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Process Simulation of a Pilot Case: Production of Perfume-Containing Microcapsules

Laureano Jiménez-Esteller, Department of Chemical Engineering, University Rovira i Virgili, Av. Països Catalans, 26, Tarragona, 43002, Spain and Rodolfo V. Tona Vásquez, Chemical Engineering, University Rovira i Virgili, Av. Països Catalans, 26, Tarragona, 43002, Spain.

1. Introduction On the basis of a radical change in the paradigm microtechnology may help to build the foundations for a new generation of chemical production plants for high added value products. Microtechnology is able to achieve process and products improvements by orders of magnitude, rather than percentage points on key sectors (pharmaceuticals, additives, pigments, coatings, food additives…). The idea behind microdevices is the combination of two concepts: · Intensification: produce more with less energy, less solvent, less inventory and reduced transport, thus reducing the environmental impact. · Miniaturization: supply better products with smaller volumes, higher efficiency and greater precision. The need for microsystem modeling arises for two reasons: (i) to allow the rapid penetration into the market it is essential that the design, manufacture and test loop is kept to a minimum; (ii) device models can lead to a higher understanding of microdevice operation. To this end, model complexity (many of the new microsystems including several sensor types along with their relevant conditioning and read out electronics) and material properties (surface effects and microscopic thermal properties) are among the most important. 2. Perfume-Containing Microcapsules (PmC) The industrial case is the synthesis and characterization of perfume-containing microcapsules (PmC). PmC are of great interest to the industrial partner as they offer a mechanism for the efficient deposition of perfumes as well as provide a long-lasting fragrance benefits. Perfume deposition on textiles is an inefficient process (» 90 % of perfume added to a detergent is lost during washing). In addition, perfumes have to be very fabric specific and this limits the possible fragrances. Encapsulation of perfume into a microcapsule helps deposition because, with careful control of the size, PmC become entrapped into the cloth fibers during washing and resist being flushed away. The production of PmC using microtechnology is at the laboratory stage. The continuous encapsulation technique is phase inversion precipitation The process occurs in a two steps procedure (Figure 1). The polymeric solution and the continuous phase is fed to the first microreactor. The continuous phase is immiscible with the solvent and is not a non-solvent for the polymer, and therefore the product stream is an emulsion containing polymer and perfume microdroplets. In the second microreactor the non-solvent phase is added, and precipitation of the polymer occurs. As a result, microcapsules are produced with the perfume encapsulated. To avoid any operational problem, and according to experimental data, the purity specifications of raw materials is very high (99-99.9 % w/w). In addition, the polymeric phase stream must be free of water [1]. 3. Integration of Process Modeling Approaches The MICAP® module is used to perform the simulation of the PmC. The MICAP® tool, developed in Matlab® [2, 3], is used to link the modeling approaches: 1. Molecular simulation to study the micellization process, the precipitation of the polymer, size of porous and the morphology of the microcapsules. 2. Computer fluid dynamics to predict the flow dynamics, the mixing, and mass/heat transfer processes in the microreactor. 3. Process simulation to predict the continuous production of the PmC, including the solvent recovery system. 4. Life cycle assessment to deal with the environmental impact and consider the sustainability. This work is focused at the process simulation level. Different modeling tools were used, as commercial process simulators are not prepared to efficiently handle microtechnology problems. The tasks are divided in two levels: (a) encapsulation of the MICAP® within Aspen Plus®; (b) PmC separation and recovery of the solvents. 3.1. Encapsulation of MICAP® and Aspen Plus® Current process modeling and simulating tools offer a broad variety of functionalities to develop reliable models. The process simulator selected is Aspen Plus®. The tool does not offer functionalities for handling microstructured unit operations, and therefore the modeling requires an additional effort to overcame some difficulties [4]. Aspen Plus® and Matlab® were linked using Active X and COM technology [5, 6], thus integrating both tools in the calculation procedure. The problem of this integration is that both calculations tools are involved in several nested loops (Figure 3) giving rise to convergence problems. As Aspen Plus® is a sequential-modular simulator, the modification of the process topology does not affect the overall convergence performance of the system. In this way, the architecture and transfer procedure of the modules is build to promote scalability, re-usability and flexibility of the model A Basic Unit Operation (BUO) was created within Aspen Plus®. The data from MICAP® is send to the BUO and data calculated from Aspen Plus® may be recovered through this BUO. The BUO acts as an encapsulate version of MICAP® within Aspen Plus® and, consequently, as a microdevice unit within the simulator (Figure 2). 4. Perfume-Containing Microcapsules Separation and Solvent Recovery The microdevice output stream contains the PmC with cyclohexane, DMF, water and perfume (vanilla). Although this separation has not been experimentally tested, it is based in the information available. Figure 3 shows a complete diagram of the process. 4.1. Recovery of cyclohexane Cyclohexane is highly immiscible with water and DMF [7, 8], and the modeling of the decanter is straightforward. Then, the adoption of microstructured technology does not offer any a priori advantage. Therefore, the model proposed a scheme with microdevices working in parallel (N = 238) and the resulting stream is processed in a decanter, where the organic phase (cyclohexane), and the aqueous phase (PmC, DMF, water and perfume) are obtained. The number of microdevies can be modified by the user, and this change of scale allows to combining multiscale process units with microstructured elements. 4.2. Recovery of microcapsules The average size of microcapsules in the laboratory is over 6 microns with a very small percentage under 4.5 microns (2% in weights). Then, a screen filter to retain particles (efficiency » 95-99 % at 4.5 microns) is enough for PmC recovery. To mimic the production line PmC must be preserved in a gel media (» 20 % liquid). In addition, the porous structure of the microcapsules retain some liquid (» 5 % w/w). 4.3. Recovery of water and DMF The filtrate liquid contains DMF, water and a small fraction of perfume. The separation of water and DMF mixtures is the testing system for pervaporation units [9, 10]. Due to miscibility, perfume is recovered with the DMF (free-water). 4.4. Minimizing the environmental impacts A key aspect in the pilot plant tests is the reuse of solvents, leading to a minimization of wastes and raw materials. Nevertheless, a life cycle assessment (LCA) is performed following the cradle to grave approach using the Ecoinvent [11] database and SimaPro® [12]. The aggregation of the impact categories into a single value (Eco-indicator 99) improves its value for the decision makers. Most of the environmental load is assigned to the DMF production, and the residual streams containing DMF. Effort is needed to minimize this stream or select an alternative solvent. 5. Conclusions It is clear that at present there are many industrial applications of microdevices (biosensors, microprocessors…), the state of the art in chemical engineering is far from the one achieved in other areas. The end goal of the IMPULSE project (“fab-on-a-chip”) is far from achieved, as microdevice has a clear advantage in some market niche (e.g. microreactors), while separation technology is far from developed. In addition to model microsystems, experimental data based on real behavior is required to tune the model predictions (drag-out, efficiencies…). 6. Acknowledgements This work has been funded by the IMPULSE EU project (NMP2-CT-2005-011816). http://aiche.confex.com/aiche/s08/t5/papers/proof.cgi?RecordType=Pa... 4 de 5 19/10/2007 18:23 Literature [1] Production of capsules using modified lab reactor - Deliverable D3.2f. IMPULSE. ETSEQ, February 2007. [2] C. Torras, and R. Garcia. The [MICAP] simulator. Registered software T-177/07. [3] Torras_MICAP_Flyer.pdf and Torras_MICAP_Oral.pdf (available at the IMPULSE website). [4] Aspen Plus® 12.1. User Guide. Aspen Technology Inc., Cambridge (MA), USA. 2003. [5] A. Bojarski, L. Jiménez, A. Espuña and L. Puigjaner. European Congress of Chemical Engineering. Copenhagen, 2007. [6] Matlab® 7.0. External Interfaces. The MathWorks, Inc. Natick (MA), 2007. pp. (8-3) - (8-129). 2007. [7] M.L. Campbell. "Ciclohexane" in Ullmann's Encylopedia of Industrial Chemistry (6th Ed). John Wiley & Sons, Inc., 2007. [8] H. Bip and H. Kieczka. "Formamides" in Ullmann's Encylopedia of Industrial Chemistry (6th Ed). John Wiley & Sons, Inc., 2007. [9] H.K. Lee, J.Y. Kim, Y.D. Kim, J.Y. Shin and S.C. Kim. Polymer, 42 (2001) 3893. [10] D.Anjali Devi, B. Smitha, S. Sridhar and T.M. Aminabhavi. Separation and Purification Technology, 51 (2006) 104. [11] Swiss Centre for Life Cycle Inventories, The Ecoinvent database, (2006). [12] Pré-Product Ecology Consultants, Introduction to LCA with SimaPro® 7, Pré-Product Ecology Consultants, (2006).