Photon Factory Activity Report 2014 #32 (2015) B

BL-6A/2013G208

Study on mixing scheme and fluctuation of an aggregate in a heavy oillarger, and/or solvent clustering which increases theapparent scattering volume due to “local densityenhancement” around the scatter. The latter phenomenon
is one of the unique properties of supercritical fluid [2].
4 Summary
SAXS profiles of asphaltene-toluene mixture atlower than 300 °C and 10 MPa were obtained to clarify
the disaggregation behavior of asphaltene in organicsolvent. It was suggested that the disaggregation ofasphaltene was mainly observed up to 200 °C.
0.045

I (s) / arb.units

1 Introduction
Asphaltene is the heaviest fraction which consistsof high molecular weight aromatic compounds, existingas aggregates in petroleum. It is important to clarify theasphaltene aggregation behavior at high temperature inorganic solvent, because the aggregation causes catalyst
deactivation in refinery process.
To examine the aggregation behavior of asphaltene
at high-pressure and high-temperature conditions intoluene,small-angle
X-ray scattering(SAXS)
measurements with synchrotron radiation were conducted.
2 Experimental
At BL-6A, SAXS measurements for asphaltenetoluene mixture were performed along an isobaric at 10MPa and temperatures up to 300 °C. The concentration ofasphaltene is 5000 mg/L. An X-ray beam was
monochromatized to λ = 1.50 Å and the observable sregion was 0.024 to 0.18 Å-1, where the scatteringparameter, s, is defined as 4πsinθ/λ (2θ : scattering angle,
λ : wavelength).
For the SAXS measurement under high-pressureand high-temperature conditions, a sample holder was
newly designed. The body is entirely made of titanium
alloy (Ti-6Al-4V), which has relatively low thermal
expansion and high resistivity against corrosion underextreme condition. Two diamond disks, 5.0 mm indiameter and 0.8 mm in thickness, were used as X-ray
windows, and they were sealed with gold O-rings. Two
cartridge heaters were inserted into the cell body.
Temperature and pressure of the sample were measured
using a thermocouple and a strain gauge, respectively.
3 Results and Discussion
Figure 1 shows the observed SAXS profiles, I(s), ofasphaltene at various conditions. All the SAXS intensities
increase with the decrease of s. The degree of intensity
increase at 29 °C is larger than those at highertemperatures, suggesting that the degree of asphaltene
aggregation is the highest at lowest temperature.
Figure 2 shows the radius of gyration, Rg, which are
obtained by the Zimm plot (1/I(s) vs s2) [1]. The values ofRg decrease from 5.1 to 3.9 nm with increasing
temperature at lower than 200 °C, corresponding to thedisaggregation of asphaltene structure by thermal energy.
The Rg increase 3.9 to 4.4 nm at 200 to 300 °C. The
increase of Rg at higher temperatures may come from thefollowing mechanism: asphaltene swelling with hightemperature toluene which makes the size of aggregate

29 ºC
101 ºC
200 ºC
250 ºC
300 ºC

0.030

0.015

0.000
0.00

0.05

0.10

0.15

0.20

-1s/Å

Figure 1. Temperature dependence of SAXS profiles ofasphaltene in toluene.
5.5

5.0Rg / nm2

Satoshi Shibuta1,*, Hiroshi Imamura1, Masato Morimoto2, Ryuzo Tanaka3, and Takeshi Morita1
1
Chiba University, Yayoi, Inage-ku, Chiba 263-8522, Japan
2National Institute of Advanced Industrial Science and Technology,
16-1 Onogawa, Tsukuba 305 - 8569, Japan
3Japan Petroleum Energy Center, 4-10 Ohnodai 1-Chome, Midori-ku, Chiba 267-0056, Japan

4.5

4.0

3.5
080

160

240

320

Temperature / ºCFigure 2. Temperature dependence of the radius ofgyration, Rg, of asphaltene in toluene.
References[1] B. H. Zimm: J. Chem. Phys., 16, 1093 (1948)[2] O. Kajimoto: Chem. Rev., 99, 355 (1999)* s.shibuta@chiba-u.jp