Hydrogen peroxide is a relatively simple material,which resembles water in many of its physicalproperties including melting point temperature,dielectric constant, and hydrogen bonding (Table 1).Hydrogen peroxide (H2O2) solutions are clear,colorless, water-like in appearance, and can bemixed with water in any proportion. At highconcentrations, H2O2 has a slightly pungent oracidic odor. It is nonflammable at anyconcentration. The oxygen exists in the peroxogroup in the comparatively unstable oxidation state-I. Therefore, depending on the co-reactant,hydrogen peroxide can function as an oxidizing oras a reducing agent. The reaction products arewater (oxidation state -n) or oxygen (oxidationstate 0). However, hydrogen peroxide actspredominantly as an oxidizer.
Table 1: Physical properties of hydrogen peroxide atdifferent concentrations
Manufacture of Hydrogen Peroxide
Electrochemical Processes
The formation of hydrogen peroxide via theelectrolysis of aqueous sulfuric acid wasdiscovered in the middle of the 19th century.During this electrolysis, peroxodisulfuric acid isformed, subsequently hydrolyzed by water to givesulfuric acid and hydrogen peroxide via theperoxomonosulfuric acid (Caro's acid)intermediate. After the change to ammoniumsulfate as the starting material was made, theproduction of H2O2 increased steadily. Until themid 1950s, around 80% of the H2O2 producedglobally followed this route. All electrochemicalprocesses lost their competitiveness after the
introduction of the AO process because of theirhigh-energy requirements (electric and thermal)created unacceptable costs. Only in places withlow energy costs, such as states from the formerSoviet Bloc, the electrochemical route continuesuntil today.
Direct Synthesis
Several companies studied the direct synthesis ofH2O2 starting from elemental oxygen andhydrogen. A process for the direct reaction ofhydrogen and oxygen represents a considerablechallenge in catalysts and process design. Thereaction is accomplished with oxygen and aheterogeneous platinum group catalyst in acidicaqueous solutions under high pressure (>50 bar)and low temperature (< 10 °C). The solutionscontain small amounts of halide as a promoter.
Anthraouinone Process
The decisive break-through in the industrialproduction of H2O2, which enabled theconstruction of large-scale plants, came with thedevelopment of the organic auto-oxidation process(so-called AO process)1. Today commercialproduction of hydrogen peroxide is carried out bythis process, an indirect reduction of gaseousoxygen with hydrogen gas through the use ofsuitable organic carrier molecules (Figure 1).Alkylated anthraquinones (such as 2-aiky!-9,10-anthraquinone) are the most commonly employed
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
carriers and are used In all Degussa-Huls H2O2plants. First, the anthraquinone reacts withhydrogen in the presence of either a nickel orpalladium catalyst to form the correspondinghydroquinone that is then air oxidized to yieldhydrogen peroxide and to reform the 2-alkylanthraquinone.
This auto-oxidation process is carried out in anorganic medium, which is known as the "workingsolution." The working solution is typically aproprietary solvent blend which is chosen for itsability to solubilize both quinones (which dissolvewell in non-polar aromatics) and hydroquinones(which dissolve well in polar solvents). Theworking solution must be non-toxic (because
Figure 2: Schematic description of manufacturing processhydrogen peroxide is used in regulated food anddrug applications) and chemically stable, in bothstrongly hydrogenating and oxidative reactionenvironments.
The crude hydrogen peroxide is then extractedwith water and the working solution is recycledback to the hydrogenator for reuse. The aqueoushydrogen peroxide from the extractor has aconcentration of only 15 - 40% and iscontaminated with dissolved organic matter whichis formed by the chemical degradation of theworking compound (anthraquinone) and theworking solution. These organic impurities can beremoved by a variety of purification methods andthe peroxide is then sent to a concentration unitwhere it is distilled up to active levels of 50-70%.Figure 2 gives an overview of the process.
Concentration of Hydrogen Peroxide
To bring the product up to concentrations above70%, Degussa-Huls runs a second distillationprocess in which the excess water is removed.Since pure hydrogen peroxide has a boiling pointof 150 °C, and the fact that water and hydrogen
peroxide do not form an azeotrope, distillation is aviable process. As a function of pressure andtemperature, the composition of the vapor phaseover concentrated solutions of hydrogen peroxidecan reach values that propagate a locally initiatedspontaneous decomposition. Hydrogen peroxidevapors can decompose explosively at atmosphericpressure if the hydrogen peroxide concentration inthe vapor phase reaches a level above 26 mol%(or 40% by weight)2. This explosion can betriggered by an energy source, contact withcataiytically active materials, or at temperaturesabove 150 °C even by cataiytically non-activematerials. As Figure 3 shows, such vaporconcentrations can occur at normal pressure andat H2O2 concentrations of 74% and higher in thesolution. At higher pressures the critical vaporconcentration falls below 26 mol%; at lowerpressure it rises. Although some references referto an "explosive range" for HTP, from a purelytechnical standpoint, the product does not explodebut rather, undergoes a spontaneous chemicaldecomposition to water and oxygen. Therefore,adding inert gases, oxygen or water vapor duringthe concentration process will have no meaningfuleffect on stability.
This is the reason why the concentration processis operated under vacuum. Now, under vacuumconditions, any oxygen gas liberated throughproduct decomposition (caused by increases intemperature or molar concentration) will not havea significant impact on the total pressure of thesystem. To our know-ledge, the initial pressurewill only be tripled during a decomposition.According to results achieved by Degussa-Hulsaccredited Safety Data Testing Center inGermany, the presence of a liquid phase does notsustain the explosion. In the vacuum distillation,water is removed at the top of the column leavingconcentrated hydrogen peroxide behind.However, there are three important factors thatmake this distillation process one that requires ahigh level of technical sophistication in order to becarried out in a safe and efficient manner
• The non-volatile impurities coming in withthe feedstock remain in the product
• The H2O2 decomposition rate increasesabout 2.3 times for each 10 °C rise intemperature
• H2O2 vapors above certain concentrationlimits can spontaneously decompose,even at ambient temperatures
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
Concentration of hydrogen peroxide by fractionalcrystallization is another option. The solid-liquidphase diagram (see Figure 3) for the systemhydrogen peroxide-water is relatively simpleshowing depression of the freezing point of eachcomponent by addition of the other componentand two eutectic points. The 70% liquid is chilledto -55 °C, which forms a two-phase systemconsisting of solid hydrogen peroxide and a 62%concentration liquid. Because the solid hydrogenperoxide occludes significant amounts of motherliquor, it gets centrifuged and separated beforethawing. The majority of impurities remain in theliquid rather than in the solid. For reuse the 62%liquid needs to be distilled to 70%. Even thoughthis process is safer than a distillation, to ourknowledge nobody is using it on a commercialscale.
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Figure 3: Liquid-vapor phase and solid-liquidphase diagrams for the system
For performance reasons, the aerospace industryis looking for higher and higher concentrations.However, as the concentration increases, thedecomposition temperature reaches and exceedsthe sintering temperatures for silver-plated gauzecatalysts (see Table 2 for adiabatic decompositiontemperatures). Thus, striving for higher HTPconcentrations goes hand in hand with thedevelopment of temperature resistant catalysts.
The calculations are based on the assumption ofcomplete decomposition in an unconfined system,in which the oxygen formed escapes at thedecomposition temperature. The gas volumes(oxygen, water vapor) have been converted todecomposition temperatures according to the idealgas law.
Table 2: Adiabatic decomposition ofstate: solution at 20 °C)
Stabilization
solutions (Initial
Aqueous solutions of hydrogen peroxide alwaysexhibit a certain degree of instability. Regardlessof the concentration, hydrogen peroxide iscontinuously decomposing in a so-called auto-decomposition. The degree of decompositiondepends on such factors as temperature, pHvalue, impurity level, material compatibility, andcontact surface finish. Typically, underappropriate storage conditions commoncommercial grades lose less than 1% of their initialconcentration per year in large bulk containers. Insmaller containers, such as drums, the rate ofdecomposition is less than 2% per year. Thelarger the ratio of container surface to hydrogenperoxide volume, the greater the activity loss.
The use of chemical stabilizers is necessitated by thesupplier's anticipation of the various shipping,storage and technical use requirements3. Differentamounts and types of stabilizing compounds areused for merchant grades: Whereas a grade for achemical synthesis application might be very lightlystabilized, a Cosmetic Grade is highly loaded withinhibitors to cope with contaminants being introducedduring formulation. High purity grades earmarked forthe electronics industry as well as HTP are thelowest stabilized versions. In some cases thesestabilizers may also improve the performance ofhydrogen peroxide in the applications.
Stability is achieved by not just adding a singlecomponent but rather a "cocktail" of differentchemicals. The primary hydrogen peroxide
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
stabilizer is tin supplied as stannate which formscolloidal stannic oxide (SnO2) particles. Normallythe tin is added as an alkali metal stannate, suchas sodium stannate trihydrate or potassiumstannate trihydrate. Unfortunately, positivelycharged tons, such as calcium, magnesium, andaluminum tend to coagulate the so! andconsequently remove the tin by settling orfiltration. Negatively charged ions such aspyrophosphates and phosphates are known aspeptizing agents and, therefore, are added toimprove the stability of colloidal stannic oxide.
Numerous organic phosphonic acids may also beused for stabilization purposes. Those stabilizersact by chelating free metals that catalyze orenhance the peroxide decomposition. However,some of these stabilizers undergo chemicalchanges in peroxide solutions which make thempoor chelators for metals, and hence thestabilizing effect is dissipated. The phosphonicacids may include those with a nitrogen atomwhich is capable of being oxidized to a N-oxide,such as amino tris(methylenej)hosphonic acid)(ATMP) and ethylenediamine tetra(methylene-Bhosphonic acid) (EDTMP), or those not capableof being oxidized, for example 1-hydroxyethyl-1,1-dip.hosphonic acid (HEDP).
In addition to these stabilizers, corrosion inhibitorsto equip hydrogen peroxide for extended storagein metal-based tanks complete the recipe.Nitrates and again pyrophosphate play animportant- role inJhis respecL _ Acids have longbeen known to be useful as buffering agents andto adjust the pH value of a hydrogen peroxideformulation within the optimum range.
Typically, the addition of stabilizer components tothe hydrogen peroxide solution occurs betweenthe concentration step and the storage of theproduct in bulk tanks.
Impurtties in Hydrogen Peroxide
As mentioned earlier, the manufacturing ofPROPULSE HTP includes several purificationsteps but the product stilt contains measurabletrace amounts of organic and inorganic impurities,some of which are poisonous to catalysts. Theorganics are measured as TOC {Total OrganicCarbon) and originate from the working solutionand fragments of the anthraquinone. Theinorganic impurities, mainly chloride and sulfate,come with the utility water supplied to the plant.Any metal contamination in the final product is the
result of equipment corrosion. Therefore, it is ofutmost importance that the hydrogen peroxidefeedstock used for the concentration hasundergone purification steps including afractionated distillation.
Specification of Hydrogen Peroxide
The Military Specification (MIL-P-16005E) issuedin 1968 and officially cancelled in 1988 was, formany years, the only formal document for highstrength hydrogen peroxide. Since the catalysttechnology has not changed appreciably sincethen, today the MIL Spec it is still considered bysome in the industry to be the only specification forhydrogen peroxide that has a demonstratedefficacy.
The specification shown in Table 3 reveals howDegussa-Hiils characterizes its PROPULSE 900Hydrogen Peroxide. Some of the stabilizers andimpurities contained in the product are reflected inthe specification. The given values are targetvalues for our production and are met for eachindividual shipment.
Table 3: Comparison of MIU-P-16005 and PROPULSE 900H2O2 specifications (all values are in mg/L unlessotherwise indicated)
This comparison lays out some differencesbetween the old MIL spec and our current product.As a company committed to Responsible Careand Product Stewardship, we have been reluctantto change the way HTP is stabilized. It is hopedthat an on-going technical dialogue between
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
suppliers and those actively involved in HTPpropellant research will allow us to structure ourproduct specifications around the realisticexpectations and technical requirements of theaerospace community.
However, the feedback received from PROPULSEHTP users is extremely positive. Special attentionshould be paid to the concentration of the product,which to our knowledge is higher than any othercurrently commercial HTP grade in themarketplace. To increase HTP strength was oneof the frequent requests from the aerospaceindustry. An intense program initiated at ourGerman R&D facilities provided additional safetydata to obtain permission from the local authoritiesto operate the distillation unit to a higher targetconcentration. As a consequence of thisachievement, Directorate of Aerospace FuelsManagement at Kelly Air Force Base has added anew product category for a Type 90* gradeperoxide. It is written around the PROPULSE 900H2O2 specification.
Transportation methods & limitations
HTP is available both bulk and non-bulkpackaging. Presently non-bulk (drum) packagingis the dominant method of distributing HTP.
Sample Containers
Degussa-Huls Corporation can provide smallsample containers to facilitate laboratory or small-scale testing. These containers approved andavailable for the distribution of up to 98% wt. HTP.These containers are 1.25 liter high-purityaluminum bottles packaged in an aluminumcontainment box (six bottles to a box).
Drums
Non-bulk packaging (i.e.; drums) available fromDegussa-HQIs Corporation comply with 49CFRPart 178 (DOT). These drums are 125-liter typeUN 6HA1, this packaging consists of a moldedHOPE inner drum encased in a stainless steelouter shell. The IMDG (International MaritimeDangerous Goods) Code only approves 1A1(inert, steel) and 1B1 (inert, aluminum) drums fortransport of hydrogen peroxide of 60% wt. orhigher, however, Degussa-Huls has a specialapproval to use the 6HA1 drums for shipping up to90.5% wt.
US DOT gives considerable flexibility in non-bulkpackaging selection, however, Degussa-HulsCorporation will only use aluminum or lined stainlesssteel packaging for domestic US shipments.
Prior to first receipt of drummed HTP, detailedinformation is provided regarding the receipt, use,and return of drums. Complimentary HTP-specificsafety training is available upon request, and isrecommended prior to first delivery of the HTP toan individual site.
Bulk Containers
ISO Containers
IM Tanks, also called ISO Containers or ISO's areused by Degussa-Huls Corporation to transport bulkquantities of PROPULSE H2O2- ISO's are classifiedas IMO Tank type 1 and DOT type IM 101. While itis approved to ship H2O2 concentrations greater than72% wt. internationally, domestic US transportationin IM 101 tanks is restricted to 72% wt or less by 49CFR Part 172. Degussa-Huls Corporation hasobtained exemption DOT-E 12003 to allow thetransport of up to 92% wt. H2O2 in IM 101 tanks andhas delivered PROPULSE HTP in bulk domesticallyover the road.
Tanker Trucks and Railcars
The requirements for bulk packaging of high-hazard liquids are given in 49 CFR Part 173.243.The definition of bulk packaging includes railcars,cargo tanks (tanker trucks) and intermediate bulkcontainers (tote bins).
No limit is placed on the concentration of hydrogenperoxide transported using property constructedrailcars and cargo tanks. Numerous other Parts of49 CFR detail the requirements for other aspects ofthe shipping process. The shipper is responsible forinsuring that the packaging chosen will allow safetransport and containment of the HTP.
Drum-Supplied Operations
Discussed below are details specific to operationsinvolving PROPULSE HTP supplied in the 125 liter,type UN 6HA1 drums. The physical parameters of thedrums are:
Net Volume 100 Liters (26.5 US gallon)Net Weight 140 kg (307 Ibs) eachOutside Diameter 484 mm (19 in)Height 806 mm (31.7 in)
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
Drum Receipt and Handling
Figure 4 - Drum HandlingDrums of PROPULSE HTP are shipped fromDegussa-HQIs Corporation's warehouse in Mobile,AL in dedicated trucks. Full pallet quantities (fivedrums) are shipped secured to plastic pallets -wooden pallets must not be used in combinationwith concentrated hydrogen peroxide. Less thanfull-pallet quantities of drums are shipped withoutpallets unless otherwise specified by thecustomer.
Drums must be stored in an area free ofcombustible materials. Indoor storage is preferredin a well-ventilated and sprinklered building. In theevent that drums must be stored outdoors, theyshould be shaded from direct sunlight andprotected from extremes in temperature. Drumsmust be stored upright in order for the pressurevents to function property, failure to store thedrums upright could result in a leak or rupture.Further recommendations for storage areas aredetailed below.
The best way to convey the drums is to keep themon a plastic pallet; however, individual drums canbe handled using a suitable lifting device on aforklift or with a drum dolly. The preferred liftingdevice supports the drum from the bottom withadditional support at the top or midsection of thedrum. Drum lifting devices that grasp the rolledseam at the top of the drum should have at leasttwo grip points (Figure 4).
NFPA Recommendations for Oxidizer StorageAreas
Municipal or corporate regulations and insurancecompanies may use some or ail of the NFPArecommendations regarding the storage ofoxidizers, which are found in NFPA 430 "Code forthe Storage of Liquid and Solid Oxidizers." NFPAclassifies oxidizers numerically from Class 1 toClass 4; these should not be confused with the 5.1hazard class used with H2O2 in transportationregulations. The NFPA recommendations aresummarized below:
Basic Reguirements:
Consult NFPA 430 for the detailed requirementsthat are outlined below:
• Approval of the authority having jurisdiction ofthe existing facilities or the design of newfacilities. The authority having jurisdiction is"the organization, office, or individualresponsible for approving equipment, aninstallation, or a procedure."
• Emergency planning and annual trainingexercises.
• Identification of materials in storage. The"NFPA Diamond" hazard label for hydrogenperoxide above 52% wt contains:
• Health: 2 (blue section)» Fire: 0 (red section)• Reactivity: 3 (yellow section)• Specific Hazard: OXY (white section)• Separation from combustible or flammable
materials.• Containment of liquid oxidizer spills.• Employee Instruction.• Fire Protection.
Many of the above requirements are alsospecified in OSHA or EPA regulations, consult 29CFR Part 1910 (OSHA) and 40 CFR Part 355(EPA) for applicability. See Figure 5 for anexample of an HTP drum storage area.
Class 3. <92% wt. H2O2:
A Class 3 Oxidizer (NFPA) is defined as anoxidizer that will cause a severe increase in theburning rate of combustible materials with which itcomes in contact or that will undergo vigorous self-sustained decomposition due to contamination orexposure to heat.
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
Specific Requirements
Storage area limits and physical arrangement varywidely depending on whether the storage area issprinklered or non-sprinklered (and furthersubclassified as "segregated", "cutoff", and"detached"). For instance the building limit variesfrom 1,500 tons for sprinklered-detached storageto 20 tons for non-sprinklered-segregated storage.Building construction requirements specify nobasements, noncombustibie materials (wherecontact with the oxidizer is possible), andventilation systems for fire emergencies. Outsidestorage tank size is not limited by NFPA 430.
Class 4. ^92% wt. H?O2:
A Class 4 Oxidizer (NFPA) is defined as anoxidizer that can undergo an explosive reactiondue to contamination or exposure to thermal orphysical shock. In addition, the oxidizer willenhance the burning rate and cause spontaneousignition of combustibles.
Specific Requirements:
Storage area limits and physical arrangementsvary depending on whether the storage area issprinklered or non-sprinklered, all storage shall bedetached. For instance the building limit variesfrom "No Limit" for sprinklered-detached storage to1 ton for non-sprinklered-detached storage.Building construction requirements specify nobasements, noncombustibie materials (wherecontact with the oxidizer is possible), andventilation systems for fire emergencies.
Figures- HTP Drum Storage
Outside storage tank size is not limited by NFPA430, however, the minimum distance to thenearest flammable liquid storage, combustible
material, inhabited building, passenger railroad,public highway, property line or tank (other thanoxidizer storage) varies. The distances specifiedare from 75 feet for quantities from 10 Ib -100 Ibto 400 ft for quantities from 5,001 Ib - 10,000 Ib.Quantities over 10,000 Ib require a distance that issubject to the approval of the authority havingjurisdiction. The number of oxidizer tanks, theirsize, and the distance between them influencesthe minimum distance to any of the sensitive areasmentioned above. The above separation distancesalso apply to buildings in which Class 4 oxidizersare stored.
Bulk Deliveries
Bulk storage system requirements
Degussa-Huls Corporation maintains a technicalservices engineering department to design andbuild bulk storage and handling systems forhydrogen peroxide. Levels of assistance availablevary from "turn-key" installations to basic technicalreview of the work of others. All bulk storage andhandling systems for H2O2 are subjected to a pre-delivery safety inspection regardless of the H2O2concentration to be used in the system.
Normally, a bulk system will be required to acceptthe entire payload of the bulk-shipping container(so that the container can be returned to service).Therefore, bulk storage tanks should be sized toaccept a minimum of 19 m3 (5,000 US gallons) orgreater depending on the delivery method.
In the US, the design, installation, and operation ofthe system will be required to comply with 29 CFR1910.119, Process Safety Management of HighlyHazardous Chemicals, since any bulk system willexceed the threshold quantity of >52% wt. H2O2(7,500 Ib). Where OSHA regulations are notapplicable, the governing safety guidelines(agency or site-specific) for occupational safetywith highly hazardous chemicals will be followed.
Bulk storage tanks must be constructed ofmaterials suitable for long-term contact with HTPand must incorporate safety features such as:
• Property sized emergency vents• Temperature sensors and alarms• Level sensors and alarms• Emergency dump valves and/or dilution water
injection
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
The bulk storage tank must be sited such that alarge spill of material would not allow contact withcombustible, flammable, or reactive materials orendanger life or property. Frequently, theauthority having jurisdiction requires at least 100%to 125% containment (by volume). While arunaway decomposition of HTP is extremelyunlikely (given proper care), it is stronglyrecommended that at least 1 unit volume ofdilution water be available for each unit volume ofHTP in storage. Complying with thisrecommendation will substantially increase thecontainment capacity required.
In the case of 92% wt. or greater and when siterequirements include compliance with NFPA 430,separation distances must be evaluated andapproved by the authority having jurisdiction (sinceany bulk delivery will exceed the 10,000 Ib limit).In many cases, extreme distance requirementscan be avoided by providing sufficient engineeringcontrols to prevent hazards to nearby sensitiveareas.
A bulk system must not allow for the return ofmaterial to the bulk storage tank once it has beenremoved. Unused material must be stored in asecondary tank for later use or destroyed (bycatalysis or dilution).
Bulk systems will be designed wherever possibleto be completely closed systems, allowing transferof material from bulk storage to the run or flighttank without requiring personal handling of thematerial. Temporary connections (e.g. quick-connects) to delivery vehicles, downstreamsystems, and flight vehicles will be selected insuch a way that they can remain uncontaminatedbetween uses and cannot be inadvertently usedfor a different product.
It is recommended that product be transferred bypumping, pressure or vacuum transfer systemsrequire careful design to minimize risks relative tosystems that employ pumps. A delivery container(ISO, tanker truck, or railcar) must be pumped out,pressurization of shipping vessels is prohibited.The use of dry N2 for purging of downstreampiping into tanks is acceptable.
ISO Container Specifications
ISO containers are ASME-coded vessels enclosedin a steel-tube framework that makes them safeand easy to handle as ocean and over-the-roadfreight. Bulk deliveries of HTP are frequently
made with this type of container. ISO's have thefollowing physical parameters:
Dimensions: 20' long x 8' wide x 8 %' highCapacity: 24,000 kg(52,800 Ib) gross weight
20,000 kg(44,000lb)payload weight14,280 liters (3,780 US gallons)based on 90% HTP payload.
Figure 6 - IM101 Container for HTP Bulk Transport
Hydrogen Peroxide Handling Basics
All aqueous solutions of hydrogen peroxiderequire special care in storage and handling. Asthe weight-percent of hydrogen peroxide insolution increases, the importance of properstorage and handling procedures increases aswell. A large body of information exists thatdescribes the requirements for safely handlinghydrogen peroxide, and no attempt to duplicate allof it is made here. Fundamental concepts toproper storage and handling of hydrogen peroxideare:
Safety Training
Proper training of personnel handling chemicals orresponding to chemical-related emergencies isessential to safe utilization of chemical products.Responsible HTP producers will assist users inmeeting these training requirements.
Process Cleanliness
Hydrogen peroxide as commercially produced isvery stable; however, contamination in manydifferent forms can reduce the stability of theproduct, and even lead to self-acceleratingexothermic decomposition. Contamination, eitherby the introduction of incompatible foreignmaterials or the use of incompatible materials ofconstructions is the leading cause of accidents
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
Drum-based handling systems, particularly onesoperated outdoors, pose substantial risks ofaccidental contamination of the product. Strictprocedures must be established and followed tomaintain safety. Bulk systems are typicallydesigned as closed systems with much lower risksof accidental contamination.
Careful review of the HTP flow through theprocess must be performed prior to the operationof a new system, or after modifications to anexisting system. HTP producers will assistcustomers with the review of HTP handlingsystems.
Use of appropriate materials of construction
Suitable materials of construction for systems thatstore and handle HTP must be carefully chosenbased on the service conditions. In general, thelist of suitable materials that have a high degree ofcompatibility is very limited. The qualitativeclassification system (Class 1 through 4 in order ofdecreasing compatibility) is adequate for initialscreening of materials only. Consult an HTPproducer and existing literature on the subject ofmaterials compatibility for detailed information onthis subject.
Presently a working group includingrepresentatives of the aerospace industry andHTP producers is developing a materials selectionprotocol for HTP use in aerospace applications.
Provide pressure relief in equipment containinghvdrooen peroxide
Like handling systems designed to contain andconvey liquefied gases, hydrogen peroxidesystems must be equipped with pressure reliefdevices. Hydrogen peroxide naturally decomposesinto water and oxygen gas at a nominal rate of0.5% - 2% per year. The oxygen gas acts topressurize piping or equipment (such as a ball orplug valve) if it is trapped. Even small volumes ofhydrogen peroxide can result in an explosiverupture of equipment if pressure relief is notprovided. Surprisingly, this basic safety issue isfrequently overlooked in the design of hydrogenperoxide storage and handling systems - despitethe fact that it has resulted in serious incidents.Since the decomposition rate of hydrogenperoxide increases by a factor of 2.3 for each 10°C
rise in temperature, storage and handling ofhydrogen peroxide at elevated temperatures mustanticipate greater volumes and higher rates of gasevolution.
Vessels, pipelines, or other process equipmentthat can act to confine hydrogen peroxide must beequipped with a pressure relief device (relief valveor rupture disk). Relief valves must be ventedoutside of the system, not back to the storagevessel or into other parts of the hydrogen peroxidesystem. Ball valves or plug valves must have ameans to relieve pressure from the flow passagewhen the valve is in the closed position (usually asmall hole drilled through one side of the ball orplug).
Use of proper personal protective equipment
The potential health effects and proper personalprotective equipment associated with hydrogenperoxide are detailed in product MSDS's,producers' publications, and other sources. As apractical matter, the most likely exposures andconsequences resulting from routine handling are:
Injuries due to direct contact with the skin or withincompatible clothing. Thermal burns from theheat of decomposition or combustion of fabric orleather clothing, and painful irritation of exposedskin are the most likely injuries. Proper protectiveclothing is described below.
Wear chemical resistant footgear constructed ofvinyl, PVC or rubber. Never wear leather footwearwhen handling hydrogen peroxide.
Protective wear for laboratory handling can be avinyl, PVC or rubber apron combined with 100%nitrile gloves (one-time use), do not use latexgloves. Drum handling, product transfers andother operations involving the flow of productunder pressure requires vinyl, PVC, rubber, orGore-Tex coveralls and jacket. Protective glovesmade of PVC, natural rubber or vinyl must beworn.
Eye contact may not be immediately irritating butwhich could lead to blindness. Proper protectionof the eyes must be maintained at all times whenworking with hydrogen peroxide. Known orsuspected contact of H2O2 with the eyes must betreated immediately by flushing with large amountsof water and examination by a physician. Properprotective gear is described below.
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
Protective gear for laboratory handling consists ofchemical goggles, worn over corrective eyewear ifnecessary. Drum handling, product transfers andother operations involving the flow of productunder pressure requires chemical goggles and aprotective face shield.
It is very important to have running water availablewhen working with hydrogen peroxide. Safetyshower and eye wash stations must be within easyreach in case of emergency. Water hose stationsmust be located wherever handling operationscould result in a spill. The use of a "buddysystem" when working around HTP is stronglyrecommended.
Proper disposal of spills
Hydrogen peroxide spills must be diluted withlarge amounts of water and allowed to decomposein an open containment area. Avoid flushing spillsinto enclosed spaces such as pipes or sewers.Never attempt to absorb hydrogen peroxide spills.Spilled hydrogen peroxide is contaminated andmust never be returned to its original container.
With respect to US ERA regulations, forconcentrations of H2O2 £ 52% wt., this material isclassified as an "Extremely Hazardous Substance(EHS)" with a "Threshold Planning Quantity" asestablished by 40 CFR Part 355 of 1,000 Ibs (454kg). The "ReportaWe Quantity" for this material isalso 1,000 Ibs (454 kg).
Special hazards specific to HTP
While high-test peroxide is safer and easier tohandle than the propellents it replaces; the usermust not be lulled into a false sense of security.Since there is virtually no water present in HTP toabsorb the heat of decomposition, this heat energyresults in high-temperature gaseous de-composition products. This property makes HTPvery useful as a propellant, but makes proper carein storage and handling essential for safety.
Volumetric expansion
All hydrogen peroxide, including HTP,decomposes naturally at a very low rate. The heatreleased by this slow decomposition is absorbedby the surroundings, and therefore the systemremains essentially isothermal. Isothermaldecomposition is the reason why pressure reliefdevices must be present in storage and handling
systems, the decomposition products are liquidwater and gaseous oxygen.
When used as a propellant, the hydrogen peroxideis induced to decompose at a rate so rapid that theheat of decomposition remains in the system(adiabatic). This heat energy vaporizes any waterpresent in solution, and produces water vapor andgaseous oxygen as decomposition products athigh temperature. The volumes of gaseousdecomposition products for various concentrationsof hydrogen peroxide are listed in Table 2.
Accidental contamination of HTP storage andhandling systems, and spills of HTP can alsoresult in adiabatic decomposition. This can createsituations where the large volume ofdecomposition products presents significanthazards. Contaminated storage tanks canexplosively rupture; large quantities of HTPflushed into drain or sewer piping can damage ordestroy the piping system from overpressure.
Heat of decomposition
Table 2 lists the adiabatic decompositiontemperature obtained from various concentrationsof H2O2. Care must be taken when handling HTPto prevent inadvertent contact of the product anddecomposition catalysts. For instance, a glovemade from a compatible material butcontaminated with a catalytic substance couldbecome very hot if it was used in contact withHTP. Non-compatible clothing, particularly leatherfootwear, will ignite on contact with HTP since thethermal effects of the decomposing HTP willquickly raise the material above its flash point (incombination with the oxidizing effects) and theevolved oxygen will accelerate the combustion ofthe material.
Conclusions
HTP is a high-strength hydrogen peroxideformulation tailored for the aerospace propulsionindustry. Presently HTP is available both in non-bulk (drums) and bulk at concentrations up to 90%wt. This storable, non-toxic propellant is easilyhandled (relative to propellants it replaces),however, it is a hazardous, energetic material.Proper safety training of personnel and carefuldesign of storage and handling equipment areessential for the safe and successful use of thisproduct.
(c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.
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