Adsorption studies for the separation ofl-tryptophan froml-serine and indole in a bioconversion medium |
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Authors: | M H L Ribeiro D M F Prazeres J M S Cabral M M R da Fonseca |
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Institution: | (1) Faculdade de Farmácia de Lisboa, Química-Física, 1609 Lisboa Codex, Portugal;(2) Laboratório de Engenharia Bioquímica, Instituto Superior Técnico, 1096 Lisboa Codex, Portugal |
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Abstract: | l-tryptophan was produced froml-serine and indole by immobilized Escherichia coli cells in organic-aqueous systems. Selective adsorption was the method chosen to enable both product separation andl-serine reutilization. Amongst various adsorbents tested activated carbons and neutral polymeric resins (XAD-4 and XAD-7) showed good performance. The neutral resins could selectively concentrate thel-tryptophan from dilute aqueous solutions and adsorbed only 5% of the unconvertedl-serine. High separation factors (l-tryptophan/l-serine and indole/l-tryptophan) were obtained with these adsorbents. Despite a lower capacity, the XAD-7 resin had the advantage of desorbingl-tryptophan with basic or acidic solutions, while organic solvents were required to desorb, at the same concentration levels, this compound from XAD-4.In a packed bed column filled with XAD-4 resin or activated carbon, totall-tryptophan adsorption and recovery were achieved at linear velocities up to 5.0 cm/min and 3.2 cm/min respectively. Successive sorbent reutilization, following continuous sorption and elution steps, was carried out in packed bed columns with the neutral resins and activated carbon.Thel-form of tryptophan, after crystallization, was identified by HPTLC.List of Symbols HPLC
High Performance Liquid Chromatography
- HPTLC
High Performance Thin Layer Chromatography
- Trp
tryptophan
- Ser
Serine
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A
amount of sorbent(g)
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c
equilibrium solute concentration in the aqueous phase (g/dm3)
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c
i
initial (before adding the sorbent) liquid phase concentration (g/dm3)
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C
T
tryptophan concentration in the inlet solution (g/dm3)
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C
To
tryptophan concentration in the outlet solution (g/dm3)
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E
z
axial dispersion coefficient (m2/s)
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k
experimental constant (Eq. 1, 2 and 3)
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K
1
rate constant of adsorption (min–1)
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L
column length(m)
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n
experimental constant (eq. 1, 2 and 3)
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q
equilibrium solid phase concentration (g solute/g sorbent)
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q
max
maximum capacity of sorbent (g solute/g sorbent)
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t
time(s)
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v
liquid velocity (m/s)
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V
volume of liquid phase(dm3)
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V
e
eluted volume(dm3)
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V
r
volume needed to saturate the column (dm3) |
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Keywords: | |
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