JORDI SANT GISBERT

4.2.2.1 Process Overview

The scFOS production process follows a generic process pattern but the benefit is that the raw materials coming into the process do not need to be pre-handled, but only diluted. The block flow diagram is shown in Figure 4.3. The sucrose will arrive in bags where they will be mixed with hot water to bring the concentration down to the correct reaction specification. The FFase and the sucrose are sent straight to the bioreactor where the reaction can take place. There is a buffer tank that is placed after the reactor, to provide a flow control between the reactor and the SMB chromatography column.

The purification step concentrates the product to a higher level, after which the product is then prepared for selling. The by-product, which also has its uses is also sold to a willing buyer in the sugar industry.

Figure 4.3: ScFOS block flow diagram illustrating the concept behind the design of the process.

4.2.2.2 Equipment Selection Reactor

There were two different types of reactors that were considered for the oper- ation of the scFOS process. The first reactor setup is a packed bed reactor (PBR). With this type of reactor, the enzyme needs to be fixed in a bed and the sucrose would flow through the fixed enzymes and react to form the scFOS. The challenge with this reactor setup is issue of immobilising the enzyme.

β-D-fructofuranosidase can be produced in numerous ways using different organisms and production techniques. Also, depending on the production method, the enzyme can be produced within the cells of the organism or the enzyme can be secreted in the supernatant. If the PBR reactor setup is chosen, the enzyme would have to be produced in a way that is conducive for the enzyme to be immobilised.

The other way to produce the scFOS is in a continuously stirred tank reactor (CSTR). In this method, the enzyme and the sucrose enter the reactor

in separate streams, where they mix in the vessel and the reaction is allowed to take place. Using the CSTR, the enzyme can exist in the supernatant and flow into the reactor in a liquid form and mix with the sucrose to form the scFOS.

The CSTR reactor setup has been chosen because a very good method to produce β-D-fructofuranosidase has been found, where the organism of Pichia pastoris is used as the host for the enzyme production. Very good yields of en- zyme are obtained by using P. pastoris and by using this method, the enzyme is secreted into the supernatant, which means that the CSTR reactor would be more suitable for the scFOS production.

Storage

Before the scFOS can be sent for purification, there needs to be a buffer tank between the two process steps so that there is control and time between the production of scFOS and the purification of the product. This is an important step of the process as it will allow time for the reaction mixture to settle and stabilise before it it sent to the SMB column.

Purification

The scFOS, before it is sold, needs to be sent to a purification unit to bring the purity up to a level of 95% or above. The impure scFOS leaves the buffer tank. There are two well known techniques that are used for the purifica- tion of the scFOS and they are simulated moving bed chromatography and activated charcoal column. They are both very effective techniques to remove the unwanted sugars (fructose, glucose and sucrose) from the process, both achieving purification rates of 95% or above. A factor that may deter the use of the charcoal column is the fact that it uses the potentially risky chemical of ethanol as an eluent in the process. SMB chromatography simply uses water as the eluent in the process.

The choice would be to use the simulated moving bed chromatography technique as it is a well recognised method that is known to be used a lot in literature and it is also known to be used by local sugar producers in South Africa for fructose production. The technique has no hazardous materials and achieves a good separation, which are the influencing factors that will favour the choice of this technology.

Product Preparation

ScFOS is known to be sold in two different forms; in the syrup form and in the powder form. Depending on what the industry demands will determine in which form the product will be sold. The good news is that the process can cater for customers that request scFOS both in the powder and syrup form. To prepare the dry scFOS in powder form, the ‘wet’ scFOS that exits the SMB chromatography column is sent to a spray dryer. The spray dryer works in a way that is shown in Figure 4.4. The stream enters the hot drying chamber through a nozzle. The nozzle essentially sprays the entering ‘wet’ stream of scFOS into the hot chamber and the moisture is then absorbed by the hot dry air.

The dried product exits out the bottom of the chamber and is sent to packaging, while the cooled air exits out the side of the chamber and is sent to a cyclone where it is cleaned. The dry product is also filtered once more and the unwanted air is also sent to the cyclone where it is ultimately sent to the exhaust.

By-product Handling

From the SMB chromatography column, comes the by product which consists mainly of glucose, fructose, and sucrose. This stream can also be sold as there are still useful sugars in this stream. This stream, like the product stream from the SMB chromatography column also needs to be dried as it contains moisture that is undesirable. The piece of equipment that is used to treat

Figure 4.4: Schematic diagram of the setup and operation of a spray dryer (Re- drawn) (Patel et al., 2009).

the by-product is an evaporator. The stream will simply enter the evaporator and be subjected to high temperatures. As the temperature of the stream increases, the moisture will evaporate out and the by-product will become dry and be ready for selling.