Gibbs Reactor - Technical Information
The Gibbs Reactor simulates a chemical reactor by solving the heat and material balances based on minimizing the free energy of the components in the reaction.
The number of chemical reactions (i.e., the number of REACTION statements) must equal the number of chemical species minus the number of effective atoms. Usually, the number of effective atoms is the number of atomic species.
The number of effective atoms differs from the number of atomic species when two or more atoms always occur together in the same proportion. For example, consider the chlorination of ethylene:
There are 3 atomic species (C, H, Cl), but C and H always occur in a 1:2 ratio. Therefore, the number of effective atoms is 2 (Cl and CH2). These two effective atoms represent the three chemical species, so only one chemical reaction is allowed.
Calculation Method
The Gibbs reactor determines the distribution of components which is expected at chemical equilibrium for the system. No prior knowledge of the chemistry of the system is required and the reaction stoichiometry need not be defined. All the components in the reactor are considered as reactants. The calculation determines the distribution of the components which gives the minimum free energy for the system. This gives the hypothetical equilibrium mixture. Depending on the reaction kinetics, it may, or may not, be possible to achieve this composition.
Reaction stoichiometry may be defined in the Reaction Data Sets Window and used in the Gibbs reactor. In this case, the calculations will be limited to these defined reactions. It is also possible to exclude components from the minimization if they are known not to be involved.
You can impose an approach to equilibrium in the Extent of Reaction Window. This may be either a temperature approach or the conversion or the rate of any component in the reaction product may be specified. If a temperature approach, DT, is entered, the equilibrium constant is determined at the temperature, T, where:
T = Treaction - DT, endothermic reaction
T = Treaction + DT, exothermic reaction
The heat of reaction is calculated by PRO/II from heat of formation data. Heat of formation data must be entered for any non-library components in the reaction.
By default, the reactor operates isothermally at the feed temperature. A different isothermal temperature or a duty may be specified instead.
The Gibbs reactor may use a VLE or VLLE method to determine the phase compositions for the product streams. See VLE Model and VLLE Model for more details.
Feeds and Products
The Gibbs reactor unit can have any number of feed streams. The inlet pressure is taken to be the lowest pressure of all the feed streams.
The reactor can have up to four process product streams, with each stream containing a different phase. The possible phases are vapor, liquid, decanted water/second liquid phase, a mixture of liquid and vapor, and solids. If there are multiple product streams leaving the reactor, the phase condition for each stream must be specified using the Product Phases Window.
