Acetals can play a primordial role in the development of biofuels. In fact, it would appear they can function as additives for biodiesel, to enhance its cetane index and so ignite more easily. They also enhance its oxidation stability and diminish nitrogen oxides emissions. Engineer Ion Agirre focused his research on the acetal known as 1.1 diethoxy butane. He examined the system of reaction usually employed for obtaining it, and proposed alternative measures for the process to be more efficient. He defended his thesis at the University of the Basque Country (UPV/EHU) with the title Innovative reaction systems for acetal (1,1 diethoxy butane) production from renewable sources. He has also published a number of articles; for example, in the Journal of Membrane Science.
1.1 diethoxy butane comes from the acetalisation reaction between ethanol and butanal. With the goal of facilitating the reaction between these two substances, use is made of ionic interchange resins. As a result of this, 1.1 diethoxy butane and water are produced, and so these products have to be separated. The main advantage of this type of acetal is that it has a renewable origin: the ethanol can be obtained from the fermentation of sugar-rich plants and the butanal from the dehydrogenation or the partial oxidation of its corresponding alcohol. Moreover, 1.1 diethoxy butane complies with the majority of the specifications required for adhering to diesel, unlike other acetals such as 1.1 diethoxy ethane, the most well-known acetal. Thus, Dr Agirre, for his thesis, opted to study the process for obtaining diethoxy butane.
Membranes the most efficient
When conventional reactors are employed in the process for obtaining diethoxy butane, they often do not manage to attain it (low conversion). This is what Dr Agirre has shown in his thesis, on studying the kinetics or velocity of reaction in a discontinuous reactor (one that it is not automatically fed, but only when the process is triggered). So, conversion at kinetically acceptable temperatures is not achieved except in 40-50 % of cases. Thus, he analysed two innovative systems for overcoming the thermodynamic limits in conventional reactors.
The first alternative studied for the thesis involved the use of reactive distillation, with which the researcher has shown that the conversions can be increased by 40 % to 50 %. Dr Agirre applied his experiments to a semi-pilot plant and carried out trials with a number of variables (reaction section height, reflux, feed configuration, and so on), until he came up with the optimum conditions. He also drew up a mathematical model based on the equilibrium stages of the plant, which has been validated by the experimental data. The model has been useful in understanding the behaviour of the system, and in enabling establishing the optimum configuration of the installations without having to undertake experiments previously.
The second innovative system involves the application of dehydration membranes or membrane reactors and, according to the thesis, is the one which gives the best results. In fact, conversions can be increased by 40 % to 70 %. Mr Agirre carried out the experiments in a discontinuous reactor with HybSi brand membranes. In this case, he undertook a number of trials with the reaction and separation within the same reactor (the dehydration membranes separate the water from the diethoxy butane). With these experiments, he developed two mathematical models for this case: the first, discontinuous, for predicting the laboratory experiments (validated); the second, continuous, which has helped in the design of a process.
The best combination
To complete the research, Dr Agirre has drawn up a number of processes at an industrial scale, based on reactive distillation and on dehydration membranes, thus completing the engineering work on conceptual processes and the estimation of costs. He concluded that the most promising option for obtaining 1.1 diethoxy butane could be the combination of dehydration membranes and conventional distillation. This option is the one that has given best results, both from the point of view of efficiency of the process as well as economically.
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