(750c) Characteristics of Distillation Residue from Rice Straw Fast Pyrolysis Oil

Characteristics of
distillation residue from rice straw fast pyrolysis oil

Hao Li, Shuqian
Xia, Peisheng Ma

Key Laboratory for Green
Chemical Technology of State Education Ministry, Collaborative Innovation
Center of Chemical Science and Engineering (Tianjin), School of Chemical
Engineering and Technology, Tianjin University, Tianjin 300072, People's
Republic of China.

Because of the shortage of oil resources and the
deteriorating environmental problems, the biomass fast pyrolysis oil deservedly
offers an opportunity as alternatives to replace fossil fuels due to its
renewable characteristics. Unfortunately, pyrolysis oil is an unstable product,
because of the abundant reactive oxygenated compounds. During storage, the
physical and chemical properties of the bio-oil were continuously changing.
Therefore, it is very necessary for pyrolysis oil to improve its properties before
they can be used in existing equipment.

To date, many techniques have been developed to
improve in the physicochemical properties of bio-oil, including hydrodeoxygenation, catalytic cracking,
distillation and emulsification.[1]Since the bio-oil contains a wide range of
compounds with different boiling ranges, separation of the components by
distillation has been regarded as a feasible method for upgrading pyrolysis oil.
Capunitan and Capareda[2] investigated fractional distillation of bio-oil
under atmospheric and vacuum conditions and obtained the useful
information for distillate fraction. Additionally, other scholars also applied the
effectiveness of distillation to improve the properties of the bio-oil by
separation of the components.[3;4] Although the high-value chemicals or
high-quality fuel were obtained from pyrolysis oil, the highest distillate
yield of pyrolysis oil was approximately 65% and a fraction of solid residue
was formed after distillation.[2] In additional, there were few studies about
the solid residues from the distillation of pyrolysis oil. In fact, such solid
residues should have high carbon contents and could be regarded as a kind of
bio-char.[5] Therefore, the application of distillation residues could be
developed until precise information regarding the properties of distillation
residues from pyrolysis oil were obtained.

In this work, the non-volatile solid residues (called distillation residue) were obtained by the
atmospheric distillation (p=101 kPa) and the vacuum distillation (p=4 kPa). The detail experimental
procedure described in our
previous paper.[6] In this work, the atmospheric distillation residue and vacuum
distillation residue yields were 48.3% and 35.2%, respectively.

In order
to obtain precise information, the distillation residues have been comprehensively and
systematically characterized, including FTIR, ¹³C NMR, XRD, SEM, TG/DTG and elemental analysis. Table 1
illustrated the elemental compositions in atmospheric distillation residue and
in vacuum distillation. The chemical compositions of the atmospheric
distillation residues and vacuum distillation residues are CH_0.9724O_0.1964N_0.0124S_0.0003
and CH_0.9989O_0.2795N_0.0122S_0.0003,
respectively. Compared with pyrolysis oil, there were significant increase in
the carbon content and remarkable reduction in the oxygen content for the
distillation residues. It may be due that the oxygenated volatile (especially
water and small active molecular) were being removed from pyrolysis oil under
distillation condition. Furthermore, the H/C atomic ratios in distillation
residues are very close to 1, which indicates the degree of aromaticity in
distillation residues is very high.
The crystallinity
and morphology of distillation residues were characterized by XRD and SEM, the
results indicated the distillation residues are amorphous (seen in Figs. 1 and
2).

Table
1. The yields and elemental compositions of pyrolysis oil,
atmospheric distillation residue and vacuum distillation residue.

^a ref[6],
^b calculated by difference.

Figure
1. XRD patterns of the atmospheric distillation residue and vacuum distillation
residue.

Figure
2. Scanning electron micrograph of (a and b) the atmospheric distillation
residue and (c and d) vacuum distillation residue.

The
FTIR and 13C NMR spectrum had been used to understand the chemical structures
of the distillation residues (seen in Fig. 3). Table 2 lists the function
groups that were identified from the FTIR spectra. The C-H stretching at 1607,
1512, 1449 and 624 cm-1 show the presence of aromatic compounds in distillation
residue.[4] Meanwhile, the clear aromatic resonances (110¨C140 ppm) were shown
in 13C NMR spectra, which illustrate the highly aromatic nature of
distillation residue (especially vacuum distillation residue).[7] This
phenomenon also consists with the results of the elemental analysis given in
Table 1.

Figure
3. FTIR and ¹³C NMR spectra of the distillation residues.

Table 2. The FTIR functional
groups of the atmospheric distillation residues and the vacuum distillation
residues.

In additional,
the thermal degradation of the atmospheric distillation residue and vacuum
distillation residue were studied by the thermogravimetric (TGA) and
differential thermogravimetric (DTG) analysis (shown in Fig. 4). The comparison of the TG/DTG curves of the
atmospheric and vacuum distillation residues illustrated the thermal
decomposition process of the atmospheric distillation residue existed in two
stages. At the first stage (< 200°æ), the atmospheric distillation residues may represent
the evaporation of moisture and other small molecule residues which weren't
completely removed from pyrolysis oil. The atmospheric distillation residues
and vacuum distillation residues at the main thermal decomposition stage (200-500°æ) may attribute to
the thermal degradation of saccharide and lignin derivative. The solid residues
of the distillation residues were greater than 40% when the temperature reached
nearly 850 °æ.
Therefore, the distillation residues have a fine thermal stability.

£Ô£Ç#Ä£Ô£Ç"/>

Figure
4. TG and DTG curves of (a) the atmospheric distillation residue and (b) the
vacuum distillation residue under nitrogen purge of 50 mL/min and heating rate
of 10 °æ/min.

In summary,
the
precise information on the non-volatile solid residues (called distillation
residue) is very important for the efficient utilization of bio-oil though
distillation process. It is the first time that the distillation residues
obtained by the atmospheric distillation (p=101 kPa) and the vacuum
distillation (p=4 kPa) have been comprehensively and systematically
characterized, including FTIR, 13C NMR, XRD, SEM, TG/DTG and elemental analysis
in this work. The experimental results suggested that the distillation residues
have higher carbon content, the highly aromatic nature, the amorphous structure
and fine thermal stability. According to all of the preceding
results, the distillation residues seem to be the raw material for further production
of aromatic compounds or as solid fuels and soil amendment.

Acknowledgements

The authors sincerely acknowledge the
Tianjin Natural Science Foundation (13JCYBJC19300)
and the National Basic Research (973) special preliminary study program (2014CB260408)
for the financial support.

References

[1] L. Zhang, R.
Liu, R. Yin, Y. Mei, Renewable and Sustainable Energy Reviews 24 (2013) 66-72.

[2] J. A. Capunitan,
S.C. Capareda, Fuel 112 (2013) 60-73.

[3] J. L. Zheng, Q.
Wei, Biomass and Bioenergy 35 (2011) 1804-1810.

[4] X. S. Zhang,
G.X. Yang, H. Jiang, W.J. Liu, H.S. Ding, Sci. Rep. 3 (2013).

[5] K. H. Kim, J.Y.
Kim, T.-S. Cho, J.W. Choi, Bioresource Technology 118 (2012) 158-162.

[6] H. Li, S. Q. Xia, Y. Li, P. S. Ma, C. Zhao, Stability evaluation
of fast pyrolysis oil from rice straw, Chemical Engineering Science 2015,
accept.

[7] C.A. Mullen, G.D. Strahan, A.A. Boateng, Energy
& Fuels 23 (2009) 2707-2718.