Research is being done to utilize microbial cells found in common soil or the oc

Question

Research is being done to utilize microbial cells found in common soil or the ocean floor to produce usable fuels, such as propane, from CO2 that has been sequestered from flue gases from power plants (a major source of CO2 emissions). The challenge here to make the process useful is to be able to produce large quantities of propane from these cells at a reasonable cost. In a first attempt to this, a company (GASBUGS INC.) attempts to mass produce propane by employing a simple continuously stirred tank reactor (CSTR). GASBUGS INC. found that keeping the reactor at 25 oC provides conditions in the reactor where the rate of death and growth of cells are equal. On a molar basis, when CO2 (density = 0.00197 g/cm3) is bubbled into the reactor at a flow rate of 1680 L/hr., complete conversion to propane is achieved in 10% excess of water, and no bacteria are lost in the output flow stream.

1. determine how much feed water is required in mol/hr. and what the daily output of propane is?

Explanation / Answer

3CO2(g) + 4H2O(l) -------> C3H8 + 5O2(g)

Now, volume of CO2 passed per hour 1680 litres

density of CO2 = 0.00197 g/cm3 = 1.970 g/litres

Molar mass of CO2 = 44 g/mole

Thus, mass of CO2 passed per hour = volume*density = 1680*1.970 = 3309.6 g

Thus, moles of CO2 passed per hour = mass/molar mass = 3309.6/44 = 75.22 ............(1)

Now, Volume of water required per hour = 110% of the volume of CO2 = 1.1*1680 = 1848 litres

Now, density of water = 1000 g/litres

Thus, mass of water required per hour = density*volume = 1848*1000 = 1848000 g

Molar mass of water = 18 g/mole

Thus, moles of water required per hour = 1848000/18 = 102666.7

Now, as per the balanced reaction; CO2 & water reacts in the molar ratio of 3:4

Also, CO2 is completely consumed

Thus, moles of propane formed per hour= (1/3)*moles of CO2 reacting = 75.22/3 = 25.073

Hence moles of propane formed per day = 25.073*24 = 601.76

Molar mass of propane = 44 g/mole

Thus, mass of propane formed per day = 601.76*44 = 26477.44 g

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