As the dependency on fossil fuel are increasing constantly, new formula is modified from the Klaus model and thus assumes a continuous compound rate and computes fossil fuel reserve depletion times for oil, coal and gas of approximately 35, 107 and 37 years, respectively. On this situation researcher are trying to develop new ways to utilize renewable resources as the feedstock for the generation of energy and production of chemical toward negative CO2 emission and fossil fuel dependency.
Innovations in renewable energy generation e.g. biodiesel are taking the spotlight of new generation. The sharp rise in world biodiesel production has created a glut of glycerol, by-product of saponification or the process of soap making and transesterification or the production of biodiesel. In order to improvise the biofuel economy and put this waste stream to good use new catalytic route must be found. Glycerol can be accounted for 10% of the by-products of biodiesel production. Since for each gallon of biodiesel produces approximately 0.75 lb of glycerol, so this would be a very practical to use glycerol for production of fine chemicals or clean fuel such as hydrogen. To meet the commercial target the oxydehydration of glycerol is one of the most promising options to be focused.
Acrylic acid is one of the most important chemical largely employed by the chemical industry for the production of super absorber, polymer, adhesive, paint, plastic & rubber synthesis, detergent etc. Various catalyst has been targeted for selectively converting glycerol to acrolein, among the supports with Lewis acidity such as α-Al2O3, SiO2 and TiO2 are been applied but the results are not satisfactory. However, metal oxide of 2nd and 3rd transition series e.g. Nb2O5, WO3/ZrO2 metal phosphates, SAPO's and zeolite are shown quite appreciable selectivity of acrolein. As a general rule, the hydration reaction is favoured at low temperatures, and the dehydration reaction is solution of glycerol was favoured at high temperatures therefore to obtain acrolein, it is necessary to use a sufficient temperature, and/or forward flow to shift the reaction. The reaction may be performed in the liquid phase or in the gas phase; perhaps this type of reaction is known to be catalysed by acids. Production of acrylic acid by direct dehydration followed by oxidation of glycerol takes place by a two-step reaction pathway which involves the formation of acrolein as an intermediate on the appropriate metal catalyst (such as W, Cu, Mn) and finally the oxidation of acrolein to acrylic acid.
Reference may be made to European patent EP 1710227B1, claimed a two-step process which includes dehydration of (˜50 wt %) aqueous solution of glycerol over alumina base catalyst impregnated with phosphoric acid & silica followed by oxidation step over alumina supported Mo—V—W—Cu—O mixed oxide. The process gives acrylic acid yield of 55 to 65%.
Reference may be made to U.S. Pat. No. 7,910,771, the prospective of single step conversion of acrylic acids from glycerol was calmed by Jean-Luc Dubois, Millery, where a single oxydehydration step of glycerol to acrylic acid was described in presence of molecular oxygen, 10-50 wt % of aqueous solution of glycerol was passed over a plate exchanger at 250° C. to 350° C.
Reference may be made to article in the Green Chemistry, 2011, 13, 2954-2962 by F. Cavani et al. where they reports a one pot transformation of glycerol to acrylic acid with a Vanadium incorporated WO3 catalyst. Under the process condition only 25% yield of acrylic acid was obtained at 280° C. Moreover, the catalyst progressively generate surface V+5 species, which resides in the hexagonal bronze structure of the catalyst, led to a decrease in the selectivity to acrylic acid and to the concomitant rise in carbon oxide formation.
Reference may be made to article in the Journal of Catalysis, 2009, 2, 260-267, in which Ueda et al. and his group reported dehydration of glycerol over vanadium phosphate oxide (VPO) in a gas phase fixed bed reactor at a temperature range of 250° C. to 350° C. At about 300° C. they found 100% glycerol conversion with 3% acrylic acid over VOHPO4.0.5H2O. With the increment of O2/N2 ratio to 6/18 the acrylic acid formation goes up to 7%, whereas when the reaction temperature rises to 350° C. the acrylic acid conversion goes to the highest of 8%.
Reference may be made to article in the Catalysis Today, 2010, 157, 351-358 in which Japanese worker Ueda and his group reported the production of acroline and acrylic acid through dehydration and oxydehydration of glycerol with mixed FeP—H catalysts. They achieved almost 100% glycerol conversion with 1.2% acrylic acid at 180° C. with a GHSV of 550 h−1.
The drawback of the processes reported so far is that all of those processes either possess low production of acrylic acid or involve multiple step process under pressurized reaction condition. In the multistep approach it was in evidence that the overall transformation includes a dehydration step to convert glycerol to acrolein which requiring adequate acidity followed by an oxidation step into acrylic acid. To overcome that boundation many researchers trying to develop a new process with a single step catalyst which can selective convert glycerol to acrylic acid in a mild reaction condition. The use of a single bi-functional catalyst aims to meet the challenge for the development of new catalytic approaches to convert glycerol into acrylic acid with a single catalyst.