A process for using white oil circulation to absorb ethanol in waste gas

Abstract

The present invention discloses a process for utilizing white oil circulation to absorb ethanol in waste gas, which comprises the following steps: Ethanol-containing waste gas is introduced into an absorption tower to contact with a white oil absorbent for absorption, obtaining a gas with entrained liquid and a white oil-ethanol mixture. The gas with entrained liquid enters a separator to separate out the purified gas, and the entrained liquid is collected in a circulation tank for recycling, and the purified gas is discharged. The white oil-ethanol mixture enters the circulation tank and together with the white oil-ethanol mixture forms a circulating absorption liquid. When the specific gravity of the white oil-ethanol mixture system is appropriate, it is pumped into a centrifugal separation system to separate ethanol and white oil. The white oil returns to the circulation tank, and the ethanol enters a storage tank for recycling. The present invention uses white oil as an absorbent, purifies ethanol-containing waste gas through the absorption of white oil, and then separates ethanol and white oil through centrifugation, which can efficiently treat ethanol-containing waste gas, achieve ultra-low emission of VOCs and recycle ethanol, and has the advantages of short process, simple operation, convenient maintenance, high efficiency, and low loss.

Description

Technical Field

[0001] The present invention relates to the field of industrial VOCs treatment and comprehensive utilization, and particularly relates to a process for using white oil to circulate and absorb ethanol in waste gas. Background Art

[0002] Ethanol, as an important organic solvent, is widely used in fields such as chemical industry, pharmaceuticals, and food processing. However, during the production processes of the above industries, unreacted ethanol often discharges with waste gas, forming volatile organic compound (VOCs) pollution. With the improvement of environmental protection requirements, the high efficiency of VOCs treatment technology and the demand for resource recovery have become the focus of the industry.

[0003] Currently, the treatment technologies for ethanol-containing waste gas mainly include the following categories: 1. Activated carbon adsorption method; ethanol in the waste gas is adsorbed by activated carbon, but there are problems such as limited adsorption capacity, high regeneration energy consumption, and difficult disposal of waste activated carbon, and the resource recovery of ethanol cannot be achieved. 2. Combustion methods (such as catalytic combustion, regenerative combustion); although they can completely degrade VOCs, they are applicable to high-concentration waste gas, and are uneconomical for low-concentration ethanol waste gas, and additional carbon dioxide emissions are generated during the combustion process, which does not meet environmental protection requirements. 3. Absorption - rectification combination method; for example, the "water absorption + rotating packed bed separation + rectification" process disclosed in Chinese invention patent CN109395534B can recover ethanol, but there are still the following defects: (1) Complex process; multiple absorption and rectification steps are required, and the equipment investment and operation and maintenance costs are high; (2) High energy consumption: a large amount of heat energy is required during the rectification process, especially for low-concentration ethanol waste gas, which is uneconomical; (3) Narrow application range: the solubility of water in ethanol is limited (about 78 g / 100 mL at room temperature), and other VOCs components in the waste gas (such as esters, aldehydes) may interfere with the absorption effect, resulting in increased difficulty in subsequent rectification.

[0004] In recent years, the absorption method has received attention due to its short process, low cost, and easy integration of resource recovery, but its core bottleneck lies in the selection of the absorbent. An ideal absorbent needs to simultaneously meet the characteristics of high selectivity, easy separability, low volatility, and controllable cost. High selectivity means being able to efficiently absorb ethanol and reduce interference from other components, and easy separability can ensure that the absorbent and ethanol can be recycled through simple physical separation; low volatility can avoid secondary pollution; and only when the cost is controllable can it be suitable for industrial promotion.

[0005] In the prior art, attempts have been made to use silicone oil, vegetable oil, etc. as absorbents, but they have obvious shortcomings. For example, the density difference between silicone oil and ethanol is small, the centrifugal separation efficiency is low (recovery rate <80%), auxiliary processes (such as distillation) are required, and they are expensive; vegetable oil is easily oxidized and deteriorated, has poor long-term operating stability, and is prone to residual impurities after separation. In addition, traditional absorption methods mostly rely on rectification or distillation to regenerate the absorbent, resulting in a longer process and increased energy consumption. Therefore, the development of a short-process, high-efficiency, low-cost ethanol waste gas treatment process to achieve ultra-low VOCs emissions and ethanol resource recovery has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the defects and shortcomings of the above-mentioned prior art, such as the complicated process for treating ethanol in waste gas and the fact that VOCs components other than ethanol cannot be effectively treated, the present invention provides a process for utilizing white oil to circulate and absorb ethanol in waste gas. White oil is used as an absorbent. Through short-process cyclic absorption technology, the absorption and separation efficiency of ethanol in waste gas is improved, thereby achieving low-carbon and green treatment of ethanol in waste gas and efficient resource recovery.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A process for absorbing ethanol in waste gas by circulating white oil comprises the following steps:

[0009] S1. Pass the ethanol-containing waste gas into an absorption tower to contact with industrial-grade white oil, the volume ratio of white oil to waste gas flow rate is 3~5L:15~30m³ / h, the action time is 40~80min, and a mixed liquid of gas entrained with liquid and white oil ethanol is obtained;

[0010] S2. The gas entrained with liquid obtained in step S1 is passed into a separator to separate the purified gas and the mixed liquid;

[0011] S3. The white oil ethanol mixed liquid obtained in step S1 and the mixed liquid obtained in step S2 are fed into a circulation tank to form a circulating absorption liquid;

[0012] S4. When the specific gravity of white oil in the circulating absorption liquid is 0.6-0.8 kg / L, pump it into a centrifuge and centrifuge it at 2000-4000 rpm for 1-5 min to separate ethanol and recyclable white oil;

[0013] S5. Recover ethanol and return white oil to the absorption tower for recycling.

[0014] Furthermore, in step S1, the volume ratio of white oil to exhaust gas flow is preferably 4-5 L: 20-30 m 3 / h, with a preferred action time of 50 - 80 min. An appropriate flow - volume ratio can ensure sufficient contact between the gas - liquid two - phase to form a stable liquid film, improving the ethanol absorption rate. The design of the action time takes into account the balance between treatment efficiency and energy consumption, avoiding incomplete absorption caused by short - time contact or redundant equipment volume caused by too long a time.

[0015] Furthermore, in step S1, the viscosity of the industrial white oil is 5 - 15 mPa·s (25°C), the flash point ≥ 150°C, and the density difference between the white oil and ethanol ≥ 0.2 kg / L. The medium - viscosity range ensures that the white oil has both good fluidity and stability of the gas - liquid mass transfer interface. The high - flash - point characteristic meets the explosion - proof safety requirements. The significant density difference significantly improves the efficiency of the subsequent centrifugal separation process and effectively avoids two - phase entrainment.

[0016] Furthermore, in step S1, the absorption tower is a packed tower, and the packing is ceramic Raschig rings with a specific surface area of 200 - 300 m² / m³ and a porosity of 80% - 90%.

[0017] Furthermore, in step S1, the operating temperature of the absorption tower is 20 - 35°C, and the pressure is atmospheric pressure.

[0018] Furthermore, in step S2, the separator is a centrifugal separator or an inertial demister.

[0019] Furthermore, in step S2, the separation factor of the centrifugal separator is 800 - 1500, and the inner wall of the separation cavity is coated with a polytetrafluoroethylene (PTFE) anti - sticking layer.

[0020] Furthermore, in step S4, the ethanol residue in the white oil after centrifugal separation ≤ 0.5 wt%, and the recovery rate of the white oil is still ≥ 95% after ≥ 50 cycles of recycling.

[0021] Furthermore, in step S1, the ethanol concentration in the waste gas is 1000 - 5000 mg / m³, and the total content of VOCs other than ethanol ≤ 10%.

[0022] Furthermore, the diameter of the ceramic Raschig rings is 25 - 50 mm, the height is 0.8 - 1.2 times the diameter, and the surface is pretreated by alkali washing to enhance lipophilicity.

[0023] The beneficial effects of the present invention are as follows:

[0024] The present invention uses white oil as an absorbent, purifies the ethanol - containing waste gas through the absorption of white oil, and then separates ethanol and white oil through centrifugation. It can efficiently treat ethanol - containing waste gas, achieve ultra - low emissions of VOCs, and can also efficiently recover ethanol, with the advantages of a short process, simple operation, convenient maintenance, high efficiency, and low loss. Brief Description of the Drawings

[0025] Figure 1This is the process flow diagram of the present invention. Specific embodiments

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereby.

[0027] In the following embodiments, unless otherwise specified, the raw materials used are commercially available, and the obtained data are the averages of more than three repeated experiments. Example 1

[0028] A process for recycling white oil to absorb ethanol in waste gas. The process flow diagram is as Figure 1 shown. The absorption tower is a packed tower with internally installed ceramic Raschig rings (pretreated by alkali washing). Waste gas with a flow rate of 25 m 3 / h and an ethanol concentration of 2200 mg / m 3 is introduced into the absorption tower and acts fully with 4 L of absorbent white oil (white oil viscosity is 10 mPa·s) for 60 minutes, obtaining waste gas with entrained liquid and a white oil-ethanol mixture. After the waste gas with entrained liquid passes through a centrifugal separator, purified gas and a mixed liquid are obtained. The obtained mixed liquid and the white oil-ethanol mixture are collected in a circulation tank to obtain a circulating absorption liquid. When the specific gravity of the circulating absorption liquid is 0.72 kg / L, it is sent to a centrifuge with a rotation speed of 2000 revolutions per minute for 3 minutes of separation to obtain ethanol and the absorbent. The obtained ethanol is recovered and stored, and the obtained absorbent is circulated into the absorption tower to act again. The VOCs concentration of the purified gas at the outlet is measured to be 2 mg / m 3 by a portable VOC detector (FID), and the absorbent recovery rate is 99.8%. Example 2

[0029] A process for recycling white oil to absorb ethanol in waste gas. The process flow diagram is as Figure 1 shown. The absorption tower is a packed tower with internally installed ceramic Raschig rings (pretreated by alkali washing). Waste gas with a flow rate of 15 m 3 / h and an ethanol concentration of 2000 mg / m 3 is introduced into the absorption tower and acts fully with 3 L of absorbent white oil (white oil viscosity is 10 mPa·s) for 40 minutes, obtaining waste gas with entrained liquid and a white oil-ethanol mixture. After the waste gas with entrained liquid passes through a centrifugal separator, purified gas and a mixed liquid are obtained. The obtained mixed liquid and the white oil-ethanol mixture are collected in a circulation tank to obtain a circulating absorption liquid. When the specific gravity of the circulating absorption liquid is 0.6 kg / L, it is sent to a centrifuge with a rotation speed of 2000 revolutions per minute for 1 minute of separation to obtain ethanol and the absorbent. The obtained ethanol is recovered and stored, and the obtained absorbent is circulated into the absorption tower to act again. The VOCs concentration of the purified gas at the outlet is measured to be 1.6 mg / m 3, the absorbent recovery rate is 96.5%. Example 3

[0030] A process for recycling white oil to absorb ethanol in waste gas. The process flow diagram is as Figure 1 shown. The absorption tower is a packed tower with internally installed ceramic Raschig rings (pretreated by alkali washing). Waste gas with a flow rate of 25 m 3 / h and an ethanol concentration of 2250 mg / m 3 is introduced into the absorption tower and reacts fully with 4 L of absorbent white oil (white oil viscosity is 10 mPa·s) for 60 minutes to obtain waste gas with entrained liquid and a white oil-ethanol mixture. After the waste gas with entrained liquid passes through a centrifugal separator, purified gas and a mixed liquid are obtained. The obtained mixed liquid and the white oil-ethanol mixture are collected in a circulation tank to obtain a circulating absorption liquid. When the specific gravity of the circulating absorption liquid is 0.7 kg / L, it is sent to a centrifuge with a rotation speed of 3000 revolutions per minute for 3 minutes of separation to obtain ethanol and absorbent. The obtained ethanol is recovered and stored, and the obtained absorbent is recycled into the absorption tower for reuse. The VOCs concentration of the purified gas at the outlet is measured to be 2 mg / m 3 , and the absorbent recovery rate is 99.8%. Example 4

[0031] A process for recycling white oil to absorb ethanol in waste gas. The process flow diagram is as Figure 1 shown. The absorption tower is a packed tower with internally installed ceramic Raschig rings (pretreated by alkali washing). Waste gas with a flow rate of 30 m 3 / h and an ethanol concentration of 2400 mg / m 3 is introduced into the absorption tower and reacts fully with 5 L of absorbent white oil (white oil viscosity is 10 mPa·s) for 80 minutes to obtain waste gas with entrained liquid and a white oil-ethanol mixture. After the waste gas with entrained liquid passes through a centrifugal separator, purified gas and a mixed liquid are obtained. The obtained mixed liquid and the white oil-ethanol mixture are collected in a circulation tank to obtain a circulating absorption liquid. When the specific gravity of the circulating absorption liquid is 0.75 kg / L, it is sent to a centrifuge with a rotation speed of 4000 revolutions per minute for 5 minutes of separation to obtain ethanol and absorbent. The obtained ethanol is recovered and stored, and the obtained absorbent is recycled into the absorption tower for reuse. The VOCs concentration of the purified gas at the outlet is measured to be 1.8 mg / m 3 , and the absorbent recovery rate is 99.8%. Example 5

[0032] A process for recycling white oil to absorb ethanol in waste gas. The process flow diagram is as Figure 1 shown. The absorption tower is a packed tower with internally installed ceramic Raschig rings (pretreated by alkali washing). Waste gas with a flow rate of 20 m 3 / h, with an ethanol concentration of 2350 mg / m 3 The waste gas is introduced into the absorption tower and reacts fully with 4 L of absorbent white oil (white oil viscosity is 10 mPa·s) for 70 minutes to obtain waste gas with entrained liquid and a white oil-ethanol mixture. After the waste gas with entrained liquid passes through a centrifugal separator, purified gas and a mixed liquid are obtained. The obtained mixed liquid and the white oil-ethanol mixture are collected in a circulation tank to obtain a circulating absorption liquid. When the specific gravity of the circulating absorption liquid is 0.77 kg / L, it is sent to a centrifuge with a rotation speed of 3500 revolutions per minute for 4 minutes of separation to obtain ethanol and the absorbent. The obtained ethanol is recovered and stored, and the obtained absorbent is recycled into the absorption tower for reuse. The VOCs concentration of the purified gas at the outlet is measured to be 1.8 mg / m 3 , and the absorbent recovery rate is 99.8%. Example 6

[0033] The method of Example 5 is adopted, and the white oil is recycled 50 times.

[0034] The experimental results show that after 50 cycles, the recovery rate of the absorbent white oil still remains at 99.5%.

[0035] Comparative Example 1

[0036] The water absorption method disclosed in Chinese invention patent CN109395534B is used to treat the same waste gas as in Example 1 (ethanol concentration 2200 mg / m³, air volume 25 m³ / h).

[0037] The experimental results show that the VOCs concentration after purification is 50 mg / m³, and an additional distillation step is required to recover ethanol, which takes 120 minutes.

[0038] Comparing with the data of Example 1 above: the VOCs concentration is 2 mg / m³, and there is no need for distillation, taking 60 minutes. Therefore, compared with the water absorption method, the technical solution of the present invention has significant advantages.

[0039] Comparative Example 2

[0040] The white oil in Example 1 is replaced with an equal amount of silicone oil, and other conditions are the same as in Example 1.

[0041] The experimental results show that after centrifugation, the separation of silicone oil and ethanol is incomplete (recovery rate 72%), and secondary treatment is required. Moreover, the cost of silicone oil is 3.2 times that of white oil.

[0042] Comparative Example 3

[0043] The centrifugal rotation speed in Example 1 is set to 1000 rpm, and other conditions are the same as in Example 1.

[0044] The experimental results show that white oil and ethanol were not effectively separated, the recovery rate of white oil was only 65%, and the concentration of VOCs after treatment increased to 30 mg / m³.

[0045] Comparative Example 4

[0046] Replace the white oil used in Example 1 with white oil having a viscosity of 20 mPa·s, and other conditions are the same as in Example 1.

[0047] The experimental results show that the absorption efficiency decreased by 30% compared with Example 1, and the separation effect was poor. The amount of ethanol remaining in the white oil after centrifugation reached 2.1 wt%.

[0048] Comparative Example 5

[0049] Use un-alkali-washed ceramic Raschig rings, and other conditions are the same as in Example 1.

[0050] The experimental results show that the wettability of white oil is poor, and the absorption efficiency is only 68% of that in Example 1.

Claims

1. A process for absorbing ethanol in waste gas by circulating white oil, characterized in that: The steps include: S1. Pass the ethanol-containing waste gas into the absorption tower to contact with industrial-grade white oil, the viscosity of the industrial-grade white oil is 5~15 mPa·s, the flash point is ≥150℃, and the density difference between the white oil and ethanol is ≥0.2kg / L. The absorption tower is a packed tower, and the packing is ceramic Raschig ring, and its specific surface area is 200~300m² / m 3 The porosity is 80%~90%. The diameter of the ceramic Raschig ring is 25~50mm, the height is 0.8~1.2 times the diameter, and the surface is pre-treated by alkali washing to enhance lipophilicity. The ratio of white oil volume to exhaust gas flow is 3~5L:15~30m 3 / h, action time 40~80min, to obtain a mixture of gas with liquid and white oil ethanol; S2. The gas entrained with liquid obtained in step S1 is passed into a separator to separate the purified gas and the mixed liquid; S3. The white oil ethanol mixed liquid obtained in step S1 and the mixed liquid obtained in step S2 are fed into a circulation tank to form a circulating absorption liquid; S4. When the specific gravity of white oil in the circulating absorption liquid is 0.6-0.8 kg / L, pump it into a centrifuge and centrifuge it at 2000-4000 rpm for 1-5 min to separate ethanol and recyclable white oil; S5. Recover ethanol and return white oil to the absorption tower for recycling.

2. The process for absorbing ethanol in waste gas by circulating white oil according to claim 1, characterized in that: In step S1, the ratio of white oil volume to exhaust gas flow is 4~5L:20~30m 3 / h, action time is 50~80min.

3. The process for absorbing ethanol in waste gas by circulating white oil according to claim 1, characterized in that: In step S1, the operating temperature of the absorption tower is 20-35°C and the pressure is normal pressure.

4. The process for absorbing ethanol in waste gas by circulating white oil according to claim 1, characterized in that: In step S2, the separator is a centrifugal separator or an inertial demister.

5. The process for absorbing ethanol in waste gas by circulating white oil according to claim 4, characterized in that: In step S2, the separation factor of the centrifugal separator is 800-1500, and the inner wall of the separation chamber is coated with a polytetrafluoroethylene anti-sticking layer.

6. The process for absorbing ethanol in waste gas by circulating white oil according to claim 1, characterized in that: In step S4, the residual ethanol content in the white oil after centrifugal separation is ≤0.5wt%, and the recovery rate is still ≥95% after the white oil is recycled ≥50 times.

7. The process for absorbing ethanol in waste gas by circulating white oil according to claim 1, characterized in that: In step S1, the ethanol concentration in the exhaust gas is 1000-5000 mg / m³, and the total content of VOCs excluding ethanol is ≤10%.

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