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Lactic acid the most widely occurring hydroxy-carboxylic acid has traditionally been used as food preservative and acidulent. So long, it has been produced through either chemical synthesis route or fermentation route the latter being the dominating one. Despite its tremendous potential for large scale production and use in a wide variety of applications, cost-effective production of high purity lactic acid has remained a challenge for decades, mainly due to high downstream processing cost. In the recent years, possibility of integration of highly selective membranes with the conventional fermentors has opened a golden opportunity for full commercial exploitation of the tremendous application potential of this wonder chemical. This paper discusses recent developments of such membrane-based processes representing process intensification in production of monomer grade lactic acid while suggesting a very promising production scheme.22329
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© 2009 Elsevier B.V. All rights reserved.
1. Introduction
The chemical and the allied process industries all over theworld
are now confronted with the big challenges of developing inno-
vative products and processes for survival in an era of emaciated
profitmargins amidst highly globalized trade competition and fast
growing environmental constraints. Thus process intensification
through revolutionary development of newproducts and processes
that ensure reducedmaterial and energy consumption and reduced
environmental impacts while offering greater flexibility in scale
of operation are the need of the hour. Production of monomer
grade lactic acid (2-hydroxypropanoic acid) a traditionally used
food preservative and acidulent has over the last few decades,
attracted attention of the world researchers.
By virtue of unique presence of both hydroxyl and carboxylic
acid groups, lactic acid can participate in awide variety of chemical
reactions like esterification, condensation, polymerization, reduc-
tion and substitution and this has contributed to its tremendous
potential as a platformchemical for a whole range of products that
have very large-volume uses for industrial production and con-
sumer products. Biodegradable thermoplastics (polylactic acid),
green solvents (ethyl, propyl, butyl lactates) and oxygenated chem-icals (propylene glycol) are a few examples of lactic acid-derived
products, market demands of which are growing exponentially
over the years [1]. Exploitation of its full potential, however,
depends largely on how cost-effectively it can be produced with
high levels of purity. Themajor technology barrier in cost-effective
production of high purity lactic acid is its down-stream separation
and purification. And this is where; membrane-based processes
are stepping in. Being modular in design, membrane-based pro-
cesses offer great flexibility in scale of production depending on
market demand. By virtue of high selectivity, membranes can
ensure high levels of separation and purification. As membranes
of chosen selectivity and permeability can easily be integrated
with conventional fermentors, membrane-based processes permit
simultaneous production and purification in the same unit. This
eliminates the need for separate purification units and results in
compactdesignwithreducedcapital investment.Membrane-based
separation and purification (barring pervaporation) involves no
phase change ensuring reduced energy consumption. Thus such
processes can meet all the goals of process intensification. In this
paper, we first briefly discuss the traditional processes to high-
light themajor problems associated with these processes and then
review the developments in membrane-based processes which
have attempted to overcome the problems of traditional processes.
The objective is to identify an environmentally benign, simple, eco-