M.A. Pérez et al. / Applied Catalysis A: General 482 (2014) 38–48
39
◦
pressure, T = 300 C), which suggests that the intramolecular dehy-
dration of 1-butanol to 1-butene and the subsequent isomerization
to trans-2-butene and cis-2-butene take place [19]. Butene was
the major product for the dehydration reaction on AAS over the
Nomenclature
AAS
ABE
BET
CFPP
CP
amorphous aluminosilicate
acetone-butanol-ethanol
Brunauer–Emmet–Teller
cold filter plugging point
cloud point
◦
whole temperature tested (flow microreactor, 105–185 C, 1 atm)
[
18]. At the same set-up and experimental conditions, selectiv-
ity to ether over H-ZSM-5 was higher than on AAS at about 2%
alcohol conversion, but it decreased remarkably on increasing
dpore
EBE
mean pore diameter (nm)
ethyl butyl ether
1
-butanol conversion [18]. In the dehydration of C5–C12 linear
◦
alcohols over -alumina (fixed bed reactor, 250–350 C, 0–4 MPa,
WHSV = 1–4 h ) it was observed that temperatures as high as
3
DEE
ISEC
DNBE
MSO
nDNBE
RVP
di-ethyl ether
inverse steric exclusion chromatography
di-n-butyl ether
mesityl oxide
mole number of di-n-butyl ether (mol)
Reid vapor pressure
−1
◦
00 C were necessary to achieve over 60% conversion of 1-butanol;
selectivity to ethers being lower than 30% [17]. Finally, 1-butanol
dehydrated selectively to butenes over microporous niobium sil-
◦
icate as well (150–300 C, 1 atm) [20]. On the contrary, the liquid
phase etherification of 1-butanol to di-n-butyl ether has been stud-
0
r
initial reaction rate (mol/(h kg of dry catalyst))
selectivity to product j
◦
DNBE
ied on heteropolyacids with different heteroatoms (200 C, 30 bars)
Sj
showing that 1-butanol dehydrates selectively to di-n-butyl ether
achieving over 80% ether selectivity with 1-butanol conversions
ranging from 30 to 80% [22].
2
Sarea
SBET
S/DVB
t
surface area determined from ISEC data (m /g)
BET surface area (m /g)
styrene-divinylbenzene
time (h)
2
It is a well-known fact that acidic ion-exchange resins are highly
selective catalysts to produce linear symmetrical ethers from n-
alcohols, avoiding byproducts as olefins [23–26]. However, to the
best of our knowledge the synthesis of di-n-butyl ether has not been
reported on ion-exchangers. Thus, the aim of the present paper is
to study the liquid-phase dehydration of 1-butanol to DNBE over
ion-exchange resins of different morphology and discuss the rela-
tionship between resins properties and their catalytic behavior.
Influence of typical 1-butanol impurities on 1-butanol dehydration
reaction is also discussed.
3
Vpore
Vsp
pore volume (cm /g)
volume of the swollen polymer (cm /g)
3
Wcat.
catalyst mass (dried) (g)
WHSV weight hourly space velocity (h−1)
XBuOH
YDNBE
conversion of 1-butanol
yield of di-n-butyl ether
Subscripts
BuOBu’ 1-(1-methylpropoxy) butane
BuOH 1-butanol
-BuOH 2-butanol
2
2. Experimental
Greek letters
2.1. Chemicals
ꢀ
ꢁ
porosity (%)
skeletal density (g/cm )
3
s
1-butanol (≥99.4% pure; ≤0.1% butyl ether; ≤0.1% water) and
2
-methyl-1-propanol (≥99.45% pure; ≤0.05% water) supplied by
Acros Organics, acetone (≥99.8% pure; ≤ 0.2% water) supplied by
Fisher Chemical and ethanol (≥99.8% pure; ≤0.02% water; ≤0.02%
methanol; ≤0.02% 2-Butanol) supplied by Panreac were used as
reactants.
hydroformylation are hydrogenated to yield 1-butanol. With this
hydrogenation step 1-butanol is obtained jointly with 2-methyl-
1
-propanol (isobutanol) as byproduct. Afterwards, the bimolecular
DNBE (≥99.0% pure; ≤0.05% water) supplied by Acros Organics,
dehydration reaction of the primary alcohol gives the correspond-
ing ether. Although superior alcohols can also be produced from
biomass by condensation of bioethanol and/or biomethanol (Guer-
bet Catalysis) [13], this is still a developing technology which is
not yet commercialized [14]. However, biomass fermentation by
microorganisms of the genus Clostridium giving place to 1-butanol
along with acetone and ethanol (Acetone Butanol Ethanol or ABE
fermentation) is being performed on the industrial scale [15,16].
Thus, di-n-butyl ether can be considered a promising oxygenate to
blend with diesel fuel as it keeps a good balance between cetane
number and cold flow properties [17] and, in addition, it can be
obtained from biomass and therefore, it could compete in the bio-
fuel target.
1
(
-butene (≥99.0% pure) supplied by Sigma–Aldrich, cis-2-butene
≥98.0% pure) supplied by TCI and bidistilled water were used for
analysis purposes.
2.2. Catalysts
Tested catalysts were acidic styrene-codivinylbenzene ion
exchange resins: the monosulfonated macroreticular ones
Amberlyst 15, Amberlyst 16 and Amberlyst 39 (high, medium
and low crosslinking degree, respectively); the oversulfonated
macroreticular resins (in which the concentration of HSO3
groups has been increased beyond the usual limit of one group per
benzene ring [27]) Amberlyst 35 (high crosslinking degree) and
Amberlyst 36 (medium crosslinking degree) which are oversul-
fonated versions of Amberlyst 15 and Amberlyst 16 respectively;
the chlorinated macroreticular resins Amberlyst 70 and CT482;
the macroreticular resin sulfonated exclusively at the polymer
surface Amberlyst 46; and the monosulfonated gel-type resins
Dowex 50W×8, Dowex 50W×4, Amberlyst 31, Dowex 50W×2
and Amberlyst 121 containing from 8 to 2 DVB%. Short names and
properties are given in Table 1.
Both an intermolecular dehydration (ether formation) and an
intramolecular dehydration (olefin formation) may occur in the
alcohol dehydration reaction. The prevailing pathway depends
on the reaction conditions as well as the reactant and catalyst
used. Solid acids such as zeolites [18], aluminum phosphates
[
19], amorphous aluminosilicates (AAS) [18], microporous nio-
bium silicates [20], -alumina [17], and heteropolyacids [21,22]
have been tested as catalysts in the dehydration of 1-butanol. In
the gas phase selectivity is highly dependent on conversion. Over
AlPO4 the dehydration of 1-butanol gives place mainly to butenes
at 1-butanol conversions >75% (fixed-bed reactor, atmospheric
It is well known that ion-exchange resins swell in polar media.
As a result, morphology changes and non-permanent pores appear.