Heterogeneous basic catalysts

The use of heterogeneous basic catalysts for the transesterification of triglycerides has long been considered the main tool to reduce processing costs in the production of biodiesel, as it would lead to simplified operations and eliminate waste streams. 

The patent and academic literature lists a number of basic heterogeneous catalysts. They are not as active as homogeneous catalysts, requiring higher reaction temperatures (200-250 °C) and pressures. 

As already mentioned, when simple alkaline derivatives, such as sodium alcoho-lates, soda or potash, are used as catalysts, one arrives at a pure product usable as fuel and a glycerol at the required standard only after many stages. 

It is also worth noting that although the IFP group reported on different mixed oxide catalytic systems, namely Ti and A1 mixed oxides [6], Bi, Ti and A1 mixed oxides [7], Sb and A1 [8] and Zn, Ti and A1 [9], none of them is able to convert the FFAs eventually present in the oil. Feedstock specifications are therefore demanding also for these basic catalytic systems. 

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The conversion of acetone to isophorone with dissolved NaOH as a catalyst is industrially practised. In the recent past, however, attempts have been made to use heterogeneous basic catalyst in the form of hydrotalcites. 

The hydrogenation reactions occurring on heterogeneous basic catalysts have characteristic features, which distinguish heterogeneous basic catalysts from transition metal catalysts.44 The key features of the base-catalyzed hydrogenation reactions are as follows ... 

The conversion of rapeseed oil and recycled oil from food production and cooking requires the development of heterogeneous basic catalysts with high stability towards water and impurities. 

When Mg-Al-C03 hydrotalcite was tested for the synthesis of DMC via transesterification, this heterogeneous basic catalyst showed good activity for the process [287]. Cu-KF/MgSiO was also reported to be capable of catalyzing such a process [84]. 

Mg/Al hydrotalcite as a heterogeneous base catalyst has been used by Samant and co-workers [170] in combination with microwave irradiation for the S3mthesis of 2-aminochromenes 118 via a multicomponent condensation of an aromatic aldehyde, malononitiile and 1-naphthol. The hydrotalcite is a heterogeneous basic catalyst and could easily be separated from the reaction mixture by simple filtration. The recovered catalyst was used for successive runs to investigate its reusability,... 

Barium hydroxide [33, 34] is a strong base which has been employed not only in organic synthesis but also for other purposes. The commercially available octahydrate, l a(OI 1)2 8 11,/) is often used after transformation to the anhydrous form at 200-500 °C. Dehydrated Ba(OH)2 activated at 200°C is denoted C-200. It is known to be a heterogeneous basic catalyst in the Horner-Wadsworth-Emmons (HWE) reaction of triethyl phosphonoacetate (69) with aldehydes 70 to give the 3-substituted ethyl acrylates 71 (Scheme 5.13) [35]. The HWE reaction proceeds at 70 °C in 1,4-dioxane with a small amount of water. The yields of products 71 are usually better than those provided by typical basic catalysts such as NaOH or... 

Table 2.11 Principal types of heterogeneous basic catalysts. Source adapted from Hattori [251].

Besides the general advantages associated with zeolites, the use of exchanged zeolites as heterogeneous basic catalysts has the additional advantage that they can be exposed to the atmosphere, because carbon dioxide and water are not absorbed too strongly and can be removed by thermal treatment. They can be used even in systems in which water or CO2 are involved as reactants or products. 

Therefore, it was an interesting and important challenge to examine if the homogeneous base could be replaced by a heterogeneous basic catalyst, thus enabling a simpler and more economic process. 

Di Serio, M. M. Ledda M. Cozzolino G. Minutillo R. Tesser E. Santacesaria. Transesterification of soybean oil to biodiesel by using heterogeneous basic catalysts. Ind. Eng. Chem. Res. 2006, 45, 3009-3014. 

Fraile. JM Garcia, Jl Marco. D Mayoral, JA Sanchez. F Monzon, A Romeo, E. Epoxidalion of electron-deficient alkenes using heterogeneous basic catalysts. Studies in Surface Science and Catalysis. 2000 130B, 1673-1678. 

Kloctstra. KR Vanlaren. M Vanbekkum. 11. Binary caesium lanthanum oxide supported on MCM-41 - a new stable heterogeneous basic catalyst. Journal of the Chemical Society Faraday Transactions, 1997 93. 1211-I220. 

F. Moeinpour, N. Dorostkar, M. Vafaei, Synth. Commun. 2012, 42, 2367-2374. Mg/La mixed oxide as an efficient heterogeneous basic catalyst for synthesis of 2-aminothiophenes under microwave irradiation. 

Sharma, Y. C., Singh, B., and Korstad, J. Latest developments on application of heterogeneous basic catalysts for an efficient and eco friendly synthesis of biodiesel A review. Fwe/90,1309-1324 (2011). 

In the beginning of the nineties, it was found that nitrogen incorporation is an effective way to synthesize new solid basic materials [5-7], Through treating various amorphous oxides with flowing ammonia at high temperatures nitridation treatment , a new family of heterogeneous basic catalysts was made [8-12]. 

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