(415a) Catalytic Conversion of Bio-Ethanol Into 1,3-Butadiene

Catalytic
conversion of bio-ethanol into 1,3-butadiene

Carlo Angelici, Bert M. Weckhuysen,* Pieter C. A.
Bruijnincx*

Inorganic
Chemistry and Catalysis, Debye Institute of Nanomaterials
Science, Utrecht University, Utrecht, The Netherlands

*b.m.weckhuysen@uu.nl, p.c.a.bruijnincx@uu.nl

Introduction

The amount of bio-ethanol produced is rapidly growing
as a result of the higher demand for biofuels and improved fermentation
technologies. This increased availability also opens up opportunities for the
use of bio-ethanol as an economically attractive feedstock for renewable bulk
chemicals. [1] The Lebedev process, i.e. the
conversion of ethanol to 1,3-butadiene, is a promising example of this
approach. Indeed, the feasibility of this route has been recently positively
assessed in a techno-economic study. [2] Importantly, The on-purpose production
of butadiene through the Lebedev process presents an
attractive solution to projected shortages in butadiene that result from the
recent shifts to lighter, shale gas-based feedstocks
for steam crackers. Here, we present our results on catalyst activity and
stability for the ethanol-to-butadiene conversion with particular focus on the
elucidation of structure-activity relationships, i.e. the influence of
preparation method on morphology and amount/strength of the active sites.

Experimental details

Single
and mixed oxides have been tested in the gas-phase synthesis of butadiene from
ethanol (2% in N₂, total gas flow 100 mL/min, 425°C). Various SiO₂-MgO
catalysts were obtained by (modified) co-precipitation (CP and CP-MOD) and
wet-kneading procedures (WK, WK-MOD and WK-AER) Supported CuO/SiO₂-MgO
catalysts were prepared via incipient wetness impregnation (IWI). Extensive
characterization of fresh and spent catalysts was performed with to assess
morphology (TEM), acid-base properties (CO₂- & NH₃-TPD,
Pyridine-IR and titration) and amount of coke produced (UV-Vis and IR).

Results and Discussion

Of the various (combinations
of) bulk oxides tested for butadiene synthesis, SiO₂-MgO mixed
oxides proved the most interesting. The preparation method and the silica
morphology were found to strongly influence both the activity and selectivity
of the catalyst. The wet-kneaded samples performed best, giving the highest
butadiene yield with little ethylene formation. The butadiene yield could be
further boosted for all SiO₂-MgO samples by impregnation with CuO. The best result, i.e. a butadiene yield as high as
50%, was achieved over the CuO/WK-AER catalyst
(Figure 1), a catalyst consisting of relatively small silica particles. Limited
deactivation was observed with time on stream for all the catalysts.

TEM
studies showed the morphology to be quite different for the various SiO₂-MgO
samples (Figure 2); in particular, the wet-kneaded samples consist of silica
spheres embedded in a thin MgO layer. Furthermore,
these materials are less acidic than the others, in agreement with the lower
amount of ethylene and coke produced for this catalyst. UV-Vis analysis
provided interesting insights not only on coke formation, but also on the
chemical nature of the CuO introduced as a promoter.

Figure 1. a) Butadiene yield with differently prepared CuO-containing
catalysts with time on stream; b) product distribution at the start and after 4
h reaction.

Conclusions

The efficient and competitive synthesis of
1,3-butadiene from bioethanol would be of great economic importance. Our
results show that catalyst preparation greatly influences butadiene yield and
clear understanding of the underlying structure-function relation will aid in
further improving the performance of these promising catalysts.

Figure 2. Morphology
differences: a) physical mixture, b) WK, c) WK-MOD, d) WK-AER, e) CP, f)
CP-MOD.

References

1.     
C. Angelici, B. M. Weckhuysen, P. C. A. Bruijnincx, ChemSusChem 2013, DOI: 10.1002/cssc.201300214.

2.     
A. D. Patel, K. Meesters, H. den Uil, E. de
Jong, K. Blok, and M. K. Patel, Energy Environ. Sci. 2012,
5, 8430.