Highly active and reusable Li-Al layer double hydroxide
catalyst for the synthesis of dimethyl carbonates from
transesterification of Ethylene carbonate and methanol
N.T.Nivangune1, A.A.Kelkar1*, V.V.Ranade2*
Chemical Engineering and process development (CEPD) Division, National Chemical
Laboratory, Pune 411008, India.
1
nt.nivangune@ncl.res.in, 1*aa.kelkar@ncl.res.in, 2* vv.ranade@ncl.res.in
1. Introduction:
Dimethyl carbonate (DMC) is an industrially important reagent and widely use in
industries. DMC is considered as a "green" chemical product with bright development
prospects. We have studied transesterification of Ethylene carbonate with methanol
(scheme 1) using calcined Li-Al layer double hydroxide (LDH). LDH is a clay mineral,
non-toxic, easy to separate and recyclable catalyst making the process environmentally
friendly.
Reaction scheme:
Scheme 1: Transesterification of Ethylene carbonate with methanol to DMC
2. Material and Methods:
Chemicals:
Ethylene carbonate (Aldrich), Ethylene glycol (Aldrich), Li (OH).H2O (Loba), Al (NO3)3
(Aldrich), Li (NO3)3 (Aldrich), Al (OH) 3 (Meark), Urea (Rankem)
Catalyst preparation:
The layered double hydroxide (LDH) with chemical composition [LiAl 2 (OH) 6] (CO3)0.5・
mH2O was prepared via three different routs i.e co-precipitation, Urea hydrolysis and
hydrothermal synthesis as per literature reports.1 The catalysts were characterized by XRD,
FT-IR, BET, TPD, TGA, XPS, SEM and TEM.
Reaction procedure:
In a typical experiment, 10 mmol of EC, 100 mmol of methanol and 2.5wt % of catalyst
were added into a 50 ml round bottom flask. The resulting mixture was stirred at 70 oC for 1
h at atmospheric pressure. After completion of the reaction the used catalyst was separated
by centrifugation, washed with methanol and activate at 450◦C/2h. This recovered catalyst
was reused in the next run under the same reaction conditions. The reaction products were
quantitatively analyzed by Agilent 6850 GC (FTD detector, HP-Innowax column).
3. Significant Results and Discussion:
Li-Al (LDH) was synthesized by co-precipitation method and characterized in detail. XRD
analysis (Fig.1) indicates the formation of highly crystalline material with a layered
structure. The morphology of catalyst was investigated by TEM (Fig.2) analysis and thin
flat (hexagonal) crystals with layered structures are observed.
003
800
Li-Al (HT)
400
110
113
006
Relative intensity
600
015
012
200
0
10
20
30
40
50
60
70
80
2 Theta
Figure 1: XRD patterns of LiAl (HT)
Figure 2: SEM image of LiAl (HT)
The catalyst was found to be highly active and selective for the synthesis of DMC. Effect
of reaction time (Fig. 3) and molar ratio of reactants (EC: MeOH) (Fig. 4) were
investigated and activity was found to be strongly dependent on the EC:MeOH molar ratio.
Conversion\Selectivity (%)
Effect of reaction time:
105
95
conv(%)
85
Selectivity(%)
75
65
0.5
1
2
3
5
Reaction time(h)
Figure 3: Effect of reaction time on conversion and selectivity
Reaction conditions: EC: 10 mmol, Methanol: 100 mmol, Catalyst: 2.5 wt % relative to
EC, Temperature: 70˚C.
Effect of Molar ratioEC:MeOH:
Conversion(%)
100
80
60
1:05
40
1:10
1:15
20
0.5
1
2
3
Reaction time(h)
Figure 4: Effect of molar ratio on conversion and selectivity
Reaction conditions: EC: 10 mmol, Methanol: 50,100,150 mmol, Catalyst: 2.5 wt %
relative to EC, Temperature: 70˚C.
ICP analysis indicated that there is no leaching of Li or Al from the catalyst. It shows high
activity during recycle experiment indicating good stability of the catalyst.
4. Conclusions:
Li-Al (LDH) calcined catalyst exhibited highe activity (Ec conversion 84% and DMC
selectivity 100%) in short reaction time (~1h) under mild reaction conditions (reflux
temperature of methanol) as compare to other reported catalysts.2, 3 Catalyst was found to
be stable during recycle study.
References:
1.
2.
3.
Vishnu Kamath Inorg. Chem.,50, 2011,5619–5627 1.
D. Srinivas , Journal of Molecular Catalysis A: Chemical, 398 ,2015, 42–49.
J. Xu et al., Applied Catalysis A: General, 484 ,2014, 1–7