A fully automatic non-neutralization and non-formal furfural continuous rectification process

Abstract

The application discloses a kind of full-automatic neutralization-free formaldehyde-free furfural continuous rectification processes, which uses the five-tower continuous rectification system formed by deacidification tower, dehydration tower, rectification tower, high-boiling substance recovery tower and liquid phase recovery tower connected in sequence.The deacidification process does not need to add any neutralization lye to avoid the generation of formaldehyde sludge from the source, the top of the dehydration tower is rich in furfural front fraction water, which enters the liquid phase recovery tower for step-by-step recovery, and the water phase is recycled.The high-boiling substance residue at the bottom of the rectification tower enters the high-boiling substance recovery tower for reduced-pressure recovery of furfural, and the heavy component residue is used as fuel.The application automatically adjusts the temperature, pressure, reflux ratio and production capacity of each tower based on online parameters through a full-automatic control system, realizes a total furfural yield of more than 95%, and there is no liquid waste and solid waste discharge in the rectification section, and the operator can remotely monitor and operate unattended.

Description

Technical Field

[0001] This invention relates to the field of distillation and purification technology in furfural production, and particularly to a fully automated continuous distillation process for furfural without neutralization or formaldehyde-free mud. Background Technology

[0002] Furfural (furanaldehyde) is an important biomass-based platform compound widely used in synthetic resins, pharmaceuticals, pesticides, food additives, and petrochemicals. Crude furfural is obtained by acid hydrolysis of agricultural and forestry waste such as corn cobs and sugarcane bagasse to produce aldehyde vapor, which is then condensed to obtain an aqueous solution of crude furfural. This solution contains a large amount of water, acetic acid, and various low-boiling and high-boiling impurities, requiring further purification by distillation to obtain the final product, furfural.

[0003] Existing five-tower continuous distillation processes still commonly use alkali neutralization to remove acetic acid in the deacidification unit. This process generates a large amount of alkaline aldehyde sludge containing furfural, resulting in product yield loss and high disposal costs as hazardous solid waste. While existing processes have initially added a wastewater treatment unit, the furfural-rich foremilk fraction is often discharged as liquid waste or only undergoes simple biochemical treatment. Furfural recovery from the high-boiling-point residue is incomplete, leading to resource waste and environmental pollution. Although a few solutions attempt to partially recover furfural from the waste liquid by adding water washing towers or recovery devices, the lack of systematic integration between units means that the solid and liquid waste problems remain unresolved at their source.

[0004] Therefore, in response to the problems mentioned above, this invention proposes a fully automated, neutralization-free, formaldehyde-free continuous distillation process for furfural. Summary of the Invention

[0005] To overcome the problems of existing furfural distillation processes, such as the need for alkali neutralization during deacidification leading to aldehyde sludge solid waste, direct discharge of foredistillate causing liquid waste and resource loss, and incomplete recovery of furfural from high-boiling-point substances, this invention proposes a fully automated, neutralization-free, aldehyde-sludge-free continuous furfural distillation process. This process employs a five-tower series continuous distillation system consisting of a deacidification tower, a dehydration tower, a distillation tower, a high-boiling-point substance recovery tower, and a liquid phase recovery tower. The deacidification process requires no addition of any neutralizing alkali, eliminating aldehyde sludge formation at the source. The furfural-rich foredistillate at the top of the dehydration tower enters the liquid phase recovery tower for staged furfural recovery, and the residual aqueous phase is reused at the system front end. The high-boiling-point residue at the bottom of the distillation tower enters the high-boiling-point substance recovery tower for depressurization to recover entrained furfural and return it to the main system. Combined with a fully automated control system, the temperature, pressure, reflux ratio, and output of each tower are adjusted and interlocked in real time, achieving a total yield of over 95% in the furfural distillation section and completely eliminating liquid and solid waste discharged during the distillation process.

[0006] The technical solution of this invention is: a fully automated, formaldehyde-free, continuous distillation process for furfural, which is based on a five-tower continuous distillation system consisting of a deacidification tower, a dehydration tower, a distillation tower, a high-boiling-point recovery tower, and a liquid-phase recovery tower connected in series. A fully automated control system is used for process monitoring and parameter adjustment. The process includes the following steps: S1, crude furfural feed enters the deacidification tower, and acetic acid and a small amount of low-boiling-point impurities are removed from the crude furfural by distillation. The acetic acid-containing fraction is collected from the top of the tower, and the deacidified furfural material is obtained from the bottom of the tower. S2, after deacidification, the furfural material enters the dehydration tower, where water and furfural-enriched pre-distillate are removed by azeotropic distillation. The furfural-enriched pre-distillate is collected at the top of the tower, and the pre-dehydrated furfural material is obtained at the bottom of the tower. S3, the preliminarily dehydrated furfural material enters the distillation column, and high-purity furfural product is obtained through distillation. The finished furfural product is collected from the top or side stream of the column, and the high-boiling residue containing furfural is collected from the bottom of the column. S4, the furfural-rich foredistillate collected from the top of the dehydration tower enters the liquid phase recovery tower. Through distillation separation, the furfural-rich phase is recovered from the top of the tower and returned to the inlet of the dehydration tower or distillation tower. The aqueous phase with furfural content of less than 0.5% is obtained from the bottom of the tower and reused in the deacidification tower, achieving zero liquid waste discharge of the foredistillate. S5, the high-boiling-point residue containing furfural collected from the bottom of the distillation column enters the high-boiling-point recovery column, where it is distilled under reduced pressure. Furfural is recovered from the top of the column and returned to the distillation column inlet, while heavy component residue is obtained from the bottom of the column. This heavy component residue is used as a heat source fuel or returned to the hydrolysis section, achieving zero solid waste discharge of high-boiling-point substances. Through the step-by-step recovery process described above, the fully automatic control system automatically adjusts the temperature, pressure, reflux ratio, and output of each tower based on online detection parameters.

[0007] Preferably, the operating conditions of the deacidification tower are: top temperature 90-110℃, bottom temperature 120-135℃, operating pressure at atmospheric or slightly positive pressure, reflux ratio controlled at 0.5-2.0, and furfural content in the acetic acid fraction collected at the top of the tower less than 0.3%. The operating conditions of the dehydration tower are as follows: top temperature 95-105℃, bottom temperature 110-125℃, operating pressure at atmospheric pressure, reflux ratio controlled at 1.0-3.0, furfural-rich forewater collected from the top of the tower with a furfural mass fraction of 8-12%, and furfural entrainment in the aqueous phase less than 0.5%. The operating conditions of the distillation column are as follows: top temperature 100-115℃, bottom temperature 130-150℃, operating pressure 10-50 kPa negative pressure, reflux ratio controlled at 2.0-5.0, finished product furfural purity not less than 99.0%, and furfural mass fraction in the high-boiling residue at the bottom of the column 5-15%. The liquid phase recovery tower has 15-25 trays. Operating conditions are: top temperature 95-100℃, bottom temperature 100-108℃, operating pressure atmospheric pressure, and reflux ratio controlled between 1.5 and 4.0. The furfural-rich phase recovered from the top of the tower must contain at least 60% furfural by mass, and the aqueous phase from the bottom must contain at least 0.3% furfural by mass. The high-boiling-point recovery tower has 10-20 trays and operates under the following conditions: top temperature 80-95℃, bottom temperature 120-140℃, operating pressure 5-30 kPa negative pressure, and reflux ratio controlled at 0.5-2.0. The furfural recovered at the top of the high-boiling-point recovery tower is returned to the middle of the distillation column, and the mass fraction of furfural in the heavy component residue at the bottom of the column is less than 1.0%.

[0008] Preferably, the fully automatic control system includes: Temperature sensors, pressure sensors, level sensors, and flow meters are installed at the top, bottom, and key side lines of the deacidification tower, dehydration tower, distillation tower, high-boiling-point recovery tower, and liquid phase recovery tower. An online purity analyzer and an automatic regulating valve for adjusting the reflux ratio, heating steam quantity and output of each tower are installed on the finished furfural extraction pipeline. All sensors, analyzers, and control valves are connected to the DCS controller; The DCS or PLC controller has a built-in material balance model and heat balance model, which can automatically calculate and adjust the reflux ratio, bottom heating amount and top output of each tower according to the real-time process parameters of each tower. At the same time, it can automatically control the start and stop and frequency of the material conveying pumps between each tower, so as to realize the stable and continuous operation of the five-tower system and automatic interlock protection within the full load range.

[0009] Preferably, the acetic acid mass fraction in the acetic acid fraction drawn from the top of the deacidification tower is 30% to 60%, and this fraction is directly fed to the acetic acid recovery system or used as a by-product; the furfural content in the aqueous phase obtained from the bottom of the dehydration tower is less than 0.1%, and it is returned to the hydrolysis section for use as makeup water.

[0010] The total furfural yield of this invention is 95-98%. Compared with the traditional two-tower continuous process of neutralization with alkali, this process completely eliminates the solid waste of aldehyde sludge generated during neutralization and the liquid waste caused by the direct discharge of pre-distillate water. Typical operating data are as follows: when the crude furfural feed rate is 10 tons / hour, the purity of the finished furfural can reach 99.2-99.5%, the steam consumption per ton of product is reduced by 15-20% compared with the traditional process, and the rectification section achieves zero liquid waste and zero solid waste discharge.

[0011] The beneficial effects of this invention are: 1. This invention adopts a physical distillation method that completely eliminates the need for alkali neutralization in the deacidification tower, thereby eliminating the generation of aldehyde sludge solid waste, avoiding the side reactions of furfural polymerization and scaling and clogging of tower internals caused by the introduction of alkali solution, and directly recovering and utilizing the acetic acid fraction at the top of the tower, thus solving the problems of hazardous solid waste, yield loss and short operating cycle caused by the addition of alkali neutralization in traditional processes.

[0012] 2. This invention separates the furfural-rich forewater from the top of the dehydration tower by adding a liquid phase recovery tower, recovering more than 97% of the furfural and returning it to the main system. The furfural content in the residual aqueous phase is less than 0.3% and is reused in the hydrolysis section. This eliminates liquid waste pollution and furfural loss caused by direct discharge of forewater, while significantly reducing the COD of the wastewater and achieving zero discharge of liquid waste in the distillation section.

[0013] 3. This invention adds a high-boiling-point recovery tower to perform vacuum distillation on the high-boiling-point residue at the bottom of the distillation tower, recovering 85-95% of the entrained furfural and returning it to the distillation tower inlet. The furfural content in the heavy component residue at the bottom of the tower is less than 1.0% and can be used as a heat source fuel. This solves the problems of incomplete furfural recovery from high-boiling-point substances in traditional processes, solid waste discharge polluting the environment and wasting resources, and achieves zero solid waste discharge in the distillation section.

[0014] 4. This invention connects a deacidification tower, a dehydration tower, a distillation tower, a high-boiling-point recovery tower, and a liquid phase recovery tower in series to form a five-tower continuous distillation system. A fully automatic control system is set up to adjust and interlock the temperature, pressure, reflux ratio, and output in real time. While achieving a total furfural yield of over 95%, the system can be operated unattended with only remote monitoring by the operator, which greatly improves the economy and stability of production. Attached Figure Description

[0015] Figure 1 The diagram shown is a schematic representation of the process flow structure of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Please see Figure 1 : First, the five towers of this invention will be described, specifically: The deacidification tower, the first tower of this invention, is used to remove acetic acid and a small amount of low-boiling-point impurities from crude furfural. This deacidification tower operates without adding sodium carbonate, lime, or any other alkaline neutralizing agent; instead, it relies on physical distillation to separate acetic acid and furfural. Its basic principle is based on the difference in boiling points between acetic acid and furfural (acetic acid boiling point approximately 118℃, furfural boiling point approximately 162℃) and their different volatilities at a certain temperature. By controlling the temperature gradient within the tower, acetic acid is concentrated at the top and collected, while furfural remains at the bottom. Because no alkali solution is added, the resinification polymerization side reaction of furfural under alkaline conditions is avoided, and the formation of aldehyde sludge is also prevented.

[0018] During operation, the deacidification tower operates under the following conditions: top temperature 90-110℃, bottom temperature 120-135℃, operating pressure at atmospheric or slightly positive pressure (slightly higher than atmospheric pressure, 1-5 kPa gauge pressure), and reflux ratio controlled at 0.5-2.0. Under these conditions, the furfural content in the acetic acid-containing fraction collected from the top of the tower is less than 0.3%, and the acetic acid mass fraction is 30-60%. This acetic acid-containing fraction can be directly transported to the plant's acetic acid recovery system for concentration and utilization, or sold as a low-concentration acetic acid byproduct, avoiding the situation in traditional processes where acetic acid is neutralized and becomes salt, entering the waste residue. The deacidified furfural material obtained from the bottom of the deacidification tower has an acetic acid content reduced to below 0.1%, and the pH value is close to neutral (6.5-7.0), which can be directly fed into the subsequent dehydration tower.

[0019] Because the above steps employ a neutralization-free operation, salt crystallization will not occur in the deacidification tower due to the addition of alkali. The internal components of the tower are less prone to scaling and clogging, resulting in a significant increase in the continuous operation cycle and a substantial reduction in the frequency of shutdowns for cleaning and maintenance costs.

[0020] Furthermore, the deacidified furfural material still contains approximately 15-25% water (mass fraction), which needs to be removed by azeotropic distillation in a dehydration tower. The operation of the dehydration tower is based on the azeotropic properties of furfural and water. Furfural and water form a minimum azeotrope under normal pressure, with an azeotropic point of approximately 97.5°C. The azeotrope contains approximately 35% furfural and 65% water by mass. This invention utilizes this property to distill the water along with a portion of the furfural from the top of the dehydration tower, thereby achieving deep dehydration of the main furfural material.

[0021] The operating conditions of the dehydration tower are: top temperature 95-105℃, bottom temperature 110-125℃, operating pressure at atmospheric pressure, and reflux ratio controlled at 1.0-3.0. The top product is a furfural-rich foremilk, with a furfural mass fraction of 8-12% and furfural entrainment in the aqueous phase less than 0.5%. In this invention, this foremilk is not directly discharged but is transported via pipeline to a liquid phase recovery tower for further treatment. The bottom of the dehydration tower yields a pre-dehydrated furfural material with a moisture content reduced to 0.5-1.5% and a furfural mass fraction exceeding 95%, which then enters a distillation tower for final purification.

[0022] The reflux ratio of the dehydration tower is automatically adjusted according to the moisture content of the feed. When the feed moisture content is high, the control system appropriately increases the reflux ratio to improve the separation effect, but the reflux ratio does not exceed 3.0 to avoid excessive energy consumption; when the feed moisture content is low, the reflux ratio can be reduced to about 1.0 to increase the throughput. Through this adaptive adjustment, the dehydration tower can achieve optimal energy consumption while ensuring that the moisture content at the bottom of the tower meets the standard.

[0023] Furthermore, the initially dehydrated furfural material from the dehydration tower enters the lower part of the distillation tower for distillation separation under negative pressure. The purpose of using negative pressure operation is to lower the boiling point of furfural, reduce the thermal polymerization side reaction of furfural at high temperatures, and at the same time reduce heating steam consumption.

[0024] The operating conditions for the distillation column are as follows: top temperature 100-115℃, bottom temperature 130-150℃, operating pressure 10-50 kPa negative pressure (absolute pressure), and reflux ratio controlled at 2.0-5.0. High-purity furfural is collected from the top or side stream, and high-boiling-point residue containing furfural is collected from the bottom.

[0025] Under negative pressure of 10-50 kPa, the boiling point of furfural decreases from 162℃ at atmospheric pressure to approximately 110-130℃, which greatly alleviates the heat-sensitive decomposition of furfural. In practice, the operating pressure can be fine-tuned according to the feed composition and product quality requirements. If a purity of over 99.0% is required, the pressure can be controlled at 20-30 kPa, and the reflux ratio at 3.0-4.0.

[0026] The high-boiling-point residue obtained from the bottom of the distillation column contains 5-15% furfural by mass, as well as furfural resin, tar-like substances, and polymerization products. This portion of the material has a high viscosity and poor flowability, and needs to be transported to a high-boiling-point recovery tower for recovery via an insulated jacket and steam-traced pipeline.

[0027] Furthermore, a high-boiling-point recovery column is used to treat the high-boiling-point residue discharged from the bottom of the distillation column. This column has 10-20 trays and operates under the following conditions: top temperature 80-95℃, bottom temperature 120-140℃, operating pressure of 5-30 kPa negative pressure, and reflux ratio controlled at 0.5-2.0. Because the furfural concentration in the high-boiling-point residue is low (5-15%) and contains a large amount of heavy components, a higher vacuum is required to enhance separation. Under a negative pressure of 5-30 kPa, the boiling point of furfural is further reduced to approximately 70-90℃, allowing furfural to be effectively distilled off from the high-boiling-point residue.

[0028] The top of the high-boiling-point recovery tower collects recovered furfural with a purity of approximately 85-95%. This is returned via pipeline to the inlet of the distillation tower and mixed with the pre-dehydrated furfural material for re-distillation, thereby recovering the entrained furfural. The bottom of the tower yields a heavy component residue with a furfural mass fraction of less than 1.0%, consisting mainly of furfural resin, tar, and small amounts of inorganic salts. This heavy component residue has a high calorific value (approximately 4000-5000 kcal / kg) and can be used as a heat source fuel in a boiler for incineration or returned to the hydrolysis section as auxiliary fuel. Due to its extremely low furfural content, incineration does not generate additional pollution, and the heat from incineration can be recovered and reused. In this way, zero solid waste emissions are achieved for high-boiling-point substances.

[0029] In the high-boiling-point recovery tower, the reboiler can be heated using heat transfer oil or steam. However, due to the high viscosity and tendency of high-boiling-point substances to coke, a forced circulation or scraped-film evaporation type is preferred for the reboiler to prevent carbonization caused by prolonged heating. During operation, the bottom temperature must be strictly controlled to not exceed 140℃ to avoid excessive cracking or polymerization of heavy components.

[0030] Furthermore, the liquid-phase recovery tower is used to treat the furfural-rich forewater fraction collected from the top of the dehydration tower. This tower has 15-25 trays and operates under the following conditions: top temperature 95-100℃, bottom temperature 100-108℃, operating pressure at atmospheric pressure, and a reflux ratio controlled at 1.5-4.0. The forewater fraction contains 8-12% furfural and 88-92% water, as well as trace amounts of acetic acid and methanol. Since furfural and water form an azeotrope, the design goal of the liquid-phase recovery tower is to concentrate furfural at the top of the tower as much as possible while minimizing the furfural content in the bottom aqueous phase.

[0031] During operation, the foredistillate enters from the middle of the column. Through multiple gas-liquid contacts between the rising vapor and the descending liquid, furfural gradually accumulates at the top of the column. Due to the presence of azeotropes, the top of the column is a furfural-rich phase, with a furfural mass fraction of not less than 60% and water of approximately 40%. This furfural-rich phase is returned to the inlet of the dehydration column or distillation column via pipeline (preferably to the dehydration column inlet due to its higher water content). The aqueous phase collected at the bottom of the column has a furfural mass fraction of not more than 0.3%, and the COD value is reduced from approximately 100,000 mg / L in the original foredistillate to below 3,000 mg / L. This aqueous phase can be directly reused in the deacidification column or at the front end of the system (hydrolysis section) as process makeup water. Since the hydrolysis section itself requires the addition of water for the reaction, and this aqueous phase contains only trace amounts of furfural and organic matter, its reuse will not adversely affect the hydrolysis reaction; on the contrary, it can recover the heat and trace amounts of furfural. Through treatment in a liquid phase recovery tower, the pre-distillate water, which was originally discharged as waste liquid, has been made available for resource utilization and zero liquid waste discharge.

[0032] In practice, when the furfural content in the feed fluctuates, the control system automatically adjusts the reflux ratio based on the online detection value of furfural in the bottom aqueous phase: if an increase in furfural content is detected at the bottom of the column, the reflux ratio is increased; if the furfural content is below the lower limit, the reflux ratio is appropriately reduced to save energy. In this embodiment, adjusting within the range of 1.5-4.0 is sufficient to meet the requirements.

[0033] The fully automatic control system will be explained next, specifically: At the hardware level, the fully automated control system includes various sensors, analytical instruments, and actuators installed on each tower and pipeline, along with a centralized DCS controller. Specifically, temperature sensors (PT100 platinum resistance thermometers, accuracy ±0.1℃), pressure sensors (gauge pressure transmitters, accuracy ±0.1%FS), level sensors (radar level gauges, accuracy ±0.5%), and flow meters (mass flow meters, accuracy ±0.2%) are installed at the top, bottom, and key side pipe locations of the deacidification tower, dehydration tower, distillation tower, high-boiling-point recovery tower, and liquid phase recovery tower. These sensors convert the real-time acquired process parameters into 4-20mA electrical signals, which are then transmitted to the analog input module of the DCS controller.

[0034] An online purity analyzer is installed on the furfural product collection pipeline. This analyzer uses near-infrared spectroscopy (NIR) technology to continuously and rapidly detect the purity of furfural and the content of major impurities (moisture, acidity, color, etc.) in the finished product. The online analysis results are updated every 1-5 minutes, serving as the basis for adjusting the reflux ratio and production rate of the distillation column.

[0035] The actuators include automatic regulating valves (pneumatic diaphragm regulating valves, equal percentage characteristic) installed on the reflux lines of each tower, steam regulating valves (linear characteristic) on the tower bottom heating steam lines, and the product regulating valves on the top product lines, as well as the material transfer pumps (variable frequency drive) between each tower. The valve position feedback signals of all regulating valves and the frequency signals of the variable frequency pumps are connected to the analog output module of the DCS controller to achieve closed-loop control.

[0036] Meanwhile, the invention also includes an emergency shut-off valve on the critical material pipeline. When the system detects dangerous conditions such as over-temperature, over-pressure, abnormal liquid level, or leakage, the controller can automatically interlock and close the shut-off valve, while simultaneously activating the nitrogen protection system to ensure the safety of the device.

[0037] The control strategy of the fully automatic control system specifically includes the following: The DCS controller has a built-in material balance model and a heat balance model. The material balance model calculates the component distribution in the tower in real time based on the feed composition, product output and reflux of each tower, and predicts the composition changes of the products at the top and bottom of the tower. The heat balance model calculates the temperature distribution and heat load requirements in the tower based on parameters such as the heating amount in the tower bottom, the condensation amount at the top of the tower and heat loss.

[0038] Under normal operating conditions, the fully automatic control system executes the following control logic: (1) The top temperature and bottom temperature of each column are the key controlled variables. The controller adopts a cascade control strategy: the bottom temperature is the main variable and the heating steam flow rate is the secondary variable. The opening of the steam regulating valve is automatically adjusted by the PID algorithm. The top temperature is the auxiliary variable, and the reflux ratio or the top output is adjusted. When the bottom temperature deviates from the set value, the controller automatically increases or decreases the heating steam flow rate. When the top temperature rises, the controller appropriately increases the reflux ratio or decreases the top output, and vice versa.

[0039] (2) For deacidification and dehydration towers, pressure control is mainly achieved by adjusting the non-condensable gas vent valve at the top of the tower to maintain the pressure inside the tower within the set value ±0.5 kPa. For distillation towers and high-boiling-point recovery towers, pressure control is achieved by adjusting the pumping rate of the vacuum pump or the opening of the non-condensable gas vent valve after the condenser at the top of the tower. The vacuum pump is frequency-controlled, and the controller automatically adjusts the frequency of the frequency converter based on the feedback from the pressure sensor at the top of the tower to stabilize the absolute pressure inside the tower within ±1 kPa of the target value (10-50 kPa for distillation towers and 5-30 kPa for high-boiling-point recovery towers).

[0040] (3) The liquid level in each tower bottom is controlled by the frequency conversion regulation of the discharge pump or the opening of the tower bottom outlet regulating valve. Single-loop PID control is adopted to maintain the liquid level within ±5% of the set value to avoid the tower flooding due to excessive liquid level or the pump cavitation due to excessive liquid level. The liquid level in each tower reflux tank is maintained stable by adjusting the speed of the reflux pump or the regulating valve on the reflux pipeline.

[0041] (4) The reflux ratio is the core parameter of the distillation column operation. In this invention, the reflux ratio control of the distillation column adopts a combination of ratio control and cascade control. The controller first calculates the theoretically required reflux ratio based on the feed rate and material balance model, and then actually executes it by adjusting the regulating valves on the reflux pipeline and the outlet pipeline.

[0042] Simultaneously, the controller receives feedback signals from the online purity analyzer of the finished product: when the purity of the finished product is lower than the set value (99.0%), the reflux ratio is automatically increased (up to a maximum of 5.0); when the purity of the finished product is higher than the set value and the energy consumption is high, the reflux ratio can be appropriately reduced (down to a minimum of 2.0). The control method for the reflux ratio is similar for the deacidification tower, dehydration tower, liquid phase recovery tower, and high-boiling-point recovery tower, but the setting range is different: 0.5-2.0 for the deacidification tower, 1.0-3.0 for the dehydration tower, 1.5-4.0 for the liquid phase recovery tower, and 0.5-2.0 for the high-boiling-point recovery tower.

[0043] (4) All material transfer pumps between towers are equipped with frequency converters. The controller automatically adjusts the pump speed according to the liquid level in the feed tank or the bottom liquid level of the next tower. For example, when the liquid level in the bottom of the distillation tower rises, the controller automatically increases the frequency of the high-boiling-point transfer pump to send more high-boiling-point residual liquid to the high-boiling-point recovery tower, and vice versa.

[0044] The controller also implements interlocking for the start-up and shutdown sequences of the five towers. During normal startup, the towers must be started in the order of the last tower first, followed by the first tower, to prevent material backflow or abnormal pressure inside the towers. During normal shutdown, the reverse is true: the feed to the first tower is stopped first, the material in each tower is gradually emptied, and the last tower is stopped last.

[0045] (5) The DCS controller has a pre-set standard start-up and standard shutdown procedure. After the operator clicks the one-click start-up button on the host computer interface in the central control room, the control system will automatically start the heating, cooling, vacuum systems and material pumps of each tower in sequence, and gradually adjust each parameter to the set value. Throughout the process, the operator only needs to monitor the changing trend of key parameters without manual intervention. Similarly, the one-click shutdown function can automatically and safely shut down the system according to the set cooling rate and discharge sequence. During normal operation, the operator can remotely view process parameters, historical curves and alarm information in real time, realizing true unattended or remote monitoring operation.

[0046] The process flow of the present invention is described below using a complete continuous operation cycle as an example. In this example, the crude furfural feed rate is set at 10 tons / hour, the mass fraction of furfural in the crude furfural is 92%, the mass fraction of acetic acid is about 5%, the moisture content is about 2%, and the high boiling point content is about 1%.

[0047] S1. Before starting the system, the operator checks the zero point, range, and communication status of all instruments through the DCS system, confirming that the internal components of each column are clean and unblocked, all valves are in the closed position, and all pumps are in standby mode. Inject appropriate amounts of bottom material into the reboilers of the deacidification column, dehydration column, distillation column, liquid phase recovery column, and high-boiling-point recovery column to bring the reboiler level of each column to 20-30%. Start the vacuum system to evacuate the pressure of the distillation column and high-boiling-point recovery column to the set values ​​(30 kPa for the distillation column and 15 kPa for the high-boiling-point recovery column). Start the cooling water circulation system to ensure that the condensers at the top of each column have sufficient cooling medium.

[0048] S2, following the order of starting the rear towers first and the front towers last, first start the heating and reflux systems of the high-boiling-point recovery tower and the liquid phase recovery tower. After the two towers are running stably, start the heating system of the distillation tower; after the distillation tower is stable, start the dehydration tower; and finally start the deacidification tower. Then, start the crude furfural feed pump and feed it to the deacidification tower at a flow rate of 10 tons / hour. After the deacidification tower starts running, the acetic acid-containing fraction collected from the top of the tower is continuously transported to the acetic acid recovery system, and the furfural material at the bottom of the tower, after deacidification, is pressurized by a pump and sent to the dehydration tower. The furfural-rich pre-distillate water collected from the top of the dehydration tower (furfural mass fraction of approximately 10%) is sent to the liquid phase recovery tower, and the preliminarily dehydrated furfural material at the bottom of the tower is sent to the distillation tower. The finished furfural product collected from the top of the distillation tower is cooled and sent to the finished product tank; the high-boiling-point residue at the bottom of the tower is sent to the high-boiling-point recovery tower. The furfural-rich phase (furfural mass fraction ≥60%) collected from the top of the liquid phase recovery tower is returned to the inlet of the dehydration tower, while the aqueous phase (furfural content ≤0.3%) from the bottom of the tower is returned to the hydrolysis section. The recovered furfural collected from the top of the high-boiling-point recovery tower is returned to the inlet of the distillation tower, while the heavy component residue (furfural content ≤1.0%) from the bottom of the tower is sent to the boiler for incineration.

[0049] S3, Once the system reaches steady state, the process parameters of each column should be maintained at the following values: The deacidification tower has a top temperature of 102℃, a bottom temperature of 128℃, atmospheric pressure (gauge pressure 0 kPa), a reflux ratio of 1.2, and a furfural content of 0.2% and an acetic acid mass fraction of 45% in the acetic acid fraction at the top of the tower.

[0050] The dehydration tower has a top temperature of 98.5℃, a bottom temperature of 118℃, operates at atmospheric pressure, has a reflux ratio of 2.0, and contains 10.5% furfural in the water at the top and 1.0% water at the bottom.

[0051] The distillation column operates at a pressure of 25 kPa (absolute pressure), with a top temperature of 108°C, a bottom temperature of 138°C, a reflux ratio of 3.5, a furfural purity of 99.3%, and a furfural mass fraction of 12% in the high-boiling residue at the bottom of the column.

[0052] The liquid phase recovery tower operates at atmospheric pressure, with a top temperature of 97.5℃, a bottom temperature of 103℃, and a reflux ratio of 2.8. The furfural-rich phase at the top of the tower contains 65% furfural by mass, while the aqueous phase at the bottom contains 0.22% furfural.

[0053] The high-boiling-point recovery tower operates at a pressure of 12 kPa (absolute pressure), with a top temperature of 86°C, a bottom temperature of 130°C, a reflux ratio of 1.0, and recovers furfural with a purity of 88% at the top and 0.8% furfural in the heavy component residue at the bottom.

[0054] Under the above parameters, the system operates continuously, producing approximately 8.75 tons of finished furfural per hour, consuming approximately 5.5 tons of low-pressure steam, and circulating approximately 200 tons of cooling water. The fully automatic control system adjusts the reflux ratio every 3 minutes based on data from the online purity analyzer to ensure that the finished product purity remains above 99.0%. Simultaneously, the DCS system records the temperature, pressure, liquid level, and flow rate data of each tower in real time. When any parameter exceeds the set alarm limit, the system issues an audible and visual alarm and automatically executes the corresponding adjustment strategy. In the event of a serious anomaly, the system automatically interlocks to cut off the feed and activates the safety protection program.

[0055] S4. When a shutdown for maintenance or raw material replacement is required, the operator presses the one-button shutdown button. The control system first stops the feed of crude furfural, then sequentially reduces the heating steam volume of each tower according to the shutdown sequence, causing the temperature of each tower to drop at a rate of approximately 30°C / hour. When the temperature of the tower bottom drops below 100°C, heating is stopped, and the material conveying pump continues to run to gradually empty the material in the tower into the storage tank. Finally, the vacuum system and cooling water system are shut down, and the system enters a safe shutdown state.

[0056] To demonstrate the technical effects of this invention, the following is a material balance table (feed rate 10 tons / hour) and energy balance data under a specific operating condition: Table 1 Material Balance Sheet (Unit: kg / h)

[0057] As shown in Table 1, this invention achieves extremely high material utilization. The foredistillate water (9450 kg / h) directly discharged in the traditional process is treated by a liquid phase recovery tower, recovering 910 kg / h of furfural (accounting for 97.3% of the total furfural in the foredistillate water). Only 25 kg / h of furfural is discharged from the system with the aqueous phase, and the furfural concentration in this aqueous phase (8040 kg / h) is only 0.31%, which can be used as process recycled water. The high-boiling-point residue at the bottom of the distillation column (813.5 kg / h) is treated by a high-boiling-point recovery tower, recovering 480 kg / h of furfural. Only 32 kg / h of furfural remains in the heavy component residue (accounting for 6.25% of the total furfural in the high-boiling-point residue). The total furfural loss of the system is only 57 kg / h, with a recovery rate of 95.1%.

[0058] Table 2 Comparison of Energy Consumption (per ton of finished furfural)

[0059] As shown in Table 2, although the power consumption of this invention increases slightly due to the addition of two recovery towers, the steam consumption is significantly reduced, and the consumption of alkali and the discharge of solid and liquid waste are completely eliminated. The overall economic and environmental benefits are very high.

[0060] The technical effects of the present invention are further illustrated by the following examples, and compared with traditional processes.

[0061] Example 1: Using the aforementioned five-tower continuous distillation system, with a crude furfural feed rate of 10 tons / hour, and the operating parameters of each tower being the values ​​measured in step S3 above, the system operated continuously and stably for 720 hours. During this period, the fully automatic control system operated normally, and no shutdowns occurred due to scaling or blockage. The average purity of the finished furfural was 99.3%, color grade 12, acidity 0.03%, and moisture content 0.1%. The total furfural yield was 95.2% (calculated as: total finished product yield / total furfural content in crude furfural). After treatment in the liquid phase recovery tower, the furfural content in the bottom effluent was an average of 0.21%, which was entirely reused in the hydrolysis section. The furfural content in the heavy component residue at the bottom of the high-boiling-point recovery tower was an average of 0.75%, which was entirely sent to the boiler for incineration. No liquid or solid waste was discharged into the environment from the distillation section. The steam consumption per ton of finished furfural was 5.1 tons, the electricity consumption was 91 kWh, and the alkali consumption was zero.

[0062] When the crude furfural has a high moisture content (5% by mass, 4% acetic acid, 90% furfural, and 1% high-boiling-point substances), the process parameters are adjusted appropriately: the reflux ratio of the dehydration tower is increased to 2.8, the reflux ratio of the liquid phase recovery tower is increased to 3.5, and other tower parameters remain unchanged. The operating results show that the moisture content at the bottom of the dehydration tower can still be controlled below 1.2%, the product purity is 99.1%, and the yield is 94.8%. The furfural content in the aqueous phase at the bottom of the liquid phase recovery tower is 0.28%, meeting the reuse requirements. Compared with processing raw materials with normal moisture content, the yield is slightly lower (from 95.2% to 94.8%), but still around 95%.

[0063] When the acetic acid content in the crude furfural was high (8% by mass, 2% moisture, 89% furfural, 1% high-boiling-point substances), the reflux ratio of the deacidification tower was adjusted to 1.8, and the top temperature was appropriately increased to 108℃. Operational results showed that the acetic acid fraction collected from the top of the deacidification tower reached 55% by mass, the furfural content was 0.25%, and the pH value of the deacidified furfural material was 6.8. Subsequent towers operated stably, with a product purity of 99.2% and a yield of 95.0%.

[0064] Comparative Example 1: This example employs a traditional two-tower continuous distillation process (a deacidification and dehydration neutralization tower and a distillation tower). The crude furfural feed rate is 10 tons / hour, and the raw materials are the same as in Example 1. In the deacidification process, sodium carbonate solution (20% by mass) is added to neutralize acetic acid. The resulting aldehyde sludge is filtered through a plate and frame filter press and disposed of as solid waste. The filtrate enters the dehydration tower. The top distillate from the dehydration tower is directly discharged to the wastewater treatment plant, while the high-boiling-point residue from the bottom of the distillation tower is transported off-site for incineration as waste residue. Operating results show that the finished furfural has a purity of 98.5% and a yield of 84.5%. Each ton of finished furfural consumes 6.3 tons of steam, 35 kg of sodium carbonate, and produces 65 kg of aldehyde sludge, with approximately 1.2 m³ of furfural-containing wastewater discharged. 3 Approximately 28 kg of high-boiling-point waste residue was produced.

[0065] Comparative Example 2: This example employs a four-tower continuous process (acid removal tower, dehydration tower, distillation tower, and high-boiling-point recovery tower). This scheme still uses alkali neutralization for acid removal, resulting in aldehyde sludge production. The top distillate from the dehydration tower is directly discharged, and there is no liquid-phase recovery tower. The raw materials are the same as in Example 1. Operating results: Product purity 99.0%, yield 88.2%, alkali consumption 32 kg per ton of product, aldehyde sludge production 60 kg, wastewater discharge 1.0 m³. 3 The total amount of solid waste (aldehyde sludge and high-boiling-point residue) is about 85 kg. Although it is an improvement over the two-tower process, the problems of pre-distillate water discharge and aldehyde sludge have not been solved, and the yield is not ideal.

[0066] Comparative Example 3: This example simulates the present invention but omits the liquid phase recovery tower and the high-boiling-point recovery tower. No alkali is added for deacidification, but the distillate water at the top of the dehydration tower is directly discharged, and the high-boiling-point substance at the bottom of the distillation tower is directly discharged. The calculated furfural yield is only 82.1% (approximately 10% furfural is lost at the top of the dehydration tower, and approximately 5% furfural is lost at the bottom of the distillation tower).

[0067] The specific parameters are shown in the table below: Table 3 Comparison of Examples and Comparative Examples

[0068] As shown in Table 3, this invention is significantly superior to all comparative examples in terms of yield, environmental friendliness, and operating cycle, while also offering advantages in product purity and energy consumption. Comparative Example 3, although also without alkali, suffers from an extremely low yield due to the lack of two recovery towers.

[0069] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A fully automated, formaldehyde-free, continuous distillation process for furfural, characterized in that, This process is implemented based on a five-tower continuous distillation system consisting of a deacidification tower, a dehydration tower, a distillation tower, a high-boiling-point recovery tower, and a liquid phase recovery tower connected in series. A fully automated control system is used for process monitoring and parameter adjustment. The process includes the following steps: S1, crude furfural feed enters the deacidification tower, and acetic acid and a small amount of low-boiling-point impurities are removed from the crude furfural by distillation. The acetic acid-containing fraction is collected from the top of the tower, and the deacidified furfural material is obtained from the bottom of the tower. S2, after deacidification, the furfural material enters the dehydration tower, where water and furfural-enriched pre-distillate are removed by azeotropic distillation. The furfural-enriched pre-distillate is collected at the top of the tower, and the pre-dehydrated furfural material is obtained at the bottom of the tower. S3, the preliminarily dehydrated furfural material enters the distillation column, and high-purity furfural product is obtained through distillation. The finished furfural product is collected from the top or side stream of the column, and the high-boiling residue containing furfural is collected from the bottom of the column. S4, the furfural-rich foredistillate collected from the top of the dehydration tower enters the liquid phase recovery tower. Through distillation separation, the furfural-rich phase is recovered from the top of the tower and returned to the inlet of the dehydration tower or distillation tower. The aqueous phase with furfural content of less than 0.5% is obtained from the bottom of the tower and reused in the deacidification tower, achieving zero liquid waste discharge of the foredistillate. S5, the high-boiling-point residue containing furfural collected from the bottom of the distillation column enters the high-boiling-point recovery column, where it is distilled under reduced pressure. Furfural is recovered from the top of the column and returned to the distillation column inlet, while heavy component residue is obtained from the bottom of the column. This heavy component residue is used as a heat source fuel or returned to the hydrolysis section, achieving zero solid waste discharge of high-boiling-point substances. Through the step-by-step recovery process described above, the fully automatic control system automatically adjusts the temperature, pressure, reflux ratio, and output of each tower based on online detection parameters.

2. The fully automated, formaldehyde-free, continuous distillation process for furfural in mud according to claim 1, characterized in that, The operating conditions of the deacidification tower are as follows: top temperature 90-110℃, bottom temperature 120-135℃, operating pressure is atmospheric or slightly positive, reflux ratio is controlled at 0.5-2.0, and furfural content in the acetic acid fraction collected from the top of the tower is less than 0.3%.

3. The fully automated, formaldehyde-free, continuous distillation process for furfural without neutralization as described in claim 1, characterized in that, The operating conditions of the dehydration tower are as follows: top temperature 95-105℃, bottom temperature 110-125℃, operating pressure is atmospheric pressure, reflux ratio is controlled at 1.0-3.0, the furfural mass fraction of the furfural-rich pre-distillate collected from the top of the tower is 8-12%, and the furfural entrainment in the aqueous phase is less than 0.5%.

4. The fully automated, formaldehyde-free, continuous distillation process for furfural in mud according to claim 1, characterized in that, The operating conditions of the distillation column are as follows: top temperature 100-115℃, bottom temperature 130-150℃, operating pressure 10-50kPa negative pressure, reflux ratio controlled at 2.0-5.0, the purity of the finished furfural product is not less than 99.0%, and the mass fraction of furfural in the high-boiling residue at the bottom of the column is 5-15%.

5. The fully automated, formaldehyde-free, continuous distillation process for furfural in mud according to claim 1, characterized in that, The liquid phase recovery tower has 15-25 trays and operates under the following conditions: top temperature 95-100℃, bottom temperature 100-108℃, operating pressure at atmospheric pressure, and reflux ratio controlled between 1.5 and 4.

0. The furfural-rich phase recovered from the top of the liquid phase recovery tower has a furfural mass fraction of not less than 60%, and the furfural mass fraction in the aqueous phase at the bottom of the tower is not higher than 0.3%.

6. The fully automated, formaldehyde-free, continuous distillation process for furfural without neutralization as described in claim 1, characterized in that, The high-boiling-point recovery tower has 10-20 trays, and the operating conditions are: top temperature 80-95℃, bottom temperature 120-140℃, operating pressure of 5-30 kPa negative pressure, and reflux ratio controlled between 0.5 and 2.

0. The furfural recovered at the top of the high-boiling-point recovery column is returned to the middle of the distillation column, and the mass fraction of furfural in the heavy component residue at the bottom of the column is less than 1.0%.

7. The fully automated, formaldehyde-free, continuous distillation process for furfural without neutralization as described in claim 1, characterized in that, The fully automatic control system includes: Temperature sensors, pressure sensors, level sensors, and flow meters are installed at the top, bottom, and key side lines of the deacidification tower, dehydration tower, distillation tower, high-boiling-point recovery tower, and liquid phase recovery tower. An online purity analyzer and an automatic regulating valve for adjusting the reflux ratio, heating steam quantity and output of each tower are installed on the finished furfural extraction pipeline. All sensors, analyzers, and control valves are connected to the DCS controller.

8. The fully automated, formaldehyde-free, formaldehyde-free continuous distillation process for furfural according to claim 1, characterized in that: The DCS or PLC controller has a built-in material balance model and heat balance model, which can automatically calculate and adjust the reflux ratio, bottom heating amount and top output of each tower according to the real-time process parameters of each tower. At the same time, it can automatically control the start and stop and frequency of the material conveying pumps between each tower, so as to realize the stable and continuous operation of the five-tower system and automatic interlock protection within the full load range.

9. The fully automated, formaldehyde-free, formaldehyde-free continuous distillation process for furfural according to claim 1, characterized in that: The acetic acid mass fraction in the acetic acid fraction drawn from the top of the deacidification tower is 30-60%.

10. The fully automated, formaldehyde-free, continuous distillation process for furfural without neutralization according to claim 1, characterized in that: The furfural content in the aqueous phase obtained from the bottom of the dehydration tower is less than 0.1%, and it is returned to the hydrolysis section for use as makeup water.

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