Supercritical gasification treatment method for causticizing waste liquid of epoxyalkane prepared by chlorohydrin method

Abstract

The invention relates to a supercritical gasification treatment method for causticizing waste liquid of epoxyalkane prepared by a chlorohydrin method, which comprises the following steps of: after the pumped NaOH causticizing waste liquid is subjected to shallow oxygen dissolution through an oxygen dissolver, pressurizing to be more than or equal to 22.1 MPa through a high-pressure pump, and carrying out heat exchange with synthesis gas subjected to supercritical gasification and supercritical high-temperature purified water in a mixed phase; the method comprises the following steps: heating a high-pressure dissolved oxygen causticization waste liquid to 400-700 DEG C by using an electromagnetic heating tubular reactor, carrying out micro self-heating supercritical gasification, enabling supercritical gasified gas and liquid to enter a supercritical delayed gasification reactor, and staying for 1-180 minutes to generate a mixed phase of synthesis gas and supercritical high-temperature purified water and high-concentration NaCl slurry; the mixed phase of the synthesis gas and the supercritical high-temperature purified water exchanges heat with the high-pressure dissolved oxygen causticization waste liquid and then is subjected to gas-liquid separation, the synthesis gas is discharged, the purified water is recycled, high-concentration NaCl slurry is switched through a bottom lock hopper of the supercritical delayed gasification reactor and diluted into strong brine with the concentration of 31.5 wt%-36.1 wt% with part of the purified water and then is discharged, and the strong brine is returned to an electrolytic bath for recycling.

Description

Technical Field

[0001] The invention provides a supercritical gasification treatment method for caustic waste liquid produced by the chlorohydrin process to produce alkylene oxide, and relates to the field of fine chemicals. Background Art

[0002] The chlorohydrin process for preparing alkylene oxide is to prepare hypochlorous acid by chlorine and water, and then C2-C7 olefins react with hypochlorous acid to obtain chlorohydrin, which is then reacted with slaked lime or caustic soda to generate alkylene oxide, and then separated by ordinary distillation method to obtain refined alkylene oxide. This process was industrialized as early as 1931. It has mature production process, short process, large operating load flexibility, good selectivity, low requirements for raw material purity, safe and stable production, low construction investment, and products with strong cost competitiveness. At present, about 40% of the world's propylene oxide production capacity is produced by the chlorohydrin process. However, the traditional chlorohydrin process device is less environmentally friendly, with large consumption of water resources and chlorine, and the caustic wastewater containing chlorides is difficult to handle, polluting the environment. At the same time, the chloric acid produced also corrodes the equipment more seriously. For example, for every ton of propylene oxide produced, about 1.5 tons of chlorine are consumed, and at least 40 tons of caustic wastewater containing a small amount of organic chloride and more than 2 tons of CaCl2 waste residue are produced.

[0003] In order to solve the three wastes and corrosion defects of propylene oxide produced by the chlorohydrin process, co-oxidation and direct oxidation methods have been developed at home and abroad. The co-oxidation method overcomes the shortcomings of the chlorohydrin process, such as high corrosiveness and large amount of sewage, but its disadvantages are long process flow, many raw material varieties, high propylene purity requirements, and expensive equipment costs. Propylene oxide produces a large number of co-products in the co-oxidation process. Each ton of propylene oxide must produce 2.5 tons of styrene or 2.4 tons of tert-butyl alcohol. The advantages of this process can only be shown when the market demand for propylene oxide and co-products matches; in addition, the COD of sewage produced by this method is high, and the treatment cost accounts for about 10% of the total investment. The advantages of the direct oxidation method are high conversion rate and selectivity, the amount of wastewater is only 30% of other existing technologies, and the energy consumption is 65% of the existing process; the process flow is simple and economical, the by-product is water, the environmental pollution is small, the land use is small, the factory infrastructure investment is small, and the investment can be reduced by 25%, but the technology is immature, the cost is high, and the safety is poor.

[0004] If the existing chlorohydrin process for producing alkylene oxides adopts NaOH causticization reaction, it can solve the problem of pollution treatment of chloride-containing caustic wastewater and low-cost recycling of concentrated brine, and realize closed-loop utilization of chlorine, and significantly reduce costs and water consumption, then compared with co-oxidation and direct oxidation, the chlorohydrin process for producing alkylene oxides has more development advantages. However, the existing caustic wastewater treatment processes have failed to achieve full resource utilization of caustic wastewater, and it is urgent to develop efficient, clean, low-energy consumption treatment and resource utilization processes and equipment technologies for caustic wastewater from chlorohydrin process for producing alkylene oxides, eliminate the industrial bottlenecks of high pollution and high water consumption of chlorohydrin process for producing alkylene oxides, and improve its market competitiveness. Summary of the invention

[0005] The invention aims to overcome the shortcomings of the existing chlorohydrin process alkylene oxide technology in treating caustic waste liquid and invent a supercritical gasification treatment method for caustic waste liquid of chlorohydrin process alkylene oxide. The invention discloses a method for treating caustic waste liquid of chlorohydrin process alkylene oxide by supercritical gasification, wherein the method comprises the following steps: shallowly dissolving oxygen in NaOH caustic waste liquid, self-heating gasification under supercritical conditions under high-pressure pumping and electromagnetic heating, separation of supercritical gas-liquid mixed phase and salt phase, high-pressure lock bucket salt discharge, and recycling of waste heat of high-temperature purified water. The method can solve the industrial bottleneck of high water consumption and difficulty in fully resource utilization of highly polluting caustic waste liquid of chlorohydrin process alkylene oxide at low cost, eliminate the serious corrosion of chlorine-containing acid generated by the treatment of caustic waste liquid to equipment, and lay a foundation for the research and development of new chlorohydrin process alkylene oxide technology with low cost, low energy consumption and closed-loop utilization of chlorine.

[0006] The technical scheme of the present invention is as follows: in the process of preparing alkylene oxide by the chlorohydrin process, after the pumped NaOH caustic waste liquid is passed through an oxygen dissolver to shallowly dissolve oxygen, it is pressurized to ≥22.1MPa by a high-pressure pump, and then heat exchange is carried out with the supercritically gasified synthesis gas and supercritical high-temperature purified water mixed phase; the preheated high-pressure dissolved oxygen caustic waste liquid is heated to 400-700°C by an electromagnetic heating tubular reactor for micro-self-heating supercritical gasification, the supercritical gasified gas and liquid enter a supercritical delayed gasification reactor and stay for 1-180 minutes to generate a mixed phase of synthesis gas and supercritical high-temperature purified water and a high-concentration NaCl slurry; the extracted synthesis gas and supercritical high-temperature purified water mixed phase are separated from the high-pressure dissolved oxygen caustic waste liquid after heat exchange, the synthesis gas is discharged, and the purified water is reused; the high-concentration NaCl slurry is switched through the bottom lock bucket of the supercritical delayed gasification reactor, and is diluted with part of the purified water to be 31.5%-36.1% of concentrated brine and then returned to the electrolyzer for recycling.

[0007] Among them, the electromagnetic heating tubular reactor is a tubular reactor in which, under the action of the electromagnetic heating controller, high-frequency alternating current generates an alternating magnetic field through the coil, and the tubular reactor wall and the internal self-mixing and strengthening internal components generate eddy current self-heating, thereby achieving uniform heating of high-pressure dissolved oxygen causticizing waste liquid, rapid temperature rise and gasification reaction; the self-mixing and strengthening internal components are regular packing type, X-cross plate type or spiral plate type.

[0008] A funnel-shaped liquid extraction port is arranged at the center of the supercritical delayed gasification reactor, the funnel is connected to the upper part of the reactor, a gas-liquid mixed phase discharge port is arranged at the top of the reactor, and two or more salt discharge lock hoppers are arranged at the bottom of the reactor; the salt discharge lock hopper is provided with a high-concentration NaCl slurry level detector.

[0009] The oxygen dissolved in the dissolved oxygen tank is 0-15% or saturated.

[0010] The present invention will be described in detail with reference to embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a process schematic diagram of the present invention.

[0012] The accompanying drawings are described as follows:

[0013] 1. Feed pump 2. Oxygen dissolver 3. High-pressure pump 4. Heat exchanger 5. Electromagnetic heating tubular reactor 6. Supercritical delayed gasification reactor 7. Gas-liquid separator 8. Electromagnetic heating controller A. NaOH caustic waste liquid inlet B. Oxygen inlet C. Synthesis gas outlet D. Purified water outlet E. Brine outlet

[0014] The process characteristics of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0015] Embodiment, in the process of preparing alkylene oxide by the chlorohydrin process, 5%-65% NaOH causticized waste liquid from the NaOH causticized waste liquid inlet A is pumped to the oxygen dissolver (2) through the feed pump (1) and saturated with the oxygen from the oxygen inlet B, and then pressurized to ≥22.1MPa by the high-pressure pump (3), and then heat exchanged with the supercritical gasified synthesis gas and supercritical high-temperature purified water in the heat exchanger (4); the high-pressure dissolved oxygen causticized waste liquid is heated to 400-700°C by the electromagnetic heating tubular reactor (5) for micro-self-heating supercritical gasification, and the supercritical gasified gas and liquid enter the supercritical delayed gasification reactor (6) ) for 1-180 minutes to generate a mixed phase of synthesis gas and supercritical high-temperature purified water and a high-concentration NaCl slurry; the mixed phase of synthesis gas and supercritical high-temperature purified water comes out from the top of the supercritical delayed gasification reactor (6), exchanges heat with high-pressure dissolved oxygen causticized waste liquid in the heat exchanger (4), and then passes through a gas-liquid separator (7) for gas-liquid separation, the synthesis gas is discharged from the synthesis gas outlet C, and the purified water is reused through the purified water outlet D; the high-concentration NaCl slurry is switched through the bottom lock hopper of the supercritical delayed gasification reactor (6), and is diluted with part of the purified water to become a concentrated brine of 31.5%-36.1%, and then returned to the electrolytic cell for recycling.

[0016] The electromagnetic heating tubular reactor (5) is a tubular reactor in which, under the action of an electromagnetic heating controller (8), high-frequency alternating current is passed through a coil to generate an alternating magnetic field, and the tubular reactor wall and the internal self-mixing and strengthening internal components generate eddy current self-heating, thereby achieving uniform heating, rapid temperature rise and reaction of the high-pressure dissolved oxygen causticized waste liquid; the self-mixing and strengthening internal components are regular packing type, X-cross plate type or spiral plate type.

[0017] A funnel-shaped liquid extraction port is arranged at the center of the supercritical delayed gasification reactor (6), the funnel is connected to the upper part of the reactor, a gas-liquid mixed phase discharge port is arranged at the top of the reactor, and two or more salt discharge lock hoppers are arranged at the bottom; the salt discharge lock hoppers are provided with a high-concentration NaCl slurry level detector.

[0018] The oxygen dissolved in the oxygen dissolver (2) is 0-15% or saturated.

[0019] The specific reaction conditions and experimental results are as follows:

[0020] (1) After saturated dissolved oxygen, at 24 MPa and 450°C, the micro-autothermal supercritical gasification reaction was 2 seconds when heated, and the supercritical delayed gasification reaction was 10 minutes. The COD removal rate was 99.1%, and the H2 content in the synthesis gas was 70% and CO was 10%.

[0021] (2) After saturation with dissolved oxygen, the micro-autothermal supercritical gasification reaction was carried out for 2 seconds at 24 MPa and 550°C, and the supercritical delayed gasification reaction was carried out for 5 minutes. The COD removal rate was 99.9%, and the H2 content in the synthesis gas was 65% and the CO content was 8%.

[0022] This method is not only used to treat NaOH causticized wastewater from the chlorohydrin process for producing alkylene oxide, but can also be used for resource disposal of high-concentration biodegradable organic wastewaters such as coking wastewater, pharmaceutical wastewater, printing and dyeing wastewater, and papermaking black liquor.

[0023] The supercritical gasification treatment method of NaOH caustic waste liquid for preparing alkylene oxide by the chlorohydrin process provided by the present invention realizes slightly self-heating supercritical gasification by shallowly dissolving oxygen in the NaOH caustic waste liquid, strengthens mixing and inhibits salt precipitation scaling corrosion while heating by eddy current self-heating through self-mixing strengthening internal components to realize rapid and uniform heating, improves gasification efficiency through supercritical delayed gasification reaction, and realizes separation of water-gas mixed phase and brine by utilizing supercritical water characteristics, recovers waste heat of high-temperature purified water and recycles it, and the effective utilization rate of electric energy is greater than 95%, and organic matter in the caustic waste liquid is completely gasified to produce H2 The production of more than 60% syngas, COD removal rate greater than 99%, brine concentration can be flexibly adjusted at low cost according to the needs of the electrolyzer, and the cost and investment of resource management of NaOH causticizing waste liquid are reduced by more than 70% compared with traditional treatment methods, laying the foundation for low-cost and low-energy chlorine closed-loop utilization, breaking the industrial bottleneck of high water consumption and high pollution of causticizing waste liquid in the production of alkylene oxide chlorohydrin method, eliminating the serious corrosion of chlorine-containing acid produced by the disposal of causticizing waste liquid to equipment, and providing reliable conditions for the implementation of new chlorohydrin method alkylene oxide technology with low cost, low energy consumption and chlorine closed-loop utilization.

Claims

1. A supercritical gasification method for treating caustic waste liquid from the production of alkylene oxide by the chlorohydrin process, characterized in that In the process of preparing alkylene oxide by the chlorohydrin process, the pumped NaOH caustic waste liquid is passed through an oxygen dissolver to shallowly dissolve oxygen, and then pressurized to ≥22.1MPa by a high-pressure pump, and then heat exchanged with the supercritical gasified synthesis gas and supercritical high-temperature purified water mixed phase; the preheated high-pressure dissolved oxygen caustic waste liquid is heated to 400-700°C by an electromagnetic heating tubular reactor for micro-self-heating supercritical gasification, and the supercritical gasified gas and liquid enter a supercritical delayed gasification reactor and stay for 1-180 minutes to generate a mixed phase of synthesis gas and supercritical high-temperature purified water and NaCl slurry; the extracted synthesis gas and supercritical high-temperature purified water mixed phase are separated from the high-pressure dissolved oxygen caustic waste liquid after heat exchange, and the synthesis gas is discharged and the purified water is reused; the NaCl slurry is switched through the bottom lock hopper of the supercritical delayed gasification reactor, and is diluted with part of the purified water to become 31.5wt%-36.1wt% concentrated brine and then returned to the electrolyzer for recycling.

2. The method for supercritical gasification of caustic waste liquid from chlorohydrin process to alkylene oxide according to claim 1, characterized in that The electromagnetic heating tubular reactor is a reactor in which high-frequency alternating current generates an alternating magnetic field through a coil under the action of an electromagnetic heating controller, and the tubular reactor wall and the internal self-mixing strengthening internal components generate eddy current self-heating; the self-mixing strengthening internal components are regular packing type, X-cross plate type or spiral plate type.

3. The method for supercritical gasification of caustic waste liquid from chlorohydrin process for preparing alkylene oxide according to claim 1, characterized in that A funnel-shaped liquid extraction port is arranged at the center of the supercritical delayed gasification reactor, the funnel is connected to the upper part of the reactor, a gas-liquid mixed phase discharge port is arranged at the top of the reactor, and two or more salt discharge lock hoppers are arranged at the bottom of the reactor; the salt discharge lock hopper is provided with a NaCl slurry level detector.

4. The method for supercritical gasification of caustic waste liquid from chlorohydrin process for preparing alkylene oxide according to claim 1, characterized in that The amount of shallowly dissolved oxygen in the oxygen dissolver is 0-15wt% or saturated.

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