Concept explainers
Citric acid (C6H8O7) is used in the preparation of many foods, pharmaceuticals, soft drinks, and personal-care products. Although it can be recovered by concentration and crystallization from citrus juices, especially lemons, modem commercial production involves synthesis by fermentation of molasses or other carbohydrates such as glucose or fructose by the fungus Aspergillus niger (A. niger). The process involves addition of the fungus to a fermenter along with glucose, nutrients, water, and air that is bubbled through the fermentation broth After the desired conversion, the resulting liquor is processed first by filtration of the cell mass and other solids from the liquid and then recovery and purification of the citric acid by crystallization.
As part of the evaluation of a proposed continuous fermentation process, you have been asked to estimate the heating or cooling requirement associated with a fermenter that is to produce 10.0 kg of citric acid per hour. Feed to the unit includes (1) an aqueous solution that is 20.0 wt% glucose
where the coefficients of the species (a, b,....) are to be determined. Experiments on the fermentation reaction have found that 70% of the glucose consumed is converted to citric acid and that the respiratory quotient (RQ) is 0.45 (RQ = moles of CO2produced per mole of O2consumed).
The following table gives data for selected process species. Information on other species may be found in Table B.l.
Species | MW(g/mol) |
|
|
glucose(s) | 180 | -1006.8 | 9.9 |
citric acid(s) | 192 | -1543.8 | 22.6 |
ammonia(g) | 17 | -46.19 | -35 |
cellular material(s) | 24.6 | -59.9 | — |
- Use elemental species balances to determine the coefficients in the stoichiometric equation.
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