Economy of Prep GC Example

It is not possible to give an absolute purification cost of large scale preparative GC, since much depends on

Paraffins (C5-C32), olefins Dienes

Vinyl acetylene

Aklyl benzenes m/p bromobenzo trifluorides

Benzyl alcohols, benzyl aldehydes a and p pinenes

Myrcene

Camphene

Limonene

Caryophyllene (azeotrope with anethole)

a and p cedrenes

Nerol, geraniol, citronellol, eugenol

Farnesols (cis-trans, trans-trans)

Citral a and b

Citronellal

Methyl ionones Anethole (cis-trans)

Methyl esters of fatty acids (soya, oleic, linoleic, linolenic, stearic, palmitic) Thiophenes (2-bromo, 3-bromo, 2-methyl, 3-methyl) Thenylamine Chlorophyridines Phosphines Indoles Ylang-ylang Virginia pine oil Clove oil Fennel oil Lemongrass oil Orange oil Lemon oil

Figure 2 Purification of cis and trans pentanediene. Column: 40 mm i.d.; 4 m long; 20% w/w squalane on Chromosorb P. Carrier gas: helium at 5cms_1; 2.6Lnim% 35°C. Injection: 4mL of mixture injected per cycle; 1 cycle every 20min. Purity: cis isomer = 99.8%; trans isomer = 99.8%.

the specific application and on the scale of the process.

The example described here is the purification of two heavy alcohols from a complex mixture.

The two alcohols to be collected are only 35% of the feedstock. Figure 3 shows the analytical chromatogram of the feed and a preparative chromatogram.

Time (min)

Figure 3 Purification of two heavy alcohols. (A) Analysis of the crude, showing the two alcohols to be recovered. (B) Successive preparative injections on an 80 mm i.d. column; one injection of 18 g every 10 min. Note: the recorder chart speed has been changed after the first four injections.

Table 4 Purification cost breakdown for a production of 36 tonnes per year of injected crude on a 400 mm i.d. column

Operating costs

Annual cost (k$ peryear)

Electricity: 1.44 1012 J 2000 h per year 8000 m3

5% of equipment cost

Replaced every 2 years

(at half the cost of a new column)

Power Manpower Hydrogen make-up Maintenance Stationary phase

Total Total

33 80 11 58 62

244 k$ per year

21.8 $ kg-1 of pure product

Investment costs (k$)

Chromatograph

1200

20% of equipment cost

Surroundings

240

Start-up and others

Miscellaneous

160

Total

1600 k$

Amortizement over 5 years

Total

320 k$ per year

Total

8.9 $ kg"1 of crude

28.6 $ kg"1 of pure product

Purificationcosts 15.7 $ kg 1 of crude

50.4 $ kg-1 of pure product

Purificationcosts 15.7 $ kg 1 of crude

50.4 $ kg-1 of pure product

Optimizing the operating conditions has led to the production of 1kgh_1 for the first alcohol and 400 g h"1 for the second on a column of 400 mm i.d. The yield of the two alcohols was 89% (mass of pure alcohol collected/mass of alcohol injected) and purity was >95%.

The economics of the process are shown in Table 4 and Figure 4. The final purification cost is 15 $ kg-1 of injected feedstock. The normal purification costs for an industrial process range between 10 and 100 $ kg"1.

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