Homogeneous catalyst removal

Experiments showed that high methyl ester yields can be achieved with solid bases and super acids under moderate reaction conditions. The solid bases were more effective catalysts than the solid super acids. High stability can be achieved by an ordinary inexpensive preparation process, and the catalyst can be separated easily from the reaction products in the heterogeneous catalysis process. The costly catalyst removal process can be avoided compared with the homogeneous process. Therefore, the heterogeneous process using a solid catalyst should be more economical for biodiesel production. 

In homogeneous process the components of the reaction mixture are mutually soluble including a homogeneous catalysts if used. Mixing of reactants is necessary if the process to be carried out either (1) consists of a series of reactions of which the rates differ significantly and at least one of the important reactions is very fast, or (2) is exothermic and fast enough to produce problems with removal of heat from the reaction zone to the surroundings. 

The reaction between mono-octyl phthalate and i5tMx tanol (see Fig. 5.4-25) in the presence of a homogeneous catalyst (rert-butyl titanate) was studied in a batch reactor (Szarawara et al., 1991). This is the second step of the reaction between phthalic anhydride and o-octanol. First the ring is opened and mono-octyl phthalate is formed. Water is removed by evaporation as it is formed. The reaction was carried out at 174 °C. The initial concentration of mono-octyl phthalate was cpno = 1.85 mol/L and the ratio of initial concentrations of iio-octanol to mono-ooctyl phthalate coc.o/cph,o = 1.4. The reaction was... 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

There are many good reasons for using multiphasic methods to carry out reactions that employ homogeneous catalysts. In general, the catalyst is immobilized in one phase and the reactants and products are supported in other phases. Ideally, once the reaction is complete the products can be removed without contamination by the catalyst and the catalyst phase is ready for immediate reuse. However, a perfect system is extremely difficult to obtain in practice, although many solvent combinations and catalyst design strategies have been developed which come close to the ideal situation. 

Catalysts are so important in chemical industry that combinatorial-type approaches will certainly be utilized as tools in the identification and optimization of both heterogeneous and homogeneous catalysts. These are, in many cases, high value-added, commercially important materials. In any research activity it makes sense to remove any choke points that impede progress. However, many engineering considerations are important in producing commercial catalytic processes thus, combinatorial-type approaches are unlikely to be a panacea. Still, a variety of unanticipated discoveries may result from various efforts that are under way. 

Even though many of the catalysts mentioned above have shown good homogeneous phase catalytic activity, they also exhibit high toxicity, requiring highly efficient catalyst removal processes. In order for this type of catalysts to... 

---