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J. of Supercritical Fluids 47 (2009) 598–610

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The Journal of Supercritical Fluids
journal homepage: www.elsevier.com/locate/supflu

Multiple unit processing using sub- and supercritical fluids
Jerry W. King ∗ , Keerthi Srinivas
Department of Chemical Engineering, 3202 Bell Engineering Center, University of Arkansas, Fayetteville, AR 72701, USAa r t i c l e

i n f o

a b s t r a c t
The past twenty years has seen an expansion of the “critical fluid” technology platform with respect to using or combining multiple types of unit operations and compressed fluids in both their sub- and supercritical states. Although supercritical fluid extraction (SFE) utilizing supercritical carbon dioxide (SC-CO2 ) has seen considerable industrial use,the high capitalization cost of building and running such production plants promotes expanding their use and functionality with respect to multi-unit operations and multiple fluids. An evaluation of the current status of implementing such an approach is provided, and a perspective of future needs suggested based on the senior author’s 40 years of experience in critical fluid processing ofagriculturally-derived materials and natural products. The use of hot compressed water is no longer limited to just supercritical water processing, but can be advantageously exploited over a wide range of temperatures and appropriate pressures to include extraction and reaction of targeted substrates, including bioactive natural products, biomass conversion for renewable fuels, and synthesis of chemicals.As noted previously, combining SFE with fractionation methods using critical fluids, and/or reaction chemistry in critical fluid media can produce a variety of extracts or products [J.W. King, Suband supercritical fluid processing of agrimaterials: extraction, fractionation and reaction modes, in: E. Kiran, P.G. Debenedetti, C.J. Peters (Eds.), Supercritical Fluids: Fundamentals and Applications,Kluwer Publishers, Dordrecht, The Netherlands, 2000, pp. 451–488.] however the modification of processing equipment such as expellers, extruders, and particle production devices extend the use of the critical fluid technology platform. Sequential unit processing using multiple fluids also has been reported although demonstrated to a limited degree—however combining both compressed CO2 and water in a unitprocess can also impart some unique processing possibilities. The concept of multiple unit and fluid processing supports an environmentally benign or “green” production platform and is consistent with processing sustainable materials. Integration of critical fluids into existing processing concepts such as biomass conversion, biorefineries, and synthesis based on methyl ester intermediates arediscussed. © 2008 Elsevier B.V. All rights reserved.

Article history: Received 31 July 2008 Received in revised form 14 August 2008 Accepted 14 August 2008 Keywords: Carbon dioxide Critical fluids Multiple fluids Unit processes Water

1. Introduction Supercritical fluids and their liquefied analogues have been traditionally used in single unit operations, i.e. extraction, fractionation, using neatSC-CO2 or with appropriate modifiers [2]. Since the 1980s, almost 38% of the supercritical fluid extraction processes have been devoted to extraction of food and natural products [3]. Beginning in the mid-1980s, columnar and chromatographic techniques followed by reactions in supercritical fluids were developed to facilitate supercritical fluid derived extracts or products [4], thereby extending theapplication of a critical fluids processing platform beyond SFE. These newer developments were investigated in part due to the complexity of many natural product matrices and the desire to concentrate specific target components for food

∗ Corresponding author. Tel.: +1 479 575 5979; fax: +1 479 575 7926. E-mail address: jwking1@uark.edu (J.W. King). 0896-8446/$ – see front matter © 2008 Elsevier...