The Purification Of La From Fermentation Broth Biology Essay

Published:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Lactic acid (LA) is an important chemical that can be used to synthesize biodegradable polymers, such as polylactic acid. The purification of LA from fermentation broth was studied by esterification and hydrolysis method. Conversion of LA into esters and subsequent hydrolysis of the purified ester into lactic acid is widely accepted way to obtain high pure lactic acid. For an example, Zhao et al. (2009) reported the lactic acid recovery from fermentation broth of kitchen garbage by esterification and hydrolysis method. The results found that the esterification yield of ammonium lactate could reach 96% and pure LA was hydrolyzed from the obtained butyl lactate in presence of a cation-exchange resin in the H form as a catalyst. Furthermore, Sun et al. (2006) researched the purification method of LA using two reactors with a rectifying column carried out recovery of LA from fermentation broth. Ammonium lactate which obtained by fermentation was directly to produce butyl lactate by reacting with butanol for 6 h, and the esterification yield of ammonium lactate was 87.7%. Then butyl lactate was reactified, and the purified butyl lactate was sequentially hydrolyzed into LA in presences of the cation exchange resin in the H form as a catalyst for 4 h, and the hydrolysis yield was 89.7% and the purity of recovery LA was 90%.

TABLE OF CONTENTS

Page

TABLE OF CONTENTS i

LIST OF TABLES ii

LIST OF FIGURES iii

INTRODUCTION 1

LACTIC ACID 2

ESTERIFICATION AND HYDROLYSIS METHOD 5

CONCLUSION 15

LITERATURE CITED 16

LIST OF TABLES

Table Page

Physical properties of lactic acid 3

LIST OF FIGURES

Figure Page

L-lactic acid and D-lactic acid 2

Diagram of commercial uses and applications of lactic acid 4

The diagram of lactic acid extraction from fermentation broth 5

The schematic diagram of the apparatus for esterification 7

and rectification (a) and for hydrolysis (b)

(a) The time profiles of the esterification yield 8

(b) The time profiles of the hydrolysis yield 9

The effects of initial concentrations of NH4LA 10

on the esterification yield

(a) The effects of catalyst on the esterification yield 11

(b) The effects of catalyst on hydrolysis yield

(a) The effects of catalyst concentration on esterification yield 12

(b) The effects of catalyst concentration on hydrolysis yield

LIST OF FIGURES

Figure Page

The effects of different catalyst on esterification yield of NH4LA 13

The time profiles of esterification yield and temperature 14

of NH4LA in the fermentation broth

The effect of catalyst on hydrolysis yield 14

PURIFICATION OF LACTIC ACID FROM FERMENTATION BROTH BY ESTERIFICATION AND HYDROLYSIS METHOD

Introduction

Lactic acid (LA) is a hydroxycarboxylic acid, which is widely used in food, pharmaceutical, leather, cosmetic and textile industries. It can be polymerized to biodegradable and biocompatible plastic, i.e. polylactic acid, which has environment-friendly and great potential for replacing petrochemical plastic. Industrially, it can be produced by either chemical synthesis or microbial fermentation. Presently, approximately 90% of lactic acid was produced by lactic acid bacteria fermentation. Fermentative production has the advantage that by choosing a strain of LA bacteria (LAB) producing only one of the isomer and optically pure product. For recovery and purification of lactic acid from fermentation broth have several methods such as solvent extraction, adsorption, ion exchange, direct distillation, electrodialysis, membrane separation and esterification and hydrolysis. The esterification and hydrolysis method is widely accepted way to recovery and purify because using this method can obtain high pure lactic acid. Therefore, the use of the esterification and hydrolysis method become thus of special interest for purify of lactic acid from fermentation broth.

Lactic acid

Lactic acid (2-hydroxy propionic acid) is a chemical compound that has a role in several biochemical processes. It is a carboxylic acid with a chemical formula of C3H6O3. Lactic acid is chiral and has two optical isomers as shown in Figure 1.

COOH COOH

HO C H H C OH

CH3 CH3

L (+)-lactic acid D (-)-lactic acid

Figure 1 L-lactic acid and D-lactic acid

Source: Ratledge and Kristiansen (2001)

Lactic acid is organic solvent that can dissolve in water but insoluble in other organic solvents. Other properties of lactic acid are presented in Table 1.

Table 1 Physical properties of lactic acid

Parameter

Chemical formula

C3H6O3

Molecular weight

90.08

Acidity (pKa)

3.85

Melting point

L : 53 °C

D : 53 °C

D/L : 16.8 °C

Boiling point

82 °C at 0.5 mm Hg

122 °C at 14 mm Hg

Dissociation constant, Ka at 25 ° C

1.37 x 10-4

Heat of combustion, Hc

1361 KJ/mole

Specific Heat, Cp at 20 ° C

190 J/mole/ °C

Source: Vickroy (1985)

Lactic acid can be produced by chemical synthesis or microbial fermentation. The chemical synthesis produced a racemic mixture of D, L lactic acid. Presently, about 90% of lactic acid made by LAB fermentation and the remainder is produced synthetically by the hydrolysis of lactonitrile. The advantage of fermentation technologies is possible to use renewable resources as substrates, such as starch and cellulose in fermentative production. In Figure 2 described the diagram of commercial uses and applications of lactic acid. Food applications reported for approximately 85% of the total lactic acid, while the nonfood industrial applications reported for only 15% of the demand.

Figure 2 Diagram of commercial uses and applications of lactic acid

Source: Wee et al. (2006)

Recovery and purification of lactic acid

Esterification and hydrolysis method

For recovery and purification of lactic acid from fermentation broth have several methods such as solvent extraction, adsorption, ion exchange, direct distillation, electrodialysis, membrane separation and esterification and hydrolysis. The esterification and hydrolysis method is widely accepted way to recovery and purify because using this method can obtain high pure lactic acid.

Figure 3 The diagram of lactic acid extraction from fermentation broth

Source: Sun et al. (2006)

The recovery process of lactic acid is shown in Figure 3. Lactate ester was produced by esterification of lactic acid or ammonium lactate in fermentation broth with the butanol. Then the purified lactate ester was hydrolyzed with water to lactic acid.

Two reactions are concerned in purification of lactic acid by esterification and hydrolysis method. They are as follows:

Esterification reaction

Ammonium lactate + butanol butyl lactate + water + ammonia

Hydrolysis reaction

Butyl lactate + water lactic acid + butanol

Sun et al. (2006) reported the extraction and purification of lactic acid from fermentation broth by esterification and hydrolysis method. To recovery of lactic acid from fermentation broth with a high yield, the effect of initial concentration of ammonium lactate, rectifying column and concentration of catalyst were investigate. The schematic diagram of the apparatus for esterification and hydrolysis method shown in Figure 4

Figure 4 The schematic diagram of the apparatus for esterification and rectification (a) and for hydrolysis (b)

Source: Sun et al. (2006)

The concentrated fermentation broth and butanol were placed into reactor equipped with a rectifying column. The apparatus for esterification and rectification is shown in Figure 4a. Lactic acid or ammonium lactate and butanol reacted to form the butyl lactate. Then, the purified butyl lactate was hydrolyzed with water to lactic acid. The apparatus for hydrolysis is shown in Figure 4b.

The effect of the rectifying column on the esterification yield and hydrolysis yield are shown in Figure 5a and 5b, respectively.

Figure 5a The time profiles of the esterification yield (condition: initial concentration of NH4LA was 30 wt. %, catalytic concentration for esterification was 1.5 wt. %, and the molar ratio of butanol to NH4LA was 3:1)

with rectifying column without rectifying column

Source: Sun et al. (2006)

In Figure 5a, indicates that the esterification yield of NH4LA was higher in the reactor with a rectifying column than that in the reactor without a rectifying column. The esterification yield after 6 h increased to 87.7 %. However, the esterification yield in the reactor without a rectifying column was only 72 % within 8 h.

Figure 5b The time profiles of the hydrolysis yield (condition: catalytic concentration for hydrolysis was 2.5 wt. %, and the molar ratio of water to butyl lactate was 15:1)

with rectifying column without rectifying column

Source: Sun et al. (2006)

In Figure 5b, indicates a similar trend of a hydrolysis yield and the maximal value was 89.7 % after 4 h in the reactor with a rectifying column and 75 % after 6 h in the reactor without a rectifying column, respectively. It could be described that though the use of the rectifying column, the content of water in the overhead phase was increased and the separation of water from the reaction system became faster, which resulted in increase of esterification and hydrolysis efficiency.

The effect of different initial concentration of NH4LA on the esterification yield is presented in Figure 6.

Figure 6 The effects of initial concentrations of NH4LA on the esterification yield (condition: esterification time 6 h, catalytic concentration for esterification was 1.5 wt. %, and the molar ratio of butanol to NH4LA was 3:1)

Source: Sun et al. (2006)

In Figure 6, when the initial concentration was lower than 30 wt. %, the esterification yield was increase with the increase of the initial concentration. However, the initial concentration was more than 30 wt. %, the esterification yield was not increased. Therefore, the initial concentration can be determined to be 30 wt. %.

In order to eliminate catalytic corrosion of a reactor, the cation exchange resin that was modified by SnCl2 was used as catalyst for the esterification reaction. The effect of catalysts on the esterification yield is shown in Figure 7a. It can be observed that the catalytic activity of modified resin is better than that of the unmodified resin. When there was no catalyst in the reactor, the esterification yield was lowest.

Figure 7a The effects of catalyst on the esterification yield (condition: esterification time 6 h, initial concentration of NH4LA was 30 wt. %, catalytic concentration for esterification was 1.5 wt. %, and the molar ratio of butanol to NH4LA was 3:1)

modified resin unmodified resin without catalyst

Source: Sun et al. (2006)

Figure 7b The effects of catalyst on hydrolysis yield (condition: hydrolysis time 4 h, catalytic concentration for hydrolysis was 2.5 wt. %, and the molar ratio of water to butyl lactate was 15:1)

Cation resin in the H+ form without catalyst

Source: Sun et al. (2006)

For this hydrolysis reaction, the effect of catalyst on hydrolysis yield is shown in Figure 7b. Comparing two hydrolysis time curves could find that the cation exchange resin in the H+ form has higher catalytic activity for hydrolyzing butyl lactate and can increase the hydrolysis reaction rate. When the hydrolysis time was over 4 h, the hydrolysis yield did not change much.

Figure 8 (a) The effects of catalyst concentration on esterification yield (condition: esterification time 6 h, initial concentration of NH4LA was 30 wt. %, and the molar ratio of butanol to NH4LA was 3:1)

(b) The effects of catalyst concentration on hydrolysis yield (condition: hydrolysis time 4 h and the molar ratio of water to butyl lactate was 15:1)

Source: Sun et al. (2006)

The effect of catalytic concentration on the esterification yield and hydrolysis yield are described in Figure 8. In the esterification reaction shown in Figure 8a, the catalytic concentration increased, the esterification yield became high and at the concentration around 1.5 wt. % the esterification yield was highest. However, the esterification yield decreased when the concentration was over 1.5 wt. %. In Figure 8b, indicated a similar trend of hydrolysis yield. The hydrolysis yield was highest, when the catalytic concentration was increased to 2.5 wt. %.

Zhao et al. (2009) determined lactic acid recovery from fermentation broth of kitchen garbage by esterification and hydrolysis method. The kitchen garbage was used as substrate in lactic acid fermentation. The esterification of NH4LA with the butanol to produce butyl lactate and hydrolysis of butyl lactate into lactic acid were investigated.

The catalyst of cation exchange resin modified by FeCl3 was used in esterification method. The effect of catalysts on the esterification yield is shown in Figure 9.

Figure 9 The effects of different catalyst on esterification yield of NH4LA

Source: Zhao et al. (2009)

In Figure 9, the catalytic activity of the modified cation exchange resin was better than that of either unmodified resin or FeCl3. It could be described that reacted FeCl3 with a sulfonate structure of the resin to form a new acidic catalytic center. Therefore, the catalytic activity of resin had been improved obviously.

Figure 10 The time profiles of esterification yield and temperature of NH4LA in the fermentation broth

Source: Zhao et al. (2009)

The esterification yield of NH4LA in the fermentation broth is shown in Figure 10. The esterification yield of NH4LA in the kitchen garbage fermentation broth was 82 % at 6 h. When the time was increased, the esterification yield did not change much.

Figure 11 The effect of catalyst on hydrolysis yield (condition: hydrolysis time 4 h, catalytic concentration was 2.5 wt. %, and the molar ratio of water to butyl lactate was 15:1)

Source: Zhao et al. (2009)

For this hydrolysis reaction, the cation exchange resin in H+ form was used as a catalyst. The effect of catalyst was shown in Figure 11. It shown that the cation exchange resin in H+ form had higher catalytic activity for hydrolyzing butyl lactate and could increase the hydrolysis yield by comparing two hydrolysis time histograms. When the hydrolysis time was over 4 h, the hydrolysis yield did not increase.

Conclusions

For recovery and purification of lactic acid from fermentation broth have several methods such as solvent extraction, adsorption, ion exchange, direct distillation, electrodialysis, membrane separation and esterification and hydrolysis. The purification of LA from fermentation broth by esterification and hydrolysis method, conversion of lactic acid into esters and subsequent hydrolysis of the purified ester into lactic acid is widely accepted way to obtain high pure lactic acid. The use of rectifying column, the esterification and hydrolysis efficiency could be increased.

LITERATURE CITED

Ratledge, C. and B. Kristiansen. 2001. Basic Biotechnology. 2nd ed. Cambridge.

Sun, X., Q. Wang, W. Zhao, H. Ma and K. Sakata. 2006. Extraction and purification of lactic acid from fermentation broth by esterification and hydrolysis method. J. Sep. Purif. Technol. 49: 43-48.

VickRoy, T.B. 1985. Lactic acid, pp. 761-776. In: Blanch, H.W., S. Drew and D.I.C.

Wang eds. Comprehensive Biotechnol. Vol. 3. Pergamon Press, Oxford.

Wee, Y.J., J.N. Kim and H.W. Ryu. 2006. Biotechnological production of lactic acid

and its recent applications. Food Technol. Biotechnol. 44(2): 163-172.

Zhao, W., X. Sun, Q. Wang, H. Ma and Y. Teng. 2009. Lactic acid recovery from fermentation broth of kitchen garbage by esterification and hydrolysis method. Biomass. Bioenerg. 33: 21-25.

Writing Services

Essay Writing
Service

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing
Service

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision
Service

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.