Effect Of Potassium On Pyrolysis Properties Of Plant Biomass

Although a little amount of mineral matters in biomass, it’s the important nutrient for plant biomass and the product yields and distributions during biomass pyrolysis are affected by presence of mineral matters, especially K, Ca, Na and Mg. Rice husk was used as the raw biomass materials in the tests, which was demineralized through water washing and mild acid washing pretreatment with HC1. The effects of K on the pyrolysis of various samples, which were prepared by mixing cellulose, hemicellulose, lignin, rice husk and model rice husk with KC1separately, were investigated using thermogravimetric (TG) analyzer. The main conclusions are as follows:K contents in treated solutions derived from rice husk pretreatments, using dry ashing, wet digestion and microwave digestion, were determined by flame atomic absorption spectrometry (FAAS). In order to avoid ionization interference of K atom, the deionization agent was added to treated solutions. The results show that400μg/mL CsCl could almost eliminate the K atom ionization interference. K content in rice husk pretreated by dry ashing was0.6384%. However, the K contents in the treated rice husk by wet digestion and microwave digestion were0.7604%and0.7786%, respectively. The experimental values of K content derived from wet digestion were well reproducible and highly stable, and relative standard deviation (RSD) of data was only0.17%. Moreover, required instrument for wet digestion was facilitating. Wet digestion was suggested analysis method compared to the others.The morphology of rice husk changes from lump structure to flaky structure in water washing process, the number of flaky and pore structure in the samples rises obviously after acid washing pretreatment. The water washing pretreatment can only remove water-soluble alkali metal. However, the acid-soluble alkali metal combined with the organic functional groups cannot be removed through the water washing process. Demineralization pretreatment could supresse the char yields during TG test of the treated rice husk. Accordingly, the maximum weight loss rate and the temperature at the maximum weight loss rate increased.The effect of KC1on the three components in biomass was complicated. The maximum rate of weight loss for cellulose decreased with the addition of KC1. However, no significant differences were observed for the pyrolysis of hemicellulose and lignin. When KC1was added into the sample, the TG/DTG curve of model rice husk could be obtained by superposition of those of the hemicellulose, cellulose and lignin. In addition, the effect of KC1addition using impregnation process on the pyrolysis of rice husk was also studied. The results showed that the K had clear catalytic effect on the pyrolysis of rice husk. However, the pyrolysis characteristics of rice husk vary with the addition methods of KC1. For example, the char yields decreased with the addition of KCl using mechanical method (except for cellulose), but the char yield and the maximum weight loss rate of impregnated rice husk increased gradually with the increase of KCl content.