(264b) Conversion of Ethyl Acetate Over Acid-Base Catalysts As a Model Reaction for Biooil Refining: Infrared and Flow Reaction Studies

Several processes are under development to convert
biomasses into renewable fuels (Huber et al., 2006;
Demirbas, 2008). The production processes of
bioethanol and ?biodiesel? (fatty acid methyl esters) are already commercial,
but they need further improvements to reduce their impact to food and
agriculture market as well as to reduce their costs. Several other processes,
such as pyrolysis and catalytic conversion of different renewable raw materials
(wood, vegetable oils, etc.) and also of wastes are under study. A common
problem of these processes is the very high oxygen content of the resulting
biooils, which prevents their massive use in several countries such as in
European union, because it may overcome the limits by law. Limits to oxygen
content are due to the need to reduce the amount of toxic oxygenated VOCs in
the waste gas and to improve the cold properties. Particularly noxious is the
presence of carboxylic acids in the fuel, because of the high melting point of
many acids which reduces cold properties, as well as to the corrosion behaviour
associated to their acidity. Carboxylic acids frequently come from incomplete
conversion of esters, such as in the case of the conversion of
triglyceride-based raw materials.

To improve the qualities of biooils as fuels, further
catalytic treatments can be performed (Bulushev and
Ross, 2011). Conversion in the presence of acidic catalysts is reported
to improve fuels reducing their oxygen content. Solid acids are also reported
to be active for the conversion trigliceride-based materials, such as palm oil,
into hydrocarbon-rich fuels (Twaiq et al., 2003).

In this work, the conversion of ethyl acetate as a model
reaction for biooil refining has been investigated onacid-base catalysts. This
ester is much shorter than the typical esters present in vegetable oils,
however, it contains the important chemical functionality (R'-O-COR) within a
short aliphatic chain (Danuthai et al., 2009).
The aim of this work is to have indication on the mechanism involved in the
acid- or base- catalyzed conversion of esters.

Experimental

Siralox 1.5/40 from Sasol was used as the catalyst for
catalytic tests.This material has typically the Lewis acidic behaviour of
transitional alumina(Bevilacqua et al., 2006).

The catalytic experiments were carried out in a
fixed-bed tubular quartz flow reactor, operating isothermally, loaded with 0.5
g of the catalyst (60-70 mesh sieved), feeding 12.5% vol/vol Ethyl Acetate (EA)
in Nitrogen with total flow rates
of either 40 cc/min or 80 cc/min. The carrier gas (Nitrogen) was passed through
a bubbler containing high purity EA (99.5%). The temperature in the experiment
was varied stepwise from 473 K to 1073 K.

EA conversion was defined as usual:

While selectivity to product i is defined as follows:

where n_i
is the moles number of compound i, and ν_i is the ratio of
stoichiometric reaction coefficients.

The outlet gases were analyzed by a Gas Chromatograph
Agilent 4890 equipped with a Varian capillary column ?Molsieve 5A/Porabond A
Tandem? and TCD and FID detectors in series. In order to identify the compounds
of the outlet gases, a GC/MS (Thermo Scientific) was used.

For FT IR studies, the adsorption/desorption process has
been studied using Nicolet 380 FT-IR Spectrometer. Pressed
disks of the pure catalyst powders were activated ?in situ? in the IR cell
connected with a conventional gas-manipulation apparatus, before any adsorption
experimentIR spectra of the surface species as well as of the gas phase were
collected upon increasing temperature in static conditions (p_EA~ 4
torr). The FT IR studies of Ethyl Acetate
adsorption/desorption have been carried out on several catalysts having
different acid-base characters such as Siralox 1.5/40, Puralox SBa-200, Siralox
30/260, Siral 30 and Pural MG 30.

Summary

Ethyl Acetate conversion over Siralox 1.5/40 catalyst
starts to be significant (1.2 %) at 573 K and increases further by increasing
temperature up to be complete at 773 K and above at 96.5 h^-1GHSV.
Following the thermal evolution, the conversion increases with further
formation of decomposition products. C₂H₄, CH₃COCH₃
and CH₃COOHare the major reaction products, while CO, CO₂,
CH₄, C₂H₆, C₃H₈, CH₃CHO,
C₂H₅OH, CH₃COOH, (CH₃CO)₂O
are minority products. The conversion also increases with decreasing space
velocity, whereas conversion decreases with extending time on stream,
due to deactivation phenomena at the catalyst surface (Figure 1).

Fig. 1. (a) The conversion as a
function of flowrate of 40 cc/min and 80 cc/min; (b)Conversion of Ethyl Acetate
over Siralox 1.5/40 as a function of time on stream, at 723 K, total flowrate
of 40 cc/min.

The FT IR spectra of Ethyl Acetate
adsorbed on Siralox 1.5/40 is reported in Figure2. Adsorption at room
temperature gives rise to bands due to molecular EA weakly adsorbed at the
surface. The band at 1705 cm^-1 can be attributed to the C=O
stretching mode of ester groups, while the sharp band at 1377 cm^-1
is essentially a CH deformation mode of -CH₃ group. The weak and
broad CH deformation mode of ?CH₂ falls at 1450 cm^-1,
whereas the band at 1280 cm^-1 is assigned to a COC stretching mode
of the ester group. A similar behaviour can be detected following EA adsorption
over other catalysts. The increased basic character of the Pural MG30 sample
(71.2% w/w Al₂O₃, 28.8% w/w MgO) allows an even stronger
adsorption of acetate species at the catalyst surface resulting in an increased
CO₂ formation in the gas phase.

Fig.2. FTIR subtraction
spectra of surface species arising from  Ethyl Acetate adsorbed over Alumina
(a: adsorption at room temperature; b: after outgassing at room temperature; c:
323 K; d: 373 K; e: 423 K; f: 473 K; g: 523 K; h: 573 K; i: 623 K; j: 673 K; k:
723 K; l: 773 K)

The gas phase IR spectra of EA decomposed on acid-base
catalysts show ethylene, acetic acid, carbon dioxide, water as the main
products. During the IR experiments ketene is also detected amongst the product
of EA decomposition in IR cell, possibly due to thermal decomposition.

Similar experiments have been carried out also following
adsorption and thermal evolution of intermediate reaction products such as
acetic acid and ethanol. The key point of ethyl acetate chemistry at the
catalytic surface seems to be the cleavage of the ester group, with the
assistance of Lewis sites.

 
Acknowledgement

This work was supported by the ?fund by EMMA in the framework of the EU Erasmus Mundus
Action 2?. EF acknowledges the University of Genova ?Progetto di ricerca di
Ateneo 2011? for funding.

  References

1.     
A. Demirbas,  2008. Biofuels sources, biofuel policy,
biofuel economy and global biofuel projections. Energy Convers. Manage. 49,
2106-2116.

2.     
G.W. Huber, S.Iborra, and A.Corma, 2006. Synthesis of
Transportation Fuels from Biomass:  Chemistry, Catalysts, and
Engineering.Chem. Rev. 106 (9), 4044?4098.

3.     
D.A.
Bulushev, J.R.H. Ross, 2011. Catalysis for conversion of biomass to fuels via pyrolysis
and gasification: A review.Catal. Today.
171, 1? 13.

4.     
F.A. Twaiq, N.A.M. Zabidi, A.R. Mohamed, S. Bhatia, 2003. Catalytic
conversion of palm oil over mesoporousaluminosilicate MCM-41 for the production
of liquid hydrocarbon fuels. Fuel Process. Technol. 84, 105? 120.

5.     
T.Danuthai, S.Jongpatiwut, T.Rirksomboon, S.Osuwan,
D.E. Resasco, 2009. Conversion of methylesters to hydrocarbons over an H-ZSM5
zeolite catalyst. Appl.Catal. A. 361, 99-105.

6.     
M. Bevilacqua, T. Montanari, E. Finocchio, G. Busca,
2006. Are the active sites of protoniczeolites generated by the
cavities? Catal. Today.116, 132-142.