(50b) An Experimental Study of Biomass Thermochemical Processing by Catatytic Pyrolysis

Catalytic pyrolysis of pine and three straw biomass was carried out to produce hydrogen-rich gas by using a powder-paticle fluidized bed (PPFB), in which used different medium particles (SiO₂,γ-Al₂O₃,NiMo/Al₂O₃ and CoMo/Al₂O₃), the effects of the medium particles and the biomass types on the pyrolysis product yield and distribution were investigated respectively. The activity of NiMo/Al₂O₃ for H₂ production was proved to be the highest, and the H₂ yield of the woody biomass was higher than that of straw biomass. The high content of inorganic metal elements (K, Na, Ca, and Mg, etc.) resulted in a high H2 yield during the rice husk pyrolysis, however, the trends were not observed during the rice husk catalytic pyrolysis in the presence of a NiMo/Al2O3catalyst.

KeywordsFbiomassGpyrolysis; catalytic pyrolysisGhydrogenGBTXN; fluidized bed

1. Introduction

Biomass absorbs the same amount of carbon during its grow-up as what it consumed as the fuels. The conversion for production of gas or liquid products, particular for thermochemical conversion process, derived from renewable biomass is expected to become one of the attractive alternative energy sources to cope with global warming and exhaustion of fossil fuel sources [1-3]. Therefore, the extensive investigations of the thermochemical conversion technologies for biomass have been carried out [4-8]. Fast pyrolysis is considered as a better technology for producing gaseous or liquid products [2,9].

Typically, fast pyrolysis produce 60-75 wt% of liquid bio-oils, 15-25 wt% of solid char, and 10-21 wt% gas, depending on the feedstock used [2,3,9]. In order to obtain the more desired product, catalytic pyrolysis conversion has been proved the most effective method of biomass utilization with the advantages of the high productivity of desired product obtained from the tar or char and the low temperature [6,10,11]. Thus, many kinds of catalysts were studied, developed and used in catalytic reforming process of biomass for desired product formation, such as Ni-based catalysts [5,8], dolomites [7], zeolites [5], and some other metal catalysts, et al. [11].

In present study, the effect of different catalysts and biomass types on the product yield and distribution from pyrolysis and catalytic pyrolysis using a dual-particle powder fluidized-bed (PPFB) reactor was investigated. This study is aimed at providing a reliable theoretical basis for developing biomass catalytic pyrolysis technologies for desired products.

2. Experimental

Agriculture wastes of rice husk, soybean straw, corn stalks, and woody biomass of pine (denoted as Chip-1, Chip-2, Chip-3, and Chip-4, respectively) were used as the raw biomass material in the catalytic pyrolysis tests.

Commercial NiMo/Al₂O₃, CoMo/Al₂O₃, γ-Al₂O₃, and inert SiO₂ were used as fluidizing medium particles. The fluidizing medium particles were ground and sieved to 250-560 μm particle size before use.

The catalytic pyrolysis of the biomass was carried out continuously in a PPFB reactor. The detailed description of the reactor has been provided elsewhere [11]. In order to confirm the test results, the material balance maintains 95%~103% in each test.

During the whole pyrolysis process, all products, gas, liquid and solid products, were collected. The material balance of the pyrolysis process was calculated by the carbon balance, with an accuracy of 100±5% for all the tests. Gas, liquid and solid products were analyzed quantitatively. The detailed analysis methods have been provided elsewhere [11].

The thermogravimetric analysis (TG) was performed using a TG-Q50 instrument.

3. Results and discussion

3.1. The biomass pyrolysis properties

The pyrolysis characteristics of rice husk, soybean straw, and corn stalks are very similar. And meantime, the slightly difference between the agricultural wastes (rice husk, soybean straw, and corn stalks) and pine is observed. The content of volatile matter released of woody biomass is slightly higher than that of agricultural wastes, and the final pyrolysis temperature of woody biomass is relatively higher than that of agricultural wastes. The maximum weight loss rate of the pine was greater than that of the other agricultural waste biomass. The maximum weight loss rate of pine reached 1.02 %/K. The maximum weight loss rate of the biomass is obtained from the soybean straw which is only 0.63%/K and is lowest among the test biomass. The lignin content of wood biomass is higher than that of the other test biomass, resulting in the pine pyrolysis temperature shifts towards the higher temperature range.

3.2 Effect of pyrolysis temperature and biomass samples on H₂ yield

The obtained results indicate that H₂ yield of pine is higher than that of straw under the same operation conditions, because of the higher content of cellulose and hemicellulose for the pine biomass. The high content of ash in rice husk and much higher than that of the other biomasses, could be responsible for the high H₂ yield of rice husk. The inorganic metal elements might have catalytic effect on the biomass pyrolysis.

3.3 Effect of catalyst on the products of biomass pyrolysis

H₂ yield and selectivity of different medium particles decreases in the following order: NiMo/Al₂O₃>CoMo/Al₂O₃>γ-Al₂O₃>SiO₂. The H₂ yield of NiMo/Al₂O₃ catalyst is the highest no matter which biomass types is used. On the other hand, the H₂ yield (3.18 wt%,daf) of pine is much higher than that of the other three straw biomass. Pine with high cellulose and hemicellulose content is favorable to the H₂ formation.

H₂ yield of pine is higher than that of stalk biomass under the same operation conditions. This might be attributed to the high content of cellulose and hemicellulose of pine. The high content of inorganic metal elements (K, Na, Ca, and Mg, etc.) in rice husk, should be responsible for the high H₂ yield during the rice husk pyrolysis. However, the trend is not observed during the rice husk catalytic pyrolysis in the presence of a NiMo/Al₂O₃ catalyst. The fundamental reason about the effect of biomass compositions and types on the catalytic pyrolysis requires further investigation.

4. Conclusions

The yields of IOG, HCG, and HCL increase with the increase of pyrolysis temperature. The significant effect of biomass types on the H₂ production was observed during catalytic pyrolysis of the biomass. It’s important to select an efficient catalyst and proper pyrolysis parameters to improve the yield of desired product. The high selectivity of BTXN could be obtained by using CoMo/Al₂O₃ catalyst, however, the NiMo/Al₂O₃ activity for H₂ production is high in the process of the biomass pyrolysis. Inorganic metal elements might inhibit the activity of NiMo/Al₂O₃ catalyst. The reason and mechanisms should require further investigation.

Acknowledgement

We thank the National Natural Science Foundation of China for financial support under the contact numbers 20976132 and 21176191, respectively.

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