Page 80 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

based on the overall process economics.

2.3.5 What Information Can Be Determined Using the Input/Output Diagram for a Process?

The following basic information, obtained from the input/output diagram, is limited but nevertheless very
important.
• Basic economic analysis on profit margin
• What chemical components must enter with the feed and leave as products
• All the reactions, both desired and undesired, that take place

The potential profitability of a proposed process can be evaluated and a decision whether to pursue the
process can be made. As an example, consider the profit margin for the toluene HDA process given in
Figure 2.1.

The profit margin will be formally introduced in Chapter 10, but it is defined as the difference between
the value of the products and the cost of the raw materials. To keep things simple we use the
stoichiometry of the reaction as our basis. If the profit margin is a negative number, then there is no
potential to make money. The profit margin for the HDA process is given in Example 2.1.

Example 2.1

Evaluate the profit margin for the HDA process.

From Tables 8.3 and 8.4, we get the following prices for raw materials and products:

Benzene = $0.657/kg

Toluene = $0.648/kg

3
Natural gas (methane and ethane, MW = 18) = $11.10/GJ = $11.89/1000 std. ft = $0.302/kg

Hydrogen = $1.000/kg (based on the same equivalent energy cost as natural gas)

Using 1 kmol of toluene feed as a basis

Cost of Raw Materials

92 kg of Toluene = (92 kg)($ 0.648/kg) = $ 59.62

2 kg of Hydrogen = (2 kg)($ 1.000/kg) = $ 2.00

Value of Products

78 kg of Benzene = (78 kg)($ 0.657/kg) = $ 51.25

16 kg of Methane = (16 kg)($ 0.302/kg) = $ 4.83