Method for synthesizing ethylene glycol diacetate by using solid super acid as catalyst

Abstract

The application discloses a method for synthesizing ethylene glycol diacetate by using a solid superacid catalyst. 2‑ The application discloses a method for synthesizing ethylene glycol diacetate by using a solid superacid catalyst of SO4 2‑ / TiO2-SiO2 type. The catalyst is prepared by co-precipitation of a titanium source and a silicon source, impregnation with dilute sulfuric acid and calcination, and has high specific surface area and rich strong acid sites. The catalyst can be used to catalyze esterification of ethylene glycol and acetic anhydride (or acetic acid) at 140-150 DEG C to efficiently generate ethylene glycol diacetate, the yield of which can be more than 90%, and the by-product is very little. The catalyst can be easily separated from the reaction system and has good recycling performance. The application has the advantages of high catalytic activity, good selectivity, no corrosion, recyclable catalyst and the like, and can be used for industrial production of ethylene glycol diacetate.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical intermediate synthesis technology, specifically relating to a method using SO4 2- A method for synthesizing ethylene glycol diacetate by direct esterification of ethylene glycol and acetic acid using a TiO2-SiO2 solid superacid catalyst. Background Technology

[0002] Ethylene glycol diacetate (EGDA) is an important high-boiling-point, environmentally friendly solvent and organic synthesis intermediate. Its solubility in water is approximately 12.5%, and it is miscible with most organic solvents, including alcohols, ethers, and benzenes. With a boiling point of 190–191°C, it exhibits low volatility, low toxicity, good solubility, and film-forming properties. Currently, EGDA is widely used in the tobacco industry, as a solvent for cellulose esters and oils, a thinner for paints and inks, an electronic cleaning agent, and in the synthesis of pharmaceuticals and pesticides. With increasingly stringent environmental regulations and the continued growth in demand for green solvents from downstream industries, the market demand for EGDA has been increasing year by year. Its efficient, clean, and low-cost synthesis process has become a research hotspot in the fine chemical industry.

[0003] The industrial synthesis of ethylene glycol diacetate mainly relies on the direct esterification reaction of ethylene glycol and acetic acid. This reaction is a typical acid-catalyzed reversible reaction, proceeding in two steps: first, ethylene glycol monoacetate is generated, followed by further esterification to produce the target product, ethylene glycol diacetate. Due to the chemical equilibrium limitation of the reaction and the differences in the rate constants and thermodynamic parameters between the two steps, a large amount of monoacetate intermediates tends to accumulate during the synthesis process. The boiling point of monoacetate (approximately 180–185 °C) is extremely close to that of the target product, diacetate, making subsequent distillation separation extremely difficult; the yield in existing published literature is around 60%.

[0004] Currently, the main methods for synthesizing ethylene glycol diacetate reported both domestically and internationally are as follows:

[0005] (1) Concentrated sulfuric acid catalytic method: This method uses ethylene glycol and excess acetic acid as raw materials, and concentrated sulfuric acid as a homogeneous acid catalyst to carry out the esterification reaction under heating and reflux conditions. After the reaction, the product is obtained by neutralization, water washing, and vacuum distillation. Concentrated sulfuric acid has high catalytic activity and low cost, and was once a commonly used route in early industrialization. However, concentrated sulfuric acid has extremely strong corrosive and dehydrating properties. At high temperatures, it easily triggers intermolecular dehydration of ethylene glycol to form diethylene glycol and diethyl ether, as well as side reactions such as acetic acid polymerization and carbonization, resulting in a dark color and high acid value of the crude product. After the reaction, a large amount of alkali solution is required for neutralization, generating high-salinity acidic wastewater, and the cost of treating the three wastes is high. Moreover, sulfuric acid is difficult to recover, and equipment corrosion is severe. It has been gradually replaced by green processes.

[0006] (2) Organic sulfonic acid catalytic method: This method uses solid strong organic acids such as p-toluenesulfonic acid (PTSA) to replace inorganic acids, and esterification is carried out under azeotropic conditions with water. The corrosiveness of organic sulfonic acids is significantly reduced compared with concentrated sulfuric acid, and the catalytic selectivity is improved. The relative content of diacetate in crude ester can reach more than 90%. However, this type of catalyst is still a homogeneous system, and after the reaction, it needs to be washed with water, alkali, or distilled for recovery. Not only are the process steps cumbersome, but the catalyst is also prone to thermal decomposition or loss during the recovery process, resulting in fluctuations in the actual yield. The neutralization process still produces saline wastewater, and the energy consumption for recovering excess acetic acid is high, resulting in insufficient overall atom economy.

[0007] (3) Lewis acid and inorganic salt catalysis: This method uses Lewis acids or metal salts such as aluminum trichloride, zinc chloride, and sodium chloride as catalysts to promote the rightward shift of the esterification equilibrium under heating conditions. These catalysts have a certain activating effect on some alcohol-acid systems, but Lewis acids such as aluminum trichloride are easily hydrolyzed in water to generate hydrogen chloride gas, which causes serious corrosion to reaction equipment and pipelines; when water is difficult to completely remove from the reaction system, the catalyst is rapidly deactivated and needs to be replenished frequently; post-treatment requires a large amount of water quenching, generating wastewater containing aluminum and chlorine heavy metals, which puts great pressure on environmental protection, and the catalyst cannot be recycled, limiting its industrial application.

[0008] (4) Enzyme-catalyzed method: This method uses immobilized lipase (such as Novozym 435) to catalyze the transesterification / esterification reaction of ethylene glycol with acetic acid or vinyl acetate under mild conditions of 40-70℃. Enzyme catalysis has significant advantages such as mild conditions, high selectivity, few side reactions, and environmental friendliness. The selectivity for the conversion of monoesters to diesters can reach over 95%. However, lipases are expensive, extremely sensitive to moisture, free acid concentration, and temperature in the reaction system, and are prone to irreversible inactivation; the reaction rate is slow, the volumetric productivity is low, and the batch reaction time is often as long as 24-48 hours; immobilized enzymes are prone to swelling and loss in organic solvents, resulting in a short cycle life; currently, this process is only in the laboratory or pilot-scale stage, and there is still a long way to go before large-scale continuous industrial production, and its economic feasibility is insufficient.

[0009] The existing methods for synthesizing ethylene glycol diacetate generally have the following common problems: (1) The reaction is limited by equilibrium. The boiling points of monoacetate and diacetate are close (difference of only 5~10℃). Conventional distillation separation requires a high reflux ratio and a multi-stage vacuum tower, which consumes a lot of energy and is prone to heat-sensitive side reactions; (2) Traditional acid catalysts are highly corrosive and have many side reactions, producing a large amount of high COD and high salinity wastewater, resulting in high environmental treatment costs; (3) Although solid acid or enzyme catalysts have green potential, they have bottlenecks such as rapid activity decay, difficulty in recovery, poor scale-up stability, and insufficient economic efficiency; (4) Azeotropic water-carrying agents (such as cyclohexane, toluene, butyl acetate, etc.) are prone to carrying free acetic acid during dehydration, increasing the load on the acid recovery system. In addition, the water-carrying agent itself requires additional distillation circulation, further increasing the operating cost; (5) The overall process flow is long, the output of waste is large, and the equipment investment and operating costs are high, making it difficult to meet the industrialization requirements of modern fine chemicals for "atom economy, process intensification, green and low carbon". Therefore, developing a new green synthesis process for ethylene glycol diacetate with high catalytic activity, good selectivity, mild reaction conditions, easy separation of mono / diesters, low emissions of waste, and easy industrial scale-up has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of existing liquid acid catalysts such as concentrated sulfuric acid, such as severe equipment corrosion, difficulty in waste acid treatment, and complex product separation, and to provide a method using SO4 2- A method for the efficient and environmentally friendly synthesis of ethylene glycol diacetate using TiO2-SiO2 solid superacid as a catalyst. This method has advantages such as easy catalyst separation and recovery, reusability, high reaction selectivity, and good product purity, and has good prospects for industrial application.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A method for synthesizing ethylene glycol diacetate using a solid superacid as a catalyst includes the following steps: using ethylene glycol and acetic acid as raw materials, in SO4 2- In the presence of a TiO2-SiO2 solid superacid catalyst and an azeotropic dehydrating agent, an esterification reaction was carried out by heating under reflux. After the reaction, the catalyst was recovered by solid-liquid separation, and the reaction solution was separated by vacuum distillation to obtain the ethylene glycol diacetate product. The reaction formula is as follows:

[0013] The SO4 2-In the TiO2-SiO2 solid superacid catalyst, the molar ratio of Ti to Si is 10:1 to 20:1, preferably 15:1. The catalyst can be prepared using the sol-gel method: tetrabutyl titanate and tetraethyl orthosilicate are hydrolyzed under acidic conditions to form a titanium-silicon composite oxide gel. After drying, the gel is impregnated with a 0.5–1.0 mol / L sulfuric acid solution for 6–10 hours, filtered, and then calcined at 500–600℃ for 2–4 hours to obtain SO4. 2- / TiO2-SiO2 solid superacid catalyst.

[0014] Based on the mass of ethylene glycol, SO4 2- The amount of the TiO2-SiO2 catalyst is 3.0 wt% to 7.0 wt%, preferably 5.0 wt%.

[0015] The molar ratio of acetic acid to ethylene glycol is 2.5:1 to 3.0:1, preferably 2.75:1.

[0016] The azeotropic dehydrating agent is selected from one of sec-butyl acetate, butyl acetate, toluene, or cyclohexane, preferably sec-butyl acetate. The amount of dehydrating agent used is 2 to 3 times (V / V) the volume of ethylene glycol added, preferably 2 times.

[0017] The esterification reaction temperature is 130℃~160℃, preferably 140℃~150℃.

[0018] The esterification reaction takes 6 to 10 hours, preferably 8 hours.

[0019] After the reaction is complete, SO4 is recovered by hot filtration. 2- The TiO2-SiO2 solid superacid catalyst can be recycled after washing and drying. The filtrate is first distilled at atmospheric pressure to recover the azeotropic aqueous agent and excess acetic acid, and then the fraction at 190-191℃ / atmospheric pressure (or corresponding reduced pressure conditions) is collected by vacuum distillation to obtain the high-purity ethylene glycol diacetate product.

[0020] This invention discloses a method using SO4 2- A method for preparing ethylene glycol diacetate using a TiO2-SiO2 type solid superacid catalyst. The catalyst is prepared by co-precipitation of titanium and silicon sources, followed by impregnation with dilute sulfuric acid and calcination, exhibiting high specific surface area and abundant strong acid sites. Using this catalyst to catalyze the esterification reaction of ethylene glycol with acetic anhydride (or acetic acid) at 140–150 °C, ethylene glycol diacetate can be efficiently produced with a yield exceeding 90% and minimal byproducts. The catalyst is easily separated from the reaction system and exhibits good recyclability. This invention offers advantages such as high catalytic activity, good selectivity, non-corrosiveness, and catalyst recyclability, and can be used for the industrial production of ethylene glycol diacetate.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Using SO4 2- / TiO2-SiO2 solid superacid replaces traditional concentrated sulfuric acid catalysts, fundamentally avoiding equipment corrosion and waste acid discharge problems, which is in line with the development direction of green chemical industry;

[0023] (2) The catalyst is in solid form, and solid-liquid separation can be achieved by simple filtration after the reaction, making the operation simple. The catalyst can be recycled after washing and drying. Experiments show that the catalyst still maintains good catalytic activity after being recycled 6 times, with the ethylene glycol conversion rate remaining above 98% and the EGDA selectivity remaining above 97%.

[0024] (3) Under optimized reaction conditions, the conversion rate of ethylene glycol can reach more than 98%, the selectivity of EGDA can reach more than 98%, and the purity of EGDA product after vacuum distillation can reach more than 99%, with a separation yield of about 88%.

[0025] (4) sec-butyl acetate is selected as an azeotropic dehydrating agent. It has strong dehydrating ability, moderate boiling point, and good compatibility with the reaction system. It avoids the toxicity problem of traditional dehydrating agents (such as benzene) and can be recycled through distillation, which further reduces production costs.

[0026] (5) The process conditions of this method are mild and the operation is stable and controllable, making it suitable for industrial-scale production at the kilogram level and larger scale. Attached Figure Description

[0027] Figure 1 This is the gas phase spectrum of the ethylene glycol diacetate prepared in Example 7 of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0029] Example 1

[0030] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2-The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation after removing light components under normal pressure, collecting the fraction from 190–192 °C. Gas chromatography analysis showed a ethylene glycol conversion rate of 99.7%, a ethylene glycol diacetate selectivity of 98.1%, a yield of 88.1%, and a product purity of 99.1%.

[0031] Example 2

[0032] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.37 g SO4 to a 250 mL four-necked flask. 2- The reaction mixture consisted of a TiO2-SiO2 catalyst (3.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation after removing light components under normal pressure, collecting the fraction from 190–192 °C. Gas chromatography analysis showed a ethylene glycol conversion rate of 96.8%, a ethylene glycol diacetate selectivity of 97.2%, a yield of 84.5%, and a product purity of 98.7%.

[0033] Example 3

[0034] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.87 g SO4 to a 250 mL four-necked flask. 2- The reaction mixture consisted of a TiO2-SiO2 catalyst (7.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation to remove light components, and the fraction collected at 190–192 °C was collected. Gas chromatography analysis showed that the ethylene glycol conversion was 99.4%, the ethylene glycol diacetate selectivity was 98.0%, the yield was 87.3%, and the product purity was 98.9%.

[0035] Example 4

[0036] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2-The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 130 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation after removing light components under normal pressure, collecting the fraction from 190–192 °C. Gas chromatography analysis showed a ethylene glycol conversion rate of 94.3%, a ethylene glycol diacetate selectivity of 97.5%, a yield of 82.1%, and a product purity of 98.5%.

[0037] Example 5

[0038] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2- The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 160 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation after removing light components under normal pressure, collecting the fraction from 190–192 °C. Gas chromatography analysis showed a ethylene glycol conversion rate of 99.1%, a ethylene glycol diacetate selectivity of 96.2%, a yield of 84.8%, and a product purity of 98.6%.

[0039] Example 6

[0040] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2- The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 22.2 mL of toluene. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation to remove light components, and the fraction collected at 190–192 °C was collected. Gas chromatography analysis revealed a 95.1% conversion rate of ethylene glycol, a 95.8% selectivity for ethylene glycol diacetate, a yield of 80.9%, and a product purity of 98.3%.

[0041] Example 7 Add 12.4 g ethylene glycol (1 eq), 30.0 g glacial acetic acid (2.50 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2-The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation after removing light components under normal pressure, collecting the fraction from 190–192 °C. Gas chromatography analysis showed a ethylene glycol conversion rate of 97.5%, a ethylene glycol diacetate selectivity of 95.4%, a yield of 83.2%, and a product purity of 98.6%.

[0042] Example 8

[0043] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2- The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 6 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation after removing light components under normal pressure, collecting the fraction from 190–192 °C. Gas chromatography analysis showed a ethylene glycol conversion rate of 93.8%, a ethylene glycol diacetate selectivity of 96.5%, a yield of 81.0%, and a product purity of 98.4%.

[0044] Example 9

[0045] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2- The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 22.2 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 12 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation to remove light components, and the fraction collected at 190–192 °C was collected. Gas chromatography analysis showed that the ethylene glycol conversion was 99.5%, the ethylene glycol diacetate selectivity was 97.3%, the yield was 86.0%, and the product purity was 99.1%.

[0046] Example 10

[0047] Add 12.4 g ethylene glycol (1 eq), 33.0 g glacial acetic acid (2.75 eq), and 0.62 g SO4 to a 250 mL four-necked flask. 2-The reaction mixture consisted of a TiO2-SiO2 catalyst (5.0 wt%) and 11.1 mL of sec-butyl acetate. A water separator, distillation column, and reflux condenser were installed. Stirring was initiated, and the temperature was slowly increased to 145 °C and maintained for 9 hours. After cooling the reaction solution to 50 °C, the catalyst was recovered by filtration. The filtrate was then subjected to vacuum distillation to remove light components, and the fraction collected at 190–192 °C was collected. Gas chromatography analysis revealed a ethylene glycol conversion rate of 91.5%, a ethylene glycol diacetate selectivity of 94.2%, a yield of 76.8%, and a product purity of 97.9%.

[0048] Stability tests were conducted on the catalyst recovered in Example 1. It can be seen that after six cycles, its activity decreased only slightly, which may be related to the loss during the catalyst separation process, indicating good stability.

[0049] Table 1 Catalyst stability test 0 99.2% 98.5% 87.9% 1 99.3% 98.3% 88.1% 2 99.1% 97.8% 87.5% 3 99.0% 97.9% 87.8% 4 98.8% 98.0% 88.0% 5 98.4% 97.9% 88.5% 6 98.5% 97.1% 86.8% 7 96.9% 95.5% 83.1% 8 95.0% 94.6% 81.5% 9 93.6% 90.5% 78.0% 10 90.1% 88.4% 75.2%

[0050] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for synthesizing ethylene glycol diacetate catalyzed by a solid superacid, characterized in that: Using ethylene glycol and acetic acid as raw materials, in SO4 2- In the presence of a TiO2-SiO2 solid superacid catalyst and an azeotropic dehydrating agent, the esterification reaction was carried out by heating under reflux. After the reaction, the catalyst was recovered by solid-liquid separation, and the reaction solution was separated by vacuum distillation to obtain the ethylene glycol diacetate product.

2. The method according to claim 1, characterized in that: The SO4 2- In the / TiO2-SiO2 solid superacid catalyst, the molar ratio of Ti to Si is 10:1 to 20:

1.

3. The method according to claim 2, characterized in that: The SO4 2- In the / TiO2-SiO2 solid superacid catalyst, the molar ratio of Ti to Si is 15:

1.

4. The method according to claim 1, characterized in that: The molar ratio of acetic acid to ethylene glycol is 2.5:1 to 3.0:1; based on the mass of ethylene glycol, SO4 2- The amount of the TiO2-SiO2 solid superacid catalyst used is 3.0 wt% to 7.0 wt%.

5. The method according to claim 4, characterized in that: The molar ratio of acetic acid to ethylene glycol is 2.75:1; based on the mass of ethylene glycol, SO4 2- The amount of the TiO2-SiO2 solid superacid catalyst used is 5.0 wt%.

6. The method according to claim 1, characterized in that: The azeotropic dehydrating agent is selected from one of sec-butyl acetate, butyl acetate, toluene, or cyclohexane; the amount of dehydrating agent used is 2 to 3 times the volume of ethylene glycol added.

7. The method according to claim 1, characterized in that: The esterification reaction temperature is 130℃~160℃, and the esterification reaction time is 6~10 hours.

8. The method according to claim 6, characterized in that: The esterification reaction temperature is 140℃~150℃, and the esterification reaction time is 8 hours.

9. The method according to claim 1, characterized in that: After the reaction is complete, SO4 is recovered by hot filtration. 2- / TiO2-SiO2 solid superacid catalyst, the catalyst is washed, dried and recycled; the SO4 2- After six cycles of recycling, the / TiO2-SiO2 solid superacid catalyst maintained an ethylene glycol conversion rate of over 98% and an EGDA selectivity of over 97%.

10. The method according to any one of claims 1 to 9, characterized in that: The SO4 2- The preparation method of the / TiO2-SiO2 solid superacid catalyst is the sol-gel method, which uses tetrabutyl titanate and tetraethyl orthosilicate as raw materials, hydrolyzes them under acidic conditions to form a titanium-silicon composite oxide gel, and after drying, impregnates it with 0.5-1.0 mol / L sulfuric acid solution for 6-10 hours, filters it, and then calcines it at 500-600℃ for 2-4 hours to obtain the catalyst.

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