麦草半纤维素的快速热裂解实验研究

采用管式炉反应器在550℃~850℃进行了半纤维素的高温快速热裂解实验,以了解其热裂解产物分布及热解规律。结果表明,半纤维素热解三相产物中,气体产物产率最大且随着温度的升高而增加,其主要成分为H₂、CO、CO₂、CH₄ 以及小分子烃类。液相产物中主要是酸类、醇类、呋喃、环戊烯酮类化合物,以及苯酚等芳香化合物,其产率随着温度的升高无明显变化。而焦炭产率则随着温度的升高而降低,且其中残留有大量的有机化合物如醇类、酮类及脱水糖等。     

稻草固定床热解过程中不同赋存状态钾的迁移转化行为

选取稻草、水洗稻草及添加质量分数为5%KCl的微晶纤维素颗粒作为热解原料,进行固定床快速和慢速热解,研究稻草热解过程中全钾和四种赋存状态钾的析出规律以及四种赋存状态钾之间的相互迁移转化。结果表明,稻草热解过程中钾的析出率随温度变化分为两个区间,热解温度低于700℃时钾的析出率受温度影响较小;热解温度高于700℃时四种赋存状态钾相继达到释放点从而导致钾析出率急剧增加;热解过程中钾的析出主要是由水溶态和残渣态钾的减少造成;同时水溶态钾和有机态钾能够发生相互迁移转化;残渣态的碳骨架钾在热解时断裂,一部分转化成水溶态钾,一部分仍以残渣态钾存在。     

DTA study of thermal degradation of bagasse and rice straw hemicelluloses

DTA curves of the title substances were recorded up to 773 K, in static air. Bagasse hemicellulose (B) exhibited three overlapping exothermic effects, at 545, 618 and 700 K, while rice straw hemicellulose (R) displayed two exothermic effects, at 548 and 635 K. The absence of the third effect for R is ascribed to the catalytic effect of silica ash in promoting volatilization of the degradation products without allowing a char residue intermediate. The activation energy associated with each stage was derived by applying the Borchardt-Daniels general method, the Prout-Tompkins law, and integrated peak areas plotted as logg() vs. 1/T. A second-order linearization of the data proved best, with apparent activation energies of 143, 249 and 289 kJ mol^–1 for B, and 131 and 189 kJ mol^–1 for R. The total peak areas for R, when normalized to ash-free mass, were equal to those evaluated for B, indicating that approximately identical energies are evolved in the temperature range studied.

---

Zusammenfassung In statischer LuftatmosphÄre wurden die DTA-Kurven der Titelsubstanzen bis 773 K aufgenommen. Bagasse-Hemizellulose (B) zeigte bei 545, 618 und 800 K drei überlappende exotherme Effekte, wÄhrend sich bei Reisstroh-Hemizellulose (R) zwei exotherme Effekte bei 548 und 635 K ergaben. Das Fehlen des dritten Effektes für R wird dem katalytischen Effekt von Kieselerdeasche bei der Förderung des Freisetzen der Abbauprodukte zugeschrieben, ohne koksige Zwischenprodukte zuzulassen. Die zu den einzelnen Stufen gehörenden Aktivierungsenergien wurden durch Anwendung der allgemeinen Borchardt-Daniels-Methode, des Prout-Tompkinsschen Gesetzes und der graphischen Darstellung der integrierten PeakflÄchen in einem logg() vs. 1/T Diagramm erhalten. Eine quadratische Linearisierung der Daten ergab die besten Ergebnisse mit den scheinbaren Aktivierungsenergien von 143, 249 und 289 kJmol^–1 für B und mit 131 und 189 kJmol^–1 für R. Die totalen PeakflÄchen für R zeigen nach Normalisierung auf aschefreie Massen die gleichen Werte, die auch für B erhalten wurden.

     

Integrated processes for use of pulps and lignins obtained from sugarcane bagasse and straw

Sugarcane bagasse and straw can be converted into pulps, oils, controlled-release formulations, chelating agents, and composites. This article reviews bagasse and straw conversion efforts in Brazil. Laboratory-scale processes were developed aiming at the integral use of these biomass byproducts. Organosolv pulping and oxidation of lignin are the most promising processes for the rational use of sugarcane residues. Fungal pretreatment and spectroscopic characterization are also discussed.     

Kinetics of pyrolysis of sugarcane bagasse: effect of catalyst on activation energy and yield of pyrolysis products

Cellulose - In this work we have attempted to use biomass as energy source which is abundantly available throughout the world. The work is focused on pyrolysis of sugarcane bagasse in a...     

Production of hydrogen and syngas via pyrolysis of bagasse in a dual bed reactor

Pyrolysis of bagasse followed by thermal cracking of tar was carried out at atmospheric pressure using a dual bed reactor. The first bed was used for the pyrolysis and the second bed was used for thermal cracking of tar. Iron fillings were used as the packed bed material in the second bed. The effects of reaction time (20 to 40 min), reactor temperature (600 to 900℃) and packed bed height (40-100 mm) on the product (char, tar and gas) yield and gas (H2 , CO, CO2 , CH4 , CnHm ) composition were studied. Over the ranges of the experimental conditions used, the operating conditions were optimized for pyrolysis temperature around 850℃, a reaction time of 30 min and packed bed height of 100 mm, thus we could obtain a gas richer in hydrogen and carbon monoxide and poorer in carbon dioxide and hydrocarbons. It was observed that compared with single bed process, dual bed process increased the gas yield from 0.397 to 0.750 m3 /kg and decreased the tar yield from 0.445 to 0.268 g/g while the heating value of the product gas remained almost constant (10-11 MJ/m3 ).     

Thermal behavior of holo- and hemicellulose obtained from rice straw and bagasse

Thermal gravimetric analysis, and differential thermal behavior of holo- and hemicelluloses obtained from rice straw and bagasse were investigated. Degradation was found to be of first order reaction. The activation energy values and the rate constants were calculated from the kinetic of weight loss. Hemicellulose was found to be less stable than holocellulose, and the stability of the samples was arranged in the order, rice straw holo- > bagasse holo- > rice straw hemi- > bagasse hemicellulose. Degradation of rice straw (holo- as well as hemicellulose) was performed via two exothermic processes, whereas bagasse hemicellulose combustion was completed through three exothermic processes. The magnitude and the shape of the exotherms depend, mainly, on the chemical composition of the sample.     

Determination of flavonoids in cultivated sugarcane leaves, bagasse, juice and in transgenic sugarcane by liquid chromatography-UV detection

A high-performance liquid chromatography (HPLC) method with photo-diode array (DAD) detection was developed to separate and quantify flavonoids in sugarcane leaves and bagasse (= the crushed sugarcane refuse from juice extraction), and in sugarcane juice. Sugarcane flavonoids consist of a complex mixture of aglycones and glycosides (including flavonolignan glycosides), and the HPLC-UV method herein proposed is suitable for their quantification as total flavonoids. This method was applied to analyze samples of cultivated sugarcane, commercial juice and transgenic sugarcane leaves. Sugarcane leaves proved a promising source of flavonoids: an average of 1.10 mg of total flavonoids/g plant material was found in fresh leaves. Moreover, the flavonoid content of sugarcane juice (0.6 mg/mL) is comparable to other food sources of flavonoids previously reported. Transgenic sugarcane leaves ("Bowman-Birk" and "Kunitz") were compared with non-modified ("control") plant samples using the proposed HPLC-UV method, which indicated that the content of total flavonoids in transgenic plants is different from that in non-modified sugarcane.     

温度对稻草流化床快速热解液相产物影响的研究

研究了温度对稻草流化床快速热解中热解油产率的影响,利用GC/MS、FT-IR考察了不同热解温度(300℃~600℃)及冷凝温度(22℃、-4.4℃)下,稻草经过热解所获得的热解油组成。结果表明,稻草在400℃热解温度下可获得最高热解油产率43.1%;冷凝温度对热解油的品质有较大影响,降低冷凝温度能够增加热解油中有机物的含量,热解油中的水分含量随之降低,同时热解油的热值也随之得到提高。     

Effect of the oxygen transfer coefficient on xylitol production from sugarcane bagasse hydrolysate by continuous stirred-tank reactor fermentation

The effect of the oxygen transfer coefficient on the production of xylitol by biocon version of xylose present in sugarcane bagasse hemicellulosic hydrolysate using the yeast Candiada guilliermondii was investigated. Continuous cultivation was carried out in a 1.25-L fermentor at 30°C, pH 5.5, 300 rpm, and a dilution rate of 0.03/h, using oxygen transfer coefficients of 10,20, and 30/h. The results showed that the microbial xylitol production (11 g/L) increased by 108% with the decrease in the oxygen volumetric transfer coefficient from 30 to 20/h. The maximum values of xylitol productivity (0.7g/[L…h]) and yield (0.58 g/g) were obtained at k _L a 20/h.     

Evaluation of the porous structure development of chars from pyrolysis of rice straw: Effects of pyrolysis temperature and heating rate

The effects of pyrolysis temperature and heating rate on the porous structure characteristics of rice straw chars were investigated. The pyrolysis was done at atmospheric pressure and at temperatures ranging from 600 to 1000 °C under low heating rate (LHR) and high heating rates (HHR) conditions. The chars were characterized by ultimate analysis, field emission scanning electron microscope (FESEM), helium density measurement and N₂ physisorption method. The results showed that temperature had obvious influence on the char porous characteristics. The char yield decreased by approximately 16% with increasing temperature from 600 to 1000 °C. The carbon structure shrinkage and pore narrowing occurred above 600 °C. The shrinkage of carbon skeleton increased by more than 22% with temperatures rising from 600 to 1000 °C. At HHR condition, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum porosity development appeared at 900 °C. The total surface area (S_total) and micropore surface area (S_micro) reached maximum values of 30.94 and 21.81 m²/g at 900 °C and decreased slightly at higher temperatures. The influence of heating rate on S_total and S_micro was less significant than that of pyrolysis temperature. The pore surface fractal dimension and average pore diameter showed a good linear relationship.     

Lime pretreatment of crop residues bagasse and wheat straw

Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of two common crop residues: bagasse and wheat straw. A systematic study of pretreatment conditions suggested that for short pretreatment times (1–3 h), high temperatures (85-135°C) were required to achieve high sugar yields, whereas for long pretreatment times (e.g., 24 h), low temperatures (50–65°C) were effective. The recommended lime loading is 0.1 g Ca(OH)₂/g dry biomass. Water loading had little effect on the digestibility. Under the recommended conditions, the 3-d reducing sugar yield of the pretreated bagasse increased from 153 to 659 mg Eq glucose/g dry biomass, and that of the pretreated wheat straw increased from 65 to 650 mg Eq glucose/g dry biomass. A material balance study on bagasse showed that the biomass yield after lime pretreatment is 93.6%. No glucan or xylan was removed from bagasse by the pretreatment, whereas 14% of lignin became solubilized. A lime recovery study showed that 86% of added calcium was removed from the pretreated bagasse by ten washings and could be recovered by carbonating the wash water with CO₂ at pH 9.5.     

Surfactant-assisted bioremediation of hexavalent chromium by use of an aqueous extract of sugarcane bagasse

Agricultural products and by-products are now widely used for removal of hexavalent chromium from waste water. This option is more efficient and less expensive than conventional physicochemical treatments. The purpose of this study was reduction of carcinogenic hexavalent chromium to non-toxic trivalent chromium by use of aqueous extracts of sugar cane bagasse, which contains a variety of reducing components, for example sugar. The rate of this process is accelerated by use of surfactant as catalyst.     

Levels of polycyclic aromatic hydrocarbons in the bio-oils from induction-heating pyrolysis of food-processing sewage sludges

This study investigated the distribution of 21 target polycyclic aromatic hydrocarbons (PAHs) in the bio-oils, which were produced during the induction-heating pyrolysis of three different food-processing sewage sludges. The total concentrations of these priority PAHs ranged from 298 to 336 mg L⁻¹. The levels of PAHs are relatively high in low molecular weight fractions such as naphthalene, acenaphthylene, acenaphthene, fluorene and pyrene, and high molecular weight fractions such as indeno[1,2,3-cd]pyrene and dibenz(a,h)anthracene. However, in consideration of carcinogenic potency, it was found that dibenz(a,h)anthracene comprised a significant proportion of toxic equivalency values for target PAHs present in the bio-oils as a basis for using toxic equivalency factor method.     

Influence of pressure in ethanol/water pulping of sugarcane bagasse

The influence of the pressure in the ethanol/water pulping of sugarcane bagasse was studied using argon pressure varying from 0.5 to 1.5 MPa. The reaction volume and activation volume were studied. For the reaction volume, temperature and time were constant and pressure was varied, and for the activation volume, temperature was constant and pressure and time were varied. The degradation of cellulose was not promoted by the pressure with positive reaction volume (4100 cm³/mol). On the other hand, degradation of xylan (polyoses) and lignin was strongly favored by the pressure and reaction volume ranged from ?1000 to ?3000 cm³/mol.