Production technology of 1, 3-propylene glycol

1 Introduction

1, 3-propylene glycol, English abbreviation 1,3-PDO, is a colorless, odorless viscous liquid, soluble in water, alcohol, ether and other organic solvents, mainly used in the synthesis of plasticizers, detergents, preservatives, emulsifiers, but also used in food, cosmetics and pharmaceutical industries, its most important use is as a polymer monomer synthesis of excellent polymer materials. 1, 3-propylene glycol can also be used to prepare other saturated polyesters, such as polypropylene glycol naphthalate (PTN) and copolyesters; In addition, it is an important monomer raw material for manufacturing a new polyester fiber with excellent performance, polypropylene terephthalate (PTT), which can replace ethylene glycol and butanediol to produce polyol polyester. Compared with PET(polyethylene terephthalate) and PBT(polybutylene terephthalate), PTT has better performance, both the high performance of PET and the ease of processing of PBT, and has broad application prospects, and is currently a hot spot in the development of new varieties of synthetic fibers. Therefore, the development of low-cost 1, 3-propylene glycol has become a hot issue of concern to scientific researchers.

2, 1, 3-propanediol preparation

2.1 Overview

1, 3-propylene glycol is the basic raw material for the synthesis of polypropylene glycol terephthalate (PTT). PTT is a new type of polyester chemical fiber in the

textile industry, the performance is obviously better than PET and PBT, to overcome the rigidity of PET and the flexibility of PBT, especially it has excellent resilience(elastic recovery can reach 100% when stretched 20%), easy dyeing (can be in the absence of carrier under normal pressure boiling dyeing), stain resistance,wear resistance, low water absorption and good color fastness (UV, ozone, nitrogen oxides), with the advantages of polyester, nylon and even spandex, can make highly fluffy BCF yarn, composite fiber, carpet, elastic fabric, nonwovens, suitable for clothing and a variety of potential uses. As a new type of polyester fiber, the development and production of PTT has attracted the attention of the world’s synthetic fiber industry.

2.2 Preparation method

At present, there are three main production methods of 1, 3-propylene glycol: acrolein process, ethylene oxide process and microbial fermentation. The first two methods have been industrialized, and the latter method is being industrialized by the United States Du Pont(DuPont) company.

2.2.1 Acrolein method

Degussa, a German company, developed an industrial route to produce PDO using acrolein as raw material and applied for a patent. The main steps of its production are as follows:

(1) Acrolein was hydrated to obtain 3-hydroxypropional (HPA)∶

CH2=CHCHO+H2O→HOCH2CH2CHO;

(2)HPA catalytic hydrogenation to obtain PDO:

HPA+H2→HOCH2CH2CH2OH.

To ensure high product yield and quality, several key steps must be strictly controlled. The yield of the product depends on the hydration reaction of acrolein, and the quality of the final product is determined by the hydrogenation effect of HPA. The key technology of this two-step reaction lies in the choice of catalyst.

2.2.2 ethylene oxide method

Shell has successfully developed a new process for small-scale industrial PDO production using the ethylene oxide route, which greatly reduces the cost. The reaction steps are as follows:

(1) Ethylene oxide reacts with CO and H2 carbonyl groups to produce HPA under the action of catalyst.

CH2OCH2+CO+2H2→HPA;

(2) PDO was generated from the separated HPA by catalytic hydrogenation.

HPA+H2→HOCH2CH2CH2OH.

The key of ethylene oxide process is the preparation and selection of catalyst. Shell has done a detailed test on this, and the latest patent shows that the improved cobalt-bisphosphine ligand catalyst and cocatalyst system of ethylene oxide carbonylation to prepare HPA, and then the traditional catalytic hydrogenation method

to produce PDO, the yield is very high, which is the so-called ethylene oxide two-step process. The process conditions are as follows: the ethylene oxide, catalyst,co-catalyst and solvent are placed in an autoclave, heated to the appropriate temperature, CO and H2 are introduced, and the reactant reacts with the catalyst in a tubular reactor, the temperature is 70 ~ 110℃, the pressure is 3.45 ~ 20.7MPa, and the products can be separated by conventional methods.

2.2.3 Microbiological method

DuPont uses carbohydrates such as monosaccharides (such as glucose and fructose) and polysaccharides (such as starch and cellulose) as carbon substrates to prepare 1,3-PDO under appropriate fermentation conditions through contact with a single microorganism of the dehydrase gene. The company has repeatedly claimed that it has made major breakthroughs in technology and will be industrialised in the near future. The production cost of 1,3-PDO is basically the same as that of existing ethylene glycol, which is an important method for the preparation of 1,3-PDO with the lowest production cost and the least pollution. Compared with chemical synthesis, it has the advantages of mild conditions, simple operation, less by-products, low energy consumption and small investment, and is a low-cost green process.

3 Production status of 1, 3-propylene glycol at home and abroad

3.1 Domestic production of 1, 3-propylene glycol

At present, the research and development units of acrolein method in China mainly include Shanghai Petrochemical, Lanzhou Petrochemical, Heilongjiang Petrochemical Research Institute, East China University of Science and Technology, etc. The research and development units of ethylene oxide process mainly include Beijing Chemical Research Institute of Sinopec, Lanzhou Institute of Chemical Sciences, etc. The research and development units of microbial fermentation mainly include Tsinghua University, East China University of Science and Technology, Dalian University of Technology, Shandong University, Jiangnan University,Southeast University, Shenyang Agricultural University, Anhui Keyuan Group and so on. However, the vast majority of research and development units are still in the pilot and pilot stage, and have not realized industrialization. As optimistic about the market prospects of 1, 3-propylene glycol, many domestic enterprises are actively developing 1, 3-propylene glycol projects, mainly Shanghai Petrochemical Co., LTD., Heilongjiang Chenneng Biological Engineering Co., LTD., Henan

Tianguo Group Co., LTD. In 2002, China began to realize the industrial production of 1, 3-propylene glycol, the first production enterprise is Shandong Zouping

Mingxing Chemical Co., LTD., the use of chemical synthesis method, the scale of thousands of tons. In 2004, Heilongjiang Cheneng Biological Engineering Co., Ltd.built a microbial fermentation method of 1, 3-propylene glycol test equipment and put into production for foreign sales. At present, only these two enterprises in China produce and sell 1, 3-propylene glycol.

3.1.1 Acrolein method

A pilot plant for the preparation of 1,3-PDO from acrolein hydration and hydrogenation was established in Shanghai Petrochemical Co., LTD. The hydration was carried out in a fixed bed reactor with cation-exchange resin catalyst, and the conversion rate reached 85% and the selectivity was greater than 90% when the mass fraction of acrolein was 13%-17%.

After hydration, it was hydrogenated in autoclave.

The catalyst was Raney nickel type metal alloy with good activity.

Good selectivity;

Large particles, easy to separate from the reactants;

It can be reused, which significantly reduces the production cost.

Heilongjiang Research Institute of Petroleum and Chemical Industry used acrolein hydrate hydrogenation to prepare 1,3-PDO,

and has also achieved stage research results, and built a 50t/a pilot plant on the basis of laboratory research.

The hydration process was carried out in a fixed bed reactor with a polystyrene chelating ion-exchange resin catalyst at 60℃ under the conditions of 15%-17% acrolein concentration and 1h-1 space velocity.

The conversion rate of acrolein was 83.2% and the selectivity of 3-hydroxypropanal (3-HPA) was 93%. The conversion rate of 3-HPA hydrogenation is 96.6% and the selectivity of 1,3-PDO is 99.6% at 60℃,5.0MPa and 9h-1 feed airspeed. The hydrohydride of acrolein was used as raw material to produce 1,3-PDO in the Petrochemical Research Institute of Lanzhou Petrochemical Company.

The process of acrolein hydration was carried out in a fixed bed reactor filled with ion exchange resin, the space speed was 3 ~ 6h-1, the mass fraction of acrolein was 14.9%, the conversion rate of acrolein was 80.1% at 60℃, and the selection of 3-HPA was made Sex was 87.5%. The hydrated 3-HPA was concentrated and hydrogenated on a 2L autoclave at 45℃ in the first stage, 120℃ in the second stage and 6.0MPa in pressure. Ni-Al alloy was used as Reney nickel catalyst. The conversion rate of 3-HPA was greater than 98.2%, and the hydrogenation selectivity of 1,3-PDO was greater than 99.2%.

3.1.2 ethylene oxide method

Lu Shunfeng et al., Beijing Research Institute of Chemical Industry, Sinopec, put ethylene oxide and syngas into organic solvent, and carried out hydroformylation reaction in the presence of cobalt carbonyl catalyst. Then air or oxygen is introduced to oxidize cobalt carbonyl catalyst to produce cobalt precipitate. The cobalt precipitate and solution were centrifuged, filtered and returned to the reactor for the next reaction. After adding deionized water to the filtrate, the 3-hydroxypropanal aqueous solution was obtained by vacuum distillation. Finally, it is hydrogenated to produce 1, 3-propanediol. This method does not use organophosphine ligand cocatalyst, nor does it need to add various types of hydroformylation reaction accelerators, and the effect is good and the cost is low.

3.1.3 Microbiological method

The production of 1,3-PDO by fermentation with Klebsiella and glucose as auxiliary substrate was studied in Tsinghua University, and it was found that 1,3-PDO

was not produced by fermentation with glucose as substrate alone. When glucose and glycerol were used as mixed substrate, the concentration of bacteria was

significantly increased. Therefore, in the fermentation of glycerol as substrate, the conversion of 1,3-PDO can be increased and the fermentation time can be

shortened by adding glucose as auxiliary substrate. The conversion rate of 1,3-PDO can be up to 64.9% by selecting the appropriate glucose addition rate. In

recent years, Professor Liu Dehua and others from the Institute of Applied Chemistry of Tsinghua University have invented a method to promote microbial

synthesis of 1, 3-propanediol by exogenous addition of bucolic acid, which is suitable for the anaerobic and aerobic fermentation process of 1, 3-propanediol. Its

advantages are: it can accelerate the utilization of glycerol by bacteria, significantly improve the concentration and production intensity of 1, 3-propanediol, and

reduce production costs. In view of the characteristics of a large amount of organic acid (salt) produced by the fermentation process of 1, 3-propylene glycol, they took the lead in the world to introduce electrodialysis desalination technology into the extraction process of 1, 3-propylene glycol, and through the processes of flocculation, concentration and rectification, the purity of the product reached 99.92% and the yield reached more than 80%. The test products were tested in Yizheng Chemical Fiber Company and Liaoyang Petrochemical Company, and the PTT obtained by polymerization of 1, 3-propanediol imported from abroad was compared. The results showed that the key technical indicators of the PTT obtained by polymerization of 1, 3-propanediol pilot products by biological method of Tsinghua University exceeded those of imported products. Xiu Zhilong et al., School of Environment and Life Sciences, Dalian University of Technology, developed a new process to produce 1,3-PDO using corn as raw material through two-step fermentation. They first turned cornstarch into a saccharifying solution; Then the glucose was converted into glycerol by aerobic bacteria such as candida, saccharomyces cerevisiae, zygosaccharomyces conjugatus, Bacillus and Aspergillus.

Anaerobic bacteria such as Klebsiella, Citrobacter and Clostridia were then used to further convert the glycerol to 1,3-PDO. The fermentation liquid obtained in the first step of fermentation can be centrifuged or filtered to remove the bacteria, the clear liquid can be directly entered into the second step of fermentation or concentrated as the batch of the second step of fermentation, and some bacteria can be recycled in continuous fermentation. The fermentation liquid of the first step is also directly subjected to the second step of fermentation without centrifugation and sterilization. On December 19, 2004, Professor Xiu Zhilong presided over the completion of the “microbial fermentation method pilot production of 1, 3-propylene glycol” project through identification, experts at the meeting believed that the project used fermentation and separation technology is obviously innovative, overall in the international advanced level. In 2004, the project was successfully scaled up in a pilot scale of 6,000 T /a at Karamay Petrochemical Company.

3.2 Foreign production of 1, 3-propylene glycol

3.2.1 Acrolein hydrating method

The most patent applications for the hydrohydride of acrolein to prepare 1,3-PDO process are German Degussa Company, followed by German Hoechst company.

The main steps of Degussa’s industrial route to produce 1,3-PDO from acrolein are:

(1) 3-carboxypropionaldehyde prepared from acrolein;

(2) 1,3-PDO was prepared by catalytic hydrogenation of 3-HPA.

The preparation of 3-hydroxypropanal by the hydration of acrolein was first made by using inorganic acid as catalyst, but its yield was low, selectivity was poor,

and side reactions occurred. Acrolein is prone to condensation or polymerization when it meets acid to generate dipropionic acid ether, etc. In order to solve these problems,Degussa company uses weakly acidic ion exchange resin as catalyst to improve the selectivity of 3-HPA, and the conversion and selectivity of acrolein hydration can be greatly improved. In the United States patent, an acidic chelating cation exchange resin containing phosphoric acid -NH-CH2-PO3H2 is proposed as a catalyst. In the range of reaction temperature of 50 ~ 80℃, the conversion rate of lelein can be maintained at 85% ~ 90%, and the selectivity of 3-HPA can reach 80% ~ 85%. Arntz et al.,Degussa Company, adopt weak acid separation The sub-exchange resin was modified with a small amount of sodium, magnesium and aluminum ions, such as the ion-exchange resin catalyst containing 0.53%Na,0.06%Mg and 0.3%Al, and the conversion rate of acrolein reached 88.9% ~90.5% and the 3-HPA selectivity was 80.4% ~ 82.8% in the reactor reaction at 50℃ for 4h. However, after the catalyst was used for 200h, the reaction conversion and selectivity began to decrease, so Degussa company and Hoechst company successively researched and developed inorganic carrier acid catalysts. Degussa Company used TiO2 or r-Al2O3 with a surface area of 50cm2/g as the carrier, impregnated with H3PO4 or NaH2PO4 solution, and obtained the active catalyst with Ti-O-P structure, which was loaded into the fixed-bed reaction device at reaction pressure of 0.1 ~ 2MPa. Under the conditions of reaction temperature 50 ~ 70℃ and feed space speed 0.5h-1, the hydration conversion of acrolein is 50%, and the selectivity of 3-HPA is about 81%. This catalyst system is easy to prepare,stable carrier, high applicable temperature and renewable use. Hoechst company used ZSM-5 molecular siolite as the active component, the catalyst prepared at the concentration of acrolein 18% ~ 19%, reaction temperature 80℃, continuous operation on the fixed bed reaction device for 1500h, the activity of the catalyst

almost unchanged, the average acrolein conversion rate of 44.3%,3-HPA selectivity of 87.7%, such as the concentration of acrolein At 12%, the conversion rate of

acrolein is 46% and the selectivity of 3-HPA is 91.7%. In addition, propionate – triethylamine buffer catalyst can also be used to hydrate the buffer pH=4, the

space velocity of acrolein liquid is 0.5h-1, the acrolein conversion is 45%, and the 3-HPA selectivity is 85%.

3.2.2 Epoxy ethane carbonylation method

The ethylene oxide process of Shell Company in the United States uses ethylene as raw material and oxidizes to ethylene oxide with silver catalyst at 280℃. The

technology is divided into one-step method and two-step method. The one-step method is that the ethylene oxide reacts to produce 1,3-PDO under the condition

of temperature of 90℃ and reaction pressure of 10MPa. In the two-step process, ethylene oxide is carbonated at 85℃, the reaction pressure is 10MPa, and the

catalyst is present. In the preparation process, ethylene oxide, CO and H2 are used as raw materials for hydroformylation to produce 3-hydroxypropanal (3-HPA),

and then 1,3-PDO is prepared by fixed bed catalytic hydrogenation. Major improvements and innovations in the technology published in the patent of Shell

Company in the United States include: ethylene oxide carbonylation catalyst using cobaltous carbon dioxide, without adding expensive phosphine ligand, the

amount of catalyst is reduced to 0.05% to 0.3% of the reaction mixture, so that the catalyst cost is greatly reduced. Using methyl tert-butyl ether as the reaction

solvent, the reaction product and catalyst were easily separated, and the concentration of 3-HPA was increased to more than 35%. By using water extraction of 3-

HPA, the recycling rate of cobalt catalyst can reach 99.6%. By controlling the water content and the concentration of 3-HPA in the carbonylation reaction, the

byproducts with high boiling point are few, and the selectivity of 3-HPA is greater than 90%, which makes the industrialization of this technology possible. Prior to

1999,Degussa was the world’s only producer of 1,3-PDO using the acrolein hydrating process. In the early 1990s, Shell company developed the process of

ethylene oxide carbonylation and hydrogenation to 1,3-PDO, and in December 1999, a 7.2×104t/a production plant was completed and put into operation. At the

same time,DuPont purchased the Degussa acrolein process technology and also built industrial plants.

3.2.3 Microbiological method

The 1,3-PDO process is based on cheap glucose or crude starch (such as cassava flour) as raw material, and 1,3-PDO is prepared by fermentation of original strains or genetically engineered bacteria. DuPont is now a global leader in the development of biological routes. There are two main types of microbial production of 1,3-PDO: DuPont and Genencor International Co., Ltd. have jointly researched and developed the technology of using glucose as substrate to produce 1,3-PDO with genetically engineered bacteria, and have applied for patents worldwide, and it is expected to achieve industrial production in 2010; Research on 1,3-PDO in glycerol biodisproportionation production in China and European countries is very active. So far, all wild strains that have been found to produce 1,3-PDO are glycerin-based bacteria. Over the years, the metabolic pathways and kinetic characteristics of glycerol biodisproportionation have been studied in depth. Under anaerobic conditions, the maximum theoretical material conversion rate of glycerol as the only carbon source is 72%, the auxiliary substrate (such as glucose) can increase the conversion rate of glycerol to 100%, and the final mass concentration of 1,3-PDO in the fermentation liquid can reach 65-70g / L. The anaerobic metabolism of glycerol mainly includes two pathways: oxidative metabolism and reductive metabolism. Microbial cells obtain the necessary substances and energy for growth through the oxidative pathway, while glycerol is catalyzed by glycerol dehydratase (GDHt) associated with vitamin B12 to dehydrate into 3-hydroxypropanal (3-HPA) through the reductive pathway, and further by 1,3-PD connected with NADH O dehydrogenase (PDOR) is reduced to 1,3-PDO.

The physiological significance of this process is to maintain the metabolic balance of NADH, where energy is the key to maintaining GDHt activity, and NADH is the driving force for the reduction of 3-HPA to 1,3-PDO. Changes in ATP, NADH and enzyme activity can cause changes in metabolic flow and affect the yield of 1,3-PDO. At present, China has completed the pilot study of glycerol fermentation to produce 1,3-PDO, and is transitioning to industrial test. Due to the high price of pure glycerol, the use of crude glycerol as a raw material will effectively reduce the cost, so that microbial fermentation to produce 1,3-PDO has stronger advantages and market competition compared with chemical methods in terms of production conditions, cost and environmental protection Force. DuPont says the cost of producing 1, 3-propylene glycol using biotechnology is close to that of the monomer EG used in PET. Microbial fermentation method shows its bright prospects for development because of its easy availability of raw materials, utilization of renewable resources and environmental friendliness. It can be expected that with the enhancement of people’s environmental awareness and the risk of depletion of one-time resources, the production of 1, 3-propylene glycol by biological conversion method will increasingly show its strong development momentum compared with chemical method.

4 Domestic and foreign market conditions of 1, 3-propylene glycol

In 2001, the production capacity of 1, 3-propylene glycol in the world was about 14×104t/a, and the manufacturers were only Shell Corporation, DuPont

Corporation and Degussa Company of Germany. In 2001, the world demand for PTT was about 20×104t, and the demand for 1, 3-propylene glycol was 7.2×104t.

According to Shell, by 2010, including non-fiber applications, the world’s annual demand for PTT will reach 100×104t, requiring 1, 3-propylene glycol 36×104t.

Nearly 45% are used in carpets and more than 50% are used in other textile fields. Industry experts pointed out that PTT fiber will be a new type of fiber focused on the development of the 21st century, and will become one of the most popular fiber varieties. According to Fiber News, the Ministry of Commerce, Industry and Energy of Korea plans to invest 199×108 won in manufacturing and application technology development of PTT fiber for the next five years. With a target of 30% of the world market in 2003, Shell predicts that the world demand for PTT fiber will exceed 100×104t by 2010. China is a big textile country, the production of chemical fiber in 2000 reached about 7 000kt, in terms of output, has been ranked first in the world for 4a consecutive years. On the other hand, China is also a major importer of chemical fiber production raw materials, and the current dependence of China’s synthetic fiber industry on imported raw materials is as high as 45%, which seriously affects the economic benefits and market competitiveness of the chemical fiber industry. China’s accession to the WTO has brought unprecedented opportunities for China’s synthetic fiber industry, but also faces unprecedented challenges, which need to be solved the most: first, to solve the problem of dependence on imports of chemical fiber raw materials; The second is to adjust the product structure and actively develop new high-performance synthetic fibers, and the performance of PTT is significantly better than PET. The development of PTT fiber has been listed by the Chinese government as one of the countermeasures for the synthetic fiber industry to join the WTO. The development of PTT fiber indicates that the basic synthetic material of 1, 3-propylene glycol is in great demand.

4.1 PTT market

1, 3-propylene glycol is an irreplaceable raw material for the synthesis of PTT polyester. PTT has good dyeability, biodegradability, stain resistance, toughness,

resilience and UV resistance of nylon and so on. In addition,PTT fiber wear-resistant, low water absorption, low static electricity and other advantages, can replace nylon in the carpet field, the application field of PTT fiber will mainly be the upgrading of traditional fiber materials (PET, PBT, PA6, PA66). Its development value is that it will become a large class of basic materials and face a demand market of several million tons. Taking the most widely used diol – glycol (raw material for synthetic PET) as an example, the current annual output of ethylene glycol in the world is 1 250×104t, of which 688×104t is used to produce polyester fiber, at the end of 2003, only a few companies in the world produce 1, 3-propylene glycol, with an annual output of less than 14×104t. According to the forecast of Shanghai Petrochemical Industry, China’s demand for 1, 3-propylene glycol in recent years is 2.5×104 ~ 3×104t/a, and the domestic long-term demand for 1, 3-propylene glycol will exceed 10×104t/a. So the market space for the product is huge. If PTT captured 10% of the existing nylon market, there would be a demand of 1.95×108 pounds of PTT per year. If PTT expands the textile materials market by 5%, it will generate 0.65×108 pounds of PTT per year. Accordingly, the market demand for 1, 3-propylene glycol will reach 1×108 pounds per year. As a monomer of PTT, 1, 3-propylene glycol will have a very broad market potential.

4.2 Pharmaceutical Market

1, 3-propanediol can be used in the synthesis of pharmaceutical intermediates, for example, the synthesis of 1, 3-dibromopropane, 3-bromo-1-propanol, 1, 3-

dichloropropane and as a carbon chain extender for pharmaceutical products, most of which are exported and the market capacity is between 500 and 1 000t.

4.3 Other Markets

1, 3-propylene glycol can also be used in the manufacture of excellent non-woven fabrics, film engineering plastics, home decoration materials, padding materials and so on. In addition, as an engineering thermal plastic,PTT polyester also has better electrical properties, insulation properties, dimensional stability and the required mechanical properties, can be used in a variety of electronic products production materials. Data show that there is a huge potential demand for PDO from downstream manufacturers, and the application of 1,3-PDO in the production of new varieties such as textile fibers and engineering plastics is under development. In particular, PTT production technology is mature, as long as the existing PET production process equipment is slightly adjusted and reformed, PTT industrial production can be achieved.

5. Closing remarks

Although chemical method is the main method of producing 1,3-PDO in the world at present, chemical method has high production cost and great environmental

pollution, so people have turned their attention to the production of biological method 1,3-PDO, and carried out a lot of research work. Compared with the

chemical synthesis method, the bioengineering method has the characteristics of mild conditions, simple operation, less by-products, good selectivity, energy

saving, less equipment investment and good environment, etc. It is a method with the lowest production cost and the least pollution. In line with the requirements of today’s “green chemical industry” and “sustainable development”, biological production of 1, 3-propylene glycol is the future development direction.