10.1002/cssc.202001551
ChemSusChem
RESEARCH ARTICLE
Synthesis of branched bio-lubricant base oil from oleic acid
Shuang Chen, Tingting Wu, Prof. Dr. Chen Zhao*
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai,
China, 200062.
Abstract: The mature manufactory of synthetic lubricant (poly-α-
olefins, PAO) proceeds with oligomerization, polymerization, and
hydrogenation reactions on petrochemical ethylene. In this work, we
utilize the inexpensive bio-derived oleic acid as raw material to
synthesize a crotch-type C45 bio-lubricant base oil via a full-carbon
chain synthesis without carbon loss. It contains several cascade
chemical processes: oxidation of oleic acid to C9 azelaic acid (further
esterification to dimethyl azelate) and C9 nonanoic acid. The latter is
then selectively hydrogenated to C9 nonanol and brominated to the
bromo-Grignard reagent. In a next step, a C45 bio-lubricant base oil
is formed by nucleophilic addition (NPA) of excessive C9 bromo-
Grignard reagent with dimethyl azelate, followed by the subsequent
hydrodeoxygenation (HDO) reaction. The specific properties of the
prepared bio-lubricant base oil are almost equivalent to those of the
commercial lubricant ExxonMobil PAO6. This process provides a
new promising route for the production of value-added bio-lubricant
base oil.
Corma et al. used a dual-bed catalyst system to realize the long-
chain fatty acid ketonization and further HDO to C35 long-chain
alkanes [9]. However, the prepared long straight-chain alkane
has a high freezing point and pour point, limiting its use as a
liquid bio-lubricant base oil. Hydrocracking or hydroisomerization
may partly improve the viscosity-temperature performance of
bio-lubricant [10], but accompanied by carbon-chain cracking and
carbon yield reduction.
In the context of preparation of the highly branched bio-
lubricant base oil, the bio-derived compounds can be subjected
to aldol condensation/hydroxyalkylation/alkylation C-C coupling
and subsequent HDO. Gu et al. [11] coupled acetone and furfural
over NaOH as
a
condensation catalyst, and then
hydrodeoxygenated over Pd/NbOPO4 to obtain branched C23
alkanes, but the properties of this bio-lubricant base oil were not
[12,13]
determined. Liu et al.
prepared C30 intermediate by C-C
coupling with substituted furan and fatty aldehyde at the
catalysis of acidic ion exchange resin, and subsequently
hydrodeoxygenated (by IrRe/SiO2 or IrMo/SiO2) to obtain bio-
lubricant base oil. Later, the same research team condensed the
furanaldehyde and long-chain ketones to C33 intermediate
ketone-furan ring intermediates [14], or the hydroxyalkylation of
alkane furans and long-chain alkenals to C25-C33 intermediates,
which were then subjected to HDO reaction via IrRe/SiO2 to
obtain bio-lubricant base oil [15]. The synthesis of cycloalkane
bio-lubricant base oil used the self-condensation of long-chain
methyl ketone catalyzed by magnesium aluminum hydrotalcite,
and followed by the HDO reaction [16,17]. However, the low
viscosity index of such naphthenic bio-lubricant as well as the
low reaction efficiency for ketone condensation limits the large-
scale application.
How to utilize the long carbon chain of biomass or
biomolecules to prepare highly branched bio-lubricant base oil
via the full-carbon chain synthesis and maximize the atomic
economy worth thinking. It should be mentioned that, the
selective regulation of molecular size and structure of lubricant is
also challenging. In this work, we synthesize a new C45 bio-
lubricant base oil with a highly symmetrical branching structure
derived from the bio-molecule oleic acid (Figure 1). The idea
comes from the efficient synthesis of long-chain tertiary diols as
precursor, formed from Grignard reaction of dimethyl azelate
and C9 Grignard reagent. The oxidative cleavage of bio-derived
unsaturated oleic acid or methyl oleate leads to the formation of
dimethyl azelate and nonanoic acid, while the former can follow
the esterification reaction with methanol, and nonanoic acid can
be selectively hydrogenated to nonanol, and then brominated to
bromononane, and eventually to form a C9 Mg-Grignard reagent.
This opens a general strategy for the synthesis of high-quality
base oil components for bio-lubricant production from renewable
biomass. And, highly branch alkanes produced in this way are
shown to have properties that make them superior bio-lubricant
base oils to the synthetic and mineral-based oils used today.
Introduction
The flourishing development of the industrial revolution is
inseparable from the improvement of lubricant quality [1]. At
present, the full-synthetic poly-α-olefins (PAO) lubricant with
excellent specification is produced by the un-selective
oligomerization of ethylene to C8-C12 α-olefins, and then
polymerization and hydrogenation of C8-C12 α-olefins to PAO
base oil. The uncontrolled two polymerization steps result in
complex separation in post-treatments [2]. Simultaneously, the
cationic polymerization used highly toxic or corrosive BF3, HF,
and AlCl3 as catalysts, causing the severe environmental
pollutions [3]
.
The motivation for the development of bio-lubricant base
oils comes from the recognition that bio-lubricant base oils
exhibit low volatility, high thermal and oxidation stability, high
viscosity index properties that are favorable for formulating fuel
economy bio-lubricants [4]. At present, bio-lubricant base oils can
be mainly categorized into ether/ester-based oxygen-containing
and paraffinic/naphthenic full-carbon chain bio-lubricant base
oils. Using long-chain acids and alcohols as raw materials for
esterification [5-7], and the provided ester bio-lubricant base oils
are shown to have high viscosity and low cost, which are
feasible for being used as the general mechanical bio-lubricant
base oils [5-7]. The ether type bio-lubricant base oil is synthesized
by etherification of long-chain alcohols/polyols, ketone
compounds, and long-chain alcohols over acid catalysts
EBSA/SiO2 or A-15 with the aids of the hydrogenation catalysts
of Ru/C, Pt/C, or Pd/C [8]. By comparison, the ether type bio-
lubricant base oil shows reduced oxygen content and viscosity,
but its low oxidation stability and low temperature fluidity lead its
unsuitablity for precision instruments.
Later, the full-carbon chain synthesis is devleoped in order
to improve the quality of bio-lubricant base oil. For example,
1
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