The mechanism for thermal decomposition of cellulose and its main products

Experiment is performed to investigate the mechanism of the cellulose pyrolysis and the formation of the main products. The evolution of the gaseous products is examined by the 3-D FTIR spectrogram at the heating rate of 5–60 K/min. A pyrolysis unit, composed of fluidized bed reactor, carbon filter, vapour condensing system and gas storage, is employed to investigate the products of the cellulose pyrolysis under different temperatures (430–730 °C) and residence time (0.44–1.32 s). The composition in the bio-oil is characterized by GC–MS while the gases sample is analyzed by GC. The effects of temperature and residence time on the main products in bio-oil (LG, 5-HMF, FF, HAA, HA and PA) are examined thoroughly. Furthermore the possible routes for the formation of the products are developed from the direct conversion of cellulose molecules and the secondary reactions of the fragments. It is found that the formation of CO is enhanced with elevated temperature and residence time, while slight change is observed for the yield of CO₂.     

Upgrading of low-boiling fraction of bio-oil in supercritical methanol and reaction network

In this work, the low-boiling fraction (LBF) of bio-oil was used as feed stock. LBF is a very complex mixture, and the three groups in LBF: acids, aldehydes and phenols, are primarily responsible for deterioration in the quality. The upgrading reactions were carried out over Pt/Al₂(SiO₃)₃, Pt/C or Pt/MgO in supercritical methanol. It is demonstrated that supercritical condition can greatly facilitate the esterification process, and after 6 h reaction, all the acids can be converted into esters even without adding any catalyst. The total amount of the three groups left in products was much less exhibited on Pt supported on active carbon and MgO in the presence of hydrogen. By investigating the model reactions, the relations between the representative compounds and major products were identified, and the conversion scheme of the upgrading reactions is proposed.     

Co-pyrolysis of walnut shell and tar sand in a fixed-bed reactor

This study investigated potential synergistic activities between tar sand and walnut shell during co-pyrolysis. A series of pyrolysis studies were conducted under specific operating conditions in a fixed-bed reactor. The highest yield of bio-oil from the co-pyrolysis was 31.84 wt.%, which represented an increase of 7.88 wt.% compared to the bio-oil yield from the pyrolysis of walnut shell alone. The bio-oils were characterized using various spectroscopic and chromatographic analysis techniques. The results indicated that the synergetic effect increased the co-pyrolysis bio-oil yield and its quality. Consequently, the results indicate that the bio-oils obtained will be suitable for the production of fuels and chemicals as feedstock after required improvements.     

Catalytic upgrading of bio-oil by HZSM-5 in sub- and super-critical ethanol

The pyrolysis bio-oil from rice husk was upgraded in sub- and super-critical ethanol using HZSM-5 as catalyst. The results showed that super-critical upgrading process performed more effectively than sub-critical upgrading process. Acidic HZSM-5 facilitates esterification in super-critical ethanol to convert acids contained in crude bio-oil into various kinds of esters. Stronger acidic HZSM-5 (low Si/Al ratio) can facilitate cracking of heavy components of crude bio-oil more effectively in super-critical upgrading process. The residue of distillated upgraded bio-oil from super-critical upgrading process decreased evidently, compared with that of distillated crude bio-oil. This work proved that crude bio-oil can be effectively upgraded in super-critical upgrading process with the aid of acidic catalyst.     

Comparative study of pyrolysis of algal biomass from natural lake blooms with lignocellulosic biomass

Pyrolysis experiments were performed with algal and lignocellulosic feedstocks under similar reactor conditions for comparison of product (bio-oil, gas and bio-char) yields and composition. In spite of major differences in component bio-polymers, feedstock properties relevant to thermo-chemical conversions, such as overall C, H and O-content, C/O and H/C molar ratio as well as calorific values, were found to be similar for algae and lignocellulosic material. Bio-oil yields from algae and some lignocellulosic materials were similar; however, algal bio-oils were compositionally different and contained several N-compounds (most likely from protein degradation). Algal bio-char also had a significantly higher N-content. Overall, our results suggest that it is feasible to convert algal cultures deficient in lipids, such as nuisance algae obtained from natural blooms, into liquid fuels by thermochemical methods. As such, pyrolysis technologies being developed for lignocellulosic biomass may be directly applicable to algal feedstocks as well.     

Process optimization of an auger pyrolyzer with heat carrier using response surface methodology

A 1 kg/h auger reactor utilizing mechanical mixing of steel shot heat carrier was used to pyrolyze red oak wood biomass. Response surface methodology was employed using a circumscribed central composite design of experiments to optimize the system. Factors investigated were: heat carrier inlet temperature and mass flow rate, rotational speed of screws in the reactor, and volumetric flow rate of sweep gas. Conditions for maximum bio-oil and minimum char yields were high flow rate of sweep gas (3.5 standard L/min), high heat carrier temperature (∼600 °C), high auger speeds (63 RPM) and high heat carrier mass flow rates (18 kg/h). Regression models for bio-oil and char yields are described including identification of a novel interaction effect between heat carrier mass flow rate and auger speed. Results suggest that auger reactors, which are rarely described in literature, are well suited for bio-oil production. The reactor achieved liquid yields greater than 73 wt.%.     

Effect of hot vapor filtration on the characterization of bio-oil from rice husks with fast pyrolysis in a fluidized-bed reactor

To produce high quality bio-oil from biomass using fast pyrolysis, rice husks were pyrolyzed in a 1-5 kg/h bench-scale fluidized-bed reactor. The effect of hot vapor filtration (HVF) was investigated to filter the solid particles and bio-char. The results showed that the total bio-oil yield decreased from 41.7% to 39.5% by weight and the bio-oil had a higher water content, higher pH, and lower alkali metal content when using HVF. One hundred and twelve different chemical compounds were detected by gas chromatography-mass spectrometry (GC-MS). The molecular weight of the chemical compounds from the condenser and the EP when the cyclone was coupled with HVF in the separation system decreased compared with those from the condenser and EP when only cyclone was used.     

High efficient conversion of CO2-rich bio-syngas to CO-rich bio-syngas using biomass char: a useful approach for production of bio-methanol from bio-oil

A novel approach for high efficient conversion of the CO₂-rich bio-syngas into the CO-rich bio-syngas was carried out by using biomass char and Ni/Al₂O₃ catalyst, which was successfully applied for production of bio-methanol from bio-oil. After the bio-syngas conditioning, the CO₂/CO ratio prominently dropped from 6.33 to 0.01-0.28. The maximum CO yield in the bio-syngas conditioning process reached about 1.96 mol/(mol CO₂) with a nearly complete conversion of CO₂ (99.5%). The performance of bio-methanol synthesis was significantly improved via the conditioned bio-syngas, giving a maximum methanol yield of 1.32 kg/(kg_catalyst h) with a methanol selectivity of 99%. Main reaction paths involved in the bio-syngas conditioning process have been investigated in detail by using different model mixture gases and different carbon sources.     

Pyrolysis of safflower (Charthamus tinctorius L.) seed press cake: part 1. The effects of pyrolysis parameters on the product yields

Safflower (Charthamus tinctorius L.) seed press cake was pyrolysed in a fixed-bed reactor. The effects of pyrolysis temperature, heating rate and sweep gas flow rates on the yields of the products were investigated. Pyrolysis runs were performed using pyrolysis temperatures between 400 and 600 °C with heating rates of 10, 30 and 50 °C min⁻¹. The obtained bio-char, gas and bio-oil yields ranged between 25 and 34 wt%, 19 and 25 wt%, and 28 and 36 wt%, respectively, at different pyrolysis conditions. The highest liquid yield was obtained at 500 °C pyrolysis temperature with a heating rate of 50 °C min⁻¹ under the sweep gas of N₂ with a flow rate of 100 cm³ min⁻¹. Employing the higher heating rate of 50 °C min⁻¹ results in maximum bio-oil yield, probably due to the decrease in mass transfer limitations. According to the results obtained under the conditions of this study, the effects of pyrolysis temperature and sweep gas flow rate are more significant than the effect of heating rate on the yields.     

Biomass fast pyrolysis in a fluidized bed reactor under N2, CO2, CO, CH4 and H2 atmospheres

Biomass fast pyrolysis is one of the most promising technologies for biomass utilization. In order to increase its economic potential, pyrolysis gas is usually recycled to serve as carrier gas. In this study, biomass fast pyrolysis was carried out in a fluidized bed reactor using various main pyrolysis gas components, namely N₂, CO₂, CO, CH₄ and H₂, as carrier gases. The atmosphere effects on product yields and oil fraction compositions were investigated. Results show that CO atmosphere gave the lowest liquid yield (49.6%) compared to highest 58.7% obtained with CH₄. CO and H₂ atmospheres converted more oxygen into CO₂ and H₂O, respectively. GC/MS analysis of the liquid products shows that CO and CO₂ atmospheres produced less methoxy-containing compounds and more monofunctional phenols. The higher heating value of the obtained bio-oil under N₂ atmosphere is only 17.8 MJ/kg, while that under CO and H₂ atmospheres increased to 23.7 and 24.4 MJ/kg, respectively.