Chemistry Reference
In-Depth Information
ratio holds true for different mass units. So 60 pounds of acetic acid can be
combined with 46 pounds of ethanol to make 88 pounds of ethyl acetate. Sim-
ilarly 60 tons of acetic acid can be combined with 46 tons of ethanol to make
88 tons of ethyl acetate. What about the conservation of mass? How is it that
60
106 pounds of starting material only makes 88 pounds of ethyl
acetate? The answer is that we also make 1 equivalent of water; in this case, it
is 18 pounds, so 106 pounds of starting material makes 106 pounds of product.
If we combine 60 pounds of acetic acid at a cost of $0.40/pound with 46
pounds of ethanol at a cost of $0.38/pound we spend $41.48 to make 88
pounds of ethyl acetate. This calculates ($41.48/88 pounds) to be a cost of
about $0.47 per pound. Compared with an anticipated selling price of $0.70,
that leaves $0.23 per pound for other costs and profit. This may not sound like
much, but if it is a 10 million pound plant, it is $2.3 million. It is probably
worth considering the project.
If the yield is 95%, we can divide the raw material costs by 0.95. So
$0.47/0.95
+
46
=
$0.49 per pound raw material cost. This is a less desirable
situation because the lower the yield, the higher the raw material costs and
also the larger amount of waste by-product that needs to be considered, often
as purification or waste disposal cost.
As a second example, we can calculate the raw material cost of phenol. To
keep the example simple, we will assume 100% yield and no value from the
production of byproducts. For the example, assume that cumene costs $0.50
per pound.
=
OH
O
H
3
O
+
O
2
+
Cumene
Acetone
Phenol
From the equation, we see that one mole of cumene makes one mole
of phenol. Taking into account molecular weight, this means that 120 g of
cumene (C
9
H
12
) makes 94 g of phenol (C
6
H
6
O). With the mass ratio of
120:94, we can say that it takes 120 pounds of cumene to make 94 pounds of
phenol. Or that it takes 1.28 (120 / 94) pounds of cumene to make one pound
of phenol. Therefore the raw material cost can be calculated: (1.28 lb cumene/
lb. phenol)($0.50 / lb. cumene)
$0.64 / lb. phenol. There are many other
things which would need to be considered in a more thorough cost analysis.
You also generate 0.62 (58 / 94) pounds of acetone per pound of phenol. The
price you can get for the byproduct acetone will be a major factor in prof-
itability of a phenol plant. You also need a radical initiator and oxygen in the
first step. The amount of radical initiator used is very small and will not have
any significance on the cost. Air is the source of oxygen and the cost is not
=
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