Week 1

Activity 1: Chemical Product

Broad category: Household

- Sub-category: Appliances/Electronics

- Chemical product: Carbonation Machine (Sodastream)

- Chemical engineering principles: Gas Absorption, Carbonation

- Category: Chemical Device

Plate 1: SodaStream Machine (Nozari,2018)

SodaStream is a “home soda maker” allowing consumers to create sparkling drinks at home.

The main principle that Sodastream uses to carbonate drinks is by gas absorption with carbon dioxide (carbonation). In which a gas mixture, in this case, Carbon Dioxide is contacted with a liquid for the purpose of dissolving the gas into the liquid.

For a beverage to be carbonated, a bottle filled with liquid of choice is fitted to the machine where the siphon releases pressurised carbon dioxide directly into the liquid.

In order to dissolve the Carbon Dioxide into the liquid, the Sodastream uses a counter-current operation when injecting the Carbon Dioxide, forcing the gas to exit the siphon from the bottom of the liquid causing the gas to flow to the top which results in mass transfer by absorption. In order for the gas to be absorbed by the liquid, the bottle is under constant pressure.

When the Carbon Dioxide comes into contact with the liquid, the molecules of the soluble gas diffuse from the main body of the gas phase to the gas-liquid interface. This causes a decrease in the concentration of Carbon Dioxide in the gas phase, resulting in a concentration driving force for the mass transfer of Carbon dioxide from the bulk gas phase to the interface. It then moves on to the liquid side interface where the concentration falls from the interface to the bulk liquid, resulting in concentration as a driving force for mass transfer from the interface to the bulk liquid phase before diffusing into the main body of the liquid.

The SodaStream also causes the pressure inside the bottle to increase the concentration of Carbon Dioxide inside the liquid. This process makes use of Henry’s Law, which states that when a gas mixture is in equilibrium with a non-ideal liquid solution, the partial pressure of the individual gas constituents can be related to its concentration using Henry’s Law.

pCO2 = H xCO2

As seen from the equation, as the vapour pressure of Carbon Dioxide increases, the number of moles of Carbon Dioxide in the liquid increases, causing its concentration to increase.