*Hundred Years of Lactitol: From Hydrogenation to Food Ingredient DOI: http://dx.doi.org/10.5772/intechopen.93365*

*Lactose and Lactose Derivatives*

scheme (5). Prolong reaction time and high temperature can induce the hydrolysis of lactitol, which leads to the formation of sorbitol and galactose, scheme (2).

Lactose can undergo dehydrogenation forming lactobionic acid, scheme (11). This situation would occur under a limited concentration of hydrogen. Subsequently, the lactobionic acid may undergo hydrolysis (scheme (13)) to form

The industrial hydrogenation of lactose is commonly done in a batch mode using sponge nickel as a catalyst. In the hydrogenation of lactose, the reaction temperature ranged from 130 to 180°C, while the pressure of hydrogen gas varied between 50 and 170 bars. **Figure 4** exemplifies a hydrogenation batch reactor. The batch reactor is charged at the top of the tank. This type of reactor is based upon the movement of hydrogen from the gas phase to a liquid phase and across a liquid-solid interface to the surface of the supported catalyst, where the hydrogen gas is adsorbed. During the reaction, hydrogen gas is consumed by the catalytic reaction creating concentration gradients across the reactor. Such gradients control the net movement of hydrogen gas to the catalyst and, therefore, the speed of the reaction. Temperature, pressure, and agitation are the main variables controlling the reaction rate and final yield. Batch reactors offer the advantage of not having large temperature gradients, and the development of velocity profiles is negligible, which simplifies the operation. The performance of a batch reactor for catalytic hydrogenation depends on the hydrogen movement across the reactor. This feature

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*3.3.4 Oxidation*

**Figure 3.**

gluconic acid and galactose.

*Reaction scheme during catalytic hydrogenation of lactose.*

**3.4 Production of lactitol**

is the principal disadvantage of the batch reactor since they are designed to control the mass transfer only through agitation.

Alternatively, catalytic hydrogenation can be performed by a continuous flow of reactants. Conceptually, the continuous operation has been exemplified in a trickle-bed reactor using structured catalysis [19]. A simplified diagram of the continuous hydrogenation of lactose is presented in **Figure 5**. The process mainly consists of feed streams, heat exchangers, reactor units, and separator. Kasehagen [25] exemplified the production of lactitol under continuous mode using a lactose solution (50% wt/wt) in water with sponge nickel (1.8%) at 160°C and 130 bar. Under such conditions, about 98% of lactose was converted into lactitol.

**Figure 4.** *Continuous-stirred tank reactor for batch hydrogenation of lactose.*

**Figure 5.** *Schematic representation of continuous hydrogenation of lactitol.*
