Development of heterogeneous catalysts supported on activated carbon and applications in biodiesel synthesis
Name: DIÊGO NUNES FARIA
Type: PhD thesis
Publication date: 28/05/2020
Advisor:
Name |
Role |
|---|---|
| JAIR CARLOS CHECON DE FREITAS | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| ÁLVARO CUNHA NETO | Internal Examiner * |
| AUDREI GIMÉNEZ BARAÑANO | External Examiner * |
| JAIR CARLOS CHECON DE FREITAS | Advisor * |
| MARTA ALBUQUERQUE MACHADO | Internal Examiner * |
| VICTOR HABER PEREZ | External Examiner * |
Summary: The development of heterogeneous catalysts useful in the reaction of
biodiesel synthesis constitutes a subject of high interest from the environmental and technological points of view. This work describes the preparation and characterization of a series of heterog eneous catalysts supported on activated carbons and their use in the synthesis of biodiesel from soybean oil. In a first stage of the work, d ifferent materials containing Ca and Na compounds dispersed in a commercial activated carbon were prepared by wet i mpregnation followed by heat treatments. Three different wet impregnation routes were employed . The firs t two routes involved the co precipitation method, with Ca(NO 3 2 .4H 2 O as the source of calcium and NaOH (route 1) or NH 4 OH (route 2) as the precipitatin g agent, which were mixed with the activated carbon in aqueous suspension; in the third method (route 3), NaOH and CaO were mixed directly with the activated carbon in aqueous suspension. T he prepared mat erials were heat treated at 800 ºC for 3 h under arg on flow. The changes caused by heat treatments in the temperature range from 500 to 800 ºC were also investigated in the case of the catalyst prepared by route 3, with the characterization of the Na and Ca containing phases formed at each temperature. The catalytic efficiency of the prepared materials was analyzedy evaluating their performance in the production of biodiesel by the transesterification reaction of soybean oil with methanol. The best catalytic efficiency was achieved for the Na,Ca based cat alyst prepared by route 3, composed mainly by a mixture of CaO and Na 2 CO 3 crystals dispersed in the porous carbon network. Catalytic recycling tests were also carried out to assess the possibility of reusing the catalyst, which revealed a drop in activity after three cycle s; however, the reused catalyst still showed significant activity, att ributed to the permanence of Na ions in the porous carbon structure. The analysis of the Ca and Na contents in the biodiesel samples synthesized in the three reaction c ycles revealed relatively low metal amounts leached into the biodiesel. In another stage of the work, h eterogeneous catalysts containing Na, Li and K carbonates disperse d in a char derived from coffee husk were produced from the reaction between the char a nd the respective alkali hydroxides during heat treatment up to 700 ºC. The catalysts containing Li and K carbonates showed high activity only in the first use, since the effects associated with the leaching of the active phases or the permanence of reacti on byproducts in the catalyst surface caused a significant drop in the biodiesel conversion yields in successive reuse cycles. The best results were achieved for the catalysts containing Na 2 CO 3 particles, which exhibited high catalytic activity even after three reuse cycles; this feature was attributed to the permanence of the Na 2 CO 3 active phase in the char support. The results obtained show that the chosen routes are promising for the development of heterogeneous carbon supported Na,Ca based catalysts wi th considerable surface area and good catalytic activity in the transesterification reaction for biodiesel production , being easily recycled and reused in several reaction cycles.
