Development in Vanillin Production Technology

1 Preface

Vanillin, scientific name 3 - methoxy - 4 - hydroxybenzaldehyde, white or light yellow needle or crystalline powder, melting point 82 ~ 83 ℃, with vanillin's characteristic sweet aroma, widely used in food, cosmetics, tobacco, medicine and other industries. It is the world's largest production of synthetic spices, widely used as fragrance, flavoring agent, used in flavors and fragrances cosmetics and food, beverage, tobacco industry, but also an important intermediate of synthetic drugs and other spices.

At present, there are dozens of foreign vanillin manufacturers, mainly Rhodia, Takasago, UBE, IFF, Monsanto, etc., with a total production capacity of 35 kt/a, mainly adopting glyoxylate and lignin method, of which more than 70% adopts guaiacol-glyoxylate method. There are about 30 domestic manufacturers of vanillin, most of them are small in scale, with production capacity of more than 1,000 tons, such as Jihua Auxiliary Plant, Zhejiang Jiaxing Zhonghua Chemical Group, Shanghai Jiahua Fine Chemical Company, Shanghai Xinhua Spice Factory, Zhejiang Xuebao Fine Chemical Company, etc., and the guaiacol-nitroso method is the main production method. [1] The production method is mainly guaiacol-nitroso method.

2 Overview of the production process

There are various methods for the synthesis of vanillin, which can be divided into guaiacol, lignin, safrole, eugenol, p-hydroxybenzaldehyde, 4-methylguaiacol, p-cresol, microbial method and so on, which are summarized as follows:

2 . 1 Guaiacol method

The scientific name of guaiacol is o-methoxyphenol. There are two main routes for the synthesis of vanillin from guaiacol:

2 . 1 . 1 Nitroso route

It is produced by condensation, oxidation and hydrolysis of guaiacol, urotropin and p-nitrosodimethylbenzene as raw materials.

The separation process of this route is complicated, the reaction efficiency is low, the production yield is about 57%, the three wastes are serious, the production of 1 t vanillin produces about 20 t of wastewater (containing phenols, alcohols and aromatic amines, nitrites), which is difficult to treat, and there are another 1 ~ 2 t of solid slag. ［This process has been eliminated in foreign countries, but it is still the main production method in China, and domestic manufacturers with large production scale are still using this method.

2. 1. 2 Glyoxalate synthesis route

Guaiacol is condensed with glyoxalic acid to 3-methoxy-4-hydroxyphenylglycolic acid under alkaline condition, and then oxidized under catalyst to get the crude product, and then purified to get vanillin: the process of vanillin synthesized by guaiacol and glyoxalic acid produces less three wastes, and the post-processing is convenient, and the yield can reach 70%, which is the most commonly used method in foreign countries nowadays. 70%, is the most commonly used method in foreign countries, more than 70% of the output of vanillin is produced by this method, such as Rhodia adopts this method, the production capacity of the company is 6 kt/a. At present, there are only a few manufacturers adopting this method in our country, the main reason is that the price of the domestic production of glyoxalic acid is comparatively high, and some key technological problems have not yet been solved, such as the reuse of wastewater (about 20t wastewater is generated by 1t vanillin), the production of the product (about 20t wastewater), and the production of the product (about 20t wastewater). Some key technical problems have not been solved, such as wastewater reuse (1 t of vanillin produces about 20 t of wastewater), product yield and other issues have not been well solved. [2] This method is mainly adopted by Snow Leopard Group, Wuxi Central Asia Chemical Company Limited, Tianjin Northern Spice Factory and Taixing Organic Chemical Factory in China.

Guaiacol method is the most important synthesis route for vanillin at present. Almost all of the foreign countries adopt the route of glyoxalate, while the old process of nitrite method is still mainly used in China, but many domestic manufacturers, such as Jihua Company and Zhonghua Chemical Industry Group, are in the process of changing the original process to glyoxalate method.

In addition, foreign countries have developed trichloroacetaldehyde method (India), the yield is about 60%; chloroform method, the yield is about 39% [3], as well as electrolytic oxidation method, the yield can reach more than 90%, and low pollution, less power consumption. [4] But there is no report of large-scale industrialized production.

2.2 Lignin method

Lignin is contained in fiber materials and pulp waste streams, mainly in the form of lignosulfonates. The paper industry produces about 7 m3 of waste liquid per ton of sulphated pulp, of which about 200 kg of lignosulfonate is contained.

Vanillin is synthesized by hydrolysis of lignosulfonate in alkaline medium and then oxidized to obtain vanillin.

This method has a wide source of raw materials, a long history of production, low cost of raw materials, and full use of waste materials, but the yield is low, only 10% ~ 15%, and the pollution problem is serious, and it is reported that every 1 t of vanillin production produces nearly 150 t of wastewater, so many countries, including the U.S., have been phasing out this route. ［However, due to the low cost of raw materials and the utilization of paper waste liquid, there is still a potential to continue the research of this method.

2.3 Eugenol method

The content of eugenol in clove oil is about 85% ~ 90%. The synthesis methods can be divided into three: direct oxidation, indirect oxidation and electrochemical oxidation. The direct oxidation method is generally used in industry: eugenol is isomerized to isoeugenol by co-heating with strong alkali, and then isoeugenol is oxidized by ozone or nitrobenzene.

The aroma of vanillin produced by this process is better, but the source of raw materials is difficult, the production cost is high, and the yield of the product is about 60%, only a few factories adopt this process at present, and the overall output is small. There are only a few factories adopting this process and the overall output is very small. Domestic manufacturers mainly include Shanghai Research Institute of Spices of China Light Industry Council. Electrochemical oxidation method can reach 74.5%, but the cost is high, [1]. 5%, but the cost is high, [6] no industrialized production has not been reported.

2.4 Safrole method

The raw material of safrole (from natural safrole oil) is converted to isosafrole by alkali treatment, oxidized to piperonal, then made into protocatechuic aldehyde, and finally obtained vanillin by dimethyl sulfate methylation.

The main problems with this process are the shortage of raw materials, the high cost (but lower than the eugenol method), the complexity of the process, and the formation of isovanillin in the product, which is difficult to remove. It was first used by Takasago in Japan, but there are very few manufacturers using this process today.

2.5 p-Hydroxybenzaldehyde method

Vanillin is obtained from p-hydroxybenzaldehyde by bromination and then methoxylation. In the past, DMF was used as the solvent for the methylation reaction, which was expensive and not easy to be recovered, but now it has been improved to use methanol as the solvent in the presence of basic copper carbonate as the catalyst and a small amount of DMF, and the total yield can reach 85% [4]. This process route is easy to obtain raw materials, simple operation, few steps, high yield; but the price of raw materials is high. According to the current price of synthesized vanillin, this process has no practical significance for production. There is no report on the domestic manufacturers directly adopting this process to produce vanillin. However, the production of p-hydroxybenzaldehyde in China is increasing year by year, and the price is decreasing year by year, so this method still has the value of utilization.

2.6 4-Methylguaiacol method

4-Methylguaiacol is present in the light component of pine tar, a forestry by-product, under the scientific name p-methyl-o-methoxyphenol. It is produced by dissolving 4-methylguaiacol in a solvent and oxidizing it directly to obtain vanillin.

This process has only one reaction step, the reaction conversion rate can be up to 96%, the process route is short, the total yield is high (> 75%), the post-treatment is simple, the three wastes produced are very small, 1 t of the product produces about 3 t of wastewater, the treatment capacity is small.

The products have pure aroma and are exported to Europe and America. This process is newly developed in recent years and has applied for a national invention patent, [10] the disadvantage is that there are few sources of raw materials. At present, only Fujian Yongan Forestry Co., Ltd. adopts this process.

2.7 P-cresol method

There are generally two routes to p-cresol, one is to use p-cresol as raw material, through oxidation, monobromination and methoxylation, which is actually an extension of the p-hydroxybenzaldehyde method. This route is simple to operate, the first step of the reaction yield reached 91%, and can be directly used in the next step of the synthesis without separation, the total yield can reach 85%. ［The total yield can reach 85%.]

Another route is the chlorination of cresols, followed by the interaction with sodium methanol and the final oxidation of vanillin. The reaction yield of this route is not as good as the former one. Cresol synthesis route is a relatively new synthesis method, which has been researched more in China, and China is rich in cresol resources, so this method has a better development prospect. At present, there is no report on the large-scale production of cresol by this method at home and abroad.

2.8 Microbiological methods

In a medium containing organic phosphates, ferulic acid or sodium ferulate is added and actinomycetes are immobilized to biotransform vanillin. [4] In the USA, a two-step technology for the preparation of vanillin from glucose has been developed and is expected to be industrialized in the near future. [1] Rhodia has invested heavily in research on biofermentation technologies to develop a new process for the production of vanillin and ethyl-vanillin as an alternative to the chemical production of vanillin.   The development of this process route is of great strategic significance and development prospects.

3 Vanillin Product Characteristics and Market Overview

There are various methods for the production of vanillin, and the above production routes of vanillin have their own advantages and disadvantages. Among the total synthesized methods, guaiacol and lignin are lower in production cost, but the products of the lignin method contain more heavy metals, which cannot be used in the food and pharmaceutical industries. Safrole, eugenol and 4-methyl-guaiacol are semi-synthetic methods, the raw materials come from natural plant extracts, the cost is high and they are natural grade products. Because safrole is harmful to human body and isosafrole is difficult to be removed from the products, which affects the aroma, the products of safrole method are generally not used in food and cosmetics. From the point of view of the quality of product aroma, eugenol and 4 a methyl guaiacol method is better, generally used in high and middle grade incense raw materials. 

In 2000, the demand of vanillin in the world was about 12 kt, and the main consuming countries were the USA, EU, Japan and China. At present, the annual demand of vanillin in China is about 1.2~1.5 kt. China is the main producer and exporter of vanillin, according to the customs statistics, the output of vanillin in China in 2000 is about 4.5 kt, and the export of vanillin is about 3.192 t. With the improvement of people's living standard and the quality of life, which leads to the development of the food industry, the pharmacy industry, the daily chemical industry, it is predicted that the global vanillin demand will increase with the rate of 5%. The global demand for vanillin is expected to increase at a rate of 5%. ［Although the European Union will limit the amount of vanillin added, there is no indication that the production and consumption of vanillin will shrink.

4 Prospect of vanillin production process

The process of preparing vanillin from guaiacol is mature, with a wide source of raw materials, among which the process of glyoxylate method is characterized by easy control, high yield and less pollution, and with the maturity of guaiacol synthesis by phenol method, the price of guaiacol is expected to decrease, which makes this process route more advantageous. Therefore, this process is the development direction for the reform of the old process of vanillin in China.

The production of vanillin from p-cresol is a newly developed process, which has been researched in depth in China. Although it has not yet been put into large-scale application, there will be progress in the near future. Since China is a large coal country with abundant cresol resources, the development of this process route has great strategic significance and development prospects. Eugenol and 4-methylguaiacol, which use natural plant extracts as raw materials, are natural grade products with good aroma and have a certain market in developed countries. This kind of process not only can fully utilize our resources, but also is a good variety for exporting and earning foreign exchange, so this kind of semi-synthetic method still has the need for development. In addition, microbial fermentation, especially the route of producing fermented products from natural raw materials, will be an important topic in the research of vanillin synthesis.

References:

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