Process intensification for the production of the ethyl esters of volatile fatty acids using aluminium chloride hexahydrate as a catalyst

Abstract

A new process for obtaining the ethyl esters of volatile fatty acids with ethanol by using aluminium chloride hexahydrate as a catalyst is proposed. Aluminium chloride not only exhibits good activity, composition equilibrium is achieved within 3e4 h at 343 K, but also induces a phase separation with a convenient distribution of the components. In fact, more than 99 %wt of the ethyl esters, together with most of the unreacted acid and ethanol, were found in the upper layer, which was well separated from the bottom phase, which contained the co-formed water and over 97.8 %wt of the catalyst. The intensification of this reaction and separation was thoroughly investigated and the operational conditions optimised. The effects of this separation on the purification of the final ethyl esters is fully investigated. A new configuration of unit operations is designed for the specific production of ethyl acetate, simulated through Aspen Plus V9® and compared with the current industrial process based on sulfuric acid catalysis. The overall production and purification of ethyl acetate is economically competitive, reduces the energy requirements by more than 50%, and is potentially a zero-waste process, resulting in cleaner production.

Intensification of Processes for the Production of Ethyl Levulinate Using AlCl3·6H2O

“…The phases were then isolated in separated vials, weighed and analyzed in terms of LA, EL, water, ethanol, aluminum, and chloride contents. The trend of distribution among the two phases already reported for acetic, propionic and butyric acids [22] was confirmed for the case of LA (Table 3). In detail, when 5 mol% AlCl 3 •6H 2 O was used, the organic phase was 83.6 wt% with respect to the overall system.…”

“…The reaction rate and the final equilibrium composition are negatively correlated with the size of the alkyl tail of the carboxylic acid [22,31]. The reaction profile (Figure 1) of the synthesis of EL appears to be coherent to this point, since slower than acetic, propionic and butyric acid conversion carried out under the same conditions [22].…”

“…The organic phase obtained from the first cycle was recovered and again reacted with fresh 5 mol% of AlCl 3 •6H 2 O in ethanol at 348 K. This operation was repeated for two times. At the end of the third cycle, a technical grade product could be directly achieved without using any high-energetic post-processing operations, namely distillation, typically adopted to purify ethyl esters from direct esterification [22]. The final organic phase should already contain an EL amount corresponding to a conversion of 90 wt% of the initial LA.…”

“…Aluminum determination was done for the two phases recovered at the end of the reaction using a 7000X ICP-MS instrument (Agilent Technologies, Santa Clara, CA, USA), following the procedure explained in detail in di Bitonto's work [22].…”

“…Very recently, hydrated salts, namely aluminum and iron chlorides and nitrates, have been reported to combine the benefits of homogeneous and heterogeneous catalysis for direct esterification. These catalysts not only resulted very active in promoting the esterification reaction under homogeneous catalysis, but they also induced a favorable separation of the resulting esters by the co-formed water, in two distinguished phases [21,22]. In detail, differently from a conventional acid catalyst, at the end of the process, the hydrated salts were entirely in the aqueous phase, allowing the complete recovery and the direct reuse in a new cycle of reaction [23,24].…”