棉秆催化热解特性及动力学建模研究

通过不同添加剂处理棉秆的热重实验,分析NaOH、Na₂CO₃、Na₂SiO₃、NaCl、TiO₂、HZSM-5六种添加剂催化棉秆热解动力学特性,结合原料的组分分析,建立三组分独立平行一级反应热解动力学模型对试样热失重行为进行模拟,采用非线性最小平方算法求解热解动力学参数。研究发现,添加剂的加入改变了三组分动力学参数,在碱性添加剂作用下,纤维素和半纤维素热解活化能都有较大程度降低,且碱性越强,纤维素热解活化能越低,而半纤维素热解活化能越高;中性添加剂NaCl对纤维素和半纤维素热解活化能的影响不大;酸性添加剂使纤维素和半纤维素的热解活化能有所增大,但所有添加剂对木质素热解活化能的影响不明显。     

不同碱处理制备多级孔HZSM-5催化剂及噻吩烷基化性能研究

用Na₂CO₃、TPAOH和TPA⁺/CO₃^2-混合碱分别处理HZSM-5分子筛,采用FT-IR、XRD、XRF、N₂吸附脱附、SEM、NH₃-TPD及Py-FTIR表征手段对各类碱处理前后的HZSM-5分子筛进行表征。结果表明,3种类型的碱处理HZSM-5分子筛后,均能形成微孔-介孔多级孔道的HZSM-5(A)催化剂,并能调变催化剂的酸性,其中,TPA⁺/CO₃^2-混合碱处理得到的HZSM-5(TPA⁺/CO₃^2-)催化剂,比表面积最大,介孔数量最多。在小型固定床反应器上,考察了HZSM-5和HZSM-5(A)催化剂的噻吩烷基化性能,结果表明,HZSM-5(TPA⁺/CO₃^2-)催化剂因为具有适当的多级孔孔道和较多的B酸中心而表现出较高的噻吩转化率和1-己烯对噻吩的选择性。     

Catalytic effects of eight inorganic additives on pyrolysis of pine wood sawdust by microwave heating

In this paper, pyrolysis of pine wood sawdust was carried out by microwave heating at ca. 470 °C under dynamic nitrogen atmosphere. Eight inorganic additives (NaOH, Na₂CO₃, Na₂SiO₃, NaCl, TiO₂, HZSM-5, H₃PO₄, Fe₂(SO₄)₃) were investigated in terms of their catalytic effects on the pyrolysis. All of the eight additives have increased yields of solid products greatly and decreased yields of gaseous products more or less. Yields of liquid products have not subjected to dramatic change. The incondensable gases produced from pyrolysis consist mainly of H₂, CH₄, CO and CO₂. All of the eight additives have made these gases evolve earlier, among which the four sodium additives have the most marked effect. All the additives have made the amount of CH₄ and CO₂ decrease, while all of them except NaCl, TiO₂ and Fe₂(SO₄)₃ have made that of H₂ increase and all of them except Na₂SiO₃ and HZSM-5 have made that of CO decrease. Alkaline sodium compounds NaOH, Na₂CO₃ and Na₂SiO₃ favor H₂ formation most. The most abundant organic component in the liquid products from pyrolysis of untreated sample and samples treated by all the additives except H₃PO₄ and Fe₂(SO₄)₃ is acetol. All the four sodium compounds favor acetol formation reaction and the selection increasing effect follows the order of NaOH > Na₂CO₃ ≈ Na₂SiO₃ > NaCl. TiO₂ goes against the formation of acetol, HZSM-5 has no marked effect on acetol formation. The two dominant organic components identified in the liquid products from pyrolysis of H₃PO₄ and Fe₂(SO₄)₃ treated samples are both fufural and 4-methyl-2-methoxy-phenol. A possible pathway for acetol formation is tentatively proposed.     

Evolution of gaseous products from biomass pyrolysis in the presence of phosphoric acid

Slow pyrolysis experiments of China fir (Cunninghamia lanceolata) wood were performed in a vertical tubular furnace at various heating rates. The raw material was pretreated by impregnation with phosphoric acid solutions of various concentrations for given times. The evolution of the gaseous products CO, CO₂, H₂ and CH₄ was analyzed online by using gas spectrometry to investigate the effect of phosphoric acid on the pyrolytic gaseous products of biomass. The addition of phosphoric acid was shown to significantly reduce the pyrolysis temperature necessary for the production of CO, CO₂ and H₂ gases, and the pyrolysis variables exerted an influence on the amount of the gases released. Moreover, phosphoric acid appreciably depressed the CO, CO₂ and CH₄ production, and promoted H₂, especially when a higher heating rate was employed. This suggested that phosphoric acid catalyzed both the primary thermal decomposition of biopolymers and the secondary reactions that took place among the pyrolytic vapor products.     

Analytical pyrolysis of carbohydrates: I. Chemical interpretation of matrix influences on pyrolysis-mass spectra of amylose using pyrolysis-gas chromatography-mass spectrometry

Inorganic additives, viz. Na₂CO₃, NaOH, HCl, ZnC₂, NaH₂PO₄, Na₂HPO₄, NaCl. MgSO₄ and sea salt, to the pyrolysis matrix change the pyrolysis-mass spectrum of amylose significantly. Carbonyl compounds, acids and their lactones, furans, pyranones anhydrosugars and aromatic substances are found in different ratios under the various conditions, as determined by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS).Carbonyl compounds, acids and lactones are released from alkaline and neutral matrices. Furans and anhydrohexoses are particularly formed under neutral and acidic conditions. Pyranones are specific for phosphate matrices. Unsaturated hydrocarbons and aromatic substances arise from strongly alkaline or dehydrating matrices. Degradation pathways are proposed for various compound categories.The results of pyrolysis-mass spectrometry and Py-GC-MS are highly compatible.     

Prediction of Electrolyte Solubilities from Minimal Thermodynamic Information

Summary.  A method is proposed that permits the proper extrapolation of thermodynamic quantities represented by the Pitzer equations from 25°C to other temperatures. The new method, which assumes temperature independent heat capacities, was tested for the NaCl*H₂O system and found very satisfactory. A new evaluation of the Na₂CO₃*H₂O system according to the CALPHAD method is presented, and solubilities for the quaternary Na₂CO₃*NaCl*NaOH*H₂O and its ternary subsystems are predicted. Limitations of (i) these predictions and of (ii) the Pitzer model regarding extrapolations to high molalities are discussed. Received April 20, 2001. Accepted May 2, 2001     

Prediction of Electrolyte Solubilities from Minimal Thermodynamic Information

 A method is proposed that permits the proper extrapolation of thermodynamic quantities represented by the Pitzer equations from 25°C to other temperatures. The new method, which assumes temperature independent heat capacities, was tested for the NaCl*H₂O system and found very satisfactory. A new evaluation of the Na₂CO₃*H₂O system according to the CALPHAD method is presented, and solubilities for the quaternary Na₂CO₃*NaCl*NaOH*H₂O and its ternary subsystems are predicted. Limitations of (i) these predictions and of (ii) the Pitzer model regarding extrapolations to high molalities are discussed.     

Microwave-assisted pyrolysis of biomass: Catalysts to improve product selectivity

This study was intended to evaluate the effects of catalysts on product selectivity of microwave-assisted pyrolysis of corn stover and aspen wood. Metal oxides, salts, and acids including K₂Cr₂O₇, Al₂O₃, KAc, H₃BO₃, Na₂HPO₄, MgCl₂, AlCl₃, CoCl₂, and ZnCl₂ were pre-mixed with corn stover or aspen wood pellets prior to pyrolysis using microwave heating. The thermal process produced three product fractions, namely bio-oil, gas, and charcoal. The effects of the catalysts on the fractional yields were studied. KAc, Al₂O₃, MgCl₂, H₃BO₃, and Na₂HPO₄ were found to increase the bio-oil yield by either suppressing charcoal yield or gas yield or both. These catalysts may function as a microwave absorbent to speed up heating or participate in so-called “in situ upgrading” of pyrolytic vapors during the microwave-assisted pyrolysis of biomass. GC–MS analysis of the bio-oils found that chloride salts promoted a few reactions while suppressing most of the other reactions observed for the control samples. At 8 g MgCl₂/100 biomass level, the GC–MS total ion chromatograms of the bio-oils from the treated corn stover or aspen show only one major furfural peak accounting for about 80% of the area under the spectrum. We conclude that some catalysts improve bio-oil yields, and chloride salts in particular simplify the chemical compositions of the resultant bio-oils and therefore improve the product selectivity of the pyrolysis process.     

Studies on TiO2/SiO2 and Pd/TiO2/SiO2 Catalysts in Photoreduction of CO2 with H2O to Methanol

The development of industry induced a massive increase in the emission of carbon dioxide into the atmosphere. A large amount of CO₂ and its general availability causes that it could be a cheap reactant in a reaction that runs in a way similar to photosynthesis in plants. Pure TiO₂ and metal doped TiO₂ are the most studied semiconductor catalysts for photoreduction of CO₂. The TiO₂/SiO₂ and Pd/TiO₂/SiO₂ catalysts were prepared and studied by temperature-programmed desorption, X-ray diffraction analysis, SEM-EDS, temperature-programmed reduction and then used for the methanol synthesis. The photoactivity of Pd/TiO₂/SiO₂ catalysts in the reduction of CO₂ with H₂O was tested at room temperature using photoreactor equipped with 16 lamps. The wavelength was characteristic of near ultraviolet. Post-reaction products were identified with gas chromatograph equipped with the flame ionization detector. Pd doping made the catalysts photoactive and the photoactivity of catalysts was changing as follows: 1%Pd/5%TiO₂/SiO₂ > 1% Pd/10% TiO₂/SiO₂ > 1% Pd/15% TiO₂/SiO₂. Optimum ultraviolet radiation time in the photoreduction of CO₂ to methanol was 7 h. An addition of Pd does not change the surface of the carrier.     

High efficiency ultra-deep dyeing of cotton via mercerization and cationization

A potentially environmentally responsible dyeing procedure for ultra-deep shades on cotton was developed using a cationization method in combination with mercerization. The effects of both treatments on dyeing performance and colorfastness properties of cotton fabrics dyed with reactive dyes were analyzed individually and in combination. Both mercerization and cationization have been proved to be effective in increasing the depth of shade on cotton. The colorfastness properties, except colorfastness to wet crocking, of mercerized–cationized cotton fabrics dyed without salt were much better than untreated cotton dyed using a conventional dyeing procedure. Unlike untreated cotton fabrics, the concentration of Na₂CO₃ in the dyeing process of mercerized–cationized cotton fabrics was lowered from 20 to 5 g/L without compromising dye fixation and colorfastness properties. With low concentrations of dyes and Na₂CO₃ and no electrolyte in the dye bath effluent, the dyeing procedure of mercerized–cationized cotton fabrics for ultra-deep shades is potentially a more environmentally benign method than conventional dyeing with reactive dyes.     

Study on the effects of flame retardants on the thermal decomposition of wood by TG–MS

The effect of three flame retardants, K₂CO₃, Na₂SiO₃·9H₂O, and Na₂B₄O₇·10H₂O on the process and composition of volatile products of the thermal degradation of wood has been investigated by the thermogravimetric (TG), differential thermogravimetry (DTG), differential thermal analysis (DTA), and the synchronous thermogravimetry–mass spectrometry (TG–MS) analysis methods. The results showed that the ion current intensity and ion peak area of m/z = 18 and 44 MS signals were increased by the flame retardants but the ion peak area of m/z = 28 MS signal was decreased (except K₂CO₃) at the meantime. What’s more, the ion current intensity and ion peak area of m/z = 60 and 68 MS signals were also decreased (except K₂CO₃), which mean that Na₂B₄O₇ can significantly enhances the dehydration and inhibits the depolymerization of wood. Although K₂CO₃ accelerates the dehydration reaction, it cannot inhibit the depolymerization reaction effectively, so the flame retardant efficiency of K₂CO₃ is decreased with the higher concentration. The catalysis of dehydration reaction of Na₂SiO₃ is the worst one.     

Thermodynamics of dissolution of lead oxide in NaOH–Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> melts

The solubility of lead oxide in NaOH + (20%)Na₂CO₃ and NaOH + (40%)Na₂CO₃ melts was studied by the isothermal saturation method. The model mechanisms of dissolution were considered. The thermodynamic parameters were calculated.     

Osmotic coefficient data for Na2SiO3 and Na2SiO3–NaOH by an isopiestic method and modeling using Pitzer's model

Osmotic coefficient and water activity data for Na₂SiO₃ and mixed Na₂SiO₃–NaOH aqueous solutions were obtained at 25°C by employing the isopiestic method. The binary Pitzer's parameters, β⁽⁰⁾, β⁽¹⁾, and C^φ, for Na₂SiO₃ and the mixing parameters, θ_{OH⁻SiO²⁻3 and} Ψ_{Na⁺OH⁻SiO²⁻3} were estimated using the osmotic coefficient data. The experimental osmotic coefficient data were correlated well with Pitzer's model. Mean activity coefficients of Na₂SiO₃ and NaOH for the solutions were predicted by Pitzer's model with the parameters obtained. Finally, the presence of metasilicic species, when sodium metasilicate (Na₂SiO₃·9H₂O) is dissolved in aqueous alkaline solution, was established by titration with hydrochloric acid.     

Investigation of catalytic property in the t-butylation of 1,2-dihydroxybenzene using FT-IR and XPS study

Catalytic properties of HZSM-5s with three different Na⁺ ion-exchange levels and SiO₂ /Al₂O₃ ratios used in tert-butylation of DHB (1,2-dihydroxybenzene) are interpreted through pyridine adsorbed FT-IR and XPS study. The DHB conversion decreases as increment of degree of Na⁺ ion-exchange level and of Si content in HZSM-5. Catalytic properties with respect to Na amount in ZSM-5 are more sensitive than those of HZSM-5s with different SiO₂/Al₂O₃ ratios. But selectivity for 4-TBC (4-t-butylcatechol) is not changed significantly. Acidic properties, i.e. acid strength and acid density are characterized by pyridine adsorbed FT-IR and XPS study. Based on FTIR and XPS analyses, DHB conversion and selectivities for DTBC (3,5-di-t-butylcatechol) and 3-TBC (3-t-butylcatechol) depend on type and strength of acid sites, with the result that strong Brønsted acid rather than weak Brønsted or Lewis acid sites are more closely related to the conversion. Furthermore, t-butyl alcohol is selectively adsorbed on the Brønsted acid site of FT-IR band at 3612 cm^-1, which signifies that the Brønsted acid site is the active site. The mechanism for t-butylation of DHB is suggested based on the FT-IR results of adsorption/desorption of reactants.     

Organic chemistry by infrared lasers: 5. Pulsed CO2 laser induced photoablative decomposition of biomass materials

Pulsed CO₂ laser irradiation of pulverized corn cobs, oak leaves, pine sawdust and processed cotton in an evacuated sealed system at 1077 cm⁻¹ affords a limited number of low molecular weight chemicals. The product mixture is very nearly the same in each reaction. The product ratios vary somewhat depending upon the initial biomass material used. The major gaseous products identified are CO, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, H₂O, acetaldehyde and acrolein. Irradiation at 1054 cm⁻¹ or 944 cm⁻¹ or under atmospheric conditions does not change the results significantly. The latter seems to indicate an ablative process wherein the cellulosic material decomposes by expelling neutral low molecular weight fragments from the biomass surface where high concentrations of radicals seem to be formed during, or very shortly after laser irradiation. Comparison with known thermolytic processes of biomass materials indicates that the laser induced ablation may be more controlled than pyrolysis. The results suggest the possibility of using the laser method for the continuous production of some of the low molecular weight chemicals and for studying the modes of decomposition of biomass materials.     

Potentiometric determination of free acidity and uranium in uranyl nitrate solutions using sulfate as complexing agent

In this paper free acid and uranium present together in the range of 0.05–3.0 meq and 20–250 mg, respectively, have been determined by potentiometric titration, using Na₂SO₄ and (NH₄)₂SO₄ complexants and NaOH and Na₂CO₃ as titrants. The results are presented as percentage recovery of free acidity and uranium over the range studied. It has been shown that percentage recovery of free acidity suggests a bias which varied from –5% to +74% at different free acidity and uranium concentrations for the Na₂SO₄–NaOH, Na₂SO₄–Na₂CO₃ and (NH₄)₂SO₄–NaOH complexant — titrant combinations. The percentage recovery of uranium always showed a positive bias which could be up to +8% for extreme free acidity — uranium ratios in the case of Na₂SO₄–Na₂CO₃ complexant — titrant combination. For the other Na₂SO₄–NaOH and (NH₄)₂SO₄–NaOH complexant — titrant combinations a positive bias of up to only +4% has been noticed.     

Phase equilibria in the NaCl–NaBO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>–KCl quaternary system

The phase diagrams of the ternary systems NaCl–NaBO₂–KCl, NaCl–KCl–Na₂CO₃, and KCl–NaBO₂–Na₂CO₃ and the quaternary system NaCl–NaBO₂–Na₂CO₃–KCl were studied by the calculation–experimental method and differential thermal analysis. Analytical models of phase equilibria were obtained, and the coordinates of ternary eutectics and a quaternary eutectic. It was shown that low-melting eutectic melts can be used as media for synthesizing oxide tungsten bronzes.     

纳米薄层HZSM-5分子筛催化甲醇制丙烯

在合成系列硅铝比纳米薄层HZSM-5分子筛的基础上,研究了纳米薄层HZSM-5分子筛催化甲醇制丙烯(MTP)的反应性能.在固定床微反装置上详细考察了工艺条件对纳米薄层HZSM-5分子筛催化性能的影响,同时与纳米HZSM-5分子筛对MTP反应的催化性能进行了比较.结果表明,纳米薄层HZSM-5分子筛具有较高的目的产物选择性和较长的催化寿命.在适宜硅铝比(n(SiO2)/n(Al2O3)=213)和反应条件下(温度470°C,甲醇质量空速为3 h-1),丙烯的选择性达到46.7%,三烯(乙烯、丙烯和C4烯烃)选择性达到78.7%.其中,丙烯/乙烯的质量比可达到6.5,是纳米HZSM-5分子筛的2倍,而芳烃的选择性比纳米分子筛明显降低.这是因为纳米薄层HZSM-5分子筛比纳米HZSM-5分子筛具有较宽的(010)晶面、较大的外比表面积和介孔孔容.     

Formation and Crystallization Behavior of Gels in the Na2O-SiO2-TiO2-ZrO2 System

SiO₂-TiO₂-ZrO₂ and 5Na₂O·95(SiO₂ + TiO₂ + ZrO₂) gels were synthesized and role of Na₂O in gel formation and crystallization behavior of gels were studied. From Si(OC₂H₅)₄, Ti(iso-OC₃H₇)₄, Zr(n-OC₃H₇)₄ and NaOCH₃ solutions in EtOH without H₂O, transparent and opaque gels were obtained. Opaque bulk gels, rich in TiO₂ or ZrO₂ composition in Na₂O containing SiO₂-TiO₂-ZrO₂ system, contain agglomerated spherical particles of diameter small <10 m, in contrast with opaque gels having large particles <30 m in alkali-free SiO₂-TiO₂-ZrO₂ system. Crystallization temperature (Tc) was measured by DTA on dried gels. Compared with the alkali-free SiO₂-TiO₂-ZrO₂ gels, 5 mol% Na₂O containing gels gave lower Tc in SiO₂ rich compositions and higher in TiO₂ rich or ZrO₂ rich compositions.     

The microstructure and optical transmittance thermal analysis of sodium borosilicate bio-glasses

The conditions to fabricate the bulk porous specimens have been studied on account of sodium borosilicate (NBS) glasses. Glass composition, heat treatment at phase separation and TiO₂ addition have been considered in this study. Original glass samples of composition in mol%: sample A: 9.19 Na₂O - 23.58 B₂O₃ - 67.23 SiO₂, sample B: 9.29 Na₂O - 3.17 TiO₂ - 23.82 B₂O₃ - 63.72 SiO₂ were prepared by melting reagent grade chemicals (Na₂CO₃, HBO₃, SiO₂ and AgNO₃) in platinum crucibles at 1480°C for 1 h in air. The melts were poured onto stainless steel plates and were annealed at 500°C for 0.5 h after cooling. Thus, obtained samples were phase separated at 700°C for 2, 15, 25 and 50 h to study their microstructure by scanning electron microscope (SEM). Besides the direct study of the microstructure by SEM, information on glass structural changes of samples are provided by measuring in situ changes by the optical transmittance thermal analysis. The isothermal measurements were carried out at 700, 720 and 740°C. The temperature of phase separation, the leaching and nucleator addition (TiO₂), significantly influence the microstructure of the resulting leached product. TiO₂ additive seems to suppress crystallization of cristobalite: especially at the extended above heat treatment phase separation runs. The phase-separated domains of glasses containing above 80 moles of SiO₂ are so small that it is very hard to observe them by SEM. The glass composition in our case was selected in a way to have relatively large phase separated areas easily observed by SEM at magnification 20 000·. The influence of TiO₂ is not too pronounced. It seems to suppress the cristobalite crystallization, especially of longer heating runs. The image analysis of leached glasses shows the prevailing content of the skeletal phase in a comparison to pores. The TiO₂ content diminishes the content of the skeletal phase. This revised version was published online in July 2006 with corrections to the Cover Date.