We are planning to isolate an antibiotic from a fermentation broth (10L) by usin

ID: 508431 • Letter: W

Question

We are planning to isolate an antibiotic from a fermentation broth (10L) by using activated carbon. The concentration of antibiotic in the broth is 1.1 x 10-6 g per g broth. 95% of the antibiotic in solution needs to be recovered. Adsorption studies at the operating conditions gave the following results:

a. Which isotherm (Freundlich, Langmuir or linear) best fits the data? b. If we use single stage adsorption, how much adsorbent is needed? Assume the density of the broth is the same as water and T = 20C

C*A x 10^6 (g A/g soln) 0.1 0.3 0.6 0.9 1.2 C*AS x 10^3 (g A/g carbon) 1.3 1.7 2.3 2.4 2.6

Explanation / Answer

a. Which isotherm (Freundlich, Langmuir or linear) best fits the data?

. In order to test which isotherm fits the data best, linear regression analysis was carried out for the adsorption data. The results are as follows:

The mass fraction of the solute in the feed can be calculated by assuming the density of the feed is the same as water.

Isotherm

Plot

Slope

Intercept

Carr. Ca0oeff

Freundlich

In X vs. In Y*

0.29

-0.87

0.99

Langmuir

1/X vs. 1/Y*

4.1 x 10^-5

381

0.97

Linear

X vs. Y*

1160

0.0013

0.95

The results indicates

that any isotherm can fit the data very well.

If we choose the the Freundlich equation, which fits the adsorption data the best, the slope and the intercept of the 10gX versus logY* plot yields the equation

y* = 0.13X^0·29 ----------------answer

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b. If we use single stage adsorption, how much adsorbent is needed? Assume the density of the broth is the same as water and T = 20C

The concentration of the inlet stream was given as

Xo= 1.1 x 10^-6.

Since 95 percent of the solute in the input liquid stream is recovered, the concentration of the outlet stream will be

X2 =0.05Xo=5.5 x 10-8

From Eq. Freundlich equation,

the amount of the absorbent required is

Ss =Ls ( Xo - X2) /bX2 =9.6 g---------------------answer

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