1. Can CO2 be an organic raw material for biorefinery?
Indra Neel Pulidindi and Aharon Gedanken*
Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel Tel: ; *
Abstract
Research Objective
Introduction
Energy insecurity, and environmental pollution are the major problems facing several nations currently. Effective utilization of renewable resources in an energy efficient and environmentally benign way is a challenge. Carbon dioxide (CO2) is abundant in nature and also effectively utilized by plants for carbohydrate synthesis via photosynthesis. Attempts for the direct conversion of CO2 to glucose are much awaited. The main stumbling block in the activation of CO2 is due to its high thermodynamic stability (standard free energy of formation, ∆G○ = kJ/mol). Infact, in their precise and elegant review on CO2 reduction, Hollander and Spialter indicated the possibility of converting CO2 to carbohydrates using radiation of 10 kHz frequency [1]. As a preliminary attempt towards the realization of this goal of producing carbohydrates from CO2, we could activate CO2 using microwave irradiation (2.45 GHz) in the presence of NaBH4 as reducing agent to produce HCOONa [2]. Formate is obtained from CO2 reduction in 75 wt.% yield and 100 % selectivity. CO2 is generated insitu by the decomposition of either (NH4)2CO3 or by the use of dry ice. Formation of formate is confirmed by NMR analysis of the reaction product. Immense possibilities for CO2 conversion to fuels demand intense research in this area.
To develop a fast chemical reduction process for the conversion of CO2 to fuels
Experimental
The CO2 reduction reaction was carried out in a domestic microwave oven operating at 2.45 GHz in a batch mode under atmospheric pressure in the presence of air. The output of the domestic microwave reactor was 1100 W. The microwave oven was operated at 100% power. The microwave oven was modified so as to have provision for a distillation column passing through the MW oven and also stirring facility during the reaction.
Pictorial representation of the CO2 conversion reaction under microwave irradiation
Typical process comprise of placing in the reaction vessel 0.35 g ( moles) (NH4)2CO3 and 0.35 g ( moles) NaBH4 in 35 mL water and subsequently subjecting the contents to microwave irradiation for 5 min. In the case of dry ice, 5.0 g dry ice, 1.0 g NaBH4 and 20 mL water were placed in a round bottom flask and subjected to microwave irradiation
Results & Discussion
Selective production of formate from CO2 reduction
CO2 reduction with NaBH4 yielded formate
CO2 – A promising Organic feedstock!
A singlet resonance at 8.3 ppm in the 1H NMR and a resonance at 171 ppm in 13C NMR establish the presence of formate anion and rule out the presence of formaldehyde or methanol or even carbonic acid.
A wt.% yield of 75 wt.% is obtained from a batch reaction with 0.35 g (NH4)2CO3 with an irradiation time of 5 min.
Additional signal of relatively lower intensity observed at ppm corresponds to the unreacted traces of (NH4)2CO3.
DEPT-135 NMR is an authentic tool to unequivocally establish the presence of formate anion. The presence of a positive peak in the DEPT-135 spectra at 171 ppm is observed which is characteristic of the formate anion. Thus, irrespective of the CO2 source (either (NH4)2CO3 or dry ice), the chemical reduction methodology currently developed yields the formate anion selectively from CO2
DEPT-135 NMR spectra of (a) commercial HCOONa (aqueous solution), (b) reaction product when (NH4)2CO3 is employed as CO2 precursor and (c) reaction product when dry ice is employed as CO2 precursor
The bands at 1394 and 1640 cm-1 correspond to the C–O and C=O bond stretching modes and are an indication of the presence of sodium formate. Typical absorption
around 215 nm originating from the reaction product (formate) can be used as an index for identifying the presence of formate anion.
(a) 1H and (b) 13C NMR spectra of reaction product from the chemical reduction of CO2 (from (NH4)2CO3)
Known path ways for CO2 reduction to chemicals
(A) FT-IR spectrum (liquid, RT) of the reaction product from the chemical reduction of (NH4)2CO3 in the presence of NaBH4 for 5 min and (B) UV–vis spectra (liquid, RT) of (a) the reaction product from the chemical reduction of (NH4)2CO3 in the presence of NaBH4 for 5 min and (b) the aqueous solution of HCOONa (authentic sample)
Summary
CO2 is selectively reduced to formate under microwave irradiation.
The reduction process is fast (only 5 min).
(NH4)2CO3 or dry ice were employed as CO2 precursors.
NaBH4 was used as reducing agent. Under similar conditions Ga metal could not reduce CO2. Zinc dust and Mg will be evaluated for CO2 reduction.
1H, 13C and DEPT NMR spectra confirmed the production of formate
from CO2.
13C NMR spectrum of (NH4)2CO3 (aqueous solution of commercial sample)
Conversion of CO2 to carbohydrates still remains a dream reaction of Chemists!
The sharp singlet signal at ppm confirm the presence of traces of unreacted (NH4)2CO3.
1H and (b) 13C NMR spectra
of reaction product from the chemical reduction of CO2 (from dry ice)
Conclusion
References
1. Hollander, J and Spialter, L (1958) J Chem Educ 35(9):
2. Pulidindi IN, Kimchi BB, Gedanken A (2014) Journal of CO2 utilization 7:19-22.
Gedanken thanks the Ministry of Science and Technology for the research grant and the Israel Science Foundation for supporting the research via a grant 12/586. Thanks are due to Ms Ela Gindy for the timely printing of the poster.
CO2, either generated in situ by the decomposition of (NH4)2CO3 or from dry ice, in aqueous medium is reduced selectively to formate using NaBH4 as reducing agent under microwave irradiation for 5 min. The chemical reduction process involving the conversion of CO2 to formate in aqueous medium is fast owing to the use of microwave irradiation. The exclusive formation of HCOONa as the CO2 chemical reduction product is established authentically through 1H, 13C, DEPT-135 NMR, FT-IR and UV–vis spectroscopic studies. NaBH4 is an efficient reducing agent for the reduction of CO2 in aqueous medium under microwave irradiation conditions. Thus a new process is developed for the chemical reduction of the thermodynamically stable CO2 molecule to a valuable fuel, formate, which can be used as such in fuel cells as a substitute to methanol or can be employed as a reservoir for hydrogen fuel or can be used as an industrial chemical. Based on the current methodology, the industrial effluent, CO2 gas could be selectively converted to HCOONa which is an environmentally benign fuel for transportation application making the process of immense commercial significance and beneficial to the electrical companies generating electricity by the combustion of coal and emanating CO2 is surplus volumes. In addition, the process is useful to most of the industries releasing CO2 into the environment. The fuel cell technology is also upcoming which needs the fuels such as HCOONa for rapid commercialization. Further studies on the economic feasibility of process and the direct conversion of CO2 to fuels using novel methodologies like sonication and microwave irradiation is underway.
Acknowledgements