**Acknowledgements**

removed the water from the reaction system after 6 hours. He obtained an increase of the DTBG yield from 28.5% to 41.5% and demonstrated that the difficulty in obtaining tri-ethers is related

> 48 56 62

> 52 60 68

> 50 58 58

> 68 75 82

**Table 4.** Conversion of glycerol and selectivity to tert-butyl ethers of glycerol at 80 ºC, 8 h reaction time and different TBA/Gly molar ratios. TBA: *tert*-butyl alcohol. MTBG: mono *tert*-butyl ether of glycerol. DTBG: di *tert*-butyl ether of

Carbon supports such as activated carbon and MWNTs can be irreversibly sulfonated to yield

Sulfonation of activated carbon does not yield materials with meaningful concentration values of surface acid sites unless a graphitic precursor such as naphthalene is coimpregnated during

MWNTs are more efficiently sulfonated at 230 ºC. In this case, only 1/6 of the surface carbon

Esterification of glycerol with acetic acid can be carried out at room temperature, but in these conditions, the selectivity is biased toward monoacetin because the esterification rate is low and monoacetin cannot be acetylated. The selectivity to TAG and DAG is increased at higher

Etherification of glycerol with tert-butyl alcohol is a complex reaction with many undesired by-products being produced. All catalysts tried were effective for converting glycerol, but

obtaining selectivities higher than 70-80% to di- and tri-ethers is still a challenge.

materials with sulfonic groups surface concentrations of about 3 milimols per gram.

*ratio Gly conversion (%) MTBG DTBG TTBG*

84 82 80

85 84 80

84 82 79

80 80 78 16 18 17

15 16 18

16 15 19

20 19 18 --- 2 3




to the presence of water.

512 Biofuels - Status and Perspective

HPA/AC

ACc

MWNTc

Amberlyst 15

**4. Conclusions**

sulfonation.

atoms are exposed.

temperatures (e.g., 60% at 100 ºC).

*Catalyst TBA/Gly molar*

2 4 6

2 4 6

2 4 6

2 4 6

glycerol. TTBG: tri *tert*-butyl ether of glycerol.

The authors are grateful to Universidade Federal do ABC and Universidad Nacional del Litoral for supporting this research work.
