| Pyrolysis of biomass to make biochar is an important way for the utilization of crop straw resources,and the resource utilization of crop straw is one of the important way to deal with energy and environmental problems in the world today.The purpose of this paper is to produce different properties of biochar from pyrolysis process of cotton stalks,and the application in the removal of heavy metals in water.First of all,the effects of the temperature,retention time and particle size on the yield and calorific value of the biomass were studied.this paper takes the typical bulk of cotton stalk as raw material to produced biochar under nitrogen gas atmosphere by slow pyrolysis.It studies the properties of the biochar and the difference from different process.The results showed that:(1)the effect of pyrolysis temperature on the yield and calorific value of the biomass was significant,and the biomass carbon yield was negatively correlated with caloric value,with the increase of the temperature,the yield of bio char decreased gradually,while the calorific value increased gradually.(2)the effect of retention time on the yield and calorific value of the bio char is obvious,but it is not as obvious as the pyrolysis temperature.At the same time,it can be seen that the yield and caloric value are negatively correlated with the increasing of the retention time.(3)there was no significant change in the yield and calorific value of the raw material particle size with respect to the first two conditions,which showed that the effect of particle size on the yield and calorific value was small.In addition,according to the general trend,we can still see a negative correlation between calorific value and yield.As the results showed that the yield and calorific value of biomass were negatively correlated with the value of three processes.Therefore,the introduction of energy yield(total energy per unit of raw materials)as a comprehensive evaluation of the yield and calorific value of biomass,and use response surface analysis method to analyze the impact of three process conditions and their interaction on the energy yield,and optimized energy yield model after testing.The model predictions showed that when the retention time of 1.29 h and the particle size of raw material was 0.32 mm and the temperature was 429?,the energy yield was 78.95%.The validity of the model was verified by experiments.In order to study the influence of pyrolysis process on the characteristics of biochar,the composition,element content,pH,surface morphology,surface groups and specific surface area of biochar were characterized by 3 factors of different pyrolysis temperature,retention time and particle size.The results showed that with the pyrolysis temperature rise,the pH of the biochar from 8.18 rose to 11.10;-OH?-C=C-and-C-H absorption peaks of intensity are weakened;specific surface area and total pore volume increased significantly.After combing the characteristics of the system,the cotton straw biochar was applied to the removal of lead ion.The results showed that the most suitable pH was 5.5 for adsorption.And the pyrolysis temperature had the greatest influence on the adsorption.In the further analysis,the Langmiur model was found to fit adsorption.Comprehensive analysis of infrared,specific surface area,adsorption isotherms and other results,the mechanism of lead was obtained: when the carbon is carbonization at lower temperature,the adsorption process is dominated by organic group complexation and ion exchange,the adsorption is slow,but the adsorption capacity is large;when the carbon is carbonization at high temperature,the adsorption process is the interaction of organic groups and inorganic salts.The research results show that the energy yield of cotton straw biochar is high,and the adsorption performance of heavy metal lead ion is good,and it has good application potential. |
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