8 Size Characterization of Petroleum Asphaltenes and Maltenes G. HALL and S. P. HERRON
Downloaded by CORNELL UNIV on October 5, 2016 | http://pubs.acs.org Publication Date: January 1, 1982 | doi: 10.1021/ba-1981-0195.ch008
Mobil Research and Development Corporation, Paulsboro, NJ 08066
The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions.
R
ecently, petroleum residua have been studied extensively (J, 2) because of the increasing importance of heavier fuels. B o t h the asphaltene (pentane-insoluble) a n d maltene (pentane-soluble) components of residua are of interest, a n d since their properties overlap, a complete study of p e t r o l e u m residua must consider both asphaltenes a n d maltenes. O n e area that has received considerable attention has been the size characterization of asphaltenes a n d maltenes (3, 4, 5). Size distribution data are useful both i n understanding the f u n d a m e n t a l chemistry of asphaltenes a n d maltenes a n d i n observing the effects of various processes o n residua sizes. In this study, six petroleum residua were characterized b y a c o m b i n a t i o n of preparative- a n d analytical-scale gel permeation chromatography ( G P C ) . E a c h r e s i d u u m was separated asphaltene
initially b y pentane deasphalting into a n
and maltene pair, both of w h i c h were separated further b y 0065-2393/81 /0195-0137$05.00/0 © 1981 American Chemical Society
Bunger and Li; Chemistry of Asphaltenes Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
138
CHEMISTRY OF ASPHALTENES
preparative G P C o n Styragel. T h e apparent molecular size distributions were obtained o n a n analytical G P C system
using μ-Styragel
columns.
These
distributions, w i t h the sulfur, n i c k e l , a n d v a n a d i u m measurements f o r each cut, were used to obtain size distribution profiles for the sulfur-, n i c k e l - , a n d v a n a d i u m - c o n t a i n i n g molecules. T h e molecular a n d elemental size d i s t r i b u t i o n data were c o m p a r e d w i t h the pore size distribution data of a small-pore d e s u l f u r i z a t i o n catalyst to illustrate the importance of catalyst pore size f o r efficient desulfurization a n d demetallation. In a d d i t i o n , the effects of both t h e r m a l a n d catalytic processing o n asphaltene size distributions were m o n i t o r e d using these data.
Downloaded by CORNELL UNIV on October 5, 2016 | http://pubs.acs.org Publication Date: January 1, 1982 | doi: 10.1021/ba-1981-0195.ch008
Experimental Samples.
T a b l e I lists the six residua studied a n d their sulfur, n i c k e l ,
v a n a d i u m , a n d weight percent vacuum
asphaltenes data. T h e A r a b i a n L i g h t is a
(1000 + ° F ) r e s i d u u m ,
while
the other
five
are
atmospheric
(650 + ° F ) residua. T h e samples were a n a l y z e d as received f r o m the refinery distillation tower. Sample Preparation.
T h e residua samples were separated into asphal
tenes a n d maltenes b y deasphalting the resid w i t h a 25:1 (v/v) amount of n-pentane.
A f t e r stirring, the m i x t u r e was a l l o w e d to sit overnight,
then
filtered through a 0.45-μ porous glass filter. T h e asphaltenes were washed w i t h several portions of pentane a n d d r i e d under v a c u u m at 9 0 ° C . Pentane was evaporated f r o m the filtrate to y i e l d the maltenes. Preparative G P C .
T h e preparative G P C w o r k was p e r f o r m e d o n the
e x p e r i m e n t a l setup shown i n F i g u r e 1. F o u r 1-in. i . d . glass columns were p a c k e d w i t h Styragel (Waters Associates) w i t h 1 ft 1 0 Â porosity, 2 ft 500 Â 4
porosity, a n d 1 ft 100 Â porosity. T h e Styragel porosités were chosen to give g o o d resolution f o r the entire range of molecular sizes f o u n d i n residua. T w o separate c o l u m n systems were used—one for maltenes, the other for asphaltenes. T e t r a h y d r o f u r a n ( B u r d i c k a n d Jackson " d i s t i l l e d i n glass") a n d p y r i d i n e ( B a k e r Instra-Analyzed) were the m o b i l e phases. A l l of the maltene
sample
was eluted b y tetrahydrofuran; however, p y r i d i n e was r e q u i r e d to remove a
T a b l e I. P e t r o l e u m R e s i d u a A n a l y z e d Description Aramco Arabian Light vacuum Kuwait Lagomedio Prudhoe Bay Wilmington
S(%) 2.77 4.17 4.24 1.80 1.61 1.96
Ni
(ppm) 5 17 13 18 17 93
V
(ppm) 22 80 50 204 49 67
Weight Percent Asphaltenes 3.6 13.2 6.7 5.0 4.8 7.8
Bunger and Li; Chemistry of Asphaltenes Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
8.
HALL AND HERRON
139
Petroleum Asphaltenes and Maltenes
Column Series Selection Valve
10
10*
0
Â
4
A
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