.4 MPa hydrogen. At these conditions the coal particles become plastic and sticky. The hydrogen provides the energy to force the sticky coal particles through the reactor. Conversion of 85% of the coal to liquids and gases is easily attained. A physical mechanism is presented based on the unreacted-core-shrinking model. This mechanism aids in the explanation of the effect of process variables on reaction rates. Projections beyond the range of the variables studied are presented. These projections indicate that the pressure of coal liquefaction processes may be reduced by (1) the use of dry coal particles and (2) the reduction of the particle size. Significant reaction rates may be attained at pressures as low as 0.7 MPa by proper adjustment of particle size and temperature.     

碱性条件下甲醇阳极氧化碳载催化剂的性能

用化学还原法制备了碳载镍、银、金三种金属单质催化剂,并研究其对甲醇电催化氧化的活性.用X射线衍射光谱(XRD)、X光电子能谱(XPS)表征催化剂的晶相结构、表面组成及价态形式.XRD测试表明均得到了纯度较高的金属单质,催化剂粒径大小在5～11 nm之间,颗粒分布均匀.用循环伏安法测定了不同催化剂对甲醇的电催化氧化的活性...     

In situ transesterification of coconut oil using mixtures of methanol and tetrahydrofuran

The conventional biodiesel production method requires oil extraction followed by transesterification with methanol. The solubility of vegetable oils in methanol is low which decreases the overall rate of reaction. To eliminate the oil extraction step and improve the overall reaction rate, simultaneous extraction, esterification and transesterification were conducted by directly mixing methanol and tetrahydrofuran (THF) co-solvent and sulfuric acid catalyst with ground, desiccated coconut meat (copra) in a batch process and continuing the reaction until the system reached steady state. After separation of the mixture, yield was obtained by measuring the content of triglycerides, diglycerides and monoglycerides in the biodiesel phase. The yield increases with THF:methanol ratio, methanol:oil molar ratio and temperature. Within the range of conditions tested, the highest yield achieved was 96.7% at 60 °C, THF:methanol volume ratio of 0.4 and methanol:oil molar ratio of 60:1. The methanol:oil molar ratio is necessarily high in order to completely wet the copra mass, but is still lower than in previous studies by other researchers on in situ transesterification. Product assays show that the resulting biodiesel product is similar to conventionally produced coconut biodiesel. The results indicate that the in situ transesterification of copra using methanol/THF mixtures merits further study.     

高温烟气颗粒物在线检测装置性能评价

为评价高温工况下颗粒物在线检测装置的性能,在催化裂化高温烟气过滤实验装置上使用光学在线颗粒物检测装置测定了过滤器下游烟气中的催化剂浓度及粒径分布,同时用离线式粉尘等动采样装置和Coulter粒径分析仪测量过滤器上游与下游的催化剂浓度和粒径分布,对在线式的测量结果进行验证。考虑了温度对在线式测量结果的影响。实验结果表明:在线式检测装置可以在操作温度320~465℃,操作压力0.21 MPa工况下实现稳定的测量,在线式测量结果和离线式测量结果吻合很好,实验和计算模拟结果表明操作温度对实验测量的影响可以忽略。在此基础上,针对煤化工行业的实际工况,提出了利用迭代方式来获得在线测量结果修正值的方法,该方法对煤化工工艺中高温气体管道内颗粒物的在线测定同样具有指导意义。     

Synthesis of well-dispersed PtRuSnOx by ultrasonic-assisted chemical reduction and its property for methanol electrooxidation

PtRuSnO_x supported on multi-wall carbon nanotubes (MWCNTs) was prepared by ultrasonic-assisted chemical reduction method. The as-prepared catalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns indicate that Pt exists as the face-centered cubic structure, Ru is alloyed with platinum, while non-noble metal oxide SnO_x exists as an amorphous state. From TEM observation, PtRuSnO_x is well dispersed on the surface of MWCNTs with the particle size of several nanometers. The electrochemical properties of the as-prepared catalyst for methanol electrooxidation were studied by cyclic voltammetry (CV) and chronoamperometry (CA). The onset potential of methanol oxidation on PtRuSnO_x and PtRu catalysts is much more negative than that on Pt catalyst, shifting negatively by about 0.20 V, while the peak current density of methanol oxidation on PtRuSnO_x is higher than that on PtRu. Electrochemical impedance spectroscopy (EIS) studies also show that the reaction kinetics of methanol oxidation is improved with the presence of SnO_x. The addition of non-noble metal oxide SnO_x to PtRu promotes the catalytic activity for methanol electrooxidation and the possible reaction mechanism is proposed.     

Catalysts for Direct Methanol Fuel Cells

The activity of in house prepared carbon-supported Pt-Ru catalysts for methanol oxidation and carbon-supported RuSe for the oxygen reduction reaction in direct methanol fuel cells (DMFCs) was investigated. The composition of Pt-Ru/C was varied both in terms of weight loading (ratio of total metal content to carbon) as well as the ratio of Pt to Ru. The measurements were carried out in a half cell arrangement in sulphuric acid at various temperatures. The weight loading and ratio of Pt to Ru were varied in order to find out the optimum weight loading of precious metal and the temperature dependence of Pt to Ru ratio on methanol oxidation reaction. It has been found that there exists an optimum in the weight loading at 60 wt.% for carbon-supported Pt-Ru catalyst towards its maximum mass activity. While 1:1 Pt to Ru ratio exhibits a higher activity than 3:2 Pt:Ru above 60 °C, 3:2 ratio exhibits a higher activity at lower temperature. It has been observed that RuSe is inactive towards methanol and it is realised that RuSe is a potential candidate as methanol tolerant oxygen reduction catalyst. The activity of carbon supported RuSe for oxygen reduction reaction (ORR) was tested in sulphuric acid in the presence of methanol. Even though the mass specific activity of the RuSe catalyst is somewhat lower than that of Pt/C, the surface activity of carbon-supported RuSe is superior than that of carbon supported Pt which indicate the unfavourable size distribution of RuSe/C catalyst.     

Monodispersed hard carbon spherules as a catalyst support for the electrooxidation of methanol

Hard carbon spherules (HCS) were used as support of Pt nanoparticles as electrocatalyst for direct methanol fuel cells (DMFCs). Scanning electron microscopy (SEM) images show that the size of the Pt particles on HCS by reduction of K₂PtCl₆ with ethylene glycol is 4-5 nm. High-resolution transmission electron microscopy (HRTEM) study reveals that the Pt particles on the HCS surface have faceted crystalline structures. The size and aggregation of the Pt particles depend on the surface properties of the carbon support and the medium of the reduction reaction. Cyclic voltammetry and galvanostatic polarization experiments show that the Pt/HCS catalyst exhibits a higher catalytic activity in the electrooxidation of methanol than either the Pt/MCMB or the commercial Pt/Vulcan XC-72 catalyst does.     

Reaction of coals in hot acidic phenol at constant acid concentration

Previous work showed that the efficient ‘depolymerization’ of bituminous coals in hot phenol containing p-toluenesulphonic acid failed to occur and that the acid was destroyed during the reaction. Four coals varying in rank from lignite to low volatile bituminous were treated with refluxing phenol containing p-toluenesulphonic acid with the acid concentration held constant. The amount of colloidal material, of pyridine-soluble material, of benzene—ethanol solubles, and the number average molecular weight of the pyridine extractables were measured as a function of time. Although the reaction proceeds better with the lower rank coals, a large portion of the products is colloidal material. Treatment of coals with hot acidic phenol does not lead to their complete depolymerization. Treatment of Bruceton coal with refluxing phenol saturated with BF₃ also failed to give complete depolymerization. The formation of colloidal suspensions during investigations employing spectral and other physical measurements may lead to results that are susceptible to misinterpretation.     

Nano-stuctured Pt-Fe/C as cathode catalyst in direct methanol fuel cell

Pt-Fe/C catalysts were prepared by a modified polyol synthesis method in an ethylene glycol (EG) solution, and then were heat-treated under H₂/Ar (10 vol.%) at moderate temperature (300 °C, Pt-Fe/C300) or high temperature (900 °C, Pt-Fe/C900). As comparison, Pt-Fe/C alloy catalyst was prepared by a two-step method (Pt-Fe/C900B). X-ray diffraction (XRD) and transmission electron microscopy (TEM) images show that particles size of the catalyst increases with the increase of treatment temperatures. Pt-Fe/C300 catalyst has a mean particle size of 2.8 nm (XRD), 3.6 nm (TEM) and some Pt-Fe alloy was partly formed in this sample. Pt-Fe/C900B catalyst has the biggest particle size of 6.2 nm (XRD) and the best Pt-Fe alloy form. Cyclicvoltammetry (CV) shows that Pt-Fe/C300 has larger electrochemical surface area than other Pt-Fe/C and the highest utilization ratio of 76% among these Pt-based catalysts. Rotating disk electrode (RDE) cathodic curves show that Pt-Fe/C300 has the highest oxygen reduction reaction (ORR) mass activity (MA) and specific activity (SA), as compared with Pt/C catalyst in 1.0 M HClO₄. However, Pt-Fe/C catalyst does not appears to be a more active catalyst than Pt/C for ORR in 1.0 M HClO₄ + 0.1 M CH₃OH. Pt-Fe/C300 exhibits higher ORR activity and better performance than other Pt-Fe/C or Pt/C catalysts when employed for cathode in direct methanol single cell test, the enhancement of the cell performance is logically attributed to its higher ORR activity, which is probably attributed to more Pt⁰ species existing and Fe ion corrosion from the catalyst.     

Role of mineral matter in the chemical reactivity of coal

Previous work showed that the solvent extraction yield of coal increased as a result of chemical reactions such as formylation, reductive acylation, acylation, amidomethylation, alkylation, reduction and depolymerization. In the work described in this Paper, dmmf coal obtained after demineralization with mixed HF-HCI acids was used for solvolytic extraction studies after depolymerization, alkylation, acylation, amidomethylation, reductive acylation and reduction reactions. In comparison with the original coal, mineral matter free coal showed less increase in extractability as a result of these reactions indicating that mineral matter present in the original coal was acting as a promoter for these reactions.     

Niobic acid and niobium phosphate as highly acidic viable catalysts in aqueous medium: Fructose dehydration reaction

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

Investigation of carbon-supported Pt and PtCo catalysts for oxygen reduction in direct methanol fuel cells

Carbon-supported Pt and Pt₃Co catalysts with a mean crystallite size of 2.5 nm were prepared by a colloidal procedure followed by a carbothermal reduction. The catalysts with same particle size were investigated for the oxygen reduction in a direct methanol fuel cell (DMFC) to ascertain the effect of composition. The electrochemical investigations were carried out in a temperature range from 40 to 80 °C and the methanol concentration feed was varied in the range 1-10 mol dm⁻³ to evaluate the cathode performance in the presence of different conditions of methanol crossover. Despite the good performance of the Pt₃Co catalyst for the oxygen reduction, it appeared less performing than the Pt catalyst of the same particle size for the cathodic process in the presence of significant methanol crossover. Cyclic voltammetry analysis indicated that the Pt₃Co catalyst has a lower overpotential for methanol oxidation than the Pt catalyst, and thus a lower methanol tolerance. Electrochemical impedance spectroscopy (EIS) analysis showed that the charge transfer resistance for the oxygen reduction reaction dominated the overall DMFC response in the presence of high methanol concentrations fed to the anode. This effect was more significant for the Pt₃Co/KB catalyst, confirming the lower methanol tolerance of this catalyst compared to Pt/KB. Such properties were interpreted as the result of the enhanced metallic character of Pt in the Pt₃Co catalyst due to an intra-alloy electron transfer from Co to Pt, and to the adsorption of oxygen species on the more electropositive element (Co) that promotes methanol oxidation according to the bifunctional theory.     

草莓状银/聚苯乙烯-丙烯腈复合微球制备及其催化性能

以可聚合单体对苯乙烯磺酸钠(Na SS)作稳定剂,采用两步阴离子稳定分散聚合法,制备了单分散聚苯乙烯-丙烯腈P(St-AN)共聚微球,研究了丙烯腈单体加入时间对聚合物微球粒径及其分布的影响。并以微球为模板通过化学沉积法得到了分布均匀、单分散草莓状的Ag/P(St-AN)复合微球。通过傅里叶红外光谱、X射线衍射、扫描电镜和紫外-可见光谱对复合微球的组成、结构、形貌及催化性能进行了表征。结果表明,反应后1~3h补加丙烯腈可以得到600~800 nm单分散模板微球。得到的Ag/P(St-AN)复合微球表面具有较均一的结构,纳米银粒子具有面心立方结构,在微球表面有较好的分散性及稳定性,同时Ag/P(St-AN)复合微球对硼氢化钠(Na BH4)还原对硝基苯酚(4-NP)具有较高的催化活性。     

Depolymerization of Turkish lignites: 3. Effect of ultraviolet radiation

The effect of u.v. radiation on the product distribution of the acid-catalysed depolymerization reaction of a lignite (C, 66.9wt%) has been investigated. The products are separated by solvent extraction and silica gel chromatography and their ¹H n.m.r. spectra and molecular weights are also measured. Larger amounts of solubilized material are formed in the u.v.-irradiated depolymerization experiments due to a greater amount of phenol incorporation in the reactions. The relative molar masses of products are lower than those obtained from thermal depolymerization experiments and they contain less hydroaromatic structures connected by fewer methylene bridges. It is suggested that u.v. radiation is making the coal more accessible for phenol in the depolymerization reactions.     

Synthesis of organo-functionalized nanosilica via a co-condensation modification using γ-aminopropyltriethoxysilane (APTES)

An easy and swift pathway in preparation of organo-functionalized silica in nanosize range with amine-terminated group via co-condensation method is reported. The process is a self-catalyzed reaction by amine group of organosilane without the addition of ammonia as a catalyst at room temperature. A modified nanosilica with particle size of ～60 nm, highly monodispersed and low aggregation was successfully produced. The use of methanol as a solvent leads to the increase in particle size. CHN, FTIR and NMR analyses revealed the presence of organo-functional group in the bulk and at the surface of the silica particles.