Übersichtsbeitrag High Pressure Processes in Biorefineries Carsten Zetzl, Krishan Gairola, Christian Kirsch, Lilia Perez-Cantu and Irina Smirnova* DOI: 10.1002/cite.201100025 An overview of high pressure processes for producing chemicals from lignocellulosic biomass is presented. Special attenti- on is given to the combination of different process steps and scale-up possibilities for the apparatus involved. Based on lite- rature and own experiments it is shown that, under the condition of an adapted choice of process parameters, high pressu- re biorefinery allows the connection and combination of different high efficient and selective unit operations to a single one-stop process that can be realized in different scales. Such reactor design can be used for numerous lab scale experi- ments providing a basis for comparable data for different types of solid biomass. The advantage of such a screening unit is the possibility of cascading processes in the same extraction vessel. Thus, the knowledge on a convergent behavior of reac- tion and extraction rates can be gained, allowing to progress in modeling of solid biomass conversion under high pressure. Keywords: Biorefinery, Extraction, High pressure process, Supercritical Fluids Received: February 23, 2011; revised: May 20, 2011; accepted: May 27, 2011 1 Introduction High pressure techniques are applied in different aspects of biomass processing: (i) the physical treatment (pelletizing, extrusion, cold-pressing), (ii) the physicochemical treatment (gas and liquid extraction, conversion, hydrolysis) and (iii) in pre-treatment (steam-explosion as a hybrid of physical and physicochemical applications). The focus of this work is on the physical-chemical aspects (ii) and (iii). The benefits of physical-chemical high pressure applicati- ons in biorefinery processes are the increase of the reaction and conversion rates and the possibility to tune the diffusi- on and adsorption/desorption conditions by the variation of process pressure, temperature and residence time. Additio- nally, in (supercritical) gas extraction applications an increa- sed solvent power can be observed at elevated pressures due to the increased density of the extraction fluid. The motivati- on is consequently to define and to identify the advantageo- us reaction conditions and the reaction environment so that the product of interest can be converted, isolated and separa- ted from the original biomass at competitive costs, in com- parison with traditional petrorefinery applications. In most cases high pressure processes may avoid external reaction media (with the exception of water, enzymes and/or bio-ga- ses), consequently high pressure biorefinery benefits of an excellent grade of sustainability. In the following, several options for biorefinery conversi- ons of the abovementioned substrates and product groups are presented (Fig. 1). Emphasis is placed on the use of high pressure engineering and the possibility to scale up the pro- cesses based on lab scale experiments. Based on literature review and own experiments it is shown that on condition of an adapted choice of process parameters, the high pressu- re biorefinery allows the connection and combination of dif- ferent high efficient and selective unit operations to a single one-stop process which can be realized in different scales. 2 High Pressure Applications in Biorefinery 2.1 Biomass as Crude Material Biomass is the end-product of photosynthesis [1] which con- verts solar energy to materially bound energy, e.g., in carbo- hydrates. Lignocellulose would be the biggest bioenergy www.cit-journal.com © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chemie Ingenieur Technik 2011, 83, No. 7, 1016–1025 – Dr. Carsten Zetzl, Krishan Gairola, Christian Kirsch, Lilia Perez- Cantu, Prof.Dr. Irina Smirnova (irina.smirnova@tu-harburg.de), Hamburg University of Technology, Institute of Thermal Separation Processes, Eissendorfer Straße 38, 21073 Hamburg, Germany. High Pressure Hydrolysis and Extraction Biomass Optional Mechanical Pre-Treatment Supercritical Fluid Extraction Liquid Hot Water Liquid Hot Water / Residue Liquid Hot Water / Enzymes Liquid Hot Water Oils / Lipids Hemicellulose, Monomers, Soluble lignin Cellulose, C6-Sugars Lignin Proteins Figure 1. High pressure applications for added value from ligno- cellulosic biomass. 1016 I. Smirnova et al.