Reactive Extraction Technology - Process Intensification for Green Chemistry - page 272

unwanted impurities from the product stream, which will maintain the final product
quality and eliminate the need for additional purification in the downstream process.
On the other hand, solid-liquid reactive extraction involves the extraction of materials
from the solid into the liquid phase, where they undergo reaction and produce the required
products. Solid biomass normally contains a large number of useful raw materials such as
lipids, hydrocarbon, fatty acids and proteins. After being extracted, these can be further
processed into highly valuable products in the energy and pharmaceuticals sectors.
By combining the extraction from solid- and liquid-phase reaction in a single reactive
extraction unit, a huge reduction in processing cost and time can be produced. Currently,
solid-liquid reactive extraction is under investigation for the production of biodiesel from
oil seeds biomass. Sometimes also termed 'in situ transesterification', this places the oil-
bearing solid biomass in direct contact with short-chain alcohol instead of pre-extracted
oil. Extraction and transesterification proceed simultaneously, with alcohol acting as both
an extraction solvent and a transesterification reagent [3]. The kinetics of solid-liquid
reactive extraction can be increased through the addition of an appropriate catalyst or
cosolvent, or by subjecting the reaction to supercritical conditions.
10.1.2 Literature Review
The integration of reaction and liquid-liquid extraction was first proposed in the 1960s
by Piret et al. [4]. A reactive extraction design method was developed for both dilute and
concentration systems which shows an enhancement in rate of reaction, volumetric
efficiency and reactant conversion. Anderson and Veysoglu [5] employed dichloro-
methane as the hydrocarbon solvent to continuously extract the epoxide products from
6-methylhept-5-en-2-one as the reaction proceeded, in order to prevent them from
degrading to undesirable products. Reactive extraction carried out for the hydrolysis of
formate esters by King et al. [6] has also proven to give higher productivity and yield and
reduced waste compared to conventional hydrolysis. Many bioprocessing operations,
such as fermentations, which are often inhibited by high concentrations of product have
taken advantage of the reactive extraction techniques to overcome their limitations [7,8].
Application of reactive extraction for the intensification of biodiesel production can help
to increase product selectivity, conversion and purity through the synergistic effect
between transesterification reaction and liquid-liquid extraction. Two immiscible liquid
phases (biodiesel-enriched and glycerin-enriched) that are formed during the trans-
esterification reaction can be removed separately during the process as extract and
raffinate [9,10].
The idea of using solid-liquid reactive extraction in transesterification was first
adopted in analytical studies in order to detect the fatty acid compositions of materials
from different organisms [11]. Its application in biodiesel production was introduced by
Harrington and D'Arcy-Evans [12] in their work on the in situ acid-catalysed ester-
ification of sunflower seed to produce biodiesel. It was reported that the yield of fatty
acid methyl ester (FAME) produced by this method was greater than that in the
conventional transesterification process. This was attributed to the capability of
in situ transesterification (using an acid catalyst) to react with lipid materials that
were not extracted from the seed by hexane. Qian et al. [13] have conducted an
experiment on the in situ transesterification of cottonseed oil using homogeneous