misnistry of education and training vietnam academiy of science and technology

Based on the actual demand for Omega-3,6,9 in Vietnam, as well as the need to improve the economic efficiency of Vietnamese basa fish, meeting the high scientific requireme[r]

EDUCATION AND TRAINING SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

LE THI THANH XUAN

SYNTHESIS OF SOME DEEP EUTECTIC SOLVENTS FROM 2-ALKYLBENZIMIDAZOLE, CHOLINE CHLORIDE AND THEIR APPLICATION FOR EXTRACTION OF OMEGA-3,6,9

FROM THE FAT OF VIETNAMESE BASA FISH

HO CHI MINH CITY – 2021

Technology – Vietnam Academy of Science and Technology

Supervisor 1: Ho Son Lam, Asso, Prof Dr

Supervisor 2: Cu Thanh Son, Dr

This dissertation will be defended by the Committee of Dissertation Evaluation at institutional level, at Graduate University of Science and Technology – Vietnam Academy of Science and Technology at… , 2021

This dissertation could be accessed at:

- The library of Graduate University of Science and Technology

- National Library of Vietnam

INTRODUCTION

Fish raising industry, especially that of Vietnamese basa fish,

is under strong development in the Mekong Delta, meeting domestic consumption demand and serving as raw processing materials for export, promoting the development of Vietnam's seafood industry However, we have used Vietnamese basa fish mainly their meat (fillet) for export and primary fats for the domestic market By-products of the processing process such as head, bones, fat, skin have not been utilized effectively but used as a fertilizer or animal feed instead If there is no appropriate treatment, we will not only waste the nutrients contained in it, but also leave them as sources of pollution to the environment

In recent years, in Vietnam, there have been a large number

of studies on the separation of omega compounds by such methods as: Hydrolysis of lipids in alkaline environment and urea precipitation or using the thermal fractionation method at high level… to improve the economic efficiency of the catfish processing However, the projects are only exploratory, without any research work on separating Omega-3,6,9 compounds from the fatty acid mixture of Vietnamese basa fish and fish fat In the world, the Omega-3,6,9 extraction methods available in research and production include chromatographic method, enzyme and distillation method, urea complex precipitation method, super liquid extraction method

Deep eutectic solvents are a newly-generated ionic liquid that can be generated by mixing the appropriate ingredients and then heating them to produce liquid with a lower freezing point than the initial individual ingredients The freezing point lowering is the result

of hydrogen bonding agent interactions Deep eutectic solvents have

special properties such as non-volatility and no vaporized pressure Therefore, they do not pose problems related to fire or explosion, are safe in transport or to the habitat, as well as biodegradability and biocompatibility They can replace toxic solvents, limit environmental pollution, and are able to be recovered and reused They are, therefore, the prioritized elements and used as solvents in extraction techniques

Separation of Omega-3,6,9 from the fatty acid mixture as well as the separation of each type of omega with a green and low-cost solvent system is a common matter concerned by researchers and manufacturers Based on the actual demand for Omega-3,6,9 in Vietnam, as well as the need to improve the economic efficiency of Vietnamese basa fish, meeting the high scientific requirements of separation and enrichment Omega-3,6,9 by using green and

inexpensive solvents, we have proposed the project "Synthesis of some deep eutectic solvents based on 2-alkylbenzimidazole, choline chloride and their application to extract Omega 3,6,9 in Vietnamese basa fish in Mekong Delta” and it was accepted by the Graduate

Academy of Science and Technology as my graduate dissertation

* The goals of the dissertation

- Synthesizing deep eutectic solvents based on choline chloride with the compounds of 2-alkylbenzimidazole / ethylene glycol and determining their structures

- Using synthetic deep eutectic solvents to enrich and separate Omega-3,6,9 from waste fat in accordance with the facrories’ procedure of processing Vietnamese basa fish for export

* The contents of the dissertation

1 Investigating the composition and fatty acid content of Vietnamese basa fish by traditional solvents and building the fatty acid separation process from the by-products gained from the Vietnamese basa fish fillet processing stages

2 Experimenting and synthesizing Deep Eutectic Solvent by using:

- Choline chloride with urea and isoforms (methylurea, thiourea and methylthiourea) to determine their properties

- 2-Alkylbenzimidazole (2-pentylbenzimidazole, zimidazole, 2-octylbenzimidazole, 2-nonylbenzimidazole), and creating

2-heptylben-a deep eutectice solvent system ethylene glycol / 2-2-heptylben-alkylbenzimid2-heptylben-azole

3 Using the synthetic deep eutectic solvents to separate and enrich Omega-3,6,9 from raw materials

4 Comparing the enrichment and separation of Omega-3,6,9 by the synthesized deep eutectic solvent

* The scientific and practical significance of the dissertation

Finding out a method of separating and enriching Omega-3,6,9 from by-products of Vietnamnese basa fish with deep eutectic solvents for high omega content Making effective use of by-products derived from processing Vietnamese basa fish for export in Mekong Delta

Contributing to enhancing the economic value of fish and protecting the environment This research orientation is quite new and of high academic value because in Vietnam there has been no research on separating and enriching Omega-3,6,9 from fat from the by-products derived from the processing of Vietnamese basa fish for export by deep eutectic solvents

CHAPTER 1 INTRODUCTION 1.1 Brief introduction to ionic liquid

1.2 Deep eutectice solvent – a new generated liquid (DES)

1.2.1 Brief introduction to DES – formation and development

In the early of 20th century, a new ionic liquid system was generated by mixing quaternary ammonium salt (2-hydroxyethyl trimethyl ammonium chloride) with several hydrogen-bonding agents such as amide, glycol or carboxylic acid (mono- diacid) They form a solvent capable of dissolving several salts and metal oxides, which is also of low cost and easy to recycle or decompose without polluting the environment

This new ionic liquid is called DES (deep eutectic solvent) The first publications on this ionic liquid system were done by Abbott and his co-researchers since 2001 To highlight DES's growing interest in green solvents, C Andrew and other researchers sought through the cited database of Web of Science Citation Database for many research works in the field of DES When the compounds making up DES are the main ones, such as amino acids, organic acids, sugars or choline derivatives, DES is known as deep natural eutectic solvents (NADES) In terms of physical and chemical

properties, NADES fully feature the green chemical principles

1.2.2 Scientific background of DES

According to Abbott [64], when a solid organic salt and a complex agent are mixed in the right ratio and heated, they will produce a liquid with a lower freezing point than the initial individual ingredients In addition, the temperature of the eutectic mixture was below the boiling point of water Lower freezing point is a result of

hydrogen bonding interaction between the complexing agent and the organic salt Hydrogen bond is a very weak bond formed by electrostatic attraction between hydrogen (bonded in a molecule) and

a strong electronegative atom of small size (N, O, F .) in another molecule or in the same molecule Hydrogen bonds can be formed between molecules or within the same molecule

1.3 Introduction to Vietnamese basa fish and the content of Omega-3,6,9 in the fish

1.3.1 Introduction to Vietnamese bas fish

1.3.2 Potentialities of Vietnamese basa fish and content of omega

in the fish

1.4 Economic values and application of Omega-3,6,9 in our lives

1.4.1 Research works on the pharmaceautical values of omega to human beings

precipitate to obtain fatty acids including saturated fatty acids and unsaturated fatty acids with omega content of 24,5% [111] There are also authors [112] using traditional solvents to extract omega from Vietnamese basa fish fat and performing transesterification to analyze and determine their composition In general, these claims are only exploratory, there is no research on separating Omega-3,6,9 compounds from the fatty acid mixture of Vietnamese basa fish by deep eutectic solvents

CHAPTER 2 EXPERIMENTAL PROCIDURES 2.1 Chemical elements, raw materials and experimental tools 2.2 Preparation of Vietnamese basa fish

2.2.1 The procedure of material processing

Raw materials of Vietnamese basa fish collected from seafood processing factories in Dong Thap were washed and drained Then the fish were cut by following the process by export seafood factories and 3 parts were obtained, including primary fat, meat (fillets) and the rest (skin, head, body, organs .) which were described as the by-products in the table We performed three times

of fish cutting procedures to determine the average weight

Table 2.2 Components of Vietnamese basa fish at the first stage of process

No Components Weight

(gam)

Percentage (%)

Weight (gam)

Percentage (%)

2.2.2 The methods of fat extraction from the by-products

The by-products were added with water and boiled for 60 minutes, then they were allowed to cool and cooled The fat obtained from the by-product was separated and put under serial extraction times with the n-hexane-methanol solvent system

Methylation: The jelly obtained after extraction was methylated with methanol and concentrated sulfuaric acid was used

as catalyst with the ratio of extracts/Methanol/Catalytic 50gam/ 100gam/1gam The esterification was carried out in a 200 ml glass flask, with reflux condenser attached for 3 hours under stirring condition and heated to 60 °C by magnetic equipment The product was vacuum-evaporated at 35 °C to remove excess methanol, then washed several times with distilled water and anhydrousized with

Na2SO4 Samples were analyzed by GC/FID to determine the chemical composition and kept intact for later Omega-3,6,9 separation studies

2.3 The Deep Eutectic solvents we synthezied and used for the dissertation

The deep eutectic solvents synthesized for enriching and separating Omega-3,6,9 from the fat extracted from by-products in Vietnam basa fish are introduced in the table below

Table 2.3 The ratio of DES weight

Methanol/Urea (Sample 1, Sample 2, Sample 3,

2.4 Synthesis of DES on the basis of choline chloride / urea and congeners

The method of synthesizing DES liquid based on choline chloride was done as follows: Choline chloride and urea were put into a heat-resistant glass beaker placed on a heated magnetic stirrer

in the ratio 1:1, 2:1 and 1:2 by mass and was heated at 60-70 °C with stirring until a homogeneous liquid was obtained Experiments showed that only samples with choline chloride / urea mass ratio 1:1 and 2:1, remained liquid after cooling The 1:2 (more urea) sample was recrystallized Therefore, we only used samples with 1:1 ratio in follow-up studies for urea isomers of methylurea, thiourea, methylthiourea (general ratio 1:1)

2.5 Synthesis of 2-alkylbenzimidazole and DES (ethylene glycol/ benzimidazole)

2.5.1 Synthesis of 2-alkylbenzimidazole and DES (ethylene glycol/

benzimidazole)

The reaction was performed between o-phenylenediamine and carboxylic acid in a ratio of 1:2 The amount of catalyst applied

Choline chloride/methylthiourea (Ch/MThi) 1:1

Ethylene glycol/ 2-pentylbenzimidazole (EG/Benz-C5) 10:1,5

Ethylene glycol/ 2-heptylbenzimidazole (EG/Benz-C7) 10:1,5

Ethylene glycol/ 2-octylbenzimidazole (EG/Benz-C8) 10:1,5

Ethylene glycol/ 2-nonylbenzimidazole (EG/Benz-C9) 10:1,5

was 10% by weight of the substances involved in the reaction A stream of argon gas was to expel the air from the reaction vessel The reaction was done at a pressure of 6-8 atm, temperature 180 oC with magnetic stirrer

2.5.2 Combination of ethylene glycol with alkylbenzimidazole to form the DES system

The ethylenglycol / alkylbenzimidazole solvent system at the rate of 10-25 grams / 100 ml of ethylenglycol has been preliminarily tested Results showed that there was not much difference in their capacity of omega separation and enrichment However, the capacity to recover alkylbenzimidazole at the rate of 15grams / 100ml ethylenglycol was the best The loss of alkylbenzimidazole was less than 10%

2.6 Methods of analyzing the chemical composition of raw materials and products

2.6.1 Analysis of omega compounds by GC-FID method

2.6.2 The methods of structural analysis of DES: FTIR, GC / MS,

2.7.1 Equipment and techniques for separating Omega-3,6,9 from acids

Methyl esters of fatty acids, methanol, DES were placed in a reaction vessel with continuous stirring and were heated at 45 °C When the mixture became homogenous, they were allowed cool and then were cooled at 4 °C for 8 hours The resulting mixture forms two

layers: the upper layer was a liquid, the lower layer was a solid The solid was then washed by cold methanol This wash solution was mixed with the original liquid layer, and let it evaporate the methanol

in a vacuum evaporator and then anhydrousized

2.7.2 The proportion of substances involved in the reactions for omega separation

CHAPTER 3 FINDINGS AND DISCUSSIONS 3.1 Findings on the acid extraction from different parts of the basa fish

3.1.1 Findings on the extraction of primary fat

3.1.2 Findings on the extraction of fillets

3.1.3 Findings on the fat extraction from the by-products of Vietnamese basa fish

1029 grams of by-products obtained after filling the Vietnamese basa fish according to the process of the export seafood factores were added with water for cooking and cooling, then 86,11 grams of floating fat (accounting for 8,37% from total by-products) were obtained Similar to catfish, 1334 grams of by-products, 163 grams of floating fat were obtained, accounting for 12,22%

Table 3.3 Findings on the fat extraction from the by-products

No Obtained elements catfish

(gam)

basa fish (gam)

19,8% and were equally compared The by-products that cannot be exported accounted for a large propotion of 59-61% After treatment, the fat recovered from catfish’ by-products were 12,22%, while that of basa fish fish were 8,37% The amount of fatty acid obtained from the fat

of catfish were 94,29% while that of Vietnamese basa fish were 87,49%

3.2 Findings on the analysis and identification of the compounds extracted from Vietnamese basa fish

3.2.1 Findings on the analysis and identification of the primary fit 3.2.2 Findings on the analysis and identification of fat from the fillets 3.2.3 Findings on the analysis and identification of the fat from the by-products

Table 3.6 Components of fat extracted from the by-products

No Fat extracted from by product catfish

(gam)

basa fish (gam)

3.2.4 Conclusions on the raw materials

The content of Omega-3,6,9 compounds in catfish and basa fish parts were quite high, especially Omega-3 and Omega-6

Furthermore, the by-products of these two fish contain many omega fatty acid compounds

3.2.5 Methyl ester of the raw materials (fat from the by-products)

The jelly of fatty acids was esterified to convert to methyl ester (methanol / fatty acid = 3/1, at the temperature 65 oC, in 3 hours under strong stirring conditions)

Table 3.10 The contents of the compounds before and after esterification

No Fatty acid Extracted jelly

(%)

Methyl ester (%)

of separation and enrichment of Omega-3,6,9 when using synthetic ionic liquids

Table 3.11 The chemical components of fatty acids in methyl ester

Classification Name of compounds Methyl ester (%)

Eicosapentaenoic acid (EPA) 20:5 (n-3) 0,42

Docosahexaenoic acid (DHA) 22:6 (n-3) và

Omega-6

γ-Linolenic acid (GLA) 18:3 (n-6) 1,05

Eicosatrienoic acid 20:3 (n-6) 0,18

Arachidonic acid (AA) 20:4 (n-6) 0,48

3.3.1 The findings on FTIR and TGA analysis

3.3.1.1 Choline chloride with urea

FTIR νmax (KBr) cm-1: of urea 3352, 3442 cm-1 (NH), 1667

cm-1 (C = O) of amide, 1457 cm-1 (CN), of choline chloride 3376 cm-1

(OH), 3019, 2956 and 2907 cm-1 (-CH2, -CH3), 1087, 1347, 1478 cm-1

of (CO), 1643, 1206 cm-1 (CN), of choline chloride/urea all have gravels to absorb urea and choline chloride, respectively However, the NH2 double tip of the urea has changed to a single tip because the

NH2 group hydrogen bonds to hydrogen bonding with the Cl- anion,

so this signal changed In addition, the wave number of the OH group