The methylation of alkenes to triptyls with dimethyl carbonate

Article abstract of DOI:10.1007/s10562-013-0972-z

A series of methylating reagents: methanol, dimethylether and dimethylcarbonate, have been evaluated for their ability to methylate 2,3-dimethylbut-2-ene to yield triptyls (a mixture of triptane and triptene). The results presented highlight that dimethylcarbonate is a far superior methylating agent compared to methanol or dimethylether, providing a higher yield of triptyls.

Full text of DOI:10.1007/s10562-013-0972-z

Catal Lett (2013) 143:370–374
DOI 10.1007/s10562-013-0972-z
The Methylation of Alkenes to Triptyls with Dimethyl Carbonate
Gareth G. Armitage
Neng Guo Sander Gaemers
•
•
Matteo L. M. Bonati
•
•
John W. Shabaker
Received: 27 November 2012 / Accepted: 31 January 2013 / Published online: 20 February 2013
Ó Springer Science+Business Media New York 2013
Abstract A series of methylating reagents: methanol,
dimethylether and dimethylcarbonate, have been evaluated
for their ability to methylate 2,3-dimethylbut-2-ene to yield
triptyls (a mixture of triptane and triptene). The results
presented highlight that dimethylcarbonate is a far superior
methylating agent compared to methanol or dimethylether,
providing a higher yield of triptyls.
additional processing costs. A separate issue for refineries
is the abundance of C to C hydrocarbons produced in
3
5
large quantities by fluidised catalytic cracking (FCC) [2]
and coking processes[2] that are becoming harder to blend
into the gasoline pool due to tightening Reid vapour
pressure (RVP) specifications[1]. Traditionally, these
unsaturated C to C streams are further reacted in alkyl-
3
5
ation units which have the ability to couple these species to
give a branched C7? product [3]. However, the alkylation
units generally employ homogeneous acid catalysts such as
HF or H SO [2].
Keywords Methylation ꢀ Triptyls ꢀ Dimethyl carbonate ꢀ
Zeolite Y
2
4
A possible solution to these two issues is the develop-
ment of a process for the production of octane-rich fuel
additives (e.g. ‘‘triptyls’’) from lighter olefins. Triptyls is
the general term for a mixture of 2,2,3-trimethylbutane
(commonly known as triptane) and 2,3,3-trimethylbut-1-
ene (triptene). Triptane has a research octane number
(RON) of 113 [4] and can be blended into gasoline to
increase its octane number. Triptane can be produced by
reacting methanol over ZnI [5], InI [6, 7] or by reacting
1
Introduction
Over the past decades governments across the globe have
introduced ever more stringent legislation on the presence
of aromatic components in gasoline. For example, the
United States environmental protection agency introduced
new regulations in 2011 that lowered the allowable ben-
zene content in gasoline from several percent to 0.62 %
2
3
[
1]. Typically, aromatic C to C components provide a
6
DME over solid acids [8–10]. Triptene has a slightly lower
RON of 108 [4] but can be easily hydrogenated to triptane
[10]. The aim of these investigations is to explore how
alkenes, ranging from C to C , can be upgraded to highly
9
significant octane boost to the final gasoline blend. How-
ever, many refineries are now forced to send these benzene-
rich streams to be hydro-treated until fully saturated. These
hydrogenated components can then be blended into the
gasoline pool, but at a significant octane loss and with
3
6
branched C and C octane-rich blend-stocks for the gas-
7
8
oline pool via sequential addition of C1 fragments.
Sequential C alkylation reactions, such as the well-docu-
1
mented methanol to gasoline (MTG) chemistry, generally
give a variety of products [11]. One of the major challenges
in developing such a process is understanding how to
control sequential C additions so that the desired C to C
G. G. Armitage ꢀ M. L. M. Bonati ꢀ S. Gaemers (&)
Hull Research and Technology Centre, BP Chemicals Ltd.,
Saltend, Hull HU12 8DS, UK
1
7
8
e-mail: sander.gaemers@uk.bp.com
branched paraffins can be produced selectively.
As a starting point the single methylation of 2,3-dim-
ethylbut-2-ene (DMB-2, 1) to 2,3,3-trimethylbut-1-ene (2)
was chosen and three methylating agents were evaluated
N. Guo ꢀ J. W. Shabaker
BP Products North America Inc., 150 W. Warrenville Road,
Naperville, IL 60563, USA
1
23

The Methylation of Alkenes
371
methanol (MeOH), dimethylether (DME) and dimethyl-
carbonate (DMC), (Scheme 1).
the reactor. The reaction was left in this configuration for
5.0 h. Liquid and gas analysis was conducted by gas
chromatography as described in the previous section.
Product selectivity and catalyst activity were defined as
follows:
2
Experimental
Selectivityð%Þ
2
.1 General Methods and Chemicals
ꢀ
ꢁ
mmol of product
¼
ꢁ100
mmol of alkenefed - mmol of alkene recovered
Zeolite Y (SAR 80) was purchased from Zeolyst Interna-
tional in the proton form. Zeolites FER (SAR 55), Beta
ꢂ1
Activity(mmol g
Þ
(
SAR 38), ZSM-5 (SAR 50) and MOR (SAR 20) were
ꢀ
Activity per acid site
ꢁ
mmol of alkene fed ꢂ mmol alkene recovered
purchased from Zeolyst International in the ammonium
form and were calcined in static air at 500 °C for 3 h
before use. All liquid reagents were purchased from
Aldrich Chemical co. and used as received. Carborundum
was purchased from Fisher Scientific and sieved to 24
mesh size. Gas phase analysis was run on an Agilent
CP9000 using an open tubular silica coated column
¼
grams of catalyst
ꢀ
ꢁ
mmol of alkene fed ꢂ mmol alkene recovered
mmol of acid sites
¼
The amount of acid sites in millimoles was deduced
from the mass and the SAR of each zeolite tested.
(
50 m 9 0.32 mm i.d.), coated with a 1.2 l thickness of
CP-Sil08CB. Liquid-phase analysis was run on an Agilent
CP9001 using an open tubular silica coated column
(
10 m 9 0.53 mm i.d.), coated with a 1.0 lm thickness of
3
Results and Discussion
CP-Sil08CB. Note that since routine GC analytical proce-
dures cannot fully separate triptane from triptene, the total
yield of these is defined in the text as ‘‘triptyls’’ [12].
Initial experiments focused on the stability of the methy-
lating components and 2,3-dimethylbut-2-ene under the
reaction conditions. Previous investigations conducted by
our team had highlighted that under certain conditions H-Y
did not appear to be a particularly active MTG catalyst and
might prove to be a useful candidate for this programme of
work (unpublished results). The stability of the starting
alkene, 2,3-dimethylbut-2-ene (1), was more difficult to
control, with double bond and structural isomerisation of
this intermediate over acidic catalyst being well-docu-
mented [14]. Our own investigations confirmed this by
highlighting that the double bond isomerisation of
2
.2 General Procedure for Catalytic Tests
The zeolite catalyst was pressed into a cylindrical pellet
d = 30 mm, l = 25 mm approx.) with a force of 12 tons
and finally crushed and sieved to a particle size of 250–
00 lm. Then 1.8 g of these particles were placed into a
(
5
quartz reactor (i.d. = 10 mm, l = 560 mm) using carbo-
rundum as a pre-heat material, separated from the catalyst
with quartz wool. The reactor was placed into a vertical
-
1
tubular furnace and a flow of nitrogen (50 mL min ) was
introduced to the top of the reactor. A condenser was
connected to the outlet of the reactor, cooled by a recir-
culating cooler set at -5 °C to trap any low-boiling com-
ponents from the reaction. Downstream of the condenser a
2
,3-dimethylbut-2-ene (1) to 2,3-dimethylbut-1-ene (3) was
facile, occurring at a temperature of 100 °C. They also
showed that the skeletal rearrangement of 2,3-dimethylbut-
1
-ene (3) to 2-methylpentene isomers, such as 4-methyl-
pent-2-ene (4), occurred at temperatures above 250 °C
unpublished results). These intermediates could then
4
0 L gas bag was attached to collect all gases from the
(
reactor. The furnace was then heated to the desired reaction
temperature at atmospheric pressure over the course of
isomerise further over the catalyst. However, this type of
methyl rearrangement was found to be significant only at
temperatures above 300 °C (Scheme 2).
6
0 min. Once at temperature a flow of methylating agent
and alkene was introduced via a syringe pump to the top of
+
_
H
+
H
MeOH
+
H O
2
Zeolite
1
3
4
1
2
Scheme 2 Isomerisation 2,3-dimethylbut-2-ene to 2,3-dimethylbut-
1-ene and skeletal rearrangement of 2,3-dimethylbut-1-ene to
4-methylpent-2-ene
Scheme 1 Methylation of 2,3-dimethylbut-2-ene to 2,3,3-trimethyl-
but-1-ene
123

3
72
G. G. Armitage et al.
We then began to investigate MeOH, DME and DMC
the DMC to DMB-2 ratio whilst keeping the reaction
temperature at 300 °C, resulted in lower activity and
reduced the selectivity to triptyls by ca. 50 %. On the other
hand, increasing the DMC to DMB-2 ratio resulted in
increased catalyst activity whilst the selectivity to triptyls
remained approximately constant. These results suggests
that the rate for methylation could be close to first order in
[DMC] at low concentrations, becoming pseudo-zero order
in [DMC] as the concentration of DMC increases.
for the methylation of 2,3-dimethylbut-2-ene (1) over the
H-Y catalyst. The analysis of the C –C components
5
7
identified the major product as 2,3-dimethylbut-1-ene (3)
for the MeOH and DME reactions. However, for the DMC
reaction the major component in the liquid-phase was
triptyls, with a selectivity of 10.2 %, compared to 1.4 and
0
.6 % selectivity for MeOH and DME respectively (Fig. 1;
Table 1: runs 1–3). The overall activity and relative yield
of liquid-phase products were also higher using DMC than
when using either MeOH or DME as methylating agents.
Further investigations on the H-Y/DMC system (Table 1:
runs 3–6) showed that decreasing reaction temperature to
One of the major products of the methylation reaction
was the isomerised starting material DMB-1. In addition,
various methyl pentene isomers were also produced as
expected. However, further analysis failed to identify any
methylated product resulting from 2,3-dimethylbut-1-ene,
such as 3,4-dimethylpent-2-ene (5), (Scheme 3). To
examine this observation further 2,3-dimethylbut-1-ene (3)
was fed instead of 2,3-dimethylbut-2-ene (1) in the DMC
methylation so that the types of methylated products could
be compared to the 2,3-dimethylbut-2-ene (1) methylation
2
50 °C resulted in reduced activity and the selectivity to
triptyls was essentially half of that at 300 °C. The decrease
in triptyls selectivity suggests that the rate constant for
methylation responds to temperature drop more signifi-
cantly than those for the side reactions. Upon decreasing
(Fig. 2; Table 1: runs 3 and 7). The comparison of the 2,3-
dimethylbut-2-ene (1) and the 2,3-dimethylbut-1-ene (3)
methylation highlighted that there was very little difference
between the type of products produced by each reaction,
indicating that under reaction conditions, 2,3-dimethylbut-
2
-ene and 2,3-dimethylbut-1-ene reach equilibrium rapidly
over H-Y. This is confirmed by plotting the selectivity to
,3-dimethylbut-1-ene versus the selectivity to 2,3-dim-
2
ethylbut-2-ene (Fig. 3). It is noteworthy that no product
was identified that related to methylation of the terminal
olefin in 2,3-dimethylbut-1-ene (3), (Scheme 3).
Having shown that DMC is an effective methylating
agent for the methylation of DMB-2 we then turned our
attention to comparing the performance of H-Y with
Fig. 1 Liquid-phase products of the methylation of 2,3-dimethylbut-
2
-ene. Comparison of MeOH, DME and DMC as methylating agents
Table 1 Selectivity to liquid-phase products and activity in the methylation of alkenes over zeolite Y
Run Number
1
2
3
4
5
6
7
8
Temperature (°C)
Methylating Agent
Alkene
300
300
300
250
300
300
300
300
MeOH
DMB-2
5:1
DME
DMB-2
5:1
DMC
DMB-2
5:1
DMC
DMB-2
5:1
DMC
DMB-2
2.5:1
DMC
DMB-2
10:1
DMC
DMB-1
5:1
DMC
MB-2
10:1
MA:Alkene
Selectivity (%)
2
2
2
2
4
2
2
-Methylbutane
0.4
0.5
0.5
0.3
0.5
1.1
0.4
0.3
0.0
0.6
0.4
1.3
0.4
1.1
4.9
29.6
0.7
-Methyl-2-Butene
,3-Dimethylbutane
,3-dimethylbut-1-ene
-Methyl-2-Pentene
-Methyl-2-Pentene
,3-dimethylbut-2-ene
3.4
2.7
1.6
1.2
2.1
0.7
1.5
9.3
13.9
0.1
7.3
8.7
10.0
0.4
3.4
6.1
2.7
0.3
0.3
0.1
0.2
0.0
0.3
1.2
0.5
1.2
0.3
0.6
0.6
1.2
1.0
15.7
1.4
29.0
0.6
12.1
10.2
25.7
63.3
17.3
5.2
17.5
5.2
5.4
9.9
4.0
Triptyls (triptene)
-
Activity (mmol g
9.5
10.0
27.0
66.6
6.8
1
)
24.1
59.4
22.3
55.0
24.7
60.8
24.8
61.1
27.9
68.8
12.6
31.0
Activity per acid site
1
23

The Methylation of Alkenes
373
3
3
2
2
1
1
5
0
5
0
5
0
5
0
+
_
H
DMC
H-Y
1
3
5
Scheme 3 Isomerisation of 2,3-dimethylbut-2-ene to 2,3-dimethyl-
but-1-ene, which can undergo methylation to 3,4-dimethylpent-2-ene
0
5
10
15
20
2
,3-dimethyl-1-butene selectivity
Fig. 3 Plot of the selectivity to 2,3-dimethylbut-1-ene vs. the
selectivity to 2,3-dimethylbut-2-ene
250 °C where we have previously shown that H-Y is still
active and where both cracking and MTG/MTO-type
chemistries are less pronounced [15] (Table 2: runs
1
1–15). The results show that of all the zeolites tested
Fig. 2 DMC methylation of 2,3-dimethylbut-1-ene compared to
2
,3-dimethylbut-2-ene
H-ZSM-5 exhibited the highest activity but also the lowest
selectivity to triptyls while H-MOR exhibited the lowest
activity and poor selectivity to triptyls. H-Y on the other
hand is shown to be the best catalyst both in terms of
activity per acid site and selectivity to triptyls.
respect to other zeolites with different frameworks and
acidities (i.e. different SARs). Initial testing was done at
3
00 °C (Table 2: runs 9 and 10) and it showed that H-FER
has a lower activity and much lower selectivity to triptyls
than H-Y. Also the total yield of liquid produced is very
low, suggesting that at this temperature H-FER possibly
catalyses cracking of the alkene or MTG/MTO-type
chemistries. We thus lowered the reaction temperature to
Having proven that the DMC/H-Y system could effec-
tively methylate 2,3-dimethylbut-2-ene (1) our attention
focused on performing sequential methylations to upgrade
2-methyl-2-butene (6) to 2,3,3-trimethylbut-1-ene (2)
under the same reaction conditions (Scheme 4; Table 1:
Table 2 Selectivity to liquid-phase products and activity in the methylation of DMB-2 with DMC over different zeolites
Run number
9
10
11
12
13
14
15
Temperature (°C)
Zeolite
SAR
300
H-Y
80
300
H-FER
55
250
H-Y
80
250
H-FER
55
250
H-Beta
38
250
HZSM5
50
250
H-MOR
20
Methylating agent
Alkene
MA : Alkene
DMC
DMB-2
5:1
DMC
DMB-2
5:1
DMC
DMB-2
5:1
DMC
DMB-2
5:1
DMC
DMB-2
5:1
DMC
DMB-2
5:1
DMC
MB-2
5:1
Selectivity (%)
2
2
2
2
4
2
2
-Methylbutane
0.5
1.1
0.1
0.6
0.0
2.1
0.1
0.3
4.3
0.2
20.3
34.8
0.4
0.3
0.0
0.3
2.7
2.2
11.2
5.3
0.5
0.5
-Methyl-2-Butene
,3-Dimethylbutane
,3-dimethylbut-1-ene
-Methyl-2-Pentene
-Methyl-2-Pentene
,3-dimethylbut-2-ene
1.6
1.2
0.1
1.1
0.5
0.8
7.3
8.7
10.8
0.2
2.1
5.6
8.8
0.3
0.1
0.3
0.2
0.6
1.2
0.3
0.7
1.1
0.7
2.7
12.1
10.2
25.7
63.3
17.3
5.2
27.3
3.0
0.8
0.5
19.1
0.6
Triptyls (triptene)
-
Activity (mmol g
0.4
0.1
1
)
24.7
60.8
16.5
28.3
21.6
26.0
28.2
44.0
16.2
10.7
Activity per acid site
123

3
74
G. G. Armitage et al.
References
DMC
H-Y, 300 °C
1
2
. ‘‘Control of hazardous air pollutants from mobile sources’’. U.S.
Environmental Protection Agency. 2006-03-29
. Meyers RA (2003) Handbook of petroleum refining processes.
McGraw-Hill, New York
6
2
Scheme 4 Alkylation of 2-methylbut-2-ene to 2,3,3-trimethylbut-1-
ene
3. Olah GA, Moln a´ r A (2003) Hydrocarbon chemistry, 2nd edn.
Wiley, Hoboken
4
. Do PTM, Crossley S, Santikunaporn M, Resasco DE (2007) In:
Spivey JJ (ed) Catalysis. The Royal Society of Chemistry, Lon-
don, pp 33–64
run 8). From the results it can be seen that 2-methyl-2-
butene (6) was successfully converted to 2,3,3-trimethyl-
but-1-ene (2) via two sequential methylations with a
selectivity of 6.8 %. In addition both 2,3-dimethylbut-1-
ene (3) and 2,3-dimethylbut-2-ene (1) were observed with a
selectivity of 2.7 and 4.0 % respectively.
5. Kim L, Wald MM, Brandenburger SG (1978) J Org Chem
3:3432
6
4
. Bercaw JE, Hazari N, Labinger JA, Scott VJ, Sunley GJ (2008) J
Am Chem Soc 130:11988
. Bercaw JE, Diaconescu PL, Grubbs RH, Hazari N, Kay RD,
Labinger JA, Mehrkhodavandi P, Morris GE, Sunley GJ, Vagner
P (2007) Inorg Chem 46:11371
7
8
9
. Ahn JH, Temel B, Iglesia E (2009) Angew Chem Int Ed 48:3814
. Simonetti DA, Ahn JH, Iglesia E (2011) J Catal 277:173
4
Conclusions
1
1
0. Daniel BJ, Gracey BP, Law DJ, Maunders BM, Sunley JG, Van
Der Waal JC (2009) Process for producing triptane using zeolite
catalysts. PCT Int. Appl. WO 2009063177 and WO 2009063178
1. Bercaw JE, Diaconescu PL, Grubbs RH, Kay RD, Kitching S,
Labinger JA, Li X, Mehrkhodavandi P, Morris GE, Sunley GJ,
Vagner P (2006) J Org Chem 71:8907
The methylation of 2,3-dimethylbut-2-ene (1) can be
achieved in much higher yield using DMC as opposed to
MeOH or DME reactants over an H-Y catalyst, which has
been shown to be the best catalyst among a series of
zeolites tested. Furthermore, it has been shown that the
double bond isomerisation of 2,3-dimethylbut-2-ene (1) to
12. Chang CD (1983) Catal Rev Sci Eng 25:1
3. Bercaw JE, Grubbs RH, Hazari N, Labinger JA, Li X (2007)
Chem Comm 2974
1
2
,3-dimethylbut-1-ene (3) does not impact the selectivity
1
1
4. Bourdillon G, Gueguen C, Guisnet M (1990) Appl Catal 61:123
5. St o¨ cker M (1999) Microporous Mesoporous Mater 29:3
of the methylation reaction towards 2,3,3-trimethylbut-1-
ene (2). Finally, the sequential methylation of 2-methyl-2-
butene (6) was demonstrated and highlights a route by
which C -alkenes can be upgraded to heavier, higher
5
octane products.
1
23