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UNITES STATES
DEPARTMENT OF THE INTERIOR
BUREAU OF MINES
OFFICE OF SYNTHETIC LIQUID FUELS
LOUISIANA, MISSOURI

CALCULATION OF THE THEORETICAL YIELD FROM ANALYSES OF SYNTHESIS AND RESIDUAL GAS

We are presenting below a method for the calculation of yields from the analyses of synthesis and residual gases.

In the computations, the analysis of the residual gas after activated carbon treatment is used.  This means, that the gasol after activated carbon treatment is used.  This means, that the gasol and possibly also gasoline which have failed to be absorbed in the carbon are not included in the yield.  No separation is possible into gaseous and liquids yield.  Computations proper are carried out on the following fundamental assumption:

   THE CARBON AND HYDROGEN BALANCE MUST BALANCE

The conversion of CO and H₂ are calculated separately.  Individual products of reaction, like CO₂, CH₄, water of the reaction, must be subtracted from the amounts converted.  Certain amounts of CO and H₂ remain.  The two amounts must exist in a certain proportion, which is obtained from the CO : H₂ ratio in the hydrocarbons formed, as like 1 : 1.18 given by Dr. Grimme for the synthesis under atmospheric pressure.  Should this proportion not be obtained from the contraction for H₂ or the volume contraction, one will have to conclude that either the analytical results or the contraction are in error.  Computations show, that when one arrives at an uncertainty, the results of analysis for CO or H₂ in the residual gas must be first of all suspected, because changes in the conversion are not important, and when there is a considerable variation of these values, e.g. by 1 point in the residual gas, the proportion of C and H₂ remain in g for the hydrocarbon synthesis will be changed only slightly.  Results will be greatly affected however by variations in the formation of CO₂.  This may be obtained by continued testing of the contraction until the required C : H₂ ratio in the products is reached.  We have another way of raising the CO₂ value in the residual gas analysis with unchanged contraction until we again get the required proportion.

A calculation of the two methods shows that the yields obtained will vary by only 3.4% from each other, and that therefore a suspicion of the source of error here present (in the contradiction or the CO₂ value) is relatively unimportant, as long as we are willing to accept either one of the two.

We may say for the computations that regardless of any assumed way of formation of CO₂, an independent 1y of the reaction which had taken place, no H₂ is necessary for the formation of water of reaction of formation of one mol CO₂ from 2 mols CO:

We will illustrate this method by the theoretical yields computated for the pressure synthesis as well as the atmospheric pressure synthesis during September.

H₂ Contraction 70.25%

A computation by this method results therefore in a good agreement with the values obtained from actual measurement.  We must mention however that our residual gas analyses in the activated carbon installations do no represent accurately the residual gas composition.  CO₂, CH_4, and C₄H₆ removed from activated carbon treatment II appear in the circulation in the residual gas after activated carbon treatment I.  The breather gases from tower III are also present in the normal pressure synthesis.  Both amounts of gases displace the theoretical yield away from the atmospheric pressure synthesis, and, conversely, in favor of the pressure synthesis.  In addition, the partial recirculation of the C₂H₆  gas, causes the residual gas analysis after activated carbon treatment I, to become incorrect, which makes the computations of yields of the normal pressure synthesis uncertain.

Basically, the method of computation appears to me to be useful, primarily for a rapid evaluation of the yield without awaiting the results of the time-consuming low temperature analysis.  The actual production during synthesis against that actually measured can be readily calculated when taking the final gas sample over the cooler and activated carbon, which is sure to remove all the hydrocarbons above the C₉ which have formed.  This method permits also finding the production of the individual reactors or stages.

To make the method described more exact, the following additional determinations would be necessary.

1)  The determination of the C : H₂ ratio in the total pressure and atmospheric synthesis (liquid and gaseous).

2)  The determination of the C number of the unabsorbed unsaturated hydrocarbons, which has been assumed in the sample calculation above to be 3.3, in agreement with the Hoesch method.  This value is surely too high.  During the first ten day of October the value used for atmospheric pressure synthesis was 2.5, because the C_nH_m in this case were certainly produced in the Dubbs unit ethylene.  No large errors could have been introduced in this way, because the C_nH_m values have no great affect upon the results.