Acid/Base Calculations

 

 

FORMULATOR can handle any number of acid/base chemistries, including polyurethanes, epoxy amines, and other acid/base stoichiometries.  FORMULATOR provides calculation tools to optimize any stoichiometric outcome.  This is done within a very simple framework of physical properties and resultant equation variables.
 
FORMULATOR acid/base calculations are based on three possible raw material properties: equivalent weight acid, equivalent weight base, and percent weight resin (or reactive; the property basis is “% wt resin”, typically 100% for a polyol or isocyanate raw material). 
 
The unit of measure for “Equivalent Weight” is grams per mole of reactant.  This is equal to the grams of the raw material that are required to make one mole of OH- or O+.  At an intermediate level, this value will apply only to the reactive portion of a raw material.  Adding inert ingredients (0% reactive) to a mixture will increase the mixture’s Equivalent Weight, since the value is relative to the total amount of the mixture.  When saved as an intermediate, only the excess acid or base portion will be expressed (in grams per mole, i.e. equivalent weight).
 
Set-Up and Raw Material Maintenance
 
Each reactive raw material (polyols, amines, epoxies, hardeners, water, etc.) must have its respective equivalent weight acid or base entered as a physical property, along with the percent weight reactive of the raw material (typically 100%, except for diluted premixes).  After entering these values, the raw materials are ready for formulation.  You may name the equivalent weight acid and base properties anything you wish, but there can be no more than one acid property and one base property defined within any FORMULATOR database.  All raw material chemistries are entered in the exact same fashion (acids go into Equivalent Weight Acid, aka NCO, and bases into Bases, aka OH).  Percent weight reactive is typically 100%.
 
Some polyol data sheets only supply the hydroxyl number.  In this case, the equivalent weight for the raw material in question can often be calculated as follows:
 
            Polyol Equivalent Weight = 56100 / hydroxyl number
 
Formulating with Equivalent Weights
 
Within Formulation Maintenance, in the Ingredients tab, you can view the equivalent weight acid and base properties as columns in the formulation (click the wrench in the toolbar to select).  You can also view the resultant equivalent number* acid and base, and percent weight reactive (aka % weight resin).  The intermediate values will display on the gross totals row (and net, if line losses apply and alter the outcome).  The equivalent weight, number, and total grams of acid and base are also available as equation variables.
 
*Equivalent number = % of ingredient’s reactive mass fraction / Equivalent Weight of the ingredient.
 
Equivalent Weight variables [Eq Wt Acid] and [Eq Wt Base]
 
The formula’s bottom line equivalent weight (acid and base) is calculated as follows:
 
                                                       Total Grams of Mixture
Eq.Wt. Base =   --------------------------------------------------------------------------
                             Grams Base 1    +   Grams Base 2    +      …
                             Eq.Wt. Base 1         Eq.Wt. Base 2
 
When used as an intermediate, the net acid or base equivalent weight will be calculated and presented.
 
Equivalent Numbers
 
Each acid and base equivalent weight property has an accompanying equivalent number.  The equivalent number is the percent weight of the reactive component of a material, divided by its equivalent weight.  The sum of these values represents the formula’s equivalent number.
 
Equivalent Number variables [Eq No Acid] and [Eq No Base]
 
The formula’s bottom line equivalent numbers are available as both columns in the formula and as variables in equation builder.  In equation builder, they are denoted [Eq No Acid] and [Eq No Base]. 
 
Intermediate acid/base values
 
Intermediates will have either an equivalent weight acid or equivalent weight base, but not both.  When used as an intermediate it is assumed that the intermediate’s acids and bases will have reacted with each other, yielding a new acid or base value (expressed as grams per mole OH-/O+).  The intermediate will reflect the net stoichiometric reaction surplus of the two (i.e. either acid or base).
 
Equivalent Weights of Intermediates
 
The equivalent weight of any intermediate is calculated as follows (the example assumes a polyol):
 
                                                         Total Grams Polyol
Eq.Wt. Polyol =   --------------------------------------------------------------------------
                             Grams Polyol 1    +   Grams Polyol 2    +      …
                             Eq.Wt. Polyol 1         Eq.Wt. Polyol 2
 
If a formula includes both acids and bases, then the intermediate values will reflect the net stoichiometric reaction between those acids and bases.  The value will be set to the total grams reactive divided by the excess moles of either O+ or OH- within the mixture (i.e. grams per mole).