Carbonization of Chinese Reed for Biochar with High Energy Density
4. Materials and Methods
of sugar, the conversion of biocrude to biochar was realized in the HTC process [28]. The SEM image for HTC conversion biocrude obtained at 200◦C to biochar is shown in Figure6.
As shown in the Figure6, the biochar obtained in the HTC of biocrude has uniform features.
Interestingly, the majority of the 2μm particles are composed of the biochar and biocrude transformed into carbon microspheres during the hydrothermal carbonization process. A comparison of biochar produced from reed and biocrude indicated that different formation pathways lead to various biochar properties. The biochar obtained the HTC of reed can be used as a higher energy density fuel for its higher carbon content. Because of the homogenization characteristics, the biochar resulting from the HTC of biocrude can provide a new method for producing carbonaceous materials.
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Figure 5. The conversion efficiency of carbon from biocrude obtained at different temperature (experiments on the HTC of biocrude at 200◦C, 2.0 h).
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Figure 6.SEM image of biochar (HTC of biocrude obtained at 200◦C), 200◦C, 2.0 h. (A: scale: 10μm;
B: scale: 2μm.)
was rapidly cooled to room temperature using air flow. The reaction time was defined as the time at the reaction temperature excluding preheating and cooling time. To study the effect of pressure on HTC process, reactor pressure was controlled by pumping water into the reactor until the set value was reached. After HTC of Chinese reed, the biochar and biocrude were separated with a 0.22μm filtration membrane. The biocrude was used as starting material for preparing carbon materials. As for the biochar produced from the biocrude, the experiments on the HTC of biocrude were carried out at 200◦C for 2.0 h in the batch reactor. The reactor was filled with liquid phase (biocrude) which was obtained from the different HTC processes and the biochar was collected through a 0.22μm filtration membrane after the reaction. The biochar obtained from biomass and biocrude was washed using deionized water and oven dried for 24 h at 105◦C.
4.3. Characterization
Surface morphology of the sample was recorded using an environmental scanning electron microscope (SEM, EVO 50, Zeiss, Jena, Germany). XRD patterns of the reed and biochar were obtained on a Miniflex powder X-ray diffractometer (Rigaku, Tokyo, Japan ) with a Cu Kαradiation source in a 2θrange from 10◦to 35◦with a scanning rate of 1◦/min. Infrared spectra (4000–400 cm−1) were analyzed by a IR100 infra-red spectroscopy (FTIR) instrument (Nicolet, Waltham, MA, USA) which was equipped with a TGS/PE detector and a silicon beam splitter with 1 cm−1resolution. The higher heating value (HHV) of reed and biochar was determined by an IKA-C200 calorimeter (IKA Works, Wilmington, NC, USA). The collected liquid solution was filtered through a 0.22μm pore-size filter prior to analysis. The main products in the resultant solution were identified based on standard compounds and their structures were further confirmed by HPLC (LC-20AD system, Shimadzu, Tokyo, Japan) equipped with an Aminex HPX-87H Ion Exclusion Column, 300 mm×7.8 mm) with a differential refraction detector (RID-10A). The column was held at 65◦C. H2SO4(0.01 mol/L) was used as the mobile phase at a flow rate of 1.0 mL/min. The peak identification was accomplished by comparison of sample peak retention times with those of standard solutions of pure compounds. The total organic carbon (TOC) in aqueous phase was measured with a TOC analyzer (Shimadzu TOC 5000 A).
5. Conclusions
Reed was converted into biochar in a temperature range of 200–280◦C for 0.5–4.0 h in a batch reactor. Compared with the residence time and pressure, the temperature plays a key role in the conversion of reed to biochar. Higher temperature is favorable for the production of a higher energy density fuel but is negative for the mass of biochar. The yield of biochar decreased when the temperature increased from 200◦C to 280◦C. The FTIR and SEM results suggested that the complete breakdown of the lignocellulosic crosslinked structure of reed is realized at higher temperature and biochar contained mainly lignin fractions. The XRD image of untreated reed and biochar indicated that the microcrystal features are converted into a non-crystalline structure in the HTC process. HTC of biocrude for biochar production were carried out from 200–280◦C and 2.0 h. The results indicated that biocrude obtained at lower temperature is favorable for biochar production and polycondensation of sugar is the major factor in the HTC of biocrude. The biochar obtained from the HTC of biocrude has a uniform particle size filled with globular carbon microspheres.
Acknowledgments: Authors acknowledge financial supports provided by the National Natural Science Foundation of China (21406255), the Shanghai Science and Technology Committee (16dz1207200) and the Youth Innovation Promotion Association CAS (2015231).
Author Contributions:Xin Huang and Lingzhao Kong conceived and designed the experiments; Chang Liu performed the experiments; Chang Liu and Lingzhao Kong analyzed the data; Chang Liu and Xin Huang contributed reagents/materials/analysis tools; Lingzhao Kong wrote the paper.
Conflicts of Interest:The authors declare no conflict of interest.
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