Rectification method for efficiently producing high-purity methanol by low-temperature heat

Abstract

This invention discloses a distillation method for efficiently producing high-purity methanol using low-temperature heat. The technology involves connecting a pressurized column and an atmospheric column in parallel, diverting crude methanol from the pre-column bottom into both columns, utilizing low-temperature heat for heating. The steam from the top of the pressurized column serves as the heat source for the reboiler in the atmospheric column. A vacuum column is then installed downstream, equipped with a flexibly configured heat exchanger to further utilize low-temperature heat. Thirdly, the recovery column is replaced with a vacuum column, using low-temperature heat as the reboiler heat source. This technology can be implemented partially or entirely, both methods yielding significant energy savings. Examples show that this technology can stably produce high-purity methanol with an ethanol content as low as 10 ppm, reducing fresh steam consumption per ton of methanol to below 0.2 tons, and increasing the plant's capacity. Compared to the traditional four-column double-effect distillation process (ethanol content approximately 50 ppm, fresh steam consumption 1.0–1.2 tons per ton of methanol), it offers significant advantages in product purity and energy consumption reduction. This invention effectively solves the problems of difficult high-purity methanol production, high energy consumption, and insufficient utilization of low-temperature heat in existing technologies, offering significant economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of methanol distillation technology, specifically to a distillation technology that optimizes the combination of pressurized towers, atmospheric towers, vacuum towers, and recovery towers, and makes full use of low-temperature heat as a heat source to achieve efficient production of high-purity methanol with an ethanol content of less than 10 ppm. Background Technology

[0002] Methanol, as a crucial basic chemical raw material, has extremely wide applications in many fields such as chemical engineering, pharmaceuticals, and agriculture. Currently, industrial methanol production mostly uses syngas as raw material, which undergoes a synthesis reaction to obtain crude methanol, which then enters the distillation process after preliminary flash separation. However, crude methanol not only contains various impurities such as ethanol, water, dimethyl ether, and acetone, but also dissolved gaseous components such as carbon dioxide, carbon monoxide, methane, argon, and nitrogen.

[0003] The quality standard system for methanol mainly includes the US Federal Grade A and Grade AA standards and my country's GB338-2011 standard. Among these, the control of ethanol content is particularly critical. For example, the Federal Grade AA standard explicitly stipulates a maximum ethanol content of 10 ppm, while the Federal Grade A standard does not specify this. Although the requirements for ethanol content in methanol have been relaxed to some extent with the continuous development of acetic acid catalyst technology, strict control is still necessary in specific high-end applications such as electronics and pharmaceuticals.

[0004] Traditional methanol distillation units are typically designed according to the US Federal Class AA standard, but in actual production, this standard is difficult to achieve due to the high technical difficulty. To reduce energy consumption, the industry has successively developed energy-saving technologies such as double-effect distillation, triple-effect distillation, quadruple-effect distillation, five-effect distillation, and even six-effect distillation, as well as heat pump distillation. While these technologies can reduce steam consumption per ton of methanol production to some extent, it remains difficult to consistently produce high-purity methanol with an ethanol content below 10 ppm in large-scale industrial practice.

[0005] Four-tower distillation technology, a relatively common methanol distillation process, combines a pre-distillation column, a pressurized distillation column, an atmospheric distillation column, and a recovery column to achieve partial cascade utilization of heat, producing methanol products with high purity. However, with the continuous expansion of industrial production scale and further increases in product quality requirements, four-tower distillation technology is not ideal in processing crude methanol with high impurity content, particularly in separating certain key impurities (such as ethanol and higher alcohols), and there is still considerable room for improvement in energy utilization efficiency. Furthermore, its process flexibility and adaptability are insufficient when dealing with crude methanol from different sources and with different compositions.

[0006] Against this backdrop, four-effect methanol distillation technology has emerged. Existing four-effect methanol distillation technology typically consists of a pre-distillation column, multiple pressurized distillation columns (e.g., pressurized column 1, pressurized column 2, and pressurized column 3), and an atmospheric distillation column. In the traditional four-effect methanol distillation process, crude methanol first enters the pre-distillation column, where heating separates low-boiling-point impurities (such as dimethyl ether and methyl formate) and dissolved gases, which are then discharged from the top. The material from the pre-distillation column bottom sequentially enters each pressurized distillation column. Each pressurized distillation column operates at different pressures, with the pressure decreasing sequentially, and the temperature of the vapor at the top of the column decreasing accordingly. The vapor at the top of the previous pressurized distillation column serves as the heat source for the reboiler of the next pressurized distillation column, achieving multi-stage heat utilization. Finally, the material from the pressurized distillation column enters the atmospheric distillation column for further separation at atmospheric pressure, yielding refined methanol product at the top, while wastewater containing small amounts of methanol and other impurities is discharged from the bottom.

[0007] While the four-effect methanol distillation technology improves energy efficiency and product purity to some extent, several problems remain to be solved. Firstly, the separation of trace impurities in crude methanol is not thorough enough, failing to meet the stringent requirements of high-purity methanol in industries such as high-end electronics and pharmaceuticals. Secondly, although multi-effect distillation is employed, low-temperature heat recovery and utilization are still insufficient; a large amount of low-temperature waste heat generated during industrial production is not efficiently utilized, resulting in relatively high overall energy consumption. Furthermore, the operating parameters of this process are complex, and the coordinated control between different towers is difficult, easily leading to operational instability, which in turn affects product quality and production efficiency.

[0008] The main problems with existing technologies are as follows:

[0009] 1. High-purity methanol production is challenging: Existing methanol distillation technologies struggle to consistently produce high-purity methanol with an ethanol content below 10 ppm. The complex composition of impurities in traditional processes, coupled with extremely stringent purity requirements, significantly increases the technical difficulty of production, making it difficult to achieve the desired purity standards.

[0010] 2. High energy consumption: Traditional methanol distillation processes require a large amount of steam for heating and a large amount of circulating water for cooling, resulting in persistently high energy consumption. Although some existing energy-saving technologies can reduce steam consumption to some extent, energy consumption remains a significant issue when producing high-purity methanol on a large scale.

[0011] 3. Insufficient utilization of low-temperature heat: Existing distillation technology has failed to fully and effectively utilize the low-temperature waste heat resources generated in industrial processes, which not only wastes a large amount of low-grade energy, but also increases the overall energy consumption and operating costs.

[0012] Therefore, there is an urgent need for a new technology to solve the above problems in order to achieve stable production of high-purity methanol and significantly reduce energy consumption. Summary of the Invention

[0013] The main objective of this invention is to provide a distillation method for producing high-purity methanol using low-temperature heat, which aims to solve the problems of high difficulty in producing high-purity methanol, high energy consumption, and insufficient utilization of low-temperature heat in the existing technology, thereby achieving stable production of high-purity methanol and significantly reducing energy consumption.

[0014] Technical solution

[0015] Specific logistics process

[0016] Process 1: For example Figure 1 As shown:

[0017] Crude methanol after pre-tower splitting: The crude methanol in the bottom of the pre-tower contains 80%-95% (mass fraction) methanol and impurities such as water and ethanol. It is mixed at a ratio of 0.8-1.2:1 and enters the parallel T1 atmospheric pressure tower and T2 pressurized tower through pipelines 2 and 3 respectively.

[0018] Atmospheric and pressurized towers process: The T2 pressurized tower is heated by steam condensate or other low-temperature waste heat. The operating pressure of the pressurized tower is maintained at 0.2-0.4 MPaG, and the top temperature of the tower reaches 90-115℃. Steam is supplied to the T1 atmospheric tower. The refined methanol (≥99% (mass fraction)) at the top of the tower is condensed by C2 and then collected through pipeline 6.

[0019] The reboiler of the T1 atmospheric distillation column and the condenser of the T2 pressurized column are the same unit, namely C2. Heating is provided by the condensate steam from the top of the T2 pressurized column, forming a double-effect distillation process. The operating pressure is 0.01-0.05 MPa (gauge pressure), and the top temperature is 65-75℃. The purified methanol (≥99% (mass fraction)) from the top of the column is condensed by C1 and collected through pipeline 4; the remainder enters the subsequent processes through pipeline 5.

[0020] Vacuum-reducing tower treatment: The bottom products of towers T1 and T2 are mixed and then enter the vacuum-reducing tower. The operating pressure of the vacuum-reducing tower is -0.02 to -0.06 MPaG, and the top temperature is 40-60℃. A tower section heat exchanger is installed (see process 2). Various heat sources are available, such as heating with C1 condensate steam. The tower section heat exchanger can be integrated with the tower or installed independently. Finally, the top product is condensed by C3 to obtain high-purity methanol (≥99.9% (mass fraction)) which is collected through pipeline 9. Alcohol-containing wastewater is discharged from the tower bottom via pipeline 10.

[0021] Recovery tower processing: The product from the bottom of the T3 vacuum distillation tower enters the recovery tower, which also operates under reduced pressure, with an operating pressure of -0.02 to -0.06 MPaG and a top temperature of 40-60℃. A side stream is installed inside the tower to collect fusel oil, which is discharged through pipeline 12.

[0022] Step 2, set up a pressure-reducing tower with a tower section heat exchanger, such as... Figure 2 As shown:

[0023] Figure 2 The process of setting up an internal tower section heat exchanger for the T3 vacuum tower: The tower section heat exchanger is installed inside the T3 tower, and the heat source of the tower section heat exchanger comes from the condensate of the atmospheric tower or other low-temperature heat.

[0024] Step 3: For pressure reducing towers where the heat exchanger is removed from the tower section, such as... Figure 3 As shown:

[0025] Figure 3 The process of removing the heat exchanger from the T3 vacuum distillation tower: The liquid material is drawn from the vacuum distillation tower, vaporized in the heat exchanger outside the tower, and then returned to the vacuum distillation tower. The heat source for the heat exchanger outside the tower comes from the condensate from the atmospheric distillation tower or other low-temperature heat.

[0026] Advantages of this invention compared to traditional methanol distillation technology

[0027] The distillation technology for producing high-purity methanol using low-temperature thermal efficiency proposed in this invention has significant advantages over traditional methanol distillation technologies in several aspects, as detailed below:

[0028] Product purity:

[0029] This invention, through the optimized combination of a pressurized tower, an atmospheric tower, a vacuum tower, and a recovery tower, and the application of a tower section heat exchanger, enables the stable production of high-purity methanol with an ethanol content below 10 ppm. The final product can achieve a methanol content of 99.9% (mass fraction) or higher. In high-end applications such as electronics and pharmaceuticals, where methanol purity requirements are extremely stringent, this invention's technology can meet their stringent control requirements for impurities, especially ethanol content, providing high-quality raw materials for these fields.

[0030] Traditional technologies: Traditional methanol distillation units are typically designed according to the US Federal AA standard, but it is difficult to achieve this standard in actual production. For example, the methanol produced by the traditional four-tower double-effect distillation process has an ethanol content of about 50 ppm. The traditional three-tower distillation technology is not ideal for separating key impurities such as ethanol when processing crude methanol with high impurity content, and it is difficult to meet the demand of high-end industries for high-purity methanol.

[0031] Energy consumption:

[0032] This invention fully utilizes low-temperature heat as a heat source. Through the parallel design of a pressurized tower and an atmospheric tower, the pressurized tower can fully utilize low-temperature heat, reducing dependence on high-temperature steam. The vacuum tower also uses low-temperature waste heat for heating, and efficiently recovers and utilizes low-temperature heat through tower section heat exchangers. The recovery tower also uses low-temperature waste heat for heating. These energy-saving measures can reduce the fresh steam consumption per ton of methanol to below 0.2 tons, far lower than common methanol distillation units (most of which consume about 1.0 ton of steam / ton of methanol, and a very small portion can reach about 0.65 ton of steam / ton of methanol), greatly reducing energy consumption, improving economic efficiency, and reducing carbon emissions, thus meeting environmental protection requirements.

[0033] Traditional technology: Traditional methanol distillation processes require a large amount of steam for heating and a large amount of circulating water for cooling, resulting in high energy consumption. Although some energy-saving technologies can reduce steam consumption to some extent, energy consumption remains a significant issue when producing high-purity methanol on a large scale. For example, the traditional four-tower double-effect distillation process consumes 1.0 to 1.2 tons of fresh steam per ton of methanol, which is far higher than the energy consumption level of the technology of this invention.

[0034] Low-temperature heat utilization:

[0035] This invention innovatively changes the series connection of the pressurized and atmospheric pressure towers to a parallel connection, introduces a vacuum tower and uses a tower section heat exchanger afterward, and introduces a vacuum recovery tower. This allows the technology to use low-temperature heat from multiple sources as a heat source for the reboiler, reducing steam consumption. The tower section heat exchanger can be flexibly configured, and its heat source can come from methanol vapor, steam condensate, or other low-temperature waste heat from the top of the atmospheric pressure tower. This fully recovers and utilizes low-temperature waste heat resources generated in industrial processes, reducing dependence on conventional heat sources such as high-temperature steam, lowering overall operating costs, and improving the system's economy and stability.

[0036] Traditional technology: Existing distillation technology fails to fully and effectively utilize the low-temperature waste heat resources generated in industrial processes, resulting in the waste of a large amount of low-grade energy. This not only increases overall energy consumption but also raises operating costs, leaving considerable room for improvement in energy utilization efficiency.

[0037] Process flexibility and adaptability:

[0038] This invention features a flexible operating device where energy-saving measures can be implemented partially or fully. The heat exchanger in the tower section can be integrated with the distillation column or installed independently. This flexible design enhances the system's flexibility and adaptability, better handling crude methanol from different sources and with varying compositions. Adjustments and optimizations can be made according to actual conditions to ensure stable system operation and product quality.

[0039] Traditional technology: Taking the three-tower distillation technology as an example, when faced with crude methanol of different compositions, its process lacks flexibility and adaptability, and the separation effect of certain key impurities will be affected, making it difficult to guarantee the stability of product quality.

[0040] Traditional technology: The traditional four-effect methanol distillation technology has relatively complex operating parameters, and the coordinated control between different columns is difficult, which can easily lead to operational instability, thereby affecting product quality and production efficiency.

[0041] In summary, the distillation technology of this invention is superior to traditional methanol distillation technology in terms of product purity, energy consumption, low-temperature heat utilization, process flexibility, and operational stability, and has broad application prospects and significant economic and environmental benefits. Attached Figure Description

[0042] Figure 1 Schematic diagram of the methanol distillation process of this patented technology

[0043] T1—Atmospheric pressure tower; T2—Pressurized tower; T3—Depressurized pressure tower; T4—Recovery tower

[0044] C1—Atmospheric pressure tower condenser; C2—Pressure-charged tower condenser and atmospheric pressure tower reboiler; C3—Vacuum-reduced pressure tower condenser; C4—Recovery tower condenser

[0045] B2—Reboiler for pressurized tower; B3—Reboiler for vacuum tower; B4—Reboiler for recovery tower

[0046] 1, 2, 3—Crude methanol; 4, 6—Refined methanol; 5—Recycled methanol from the bottom of the atmospheric distillation column.

[0047] 7—Recycled product from pressurized tower; 8—Feed to vacuum tower; 9—High-purity methanol; 10—Wastewater containing alcohol;

[0048] 11—Methanol recovery; 12—Fusel oil; 13—Wastewater that meets discharge standards.

[0049] Figure 2 Schematic diagram of a pressure reducing tower with heat exchangers in sections.

[0050] Figure 3 Schematic diagram of a pressure reducing tower with the heat exchanger removed from the tower section. Detailed Implementation

[0051] Example

[0052] This embodiment employs some of the energy-saving measures of the present invention for the technical transformation of a 500,000-ton-per-year four-tower double-effect methanol distillation unit. The key points of the transformation are: 1. The connection between the pressurized tower and the atmospheric tower is changed from series to parallel; 2. A vacuum tower is added after the atmospheric tower; 3. Low-temperature heat or steam condensate is used as a heat source instead of steam; 4. The vacuum tower is created using an ejector method; 5. The process parameters of the pressurized tower are adjusted (refer to the parameters given in this patent); 6. The recovery tower was not modified.

[0053] The original process included four distillation columns: a pre-distillation column, a pressurized column, an atmospheric column, and a recovery column. The pre-distillation column was used to remove light components; the bottom product of the pre-distillation column entered the pressurized column, the bottom product of the pressurized column entered the atmospheric column, and the bottom product of the atmospheric column entered the recovery column. A side stream was provided in the atmospheric column to collect fusel oil. The top temperature of the pressurized column was approximately 120°C, forming a double-effect distillation process with the atmospheric column. The condensation of the top product from the pressurized column provided heat for the reboiler in the atmospheric column. The recovery column was used to recover methanol from the wastewater.

[0054] The original process actually produces 460,000 tons of methanol per year, with an ethanol content of approximately 50 ppm, mostly around 80 ppm. The pre-tower reboiler is heated by steam condensate, while the reboilers in the pressurized tower and recovery tower are heated by steam. The fresh steam consumption is 1.0 ton of steam / ton of methanol.

[0055] The improvements are as follows: 1. While obtaining methanol containing 50 ppm ethanol, a stable methanol content of 10 ppm ethanol is also achieved; 2. Production capacity is increased to 600,000 tons / year, with a maximum of 660,000 tons / year, of which the production of high-purity methanol containing 10 ppm ethanol reaches over 150,000 tons / year; 3. Fresh steam consumption is reduced to 0.17–0.18 tons of steam / ton of methanol per ton of methanol; 4. All environmental protection indicators are met. The results show that the distillation technology of this invention has significant advantages in reducing energy consumption and improving product purity, and can withstand the test of industrial practice. Key process data are listed in Table 1.

[0056] Table 1 Key Data Table of Embodiments

[0057] Crude methanol feed mass flow rate ratio (pressurized tower: atmospheric tower) 1.2:1 Operating pressure of the pressurization tower (MPaG) 0.3 Temperature at the top of the pressurized tower (°C) 104 Atmospheric pressure tower operating pressure (MPaG) Atmospheric pressure Temperature at the top of the atmospheric pressure column (°C) 67 Operating pressure of pressure reducing tower (MPaG) -0.05 Temperature at the top of the pressure reducing tower (°C) 45 Recovery tower operating pressure (MPaG) -0.05 Temperature at the top of the recovery tower (°C) 48 Fresh steam consumption per ton of methanol (tons) ～0.18 High-purity methanol ethanol content (ppm) <10

[0058] In summary, the distillation method for producing high-purity methanol using low-temperature heat efficiency provided by this invention effectively solves the problems of existing technologies through innovative tower structure design and low-temperature heat utilization, and has broad application prospects and significant economic and environmental benefits.

Claims

1. A distillation method for producing high-purity methanol using low-temperature heat at high efficiency, characterized in that, Includes the following steps: The pressurized tower and the atmospheric tower are designed in parallel. Crude methanol from the pre-tower bottom is fed into the pressurized tower and the atmospheric tower respectively at a ratio of 0.8-1.2:

1. The mass fraction of methanol in the crude methanol is 80%-95%. The pressurized tower uses the low-temperature waste heat of the steam condensate for heating in its bottom, and the methanol vapor generated at the top of the tower serves as the heat source for the atmospheric pressure tower; the operating pressure of the pressurized tower is maintained at 0.2-0.4 MPaG, where G represents gauge pressure; the temperature at the top of the tower reaches 90-115℃. The atmospheric distillation column is heated by the condensed steam at the top of the pressurized column to form a double-effect distillation. The operating pressure of the atmospheric distillation column is 0.01-0.05 MPaG, and the top temperature is 65-75℃. A depressurization tower is installed after the pressurization tower and the atmospheric tower. The bottom of the depressurization tower is heated by the low-temperature waste heat of the steam condensate, and the top of the tower is cooled by circulating water or air. The depressurization tower is equipped with a tower section heat exchanger. The heat source of the tower section heat exchanger comes from the low-temperature waste heat of the methanol vapor or steam condensate at the top of the atmospheric tower. The pressure reducing tower operates at a pressure of -0.02 ~ -0.06 MPaG and has a top temperature of 40-60℃. A recovery tower is installed after the pressure reducing tower. The bottom of the recovery tower is heated by the low-temperature waste heat of the steam condensate, and the top of the tower is cooled by circulating water or air. A side stream is installed inside the recovery tower to extract fusel oil. The operating pressure of the recovery tower is -0.02 ~ -0.06 MPaG, and the temperature at the top of the tower is 40-60℃.

2. The distillation method for producing high-purity methanol using low-temperature heat efficiency according to claim 1, characterized in that, The heat exchanger of the tower section can be integrated with the pressure reducing tower, or it can be set up independently.

3. The distillation method for producing high-purity methanol using low-temperature heat efficiency according to claim 1, characterized in that, The condensate at the top of the atmospheric pressure column is used as low-temperature heat.

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