Sulfuric acid is widely used as raw material in various industries such as textile, pigment, dyes, metal processing, pharmaceuticals, pulp and paper industries,etc. Spent acid recovery process is designed to regenerate or recover sulfuric acid from a variety of spent acid containing a varying degree of contaminants. Spent acid contains 15% oleum, 70% H2SO4, 0.01% iron, and 0.002% ammonia. Spent acid must be relatively pure &concentrated acid, for reuse in main process which includes gasoline nitration to produce pestisides, acrylonitrile & methyl methacrylate process. Oleum is used in industries such as metallurgical industries,etc.Oleum is produced in contact process,distillation of iron sulfates at nordhausen.there are very large amount of oleum required in various proceses industries in india.there are no methods for recovery of oleum in india so it is challenge to recover oleum from spent acid.
1.1 What Is Oleum?
â¢ Oleum (latin oleum = âoilâ), or fuming sulfuric acid, is a solution of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid.
â¢ Oleums can be described by the formula ySO3.H2O where y is the total molar sulfur trioxide content.
â¢ The value of y can be varied, to include different oleums. they can also be described by the formula H2SO4.xSO3 where x is now defined as the molar free sulfur trioxide content.
â¢ Oleum is generally assessed according to the free so3 content by weight. it can also be expressed as a percentage of sulfuric acid strength for oleum concentrations, that would be over 100%. for
â¢ Example, 10% oleum can also be expressed as H2SO4.0.13611SO3, 1.0225so3.H2O or 102.25% sulfuric acid.
â¢ The conversion between % acid and % oleum is: % acid = 100 + 18/80 * % oleum
â¢ Oleum (fuming sulfuric acid, H2S2O7) is corrosive and commonly made in various strengths, consisting of so3 dissolved in 100% h2so4.
â¢ Therefore, 20% oleum contains 20% so3 and 80% H2SO4 by weight. contingent on strength, vapor pressure is such that escaping so3 fumes combine with moisture in the air to form sulfuric acid mist particles.
â¢ These sulfuric acid mist particles are typically visible and can create dense white clouds of fumes. normally turbid, off-white liquid solution of uncombined SO3 dissolved in H2SO4
1.2 Physical Properties of Oleum, Sulfur Trioxide, and Sulfuric Acid
ï Oleum is excess sulfur trioxide dissolved in sulfuric acid. another name for oleum is âsulfuric acid, fumingâ.
ï It is sometimes shipped by railcar under un 1831. the chemical may also betransported tanker truck, pipeline or in smaller containers. the emergency responseguidebook under un 1831 makes a distinction between âsulfuric acid, fuming, with less than 30% free sulfur trioxideâ and âsulfuric acid, with not less than 30% free sulfur trioxideâ.
ï For example, a tank car containing 90 tons of oleum with 30% free sulfur trioxide contains 60 tons of sulfuric acid and 30 tons of free sulfur trioxide dissolved in the sulfuric acid. sometimes this is called â30% oleumâ.
ï Oleum and sulfuric acid comes in different strengths, which have different melting and boiling points and different densities.
Table 1. Physical Properties of Different Oleum Strengths (pure sulfuric acid and pure sulfurtrioxide listed for comparison)
% Free Sulfur trioxide Melting
Point Sp Grav. Liquid
(water=1) Vapor Pressure
0 (pure sulfuric acid) 10Â°C/50Â°F 337Â°C / 639Â°F 1.84
20% 2Â°C / 35.6Â°F 138Â°C / 280Â°F 1.93
34% 20Â°C / 68Â°F 112Â°C / 233Â°F 1.92 0.007 atm
65% 5Â°C / 41Â°F 60Â°C / 140Â° 1.99 0.104 atm
100% (pure sulfur
trioxide, gamma form) 16.8Â°C /
45Â°C / 113Â°F 1.92 0.57 atm (25Â°C)
100% (pure sulfur
trioxide, beta form)
45Â°C / 113Â°F 1.92 0.45 atm (25Â°C)
100% (pure sulfur
trioxide, alpha form)
gamma, bp 45Â°C
1.92 0.096 atm (25Â°C)
ï The melting point of Sulfuric acid is somewhat of a hard thing to define. Temperatures reported In the Literature can vary from The values given In Table 1, and represent the difficulty In defining the amount of Sulfur trioxide present, or a temperature
ï When Sulfuric acid changes from a âViscous Liquidâ to a âSolidâ.
% Sulfuric acid
Sp Grav. Liquid
(water=1) at 20Â°C
10% (1 Normal
-2Â°C/28.4Â°F 102Â°C / 215Â°F 1.07 0.022 atm
33.5% (battery acid) -64Â°C / -83Â°F 110Â°C / 230Â°F 1.24 0.017 atm
60% (fertilizer acid -64Â°C / -83Â°F 140Â°C / 284Â°F 1.50 0.004 atm
73.6% (Glover acid) -39Â°C / -38Â°F 178Â°C / 352Â° 1.65 0.0006 atm
-32Â°C / -26Â°F 337Â°C / 639Â°F F 1.83 <0.001atm
98% (commercial) -2Â°C / -28.4Â°F 337Â°C / 639Â°F 1.84
Table 2. Physical Properties of Different Sulfuric Acid Solution
Free SO3 20 30
Equivalent % H2SO4 104.5 106.75
Specific Gravity 1.915 1.952
Boiling Point 286 Â°F (141Â°C) 246Â°F (119Â°C)
Freezing Point 35Â°F (1.7Â°C) 71Â°F (21.9Â°C)
Weight/US Gallon 7.64 kg (15.97 lbs) 7.38 kg (16.27 lbs)
Flammability Not flammable Not flammable
Flash Point Not applicable Not applicable
Table 3: Typical physical properties of common grades of oleum
Test Test Value
Sulphuric Acid (as H2SO4) 75 Â± 1%
Iron (Fe) 0.01
Copper Less than 0.0001
Zinc Less than 0.0001
Nitrate Less than 0.0002
Nitrite/ Ammonia 0.002
Chloride Less than 0.0005
Arsenic Less than 0.00001
Manganese Less than 0.0001
Residue on Ignition 0.026
Organic Matter 0.01
Water Content 24.50
CHEMICAL COMPOSITION OF SPENT ACID (% BY WEIGHT)
2. Application Of Oleum:
â¢ Setting up of highly concentrated Sulfuric acid
â¢ Production of caprolactam and nylon
â¢ Nitration Processes in combination with nitric acid
2.1 SULFURIC ACID PRODUCTION
ï Oleum is an important intermediate in the manufacture of sulfuric acid due to its high enthalpy of hydration.
ï When SO3 is added to water, rather than simply dissolving, it tends to form a fine mist of sulfuric acid, which is difficult to manage. However, SO3 added to concentrated sulfuric acid readily dissolves, forming oleum which can then be diluted with water to produce additional concentrated sulfuric acid.
2.2 AS AN INTERMEDIATE FOR TRANSPORTATION
ï Oleum is a useful form for transporting Sulfuric acid compounds, typically in rail tankcars, between oil refineries (which produce various Sulfur compounds as a by product of refining) and industrial consumers. certain compositions of oleum are solid at room temperature, and thus are safer to ship than when liquid. solid oleum can then be converted in to liquid at the destination through steam heating or dilution or concentration.
ï This requires some care to prevent overheating and evaporation of sulfur trioxide. To extract it from a tank car requires careful heating using steam conduits within the tank car.
ï Great care must be taken to avoid overheating, as this can increase the internal pressure within thetank car to a value exceeding the limit of the tankâs safety valve.
ï In addition, oleum is less corrosive to metals than sulfuric acid, because there is no free water to attack the surfaces. because of that, sulfuric acid is sometimes concentrated to oleum for in-plant pipelines and then diluted back to acid for use in industrial reactions.
ï In Richmond, California In 1993 a significant release occurred due to overheating, causing a release of sulfur trioxide that absorbed moisture from the atmosphere, creating a mist of micrometre-sized sulfuric acid particles that formed an inhalation health hazard. this mist produced adverse health effects on residents and workers over a wide area.
2.3 ORGANIC CHEMISTRY
ï Oleum is a harsh reagent, and is highly corrosive. one important use of oleum as a reagent is the secondary nitration of nitrobenzene.
ï The first nitration can occur with nitric acid in sulfuric acid, but this deactivates the ring towards further electrophilic substitution. a stronger reagent, oleum, needed to introduce the second nitro group on to the aromatic ring.
2.4 Explosives manufacture
ï Oleum is used in the manufacture of many explosives with the notable exception of nitrocellulose. (in modern manufacturing of nitrocellulose, the h2so4 concentration is often adjusted using oleum)
ï The chemical requirements for explosives manufacture often call for anhydrous mixtures containing nitric acid and sulfuric acid. ordinary commercial grade nitric acid consists of the constant boiling azeotrope of nitric acid and water, and contains 68% nitric acid. mixtures of ordinary nitric acid in sulfuric acid therefore contain substantial amounts of water and are unsuitable for process
3 USES OF OLEUM
ï In sulfonation and nitration process
ï leading source of sulfonation
ï For powdered/synthetic laundry products
ï High-strength adhesives oilrefining
ï Sulfuric acid is used in the iron and steel industry to remove rust and scale from rolled sheets and billets.
ï The manufacture of many chemicals use sulfuric acid or oleum or sulfur trioxide in its manufacture.
ï Oleum is used as a dehydrating agent in the manufacture of many kinds of explosive such as TNT.
4 PROCESS FOR RECOVERY OF OLEUM
4.1 RECOVERY OF OLEUM BY CONTACT PROCESS:
Brief process description of contact process:
ï Sulphur powder is melted and burned in presence of oxygen to produce sulphur dioxide gas.
ï The heat from the hot gases recovered to produce steam in a boiler.
ï Three converter filed with catalyst are arranged in series where oxygen and sulphur dioxide are reacted to form sulphur trioxide and heat produced from the reaction is removed by the heat exchanger arranged in between them.
ï Sulphur trioxide produced form the converter is fed to economizer to heat the boiler feed water.
ï In oleum tower so3 is absorbed by the oleum circulation and unabsorbed so3 is absorbed in the absorber.
ï Water is added to the acid tank to produce h2so4 by reacting with oleum.
Process flow diagram of sulphuric acid manufacturing by contact process technology:
The reaction between sulfur dioxide and oxygen is done in 4-bed arrangement converter. The chemical reaction is exothermic and depends on control of reaction temperature. to achieve maximum conversion and reaction rate, optimum temperature range found from 400 to 500oc.
To maintain this temperature at catalyst contact each outlet stream from the beds are passed to economizer coils. Excess heat is removed and temperature is controlled by this heat exchange system strategy.
Converter Catalyst Beds Inlet Temperature, Oc Outlet Temperature, Oc Heat Exchanger Cooling, Oc Conversion Per Pass Through Beds
1st Bed 400 600 600 To 450 75%
2nd Bed 450 500 500 To 420 90%
3rd Bed 420 480 480 To 410 95%
4th Bed 410 430 Passed To Preheater/ Economizer 98%
Engineering Equipment Options In Designing:
Acid coolers models applicable to use in the contact process designing:
â¢ Cascade coolers
â¢ Shell and tube heat exchangers
â¢ Plate type heat exchange system
â¢ Open air coolersacid towers selection:
â¢ moc of towers:
1. Cast iron
2. Carbon steel lead/teflon lining
3. Stainless steel types of packing:
1. Triple spiral rings
2. Berl saddles
3. Ceramic saddles
Area Of Scientific Research/Conclusions On Contact Process:
Effect Of Catalyst On SO3 Formation:
Catalyst Process Difficulties/ Bottlenecks
Platinum Catalyst Quickly Deactivated Due To Sulfur Poisoning
Copper Oxide Low Conversion
Iron Oxide Pore Blockage
Chromium Oxide Low Conversion
Vanadium Pentoxide Long Life, 98% Conversion
Magnesium Sulfate Need Platinum Support
Ruthenium Effective Only In Last Bed Of Reactor
3.1 Method of Sulphur Bearing Effluent Treatment In Current Practice
Following practices are adopted to handle Sulphur containing effluent waste:
ï,§ Sulphur containing effluent generated from copper phthalocyanine blue alpha pigment is used in the manufacture of copper phthalocyanine crude pigment. about 20% of sulphur containing effluent is utilized in this way.
ï,§ Some sulphur containing effluent are found to be useful for manufacturing low value inorganic salts namely â” ferrous Sulphate, aluminium sulphate, copper sulphate zinc sulphate etc. the quantity utilized in this way is about 5% of total available effluent.
ï,§ Some sulphur containing effluents which contains acidity of more than 50 % and above are used for phosphoric acid / dicalcium phosphate generation. The sulphur containing effluent is treated with rock phosphate to get phosphoric acid and gypsum. about 5- 10% of total effluent is utilized in this way.
ï,§ Neutralization with Lime
Remaining Sulphur bearing effluent is neutralized with lime to generate solid waste. Solid waste generated during the neutralization process is disposed off at landfill site (BEIL). BEIL (Bharuch Enviro Infrastructure Ltd.) having design capacity of approx 50,000 MT/year. Total solid waste generated during the neutralization process is approx 449.647 MT/day. This scenario clearly predicts that the disposal of solid waste is the biggest problem in this neutralization process. Also this neutralization process creates environmental problem and proves destructive for the ecology.
Neutralization with Liquor Ammonia
Some industries neutralize the Sulphur bearing effluent with liquor ammonia (available as spent ammonia) and generate effluent having high ammonical nitrogen content. This effluent creates problems at common effluent treatment plant. During neutralization, 1346.93 kg solid waste generated due to treatment of 1 MT of sulfur.
Total solid waste generated during the neutralization process is 436.405 MT/day this figure showing that disposed of solid waste is the biggest problem of this neutralization process. Also this neutralization process creates environmental problem and not eco friendly.
4.1 Manufacturing Process
4.1.1 Process of Treatment of Sulphur Bearing Effluents
The process may be divided into the following four (4) steps:
ï Pre concentration of sulphur bearing effluent to minimize the amount of water present in the effluent
ï Formation of sulfur dioxide by the thermal decomposition of spent acid (and the combustion of hydrogen sulfide gas and sulfur where these feeds are also available).
ï Cooling and purification of the sulfur dioxide process gas (gas cleaning)
ï Conversion of sulfur dioxide to sulfur trioxide.
ï Absorption of sulfur trioxide in sulfuric acid.
5 SAFETY PRECAUTION
ï oleum is used in industrial applications and other processes where workplace exposures can occur.
there are no direct consumer applications for oleum.
ï Oleum is dangerous to human health. oleum is rapidly destructive to all body tissues, causing severe burns which may result in scarring.
ï Oleum is consumed in industrial manufacturing processes or recovered and re-used. oleum can make its way into the environment through unintentional releases (spills) and industrial or consumer discharges. oleum will not bioaccumulate and is not biodegradable.
ï When released into the upper atmosphere, oleum exists as sulfuric acid particles or droplets. the acid particles dissolve in clouds, fog, rain, or snow, resulting in very dilute acid solutions. this may impact the environment as wet acid deposition (âacid rainâ).
5.1 Exposure Potential
Workplace Exposure â”
ï Oleum is toxic by ingestion, inhalation or contact with skin and eyes. potential exposures may occur at an oleum manufacturing facility or at a manufacturing facility tha handlesoleum.
ï Exposure may also occur in the event of transportation incident. persons involved in maintenance, sampling and testing activities, or in the loading and unloading of oleum containers are at greater risk of exposure.
ï Following good safe handling practices will minimize the likelihood of exposure to oleum. persons involved in exposure risk activities should always wear proper personal protective equipment such as rubber gloves and boots, a chemical resistant full acid suit, goggles, face shield, an approved respirator and a hard hat.
5.2 Environmental Releases
ï Oleum releases sulfur trioxide gas (so3) gas when spilled. the so3 quickly reacts with moisture in the air to form tiny droplets of sulfuric acid mist.
ï These h2so4 mist particles appear as a white cloud. spills of oleum should be contained and isolated from waterways, sewers and drains. oleum will react violently with water and a considerable amount of heat is generated during dilution.
ï Small spills of oleum should be carefully diluted and then soaked up with an approved absorbent material which can be swept or shoveled up and placed in a suitable container for disposal.
ï The contaminated area should be washed down with water. lime or soda ash (sodium carbonate) may be used to neutralize contaminated water.
ï Larger spills of oleum should be contained and carefully diluted with water before neutralizing with a suitable neutralizing agent. disposal should be in accordance with applicable local, state or federal regulations. Persons attempting to clean up oleum spills should wear proper personal protective equipment (see guidelines in the safety data sheet).
ï If required, report spills to the appropriate local, state and federal authorities.
Oleum is not flammable. however, hydrogen gas is produced when oleum comes in contact with certain metals. hydrogen gas is explosive in some circumstances.
5.3 Health Information
ï Oleum is corrosive and toxic by ingestion, inhalation or contact with skin and eyes. effects can be immediate. in the event of exposure to the skin or eyes, the area should be washed with water for at least 30 minutes. Please consult the safety data sheet for additional information.
ï Exposures to oleum can produce the following adverse health effects:
Contact – Skin exposures to oleum can cause symptoms ranging from minor skin irritation to painful redness and swelling. severe burns can occur if treatment is delayed. Eye exposure to oleum or so3 may result in severe eye irritation, burns or even blindness.
ï Oleum is harmful if inhaled. it can cause upper respiratory tract irritation, lung irritation, chest pain, wheezing, shortness of breath, a burning sensation, tickling of the nose and throat and sneezing.
ï Repeated exposure to high levels of oleum mist may cause etching of tooth enamel in persons who breathe through their mouths.
ï Oleum Is Harmful If Ingested. It Can Cause Irritation, Abdominal Pain, Corrosion, Burns To Mouth And Esophagus And Death.
Other Effects â”
ï Based on available data at the time of their review, the international agency for the regulation of cancer (IARC) and the us national toxicology program (NTP) considered strong inorganic acid mist containing sulfuric acid to be a human carcinogen. In 2012 iarc dropped the words âcontaining sulfuric acidâ from their classification citing uncertainty regarding the specific carcinogenic component. Exposure to these strong inorganic acid mists may be encountered in an industrial setting. However, some later epidemiology studies were negative for respiratory cancer. also, animal studies not considered by NTP and IARC were negative for carcinogenicity.
5.4 Environmental Information
ï Oleum is readily neutralized and will therefore be degraded within the wastewater treatment process. Due to this rapid degradation, an exposure of surface waters to oleum is expected to be negligible.
ï Since ecotoxicological effects of the substance solely result from changes in ph, oleum is considered to not be acutely harmful to aquatic organisms. further, oleum does not accumulate in the food chain.
ï An exposure assessment was performed for the identified uses and resulted in releases that do not pose a risk for aquatic life. consequently, all identified uses are considered to be safe for the environment.
5.5 Physical hazard information
ï oleum is extremely corrosive to many metals. please consult chemical compatibility tables before selecting vessels, piping, pumps and/or valves for use in oleum service.
ï Exposure of some metals to oleum can result in the evolution of flammable hydrogen gas. If allowed to accumulate in a confined space. Hydrogen gas can present a fire or explosion hazard.
6 LIST OF INDUSTRIES
1) Novel spent acid management, ahmedabad manufacturer of spent sulphuric acid, spent acid, spent acid, sulphuric acid, spent sulphuric acid, gypsum
2) 2 Kiri industries limited, ahmedabad trading house exporter and manufacturer of spent sulphuric acid, sulphuric acid 98%, reactive dyes, dye intermediates, vinyl sulphone ester, acetanilide flakes, ulpho gama acid, acid dyes, direct dyes, sulphuricindo texchem, bharuch spent sulphuric acid, spent sulphuric acid
3) Radha madhav surfactants pvt. ltd., surat manufacturer of spent sulphuric acid (both commercial and industrial), detergent chemicals – sulphuric acid, detergent chemicals – sulphuric acid, linear alkyl benzene sulfonic acid, spent sulphuric
4) Akshay industries, nashik manufacturer of spent sulphuric acid, hydrochloric acid, chloral, ethyl chloride, hydrochloric acid, spent sulphuric acid
5) Manufacturer of spent sulphuric acid, linear alkyl benzene suphonic acid, linear alkyl benzene suphonic acid, spentsulphuric acid
â¢ Purification of spent acid
â¢ Process for treating waste acid
â¢ Process for sulfuric acid regeneration
â¢ CDM on spent acid recycle-A case study
Process of treatment of sulfur bearing effluents
â¢ CDM on spent acid recycle-A case study
Neutralization with liquor ammonia