Microsoft Word - 3Galluzzi_Revised Manuscript.docx DOI: 10.3303/CET2184021 Paper Received: 27 August 2020; Revised: 10 December 2020; Accepted: 17 February 2021 Please cite this article as: Chianese A., Picano A., Stoller M., 2021, Spinning Disk Reactor to Produce Nanoparticles: Applications and Best Operating Variables, Chemical Engineering Transactions, 84, 121-126 DOI:10.3303/CET2184021 CHEMICAL ENGINEERING TRANSACTIONS VOL. 84, 2021 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Paolo Ciambelli, Luca Di Palma Copyright © 2021, AIDIC Servizi S.r.l. ISBN 978-88-95608-82-2; ISSN 2283-9216 Spinning Disc Reactor to produce Nanoparticles: Applications and Best Operating Variables Angelo Chianesea,*, Alfredo Picanoa, Marco Stollerb a Labor srl, Via G. Peroni 386, 00131 Rome, Italy b Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy angelo.cianese@fondazione.uniroma1.it A spinning disc reactor (SDR) is a useful equipment to produce monodisperse nanoparticles with controllable properties, as particle size and particle size distribution. Since the late 90s, this technology has been successfully proven for the reaction and solvent-antisolvent precipitation process. This paper reviews the works on the use of SDR to produce inorganic and organic compounds. Firstly, the more significant works on the subject are presented concerning the produced compound, then the factors influencing the process performances are examined in the light of the results in the literature. Finally, some considerations on the fluid stream's hydrodynamics modelling along the disc surface are attempted. 1. Introduction This paper concerns the use of the spinning disc reactor technology for producing nanoparticles by precipitation-reaction. The liquid reagents streams are directed towards the centre of the disc, which is rotated rapidly (300 and 3000 rpm) resulting in a thin fluid film (1 to 200 nm). The thickness of the fluid layer and the large contact area between it and the disc surface induces high heat and mass transfer. Finally, the drag forces between the moving fluid and the disc surface enable very efficient and rapid mixing (micromixing) among the reagents in the liquid streams flowing along the disc surface. The production of nanoparticles, defined as particles less than 100 nm, implies applying a procedure that fosters the nucleation rate and limits the growth and agglomeration rates. When the limiting reagent achieves its maximum value, supersaturation and reaction rate reaches the ultimate value, and the nucleation rate is maximized. A prerequisite is to attain a micromixing among the reagents, which is the complete mixing of the inlet fluid streams into the reactor. Typically, the micromixing time is lower than 1 ms. The spinning disc reactor (SDR) is the more flexible and straightforward equipment for the mixing intensification among liquid streams flowing over its surface. It may be operated in continuous mode to produce a commercial amount of the solid product. Moreover, it is inherently safer than the traditional stirred tank reactors and its operation at lab scale can be easily scaled up (Bodhoo, 2013). An SDR 500 mm in diameter can typically process about 150 kg/h of material with water-like viscosity. Fig. 1 shows an SDR produced by LABOR srl. The fluid streams are fed over the disc at the central point or along the disc radius. The feeding point criterium is a compromise between the maximum local mixing and the residence time to be attained for the best solid production process performances. The disc may be maintained at a suitable temperature by a heating coil put under the disc or circulation of a thermostatic fluid stream within the disc plate. The rotation speed is usually variable and strictly controlled. The disc, usually made of copper or stainless steel, has a smooth or grooved surface. In the latter case waves and ripples are generated within the disc's liquid layer to increase the turbulence. In some works, a vertical SDR with a horizontal rotating shaft is adopted to allow an easier discharge of the slurry. A novel and higher dissipation energy equipment consist of two coaxial rotating discs (DSDR) (Farahani et al., 2017). The upper disc may rotate both clockwise and counter-clockwise. The Authors investigated the performance of DDSR in the synthesis of barium sulfate through the precipitation process. Smaller particles with narrower particle size distribution are some advantages of this new equipment. 121 A B Figure 1. SDR designed and constructed by LABOR srl, (A) scheme of the disc and the plate for the location of the feed stream; (B) photo of the SDR pilot plant  2. Nanoparticles produced by SDR technique The spinning disc reactor (SDR) technology, also named spinning disc processing (SDP), has been introduced at the University of Newcastle by the pioneering work of C. Ramshaw on process intensification (PI), on the improvement of heat transfer on rotating surfaces (Jachuck and Ramshow, 1994). They successfully experimented its use for a pre-polymerization for the manufacture of polystyrene (Jachuck and Ramshow, 1997). At the end of the last century, from the collaboration between the University of Newcastle and the Sapienza University of Rome, the SDR technology was applied to barium sulfate reaction-precipitation (Cafiero et al., 1999). Even in the absence of more advanced investigation instruments, now available, as nano-sizer it was evident the SDR's advantage to produce nanoparticles by precipitation-reaction. During the last 20 years, the SDR technology has been applied to produce various nanoparticles through reaction-precipitation or by the solvent-antisolvent (S-AS) process. Both inorganic and organic products were produced, like composite nanoparticles for the drug release, battery application, etc. In Table 1, a list of material produced as nanoparticles by the SDR technique is shown. Table1. Nanoparticles produced by SDR technique and the adopted operating parameters Material Authors Disc diameter cm No. Feed points/distance from centre, cm Finest particle nm RPM at finest particle Ag, silver Kisyelovab et al. 2016 9 1/2 28 nm 900 rpm Ag Tai et al. 2009 19.5 Vertical disc 1 < 10 nm PVP > 500 rpm AgCl, silver Chloride Dabir et al. 2014 15 - 20 1 37 nm 1500 rpm AgI, silver Iodide Liu et al. 2012 19,5 1 66 nm PVP 4000 rpm BaSO4, barium sulfate Cafiero et al. 2002 50 1 700 nm 1000 rpm BaSO4 Farahani et al. 2017 20 4/1,4,7,10 23 nm 4750 rpm Ca10(PO4)6(OH)2, Hydroxyapatite De Capraris et al. 2012 8.5 1/2,3 80 nm 1400 rpm Cu, copper Marchetti et al. 2019 8.5 2,4/2.5 26 nm 1400 rpm Cu Ahoba-Sam et al. 2018 10 1 3.2 nm 2400 rpm CuO, copper oxide after calcination Chang et al. 2011 20 Vertical disc 1 45 nm 4000 rpm Fe nZVI, iron nanozerovalent Vilardi et al. 2019 8.5 5/1.5, 2, 2.5, 3, 3.5 28 nm 1400 rpm Fe3O4, magnetite Chin et al. 20 1 10-200 nm 2000 rpm 122 encapsulated in chitosan 2006 Fe3O4, magnetite Chin et al. 2008 10 1 3-5 nm 2500 rpm FeO4 Haseidi et al. 2016 10 1 6 nm 5000 rpm KNO3, potassium nitrate Vilardi et al. 2017 8.5 1 with recirculation < 250 nm 140 rpm Mg(OH)2, magnesium hydroxide Tai et al. 2017 12 1 47 nm 2000 rpm Pd, palladium Zou et al. 2011 10 1 160 nm 1500 rpm S, sulfur core to be coated with TiO2 Dell’Era et al. 2019 8.5 1 60 nm 1400 rpm TiO2, titanium dioxide Mohammadi et al. 2014 30 3/0,5,10 < 5 nm 1200 rpm ZnO, zinc oxide Stoller et al. 2020 8.5 4/1.5, 2, 2.5, 3 50 nm 1400 rpm ZnO Hartleb et al. 2007 10 1 1 nm 3000 rpm -carotene Anantachoke et al. 2006 10 1 40 nm 1000 rpm Chitosan for drug loading Loh et al. 2010 10 1 20 nm 1000 rpm Curcumin Khan et al. 2014 15,18 1 S-AS process 220 nm 1500 rpm Nimesulide Rathod et al. 2018 18 1 S-AS process 192 nm 300 rpm Starch Cana et al. 2019 30 1 S-AS process 90 nm 1200 rpm Table 1 shows in order, metallic, inorganic compounds, and organic ones. Some nanoparticles, after production are functionalized by coating with chitosan (Chin et al., 2006), oleic acid (Haseidl et al., 2016), or titania (Dell’Era et al., 2019) to their more specific use. Looking at the characteristics of the adopted SDR, we notice that the disc diameter is in the range of 8.5 – 30 cm, apart from a value of 50 cm used to produce barium sulfate in the first application (Cafiero et al., 2002). The applied rotational velocity of the disc is between 500 and 5000 rpm. The relatively small disc diameter adopted is due to these main reasons: the need to limit the residence time of the born nanoparticles over the disc and thus of their size growth, and to achieve a high disc rotation per minute, suitable to attain the micromixing of the fluid streams over its surface. In some cases, there is a gas atmosphere inside the spinning disc case to accomplish the reaction. Examples are the reduced atmosphere of H2 in Pd's production (Zou et al., 2011) and that one of carbon dioxide for carbonation of calcium hydroxide to produce calcium carbonate (Tai et al., 2005). The SDR technique's performance in terms of average nanoparticle size is very satisfactory: for the inorganic compounds, besides a few cases, the value is lower than 100 nm and often smaller than 10 nm. Nanoparticles of organic compounds produced by the S-AS process exhibit higher size values, mainly because a harder supersaturation control. The comparison between the performances of a stirred tank reactor (STR) and an SDR shows that the better fluid mixing of the SDR leads to a substantial size reduction of the produced solid particles, but to an increase of the energy consumption for unit weight of the solid product because of the higher induced turbulence. Cafiero et. al. (2002) reported a value of 115 W/kg for the precipitation-reaction of BaSO4, whereas Khan et al. has evaluated an energy consumption of 473 W/kg of curcumin produced by an S-AS process (Khan and Radhot, 2018). 3. Main control parameters for SDR The main SDR control parameters are the disc speed, the nature of the disc surface (smooth or grooved), and the feed liquid streams' flow rates. Further parameters are the attained supersaturation of the product that precipitates, the number of the feeding point and their location, finally the adopted, if any, stabilizing agent. Obviously, supersaturation has a direct effect on the nucleation rate of the solid. Its increase due to higher concentrations of the reagents or lower ratio S-AS values leads to reducing the particle size (PS). The drawback is the increase of the agglomeration rate, which the presence of dispersion agents should face, often adopted. 123 Disc rotation speed increases both micromixing and the process yield, whereas it reduces the liquid residence time. Ahoba-Sam at al. (2018) has shown that increasing the rotation speed and thus shortening the residence time leads to both a reduction of growth and agglomeration of nanoparticles, thus reducing their size, since the fluid pattern is like a plug flow. In the production of TiO2, a rotation speed increase from 200 to 1200 rpm determined a micromixing time reduction from 3.5–6 ms, as a function of the liquid flow rate, down to 0.3 – 0.5 ms, correspondingly the median PS decreases from 16 to 5 nm (Mohammadi et al., 2014). Almost a linear PS decrease for nimesulide in the range 500-3000 rpm was observed by Rathod et al. (2018). The effect of the rotation speed is not evident for some processes. PS slightly decreased for Mg(OH)2 from 58 to 48 nm for an increase of rotational speed in the range 400-2000 rpm (Tai et al., 2007) and it was not significant in the precipitation of silver in the range 500-4000 rpm (Dabir et al., 2015). For magnetite, a continuous decrease from 10 nm to 6 nm occurred in the range 500-5000 (Haseidl et al., 2016). Still, the drawback was the reduced magnetic response, similar behaviour has been observed by Chin et al. (2008), but the reduced magnetizability was in this case almost negligible. The effect of the disc surface, i.e. smooth or grooved, has been examined by several Authors with contradictory results. Smooth and grooved discs are equivalent in the production of starch (Sana et al., 2019), there is a benefit in terms of PS reduction for grooved disc 15 cm in diameter, but not for the disc 18 cm in diameter (Rathod et al., 2018). The PS of ZnO is lower with the smooth disc (Hartlieb et al., 2007). In conclusion, the disc surface choice in the absence of definite indications must be left to the experimentation. A factor initially neglected in the experimental works and later always more often investigated has been the feed location. There are two aspects to be considered the location point over the disc, i.e. the distance from the disc centre, and the splitting of each fluid stream. The fluid stream moving away from the disc centre is fed where high turbulence takes place, whereas the fluid stream splitting reduces the local concentration of the generated nuclei and the agglomeration of the particles as well (Marchetti and Stoller, 2019). Both aspects appear to be advantageous to reduce the produced nanoparticle size. The effect of the feed distribution pattern was explored by Farhani et al. (2017) by introducing the feed solution up to 16 points along the disc periphery by a slight decrease of the PS. By moving the location feed point from 2 to 3 cm for a disc 4.25 in radius, a significant reduction of PS was observed by de Capraris et al. (2012). Vilardi et al. (2019) observed a PS reduction by putting the feeding point away from the centre up to 3 cm, a subsequent displacement to 3.5 cm was not advantageous. The importance of the use of a stabilizing agent was shown by many Authors and affected many process performances, among them the stabilization of the solid solution, the PS reduction, and the increase of the process yield and the crystal form (Liu et al., 2012). It is interesting to point out that the use of NaHMP in the production of CuO nanofluids (NF) improved both solution stabilization and NF conductivity (Chang et al., 2011). Moreover, a surfactant can be an important parameter in the "bottom-up" synthesis of nutraceutical nanoparticles (Annatachoke et al., 2006). Some Authors have proposed some modification in the geometry of the configuration of the SDR. Tai et al. (2007) have adopted a disc with a horizontal axis to an easier discharge of the solid suspension. Farahani et al. (2017) carried out the precipitation-reaction of barium sulfate using a double coaxial disc 20 cm in diameter. The upper disc can be drive counter-clockwise, whereas the lower disc may round clockwise and counter-clockwise. The location of the feeding point was also examined, and the minimum PS of 23.4 nm was obtained by operating at 4750 rpm with a feed location point 7 cm away from the disc centre. 4. Model of hydrodynamics of the liquid streams on the SD surface Identifying the local turbulence, i.e. the local micromixing times and the residence time of the fluid all over the disc, can be usefully done using the liquid film's modelling hydrodynamics over the disc surface. The first attempt to develop such a model in 2D has been made by Bathelia et al. (2009). More recently, the Sapienza University of Rome's research work team developed a hydrodynamic model for the precipitation- reaction of hydroxyapatite (HPA), a smooth disc 8.5 cm in diameter was adopted (de Caprariis et al., 2012). The film thickness varies from 300 nm near the feed injection to 50 nm at the disc extremity. The feeding points of the two reagent fluid streams are located 2 cm from the disc centre. The disc diameter is about three orders of magnitude greater than the maximum film thickness; therefore, a 2D model was developed using a fine grid on the vertical direction and a large one in the radial direction. The hydroxyapatite concentration profiles in the liquid phase and the local reaction rates, at a film height of 35 m, are shown in Fig. 2 (de Caprariis et al., 2015). The obtained results seem realistic and clearly show that the maximum reaction rate corresponds to the feeding points, whereas the produced HPA reaches the maximum concentration at the disc periphery. 124 Figure 2. Fluid dynamics over the SDR surface in the production of hydroxyapatite (HPA)at a film height of the liquid layer of 35 m: (A) HPA concentration; (B) reaction rate 5. Conclusions Twenty years of research has shown the great utility of SDR technology in producing organic and inorganic nanoparticles. The main success reasons are excellent mixing between liquid streams, which enables local micromixing, effective heat and mass transfer, ideal for gas-liquid reactions, the potential for sequential reagents for tailored products, and continuous operation mode. After the traditional use for the precipitation- reaction process, more recent applications have concerned solvent-antisolvent precipitation. The energy required by this technology to allow micromixing conditions is higher than that one needed by the STR equipment. Still, any comparison between the two technologies in terms of the reduced size of the produced particles is in favour of SDR. Finally, modelling of the mixing process has been successfully studied in two dimensions. New advances are expected in the future for a complete simulation of the precipitation process, including the birth, growth, and agglomeration of the solid particles. References Ahoba-Sam C., Boodhoo V.K., Olsbye U., Jens K.J., 2018, Tailoring Cu Nanoparticle Catalyst for Methanol Synthesis Using the Spinning Disc Reactor, Materials, 11, 154 Anantachoke N., Makha M., Raston C.L. Reutrakul V., Smith N.C., Saunders M., 2006, Fine Tuning the Production of Nanosized β-Carotene Particles Using Spinning Disc Processing, Journal of the American Chemical Society, 128, 13847-53 Bathelia T.J., Utikar R.P., Pareek V.K., Tafe M.O., 2009, Characterizing liquid film thickness in spinning disc reactors, Seventh International Conference on CFD in the Minerals and Process Industries CSIRO, Melbourne, Australia Bodhoo K.V.K., 2013, Spinning Disc Reactor for Green Processing and Synthesis, in Process Intensification for Green Chemistry: Engineering Solutions for Sustainable Chemical Processing. John Wiley and Sons, pp. 59-90 Cafiero L., Chianese A., Jachuck R., Precipitation of barium sulphate using a spinning disc crystallizer, 14th European Symp. on Ind. Crystallization, Cambridge 12-16 sept. 1999 Cafiero, L.M., Baffi G., Chianese A., Jachuck R.J.J., 2002, Process Intensification: Precipitation of Barium Sulfate Using a Spinning Disc Reactor, Ind. Eng. Chem. Res., 41, 5240-5246 Chang M.H., Liu H.S., Tai C.Y., 2011, Preparation of copper oxide nanoparticles and its application in nanofluid, Powder Technology, 207, 378–386 Chin S.F., Makha M., Rastan C.L., 2006, Encapsulation of Magnetic Nanoparticles with Biopolymer for Biomedical Application, International Conference on Nanoscience and Nanotechnology, 374-6 Chin S.F., Iyer K.S., Ralston C.L., 2008, Size Selective Synthesis of Superparamagnetic Nanoparticles in Thin Fluids under Continuous Flow Conditions, Adv. Funct. Mater., 18, 922–927 Dabir H, Dvarpanah M., Ahmadpour A, 2015, Effects of different operating parameters on the particle size of silver chloride nanoparticles prepared in a spinning disc reactor, Aplied Physics A, 120, 105-113 de Caprariis B., Di Rita M., Stoller M., Verdone N., Chianese A.,2012, Precipitation-reaction by a spinning disc reactor: Influence of hydrodynamics on nanoparticles production, Chemical Engineering Science, 76, 73– 80 125 de Capraris B., Stoller, M., Chianese A., Verdone N., 2015, CFD model of a spinning disc reactor for nanoparticle production, CET 43, 757-762 Dell’Era A., Scaramuzzo F.A., Stoller M., Lupi C., Rossi M., Passeri D., Pasquali M., 2019, Spinning Disc Reactor Technique for the Synthesis of Nanometric Sulfur TiO2Core–Shell Powder for Lithium Batteries, Appl. Sci, 9, 1913 Farahani H.B., Shahrokhi M., Dehkordi A.M., 2017, Experimental investigation and process intensification of barium sulfate nanoparticles synthesis via a new double coaxial spinning discs reactor, Chemical Engineering and Processing, 115, 11–22 Hartlieb K.J., Raston C.L., Saunders M., 2007, Controlled Scalable Synthesis of ZnO Nanoparticles, Chem. Mater., 19, 5453–5459 Haseidl F., Muller B., Hinrichsen O., 2016, Continuous-Flow Synthesis and Functionalization of Magnetite: Intensified Process for Tailored Nanoparticles, Chem. Eng. Technol., 39, 2051–2058 Jachuck R.J.J., Ramshow C., 1994, Process Intensification: Heat transfer characteristics of tailored rotating surfaces, Heat recovery system & CHP, 14, 475-491 Jachuck R.J.J., Ramshaw C., Boodhoo K., Dalgleish J.C., 1997, Process intensification: The opportunity presented by spinning disc reactor technology, ICHEME Symp. series 141, 38 Khan W.H., Rathod V.K., 2014, Process intensification approach for preparation of curcumin nanoparticles via solvent–nonsolvent nanoprecipitation using spinning disc reactor, Chemical Engineering and Processing, 80, 1–10 Kisyelovab T, Novruzova A., Hajiyeva F., Ramazanova M, Chianese A., 2016, Effect of the Reactor Configuration on the Production of Silver Nanoparticles, CET, vol 121-126 Liu H., Wang Y., Li C., Thai C., 2012, Characterization of AgI nanoparticles synthesized in a spinning disc reactor, Chemical Engineering Journal 183, 466– 472 Liu H., Wang Y., Tai C., 2012, Characterization of AgI nanoparticles synthesized in a spinning disc reactor, Chemical Engineering Journal, 183, 466-472 Loh J.W., Schneider J., Carte M., Saunders M., Lim L.Y., 2010, Spinning Disc Processing Technology: Potential for Large-Scale Manufacture of Chitosan Nanoparticles, Jl. of Pharmaceutical Sciences, 99, 4226-4336 Marchetti A., Stoller M., 2019, On the Micromixing Behavior of a Spinning Disc Reactor for Metallic Cu Nanoparticles Production, Appl. Sci., 9(16), 3311 Mohammadi S., Harvey A., Bodhoo K.V.K, 2014, Synthesis of TiO2 nanoparticles in a spinning disc reactor, Chemical Engineering Journal, 258, 171–184 Rathod W.R., Rathod V.K., 2018, Continuous preparation of nimesulide nanoparticles by liquid antisolvent precipitation using spinning disc reactor, Journal of Chemical Technology & Biotechnology, 94, Issue 3 Sana S., Boodhoo K., Zivkovic, 2019, Production of starch nanoparticles through solvent-antisolvent precipitation in a spinning disc reactor, Green Process Synth, 8, 507–515 Stoller M., Ochando-Pulido J.M., 2020, ZnO Nano-Particles Production Intensification by Means of a Spinning Disc Reactor, Nanomaterials 10, 1321 Tai C.Y., Chang M.H., Liu H.S., 2007, Synthesis of Magnesium Hydroxide and Oxide Nanoparticles Using a Spinning Disc Reactor, Ind. Eng. Chem. Res., 46, 5536-5541 Tai C.Y., Tai C.T., 2005, Synthesis of nanosized calcium carbonate particles using high reactive precipitation technique, VDI Berichte, (1901 II), art. no. D-13, pp. 843-848. Vilardi G., Stoller M., Di Palma L., Boodhoo K., Verdone N., 2019, Metallic iron nanoparticles intensified production by spinning disc reactor: Optimization and fluid dynamics modelling, ai Vilardi G., Stoller M., Di Palma L. Verdone N., 2017, Continuous production of KNO3 nanosalts for the fertilization of soil by means of a Spinning Disc Reactor, 15th International Conference on Environmental Science and Technology, Rodes, Gr., 00226 Zou J., Iyer K.S., Stewart S.G., Raston C. L., 2011, Scalable synthesis of catalysts for the Mizoroki–Heck cross coupling reaction: palladium nanoparticles assembled in a polymeric nanosphere, NewJ. Chem., 35, 854–860 126