Issue 24/2015 - Explosion-proof transformation of the extraction and purification process of hydrogen peroxide plant

First, the process flow introduction

At present, the production process of hydrogen peroxide at home and abroad is mainly palladium catalyst-anthraquinone method, and the process flow mainly includes hydrogenation, oxidation, extraction purification and regeneration processes
.

1.
In the hydrogenation process
, heavy aromatic hydrocarbons are used to dissolve 2-ethylanthraquinone and tetrahydro2-ethylanthraquinone, and trioctyl phosphate that can dissolve hydroanthraquinone are mixed into a working solution
in a certain proportion.
The working liquid is hydrogenated by catalytic (using palladium metal as catalyst) to reduce part of the anthraquinone hydrogenation to hydroanthraquinone to obtain hydrogenated liquid
.

2.
The oxidation process
uses air to oxidize hydrogenated liquid, hydroanthraquinone is reconverted into anthraquinone and hydrogen peroxide is produced in the working solution at the same time to obtain the oxidation solution
.
The oxidized air brings out part of the working liquid, collects and reuses it by condensation, and the exhaust gas is adsorbed by activated carbon and then emptied
.

3.
The extraction and purification process
extracts hydrogen peroxide in the oxidation solution with pure water and purifies it by pure heavy aromatic hydrocarbon reverse extraction to obtain about 27.
5% commercial hydrogen peroxide
.

4.
The working liquid extracted by the regeneration process is purified and regenerated after cleaning, drying, alkali separation, alumina clay adsorption, etc.
, and is reused in the hydrogenation process

.
The working fluid is recycled to form a continuous production system
.
The working liquid alkali washing and water washing are respectively multi-stage counter-current washing, the alkali washing wastewater is discharged as waste liquid, and the washing wastewater enters the sewage treatment station
.

Second, the transformation of the extraction and purification process

1.
There are safety hazards
in the traditional processThe traditional extraction and purification process flow is as follows: using the difference in the solubility of hydrogen peroxide in water and working liquid and the density difference between the working liquid and water, the working solution containing hydrogen peroxide is extracted with pure water in the extraction tower to obtain hydrogen peroxide aqueous solution
.
The hydrogen peroxide aqueous solution is purified by heavy aromatic hydrocarbons in the purification tower to obtain hydrogen peroxide products
with a concentration of 27.
5%.
After the extraction liquid in the upper part of the extraction column overflows through the pipeline to the extractor separator, it enters the post-treatment process, and the hydrogen peroxide content in the extraction liquid is controlled below 0.
35g/L
.
See Figure 1
for details.

The extraction and purification process is the main process
for the production of hydrogen peroxide.
The danger of this process comes from the series mixing of different materials and the intrusion
of impurities.
In the extraction tower and purification tower to store a large amount of hydrogen peroxide, all impurities that can promote its decomposition (such as alkali, metal ions, catalyst powder, alumina powder, etc.
) will cause the rapid decomposition of hydrogen peroxide, so that the temperature and pressure rise, resulting in the working fluid from the system vent or the weak point of the equipment, combustion and explosion accidents
.
These impurities are entrained by the working fluid, hydrogenation, oxidation and post-treatment processes before entering the
extraction column.

The extraction and purification process is atmospheric operation, and in the traditional process, the extraction tower, the extraction liquid separator and the venting pipeline of the working liquid metering tank are introduced into the high aggregate tank and then vented
centrally.
The upper part of the extraction tower from the outlet to the inlet of the extractive liquid separator is about 10 meters different, when the extractive liquid overflows, a large amount of air enters from the top vent port of the extraction tower, and the extractive liquid enters the extractor separator, which is very easy to generate static electricity
.
Moreover, the top of the extraction tower is aromatic hydrocarbon vapor, if improper operation or other reasons cause the decomposition of hydrogen peroxide in the extraction tower is uncontrollable, the temperature of the aromatic hydrocarbon vapor at the top exceeds 45 °C, which can easily cause the flash explosion
of heavy aromatic hydrocarbons in the gas phase space at the top of the extraction column.

2.
Explosion-proof transformation
first, the extraction tower is vented separately (separated from the venting of the extractor separator and the working liquid metering tank, and the high-level aggregate tank is removed); The outlet interceptor of the extractive liquid is moved upwards to reduce the gas phase space
at the top of the extraction column.

Second, the gas phase space of the extraction tower, the extractive liquid separator and the working liquid metering tank is protected by nitrogen filling to reduce the oxygen content
of the gas phase space.
In the upper part of the extraction tower, the remote pressure change and oxygen content are set up online analysis, and the remote pressure change and the nitrogen control valve form a control loop to ensure the slight positive pressure at the top of the extraction tower and the oxygen content in the gas phase space below 5%, so as to ensure that the aromatic hydrocarbon vapor in the gas phase space is far away from its explosion range
.

Thirdly, the packing in the interface area of the extraction column and the packing in the extractive liquid separator are changed from polypropylene modified filler to stainless steel corrugated plate packing that is not easy to accumulate static charge
.
The extraction tower residual liquid outlet interceptor is deeply equipped with a rounded serrated structure in the upper part of the half-pipe part inside the extraction tower, which is conducive to gas breaking and reducing the problem of liquid gas in the extraction liquid outlet pipeline; The outlet pipeline of the extractive liquid is led to the top of the tower by a gas phase tube, which is conducive to the balance between the top of the extraction column and the outlet pipeline of the
extractive liquid.
All pipelines, including the extraction column residual liquid outlet pipeline, should be electrostatically grounded (electrostatic jumping between flanges).


Fourth, the top of the extraction tower is equipped with two sets of remote level gauges, which form an interlock with the oxidizing liquid pump, and stop the pump when the liquid
level is high.

Fifth, a gas-liquid separation device is set up at the top of the extraction tower, and a guide pipe is set up in the lower part to ensure that the droplets separated from the released air return to the system
.

The process flow of extraction and purification after the transformation is shown in Figure 2
.

3.
The design of the modified effect
extraction tower and the residual liquid separator nitrogen filling protection, the transformation of the top internals of the extraction tower, and the re-selection of packing have played a great role
in the safe and stable operation of the atmospheric pressure operation part of the hydrogen peroxide unit.
Compared with the traditional process, after the transformation, the intrinsic safety is guaranteed and has strong promotion value
.

This process is calculated from the safety aspect: reduce the gas phase space at the top of the extraction column, the extractor separator and the working liquid metering tank; Reduce the oxygen content of the gas phase space at the top of the extraction column, extractive liquid separator and working liquid metering tank to ensure that the aromatic hydrocarbon vapor in the gas phase space is far away from its explosion range and ensure intrinsic safety; Reduce the accumulation of static electricity inside the extraction column, the extraction liquid separator and the extraction tower residual liquid pipeline and export
it in time.

Before the transformation of the extraction and purification process, the total carbon content of 27.
5% hydrogen peroxide was about
300×10-6.
Since the start-up after the transformation, the hydrogen peroxide plant has reached full production, and the total carbon content of 27.
5% hydrogen peroxide is less than 100×10-6, which is lower than that of similar scale plants in China, and does not need to be refined to meet the production requirements of caprolactam plants; After the nitrogen filling protection is set at the top of the extraction tower, the oxygen content of the gas phase space is below 5%, the outlet temperature of the extract liquid is lower than 45 °C, and other process indicators are within the normal range
.