Xifeng Zhu

Catalytic pyrolysis of cellulose with sulfated metal oxides: a promising method for obtaining high yield of light furan compounds.

Pyrolysis-gas chromatography/mass-spectrometry (Py-GC/MS) was employed to achieve fast pyrolysis of cellulose and on-line analysis of the pyrolysis vapors. Three sulfated metal oxides (SO(4)(2-)/TiO(2), SO(4)(2-)/ZrO(2) and SO(4)(2-)/SnO(2)) were prepared and used for catalytic cracking of the pyrolysis vapors. The distribution of the pyrolytic products was significantly altered by the catalysts. Those important primary pyrolytic products, such as levoglucosan and hydroxyacetaldehyde, were significantly decreased or even completely eliminated. Meanwhile, the catalysis increased three light furan compounds (5-methyl furfural, furfural and furan) greatly. In regard to the selectivity of the three catalysts, the SO(4)(2-)/SnO(2) was the most effective catalyst for obtaining 5-methyl furfural, while the SO(4)(2-)/TiO(2) favored the formation of furfural and the SO(4)(2-)/ZrO(2) favored the formation of furan.

Determination of effective moisture diffusivity and drying kinetics for poplar sawdust by thermogravimetric analysis under isothermal condition.

The current study presents a thermogravimetric method to determine the effective moisture diffusivity and drying kinetics of biomass. Drying experiments on poplar sawdust were performed at four temperatures (60, 70, 80, and 90°C) by a thermogravimetric analyzer (TGA). The major assumption in experimentally determining effective diffusivity by Ficks diffusion equation is that drying is mass transfer limited and temperature remains isothermal during drying. The results indicated that TGA could well achieve these determining conditions. The drying process of sawdust mostly took place in the falling rate period. Midilli-Kucuk model showed the best fit for all experimental data. The effective diffusivity values changed from 9.38 × 10(-10)m(2)/s to 1.38 × 10(-9)m(2)/s within the given temperature range, and the activation energy was calculated to be 12.3 kJ/mol.

Biodiesel production from waste cooking oil using a heterogeneous catalyst from pyrolyzed rice husk

A solid acid catalyst was prepared by sulfonating pyrolyzed rice husk with concentrated sulfuric acid, and the physical and chemical properties of the catalyst were characterized in detail. The catalyst was then used to simultaneously catalyze esterification and transesterification to produce biodiesel from waste cooking oil (WCO). In the presence of the as-prepared catalyst, the free fatty acid (FFA) conversion reached 98.17% after 3h, and the fatty acid methyl ester (FAME) yield reached 87.57% after 15 h. By contrast, the typical solid acid catalyst Amberlyst-15 obtained only 95.25% and 45.17% FFA conversion and FAME yield, respectively. Thus, the prepared catalyst had a high catalytic activity for simultaneous esterification and transesterification. In addition, the catalyst had excellent stability, thereby having potential use as a heterogeneous catalyst for biodiesel production from WCO with a high FFA content.

In-depth investigation on the pyrolysis kinetics of raw biomass. Part I: Kinetic analysis for the drying and devolatilization stages

An in-depth investigation was conducted on the kinetic analysis of raw biomass using thermogravimetric analysis (TGA), from which the activation energy distribution of the whole pyrolysis process was obtained. Two different stages, namely, drying stage (Stage I) and devolatilization stage (Stage II), were shown in the pyrolysis process in which the activation energy values changed with conversion. The activation energy at low conversions (below 0.15) in the drying stage ranged from 10 to 30 kJ/mol. Such energy was calculated using the nonisothermal Page model, known as the best model to describe the drying kinetics. Kinetic analysis was performed using the distributed activation energy model in a wide range of conversions (0.15-0.95) in the devolatilization stage. The activation energy first ranged from 178.23 to 245.58 kJ/mol and from 159.66 to 210.76 kJ/mol for corn straw and wheat straw, respectively, then increasing remarkably with an irregular trend.

Catalytic Fast Pyrolysis of Cellulose to Prepare Levoglucosenone Using Sulfated Zirconia

Sulfated zirconia was employed as catalyst for fast pyrolysis of cellulose to prepare levoglucosenone (LGO), a very important anhydrosugar for organic synthesis. The yield and the selectivity of LGO were studied in a fixed-bed reactor at different temperatures and cellulose/catalyst mass ratios. The experiments of catalyst recycling were also carried out. The results displayed that from 290 to 400 °C, the liquid and solid accounted for more than 95 wt % of products, and the higher temperature led to more liquid and less solid products. The introduction of SO₄²⁻/ZrO₂ could promote cellulose conversion and LGO production. The temperature had a similar effect on the yield and selectivity of LGO at different cellulose/catalyst mass ratios. The maximum yield was obtained at 335 °C. Although the structure of the parent ZrO₂ was retained after recycles, which was confirmed by X-ray diffraction and N₂ adsorption-desorption measurements, the activity of SO₄²⁻/ZrO₂ could only be partially recovered by simply calcination. The catalytic activity decrease could be mainly attributed to SO₄²⁻ leaching, and the activity could be restored by further impregnation of H₂SO₄.

Reduction in time required for synthesis of high specific surface area silica from pyrolyzed rice husk by precipitation at low pH

Porous silica with a high specific surface area (SSA) was prepared from pyrolyzed rice husk (PRH) by adding H(3)PO(4) to sodium silicate solution (SSS) until the pH values of 5.7, 5.0, 4.1 and 3.2 were achieved. The preparation process involved producing SSS from PRH, forming silica-polyethylene glycol (PEG) composites using SSS, H(3)PO(4) and PEG, and calcinating the composites. The required preparation time was below 10h, and the SSA of the sample prepared at pH 3.2 reached 1018 m(2)/g. Decreasing pH significantly increased the amount of PEG incorporated into the silica-PEG composites, and hence more pores were generated in the lower pH sample when the PEG was destroyed by calcination at 500°C. The process developed in this study could lead to more efficient conversion of rice husk into high value-added porous materials that might be used for the adsorption of gas and heavy metal ions.

Comparative study on pyrolysis of lignocellulosic and algal biomass using pyrolysis-gas chromatography/mass spectrometry

The cornstalk and chlorella were selected as the representative of lignocelulosic and algal biomass, and the pyrolysis experiments of them were carried out using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The physicochemical properties of samples and the pyrolytic product distribution were presented. And then the compositional differences between the two kinds of pyrolytic products were studied, the relevant pyrolysis mechanisms were analyzed systematically. Pyrolytic vapor from lignocellulosic biomass contained more phenolic and carbonyl compounds while that from algal biomass contained more long-chain fatty acids, nitrogen-containing compounds and fewer carbonyl compounds. Maillard reaction is conducive to the conversion of carbonyl compounds to nitrogenous heterocyclic compounds with better thermal stability.

Study on pyrolysis characteristics of lignocellulosic biomass impregnated with ammonia source

The current study presents the pyrolysis characteristics of rice husk impregnated with different kinds of ammonia source (ammonium acetate, urea, ammonium sulfate and ammonium dihydrogen phosphate) in a fixed bed reactor. The introduction of ammonia source in pyrolysis process achieved the conversation from carbonyl compounds to nitrogenous heterocyclic compounds. The liquid product of urea-impregnated biomass has higher content of nitrogenous heterocyclic compounds (8.35%) and phenols (30.4%). For ammonium sulfate and ammonium dihydrogen phosphate-impregnated biomass, the quantity of compounds in liquid products reduces remarkably, and the gas products are rich in CO and H2. All the solid products of pyrolysis have great potential application in biochar-based fertilizer and activated carbon for their high N content.

TG-FTIR analysis of bio-oil and its pyrolysis/gasification property

Abstract The process of bio-oil pyrolysis/gasification and gas evolution characteristic was studied using a thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TG-FTIR). Pyrolysis/gasification of bio-oil and its fractions were also performed in a fixed bed. As a result, the process of bio-oil pyrolysis/gasification can be divided into two stages. The first is volatilization and pyrolysis of the light compounds at low temperature and the second is cracking and polymerization of the heavy compounds at high temperature. The values of activation energy are 35–38 kJ/mol in the first stage and 15–22 kJ/mol in the second stage, respectively. With temperature increasing, the conversion of pyrolysis/gasification grows higher and the yield of synthesis gas (syngas) increases. However, the calorific value of the gas has an inverse correlation with the temperature. In comparison, the light fraction (LF) makes more contribution to the overall H2 release; while CO and CH4 are mainly generated from the heavy fraction (HF).

Ex-situ catalytic pyrolysis of wastewater sewage sludge - a micro-pyrolysis study.

Concerns over increasing amounts of sewage sludge and unsustainability of current disposal methods have led to development of alternative routes for sludge management. The large amount of organics in sewage sludge makes it potential feedstock for energy or fuel production via thermochemical pathways. In this study, ex-situ catalytic pyrolysis using HZSM-5 catalyst was explored for the production of olefinic and aromatic hydrocarbons and nutrient-rich char from sewage sludge. The optimal pyrolysis and catalysis temperatures were found to be 500°C and 600°C, respectively. Carbon yields of hydrocarbons from sewage sludge were higher than for lignocellulose; yield differences were attributed to the high extractives content in the sludge. Full recovery of most inorganic elements were found in the char, which suggests that catalyst deactivation maybe alleviated through ex-situ catalytic pyrolysis. Most of the nitrogen was retained in the char while 31.80% was released as ammonia, which suggests a potential for nitrogen recycling.