276347 Nano-TiO2 Sol-Gel Synthesis in the Spinning Disc Reactor

Wednesday, October 31, 2012: 9:45 AM
Oakmont (Omni )
Somaieh Mohammadi, Chemical Engineering and Advanced Materials, Newcastle University, Newcastle Upon Tyne, United Kingdom and Kamelia Boodhoo, Chemical Engineering and Advanced Materials, Newcastle University, Newcastle, United Kingdom

Nano-TiO2 sol-gel synthesis in the spinning disc reactor

Somaieh Mohammadi* and Kamelia V.K. Boodhoo

School of Chemical Engineering & Advanced Materials, Newcastle University, Merz Court, Newcastle Upon Tyne, NE1 7RU, UK

Abstract

The purpose of the experimental study is to determine the feasibility of producing nanoparticles of TiO2 in a continuous spinning disc reactor (SDR) which represents an example of a process intensification technology. The primary characteristics of the SDR relevant to this study are the thin film flow of the liquid on its surface, the very vigorous mixing within the film and the extremely short and controllable residence times of the liquid. A liquid-liquid sol gel technique would be chosen to investigate experimental parameters of rotational speed, flowrate and concentration and disc surface configuration. The nanopowders of TiO2 synthesized by sol gel method in the spinning disc reactor will be compared with the nanopowders produced in a conventional stirred tank reactor.

Preliminary results indicate that the higher the liquid flowrate on the disc and the higher the rotational speed of the disc, the smaller the particle size and the narrower particle size distribution (PSD) in the SDR. In the relative conditions the nanopowders produced by Stirred tank reactor had wider PSD.

Keywords: TiO2, Spinning disc reactor, particle size distribution

Introduction

Nowadays there is an increasing number of industries that rely on nano titanium dioxide (TiO2) which is used in a variety of products such as white pigment and white food colouring, cosmetic and skin care products, photocatalysts for use under ultraviolet light and surface coatings amongst others. Although the processes for making titanium dioxide are well-established and developed, new processing methods which are more economical and have the potential to offer better product characteristics are important in driving the TiO2 industry forward to continue to be profitable. In recent years, the spinning disc reactor (SDR) has been developed as process intensification equipment where rapid mass and heat transfer rates can be obtained from the thin film of liquid produced due to centrifugal acceleration of rotating disc. In developing these characteristics, the SDR is considered a tool of process intensification due to its compactness, flexibility as an inherently safe and continuous reactor technology and its capability to deliver better product quality. The spinning disc reactor would appear to be an excellent candidate for industrial applications due to its very short and controllable residence time. SDR is also a highly intensified reactor when dealing with rapid exothermic reactions and viscous liquids such as bulk polymerization [1], solution[2], condensation[3] and also cationic polymerization [4] of styrene. The SDR thin films, on the other hand, offer higher mixing intensity and high heat and mass transfer rates [5] which results in tighter molecular distribution and higher quality of polymer product [6, 7]. Spinning disc reactors were previously investigated in the precipitation of barium sulphate [8] and calcium carbonate [9]. It was found that high rapid mixing coupled with high levels of supersaturation lead to very small crystals with a tighter size distribution being produced. This was considered to produce better quality than conventional process techniques used in the pharmaceutical industry [10]. It was shown that the precipitation of barium sulphate on a spinning disc yielded significantly smaller crystals than the batch technique. The main factor controlling the crystal size was the very high rates of mixing experienced on the spinning disc, which lead to the rapid depletion of supersaturation, and much higher nucleation rates. Cafiero et al [12] also demonstrated that the energy input in the spinning disc process was much lower than the use of a T-mixer arrangement, suggesting that operating costs would also be reduced along with attaining better control of crystal size. With the understanding that the rapid mixing and high supersaturation leads to very small crystals being produced along with very short residence times and tighter CSD, it was hypothesised that a similar circumstance could exist for titanium dioxide precipitation routes. The morphology of titanium dioxide is more complicated than that of barium sulphate, capable of forming three different crystal forms, and therefore emphasis on making the right size shape and form is important in the final product. Understanding the morphology from this rapid precipitation method is a factor in the present study.

This work aims to develop and demonstrate a novel processing method on the basis of the spinning disc reactor (SDR) for the production of titanium dioxide nanoparticles in order to enhance the efficiency and the higher quality products. The spinning reactor seems more desirable due to its considerably lower specific energy consumption. Additionally this technique is utilized to give high flow rate and very short residence time in continuous mode of operation [11].

Materials and Methods

The production process of the titanium dioxide nanoparticles consisted of the reaction between distilled water and titanium tetra isopropoxide (TTIP) at 50oC under nitrogen and the subsequent precipitation of the produced titanium dioxide. The adopted apparatus is equipped with a disc of 20 mm of diameter rotating at 300- 1200 rpm. The two reagent solutions were separately fed at the centre of the disc as indicated in Fig. 1. The total feed flow rate of reagent solutions was between 1.66- 5 ml/s. A pH value of the distilled water was equal to 1.5 was achieved by the addition of nitric acid to the distilled water reservoir. The ratio of water to TTIP was between 2 and 8. For sake of comparison the same procedure was applied by using a baffled stirred vessel, 250 ml in capacity.

Figure1. Schematic of TiO2 experiments set up

Results highlights

Exploratory works and primary studies show that the SDR technology gives increased number of particles with controlled size, shape and size distribution to reach quality requirements. It has been observed that under comparable operating conditions, the SDR provides more uniform and smaller nanoparticles with respect to a mechanically stirred vessel. The nanoparticles produced by the SDR also have a narrower size distribution than the STR.

References

1. Moghbeli, M.R., S. Mohammadi, and S.M. Alavi, Bulk free-radical polymerization of styrene on a spinning disc reactor. Journal of Applied Polymer Science, 2009. 113(2): p. 709-715.

2. Boodhoo, K.V.K. and R.J. Jachuck, Process intensification: spinning disk reactor for styrene polymerisation. Applied Thermal Engineering, 2000. 20(12): p. 1127-1146.

3. Boodhoo Kamelia, V.K., A.E. Dunk William, and J. Jachuck Roshan, Continuous Photopolymerization in a Novel Thin Film Spinning Disc Reactor, in Photoinitiated Polymerization2003, American Chemical Society. p. 437-450.

4. Boodhoo, K.V.K., et al., Classical cationic polymerization of styrene in a spinning disc reactor using silica-supported BF3 catalyst. Journal of Applied Polymer Science, 2006. 101(1): p. 8-19.

5. Aoune, A. and C. Ramshaw, Process intensification: heat and mass transfer characteristics of liquid films on rotating discs. International Journal of Heat and Mass Transfer, 1999. 42(14): p. 2543-2556.

6. Boodhoo, K.V.K. and R.J. Jachuck, Process intensification: spinning disk reactor for styrene polymerisation. Applied Thermal Engineering, 2000. 20(12): p. 1127-1146.

7. Boodhoo Kamelia, V.K., A.E. Dunk William, and J. Jachuck Roshan, Continuous Photopolymerization in a Novel Thin Film Spinning Disc Reactor, in Photoinitiated Polymerization2003, American Chemical Society. p. 437-450.

8. McCarthy, E.D., W.A.E. Dunk, and K.V.K. Boodhoo, Application of an intensified narrow channel reactor to the aqueous phase precipitation of barium sulphate. Journal of Colloid and Interface Science, 2007. 305(1): p. 72-87.

9. Burns, J.R. and J.J. Jachuck, Monitoring of CaCO3 production on a spinning disc reactor using conductivity measurements. Aiche Journal, 2005. 51(5): p. 1497-1507.

10. Oxley P, Brechtelsbauer C, Ricard F, Lewis N, Ramshaw C , Evaluation of Spinning Disk Reactor Technology for the Manufacture of Pharmaceuticals. Ind. Eng. Chem, 2000. 39(7): p. 21752182.

11. Cafiero, L.M., et al., Process intensification: Precipitation of barium sulfate using a spinning disk reactor. Industrial & Engineering Chemistry Research, 2002. 41(21): p. 5240-5246.

 


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