HYDROGEN PEROXIDE PLANT - FIXED BED TECHNOLOGY

HYDROGEN PEROXIDE PLANT - FIXED BED TECHNOLOGY

DESIGN BASIS

The design of the plant is based on parameters, data and information contained in this section. A change of any data herein may require a change in the design of the plant and/or the performance of the Plant.

1.            Plant Capacity

The plant is designed to produce:

50.000 MTPY, 30% crude grade hydrogen peroxide

or,

30.000 MTPY, 50% technical and chemical grade hydrogen peroxide.

Annual operating hours of the hydrogen peroxide plant is 8000.

2.            Product Quality

  30%                             50%

Hydrogen Peroxide (% w/w) ≥                        30                                50

Free Acid (%w/w) ≤                                       0.040                           0.040

Non volatile residue (%w/w) ≤                        0.10                             0.10

Stability (%)≥                                                 97                                97

Appearance                                                colorless                      colorless           
                                                                transparent                  transparent

                                                                    liquid                            liquid

  

MANUFACTURING PROCESS

The manufacturing process involves the catalysis of the reaction of H₂ with atmospheric O₂ to give H₂O₂.

Hydrogen peroxide is manufactured using the anthraquinone process. Anthraquinone (Q) is used as a H₂ carrier. This process is a cyclic operation where the alkyl anthraquinone is reused. The Synthesis Loop consists of sequential hydrogenation, filtration, oxidation, extraction, purification, concentration, stabilization and storage stages.

A number of ancillary processes are also involved.

Step-1: Hydrogenation

An alkyl anthraquinone is dissolved in two solvents, one nonpolar and the other polar. Collectively the anthraquinone and solvents are called the working solution. This working solution is recycled.

The working solution in the working solution receiver is transferred by working solution pump through the preheater and then to the hydrogenation reactor. The hydrogen from the hydrogen compressor passes from the preheater and then enters with the working solution into the top of hydrogenation reactor. The working solution and the hydrogen pass a distributor and flow uniformly downwards. During the process of flowing, the hydrogenation reaction takes place with the action of catalyst. The temperature of hydrogenation reactor is controlled according to the efficiency of hydrogenation. Catalytic hydrogenation converts 2-ethylanthraquinone in the working solution to 2-ethylanthrahydroquinone, and converts 2-ethyltetrahydroanthraquinone to 2-ethyltetrahydroanthrahydroquinone. The flow rate of hydrogen fed into the hydrogenation reactor is controlled to around 45^oC according to the pressure at the top of hydrogenation reactor and recorded before the hydrogen preheater. The temperature of the working solution of the outlet of preheater is controlled according to the efficiency of hydrogenation. The working solution at the bottom of the hydrogenation reactor under the action of pressure inside the reactor passes through a filter, liquid-gas separator (at the same time, part of working solution passes through hydrogenated white earth bed regenerator) then enters hydrogenated W.S. receiver. There is a level control at the bottom of hydrogenation reactor (to control the take-off rate according to the level). The unreacted hydrogen discharge from the lower part of hydrogenation bed and passes through a condenser and a condensate-metering tank, the organic liquid is separated.

The hydrogenation stage is carefully controlled to avoid over-hydrogenation of the anthraquinone rings. Basicity and moisture content are important for optimum catalyst and activity.

Step-2: Filtration

The working solution that now contains hydrogenated anthraquinone is then filtered to remove any trace levels of catalyst. If the catalyst is not removed then it will decompose the hydrogen peroxide in later stages, reducing yields and causing potential hazards.

Step-3: Oxidation

The hydrogenated working solution from the receiver is fed to the bottom of upper section of oxidation reactor by pump, combining in parallel flow with the air coming from the separator of the lower section of oxidation reactor, flow upward to precede oxidation. The partially oxidized W.S. is fed along with the air into the upper section separator. Gas and W.S. get separated. By the pressure inside the separator and the action of static level, the W.S. leaving the bottom of separator is fed into the bottom of the lower section, combining in parallel flow with the fresh air sent by the air compressor; flow upward to precede a second oxidation. The oxidized W.S. leaves from the top of lower section of oxidation reactor and enters in the separator of lower section. The gas is fed to the upper section of the oxidation reactor. The oxidized W.S. passes a cooler and is sent to the oxidized W.S. receiver. The take-off rate is controlled according to the level in the separator.

The tail gas from the separator of the upper section is condensed, separated and absorbed by active carbon, and then vented. The venting rate is controlled according to the pressure in the separator of the upper section. The temperature of the oxidation reactor is controlled according to the efficiency of oxidation. The air feeding rate is controlled according to the oxygen content in the tail gas. In the process of oxidation, 2-ethylanthrahydroquinone is oxidized to 2-ethylanthraquinone, and 2-ethyltetrahydroanthrahydroquinone is oxidized to 2-ethyltetrahydroanthraquinone, and the hydrogen peroxide is formed at the same time. As no catalyst is used, hence this step is often referred to as auto-oxidation.

Step-4: H₂O₂ Extraction

The oxidized W.S. in the receiver is sent by a pump to the bottom of the extraction column. The demineralized water from the demineralized water make-up tank is sent by a pump to the top of the extraction column. The dematerialized water flows downward from the top and oxidized W.S. flows upward from the bottom, the dematerialized water and the oxidized W.S. contact counter- currently and proceeds extraction. The water reaches the bottom of the extractor and contains 25-35% w/w crude hydrogen peroxide, whilst the working solution that leaves the top of the extractor is free of hydrogen peroxide and is pumped back to the hydrogenator. This working solution now contains the original alklyanthraquinone and tetrahydroalkylanthraquinone. The pure water extracts the hydrogen peroxide in the oxidized W.S. and a water solution of 30 wt% hydrogen peroxide is formed, it is called extracting.

The extractant leaves the bottom extraction column passing a purification column to remove the organic impurities, then sent to the Concentration Unit as crude product. The take-off rate is controlled by the concentration of extractant. The W.S., after extraction, is called raffinate, it leaves from the upper part of the extraction column, passing a separator to remove the most part of carrying over water content, and then sent to the post-treatment section. The level in the separator controls the take off rate. The water feed rate to the extraction column is controlled by the interface level at the top of the extraction column between the raffinate and the extracting water. The aromatic solvent feeding rate to the purification column is controlled by the efficiency of the column.

Step-5: Post Treatment

The raffinate coming from the separator is fed into the bottom of the drying column flows from the bottom to top, passing the K₂CO₃ medium, the most part of H₂O₂ content in the raffinate is decomposed, the raffinate and the K₂CO₃ medium form two different layers at the middle of the column. The raffinate goes to the inner separator in the top section to remove the carrying-over of K₂CO_3. Then the raffinate enters a K₂CO₃ settling tank to separate remaining K₂CO₃, and then enters the white earth bed regenerator, passing upward through the Al₂O₃ layer, and then the W.S. is purified and enters into the W.S. receiver. The K₂CO₃ discharged from the bottom of the drying column is concentrated and cooled, sent back to the drying column by a pump.

Step-6: Concentration Unit

In the Concentration Unit, the crude hydrogen peroxide solution from the Reaction Unit is concentrated to final hydrogen peroxide solution with a concentration of 50%. A vacuum distillation system is utilized to purify and concentrate the crude hydrogen peroxide. Distillation must take place at reduced pressure due to the risk of uncontrollable decomposition at higher temperatures. The liquid feed with a concentration of 30% hydrogen peroxide is collected in the feed drum. From there it is forwarded by pump to the falling film evaporator, passing through the crude feed filter and the crude feed preheater, where it is warmed up by the bottoms product. In the falling film evaporator the feed is nearly totally vaporized, resulting in a vapor phase and a liquid phase called purge. The vapor is passed through a demister removing almost all the droplets carried over the vapor. The purge is drawn off from the evaporator with a H₂O₂ concentration of approx. 51 wt%. The evaporator is heated up by low pressure steam generated by mixing of column overhead vapors with live steam within a steam ejector. The liquid phase from the evaporator is pumped by a pump. Part is recirculated to the evaporator and part is pumped to battery limits, passing first through the cooler, and stored as technical grade hydrogen peroxide, which can be diluted to other concentrations using demineralized water. The vapor phase from evaporator is fed to the column. The column is equipped with special packing. The mass transfer between hydrogen peroxide and water is carried out at the surface of the packing, where liquid phase (demin. water) is in close contact with the gas phase (vapor). A reboiler is installed in the bottom of the column. The chemical grade product flows by gravity through the feed preheater, where it is cooled into the product tank. Part of the cooled product is recirculated by the product pump back to the tank and part is pumped out to the battery limits.

Step-7: Stabilization

Whatever the quality of the water, diluting hydrogen peroxide always tends to affect the stability of the product. It is therefore advisable to add small amounts of stabilizers to avoid the solutions decomposition.

For diluted solutions of hydrogen peroxide at concentrations lower than or equal to 30%, the pH should be adjusted to between 2 and 3 with a solution of Sodium Steanate.

According to applications, other stabilizers may be added such as orthophosphoric acid, ortho-oxyquinoline sulphate, dipicolinic acid, aminomethylene phosphonic acids and derivatives, etc.

In all cases, the pH of hydrogen peroxide solutions should be checked after dilution, and should be below 3.

Step-8: Storage

Four storage tanks are provided to store the Hydrogen Peroxide product in bulk. As a rule, storage capacity should be at least equal to 1.5 times the volume of any delivery if operations are to run smoothly.

Storage tanks are located outside buildings, away from combustible materials as well as heat sources.

For safety reasons, all hydrogen peroxide transfer pipes are set up outdoors, in readily accessible areas, and with unrestricted flow at both ends. Because of possible gas formation, no hydrogen peroxide is allowed to remain trapped in a section of pipe or in a closed vessel if there is no possibility for expansion. The pipes are designed so that no liquid may be allowed to flow from the storage tanks back to the supply containers. In case the analysis report is satisfied, the product is sent by a pump to the product overhead tank and filled into the drums with packaging machine.

Step-9: Packaging

A certain amount of stabilizer is added to the final product in the product tank, stirring by compressed air for two hours, at the same time the organics in the product are blown out.

Hydrogen Peroxide product is available to customers in standard packing of 30 kg Polyethylene containers.

INPUT REQUIREMENTS

1.            Raw Materials Specifications

1.1       Heavy Aromatic Hydrocarbon:

Main component                                          : Isomer of Trimethyl Benzene

Aromatics Contents min.                            : 96%

Boiling Range                                              : 150-200°C

Density                                                          : 0.87-0.88 g/cm³ (20°C)

Total Sulphur Content max.                       : 5 ppm

1.2       Ethyl Anthraquinone

Appearance                                                  : Pale yellow powder or flake

Purity                                                              : 98%

Melting Point min.                                        : 108°C

Insoluble residue in Benzene max.         : 0.3%

1.3       Trioctyl Phosphate

Purity min.                                                     : 99%

Density                                                          : 0.92 ± 0.003 g/cm³

Interfacial Tension with water min.                : 18 dyne/cm

Acid Value max.                                           : 0.1 mg KOH/g

Appearance                                                  : Colorless transparent liquid.

1.4       Phosphoric Acid

Purity min.                                                     : 85%

Chloride max.                                               : 0.0003%

Fe max.                                                          : 0.003%

1.5       Activated Alumina

Appearance                                                  : White spherical grains

                                                                          (Φ = 3-5 mm)

Activity min.                                                   : 60% (Absorption, Acetic Acid)

Strength min.                                                : 50 N/grain

1.6       Potassium Carbonate

Appearance                                                  : White powder

Purity                                                              : 92%

1.7                         Hydrogen

Purity min.                                                     : 98.5 (v/v)

Oxygen max.                                                 : 0.3% (v/v)

Carbon dioxide max.                                   : 5 ppm

Carbon monoxide max.                              : 5 ppm

Chlorine max.                                               : 1 ppm

Methane max.                                               : 1.5 % (v/v)

Pressure (Abs.) min.                                    : 0.55 MPa                

1.8       Air

Pressure                                                        : 0.65 MPa

Dust, rust, oil                                                 : None

1.9       Nitrogen        

Purity min.                                                     : 99% (v/v)

Oxygen max.                                                 : 1 % (v/v)

Pressure (Abs.) min.                                    : 0.55 MPa

1.10    Demineralized Water         

Electrical Conductivity max.                       : 0.0001 S/cm

pH                                                                   : 6-7

Pressure (Abs.) min.                                    : 0.6 MPa

2.            Utilities Specifications

All data are at battery limit, ground level, except otherwise specified. The battery limits of the plant are assumed to comprise the equipment listed in related appendix with all interconnections within the individual Plant sections.

For connections to other Plant sections and to installations outside the Plant, the battery limits are assumed to be located within 1.0 m from the edge of the respective Plant sections.

2.1       Steam

Pressure                                                        : 0.6MPa (g)

Temperature                                                 : Saturated

2.2       Cooling Water

Pressure min.                                               : 0.4 MPa (g)

Supply Temperature                                    : 30 °C

Return Temperature                                    : 35 °C

2.3       Chilled Water

Pressure min.                                               : 0.4 MPa (g)

Supply Temperature                                    : - 2 °C

Return Temperature                                    : 4 °C

2.4       Electric Power Supply

Voltage                                                          : 380/220 V

Phases/Frequency                                      : 3/50 Hz

Class                                                              : IP 55

2.5       Instrument Air

Pressure min.                                               : 0.6 MPa (g)

Dew Point                                                     : - 40 °C

Oil and dust free

CONSUMPTION FIGURES (Average of 2000, 2001, 2002 years’ real figures)

1.         Raw Materials (Per Ton 50% H₂O₂)

ITEM                                                         UNIT                                         QUANTITY

Aromatic Hydrocarbon                                kg                                                  6.66

2-Ethyl Anthraquinone                               kg                                                  1.11

Trioctyl Phosphate                                       kg                                                  0.68

Phosphoric Acid                                          kg                                                  0.65

Activated Alumina                                       kg                                                  3.90

Potassium Carbonate                                 kg                                                  1.43

Hydrogen                                                      Nm³                                              380

Air                                                                   Nm³                                              2014

Nitrogen                                                         Nm³                                              5

Dematerialized Water                                  m³                                                 0.80

Stabilizer                                                       kg                                                 0.015        

Palladium Catalyst                                      kg                                                  0.15

2.         Utilities (Per Ton 50% H₂O₂)

ITEM                                           UNIT                                         QUANTITY

Steam                                          Mt                                                 0.88
Cooling Water                               m³                                                  395

Chilled Water                                m³                                                  10

Electric Power                               kWh                                               420  

WASTE OUTPUT

1.         Waste Water COD               : 1000-2000 ppm

Quantity                                        : 0.4 m³ / ton 50% H₂O₂                  

2.         Solid Waste

Spent activated alumina with small amount of aromatics

Quantity                                             : 3.90 kg / ton 50% H₂O₂

ROLE OF THE LABORATORY

The purpose of the laboratory is to provide information on the process performance and to carry out quality control testing of hydrogen peroxide. Proprietary equipment is used to measure the synthesis loop operation at each stage of the process. This information is used by operations personnel to control the loop.

Utility testing is carried out in support of on-line process instrumentation.

  

ENVIRONMENTAL IMPLICATIONS

The process is inherently very friendly to the environment. The major sources of waste are liquid wastes from decant water cooling tower blow down and demineralization plant wash water. Both of these effluents are pH adjusted before being pumped to drain. Their benign nature and the presence of part per million levels of peroxide make them easy to treat.

Gaseous emissions of solvents are minimized through the waste gas system and by having solvent storage tanks vented to activated carbon scrubbers. Liquid solvent waste is incinerated as necessary.