| Energy is an important material basis for survial and development of today's hunman beings.The using fossil energy will cause environmental pollution and face the shortage of resources in the near future,therefore renewable energy has attacted more and more attention.Biomass resourse is an promissing and valueable renewable energy sources.Biomass comes from a wide range of sources and there are many different technologies that have been applied in biomass utilization.Fast pyrolysis as a thermo-chemical conversion,can achieve the conversion of biomass into liquid,gas and solid products in a condition of absence of oxygen and moderate temperatures in a short reaction time.The liquid products,known as bio-oils,is rich in orgainc compounds that can be used for fuels or extraction of high value-added chemicals.In this paper,the distillation experiment was carried out with walnut shell bio-oil as raw material.The varitation trends of distilled fraction in the whole process was described and the change of carbon precursors and activated carbon in the process of praparing activated carbon from distillation residues was studied,which open up a new avenues for the use of distillation residues.Distillation of bio-oil derived from pyrolysis of walnut shell was investigated under different vacuum degrees and distillation temperatures.The vacuum degress is set to 40 mmHg,100 mmHg,300 mmHg and 760 mmHg and the distillation temperature is from ambient temperature to about 220 ?.Results revealed that in the initial stage of bio-oil distillation,most of the moisture,methanol and other low molecular weight compounds can be obtained and the higher the vacuum degree the lower the temperature at which the fraction began to distill.With the increase of temperature,the acetic acid and the phenolic compounds began to distill and under relatively low pressure,the concentration of acetic acid and phenols was facilitated,respectively.When the distillation temperature was up to 220?,the volume of the residues in the distillation flask started to swell due to the liquid-phase polymerization or pyrolysis of the oxygenate-rich bio-oils which blocks the overflow of the gas under the shell,and thus swell,then fill the distillation flask slowly.The higher vacuum degrees,the more moderate the swelling.The distillation residue accounts for 40-50 wt%,and the higher vacuum degrees of distillation,the less residue was obtained.The distillation residue mainly contains phenols,oligosaccharides and aliphatics.During the whole distillation process,the variation trend in these compounds under different vacuum degrees were not remarkable.The activated carbons were prepared from walnut shell bio-oil distillation residues by using KOH activation method.Two factors which have an impact on the pore structure of activated carbon were investigated,(?)carbonization temperatures and(?)heating rates.The carbon precursors and activated carbons were characterized by Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD)and Scanning electron microscope(SEM).The carbonization temperatures were set to 300 ?,400?,500 ?,600 ? and 700 ?,respectively,and the heating rates were set to 5 ?/min,10 ?/min and 15 ?/min,respectively.Results revealed that the activated carbons prepared from walnut shell bio-oil distillation residues treated with 10 ?/min,400 ?for 2 h,then activated with KOH(3:1)have the highest specific surface area(2056 m2/g)?Its iodine adsorption capacity is 1091 rg/g and the adsorption capacity of methylene blue(MB)is 407 mg/g.The carbonization temperature and heating rates have effect on the micro-crystalline size and surface function groups which play a decisive role in the activation process.It was found that the specific surface area of the differently treated carbon precursors were small(400 m2/g or less),and the specific surface area was greatly increased after activation by KOH(1000 m2/g or more).It is indicated that the pore development is mainly related to the activation of pores by KOH.In the further characterization of the carbon precursors and activated carbon obtained by different treatments,the results of FTIR and XPS(X-ray photoelectron spectroscopy)analysis show that the carbonization temperature and heating rate affect the intensity of C-C and C=O functional groups in the carbon precursors,which affects the subsequent KOH activation process.Raman spectroscopy analysis shows that the ordered carbon in the carbonized material coexists with the disordered carbon.The carbonization temperature and heating rate affect the degree of structural defects in the carbon precursor.The XRD analysis also shows that the carbon precursors is mostly amorphous and there are a small amount of carbonaceous crystallites.The carbonization temperature and heating rate affect the quantity and size of carbonaceous crystallites,which affects the function of KOH activation.The TEM(Transmission electron microscope)images also show the worm-like appearance of the carbon precursors,and it is found that some lattice fringes are present,and the activated carbon is part of the graphite layer appeared in the TEM image,which proved that the samples had a graphitization transition.Through the above characterization methods,it is found that the influence of carbonization temperature on functional groups and carbonaceous crystallites is greater than that of carbonization rate.The SEM images can observe that the prepared activated carbon has abundant pores,which proves that the distillation residue can be a raw material for preparing activated carbon.In summary,this paper uses the walnut shell bio-oil as raw material for distillation experiments,and studies the effects of different distillation temperatures and vacuum degrees on the fractions,and describes the phenomenon of residue swell at the end of distillation.At the same time,this paper also study the preparation of activated carbon using the distillation residues,and different methods were carried on to characterize the effect of carbonization temperature and heating rate on the carbonization.This study provides a new way for utilization of bio-oil distillation residues and and also provided a research basis for the systematic application of bio-oil. |
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