CHEMITHON
`
`Sulfonation and Sulfation
`Processes
`
`NormanC. Foster, Ph.D., P.E.
`
`5430 West Marginal Way SW
`Seattle, WA 98106 — USA
`Tel:
`(206) 937-9954
`Fax:
`(206) 932-3786
`E-Mail: chemoffice@chemithon.com
`www.chemithon.com
`
`1
`
`TIDE 1025
`
`

`

`CHEMITHON
`
`Sulfonation and Sulfation Processes
`
`Norman C. Foster, Ph.D., P.E.
`
`Introduction
`
`Sulfonation and sulfation are major industrial chemical processes used to makea diverse
`range of products, including dyes andcolor intensifiers, pigments, medicinals, pesticides
`and organic intermediates. Additionally, almost 500,000 metric tons per yearof lignin
`sulfonates are produced as a by-product from paper pulping. Petroleum sulfonates are
`widely used as detergent additives in lubricating oils. However, the majority of the 1.6
`million metric tons of sulfonates and sulfates produced annually in the United States!!!
`are used as surfactants in laundry and consumerproducts applications. This chapter
`focuses only on commercial techniques for production of detergent range sulfonates and
`sulfates.
`
`Basic Chemistry
`
`Although sulfonates and sulfates are similar in structure, there are important differences.
`Figure 1 showsthe reaction to produce a sulfonate. Sulfur trioxide (SO,) reacts with an
`organic molecule — in this case an alkyl benzene — to form a sulfur-carbon bond. One of
`the characteristics of this processis that the resultant alkyl benzene sulfonic acid is a
`stable molecule.
`
`Figure 1. Sulfonation
`
`OU
`
`I
`
`UI
`
`O
`
`Sulfur
`Trioxide
`
`Alkyl Benzene
`
`Alkyl Benzene Sulfonic Acid
`
`Page | of 36
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`© 1997 The Chemithon Corporation
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`

`

`CHEMITHON
`
`Sulfation, on the other hand, involves forming a carbon-oxygen-sulfur bond as shown in
`Figure 2. The resultant alcohol sulfuric acid is not hydrolytically stable. Unless
`neutralized, it decomposes to form sulfuric acid and the original alcohol.
`
`Figure 2. Sulfation
`
`Ol
`
`I
`
`O
`
`Sulfur
`Trioxide
`
`Primary
`Alcohol
`
`Alcohol
`Sulfuric Acid
`
`Becausetheyare stable, sulfonic acids can be isolated, stored and shippedasanarticle of
`commerce. Sulfates, due to their instability, are available only as neutral compounds.
`This stability difference in the products of reaction with SO, also has a profound impact
`on the choice of process used to produce sulfonates or sulfates. Some processes, such as
`oleum sulfonation, cannot be used to make alcohol sulfates containing a low level of
`inorganic sulfate. Howeverothers, such as sulfamic acid sulfation, cannot be used to
`make sulfonic acids.
`
`Figure 3. Viscosity Increase on Sulfonation
`
`Acid
`vines
`Viscosity
`iscosity
`@ 40 - 50°C
`(cp)
`Feedstock
`
`
`SO, is an aggressive electrophilic reagent that rapidly reacts with any organic compound
`containing an electron donor group. Sulfonationis a difficult reaction to perform on an
`industrial scale because the reaction is rapid and highly exothermic, releasing
`approximately 380 kJ/kg SO, (800 BTUsper pound of SO,) reactedl?]. Most organic
`compounds form a black char on
`contact with pure SO, due to the
`rapid reaction and heat evolution.
`Additionally, as shown in Figure
`3, the reactants increase in
`>
`.
`viscosity between 15 and 300
`times as they are converted from
`the organic feedstock to the
`
`
`
`sulfonic acid(”|. This large
`increase in viscosity makes heat
`removaldifficult. The high
`viscosity of the formed products
`reduces the heat transfer
`coefficient from the reaction mass.
`Effective cooling of the reaction massis essential because high temperatures promote
`
`Branchedalkylbenzene
`Ethoxylated alcohol
`Tallow alcohol
`Alphaolefins
`
`1000
`500
`150
`1000
`
`Page 2 of 36
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`© 1997 The Chemithon Corporation
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`

`

`CHEMITHON
`
`side reactions that produce undesirable by-products. Also, precise control of the molar
`ratio of SO, to organic is essential because any excess SO,, due to its reactive nature,
`contributes to side reactions and by-product formation. Therefore, commercial scale
`sulfonation reactions require special equipment and instrumentation that allowstight
`control of the mole ratio of SO, to organic and rapid removalof the heat of reaction.
`
`Historically, the problem of SO, reactivity has been solved by diluting and/or
`complexing the SO, to moderate the rate of reaction. Commercially, the diluting or
`complexing agents (Figure 4) include ammonia (sulfamic acid), hydrochloric acid
`(chlorosulfuric acid), water or sulfuric acid (sulfuric acid or oleum) and dry air(air/SO,
`film sulfonation). Control of the ratio of SO, to organic raw material is vital to achieving
`the desired product quality with use of any of the agents. Additionally, these processes
`require heat removal to maintain product quality. As we examineeach ofthese industrial
`processes we will see how they have been engineered to achieve these requirements.
`
`Figure 4. Agents to Reduce SO; Reactivity
`@ Ammonia
`0
`NH,+SO; —*
` HO-S-NH,
`Wl
`O
`
`O
`@ Hydrochloric Acid
`HC1+SO,; —> H-O- 8 -Cl
`
`O
`
`Sulfamic Acid
`
`Chlorosulfonic Acid
`
`O
`O
`@ Water
`H,0+ SO; —> H-O-S-O-H + SO,—> SO,° H-O-S-O-H
`Ul
`O
`O
`Sulfuric Acid
`Oleum
`
`@ Dry Air
`Dry Air + SO; — 2.5 to 8% SO, in Dry Air
`
`Commercial Sulfonation Processes
`
`Sulfamic acid (NH,SO;H)is used to sulfate alcohols and ethoxylated alcohols to form an
`ammonium neutralized salt. A typical reaction is shown in Figure 5. The reaction goes
`
`Page 3 of 36
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`© 1997 The Chemithon Corporation
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`

`CHEMITHON
`
`directly to the ammoniumsalt of the alcohol sulfuric acid. Sulfamic acid is an expensive
`reagent, costing approximately US$0.51 per pound of reactive SO;. Sulfamic acid
`sulfation is a mild and specific sulfating reagent suitable for making ammonium
`neutralized alcohol ethoxylates. Another major advantage of sulfamic acid is that it
`selectively sulfates alcohol groups and will not sulfonate aromatic rings. Therefore,its
`majoruse is sulfation of alkyl phenol ethoxylates. This specificity prevents formation of
`mixed sulfate-sulfonate compounds. Sulfamic acid is easily handled andreacts
`stoichiometrically with the alcohol or ethoxy alcohol. It readily adapts to making small
`quantities of material in low cost batch equipment.
`
`Figure 5. Sulfamic Acid Sulfation
`
`CH, - (CH,), <o)- (O - CH,- CH,),- OH + NH,SO,H =——>
`
`Alkyl phenol ethoxylate
`
`Sulfamic
`Acid
`
`Heat
`
`CH; - (CH,)s €0)>-
`
`?
`(O - CH, - CH), - O- § - O° NH,°
`
`O
`
`Alkyl phenol ethoxylate ammonium sulfate
`
`Chlorosulfuric acid (C1ISO,H)is also widely used to produce alcohol sulfates, alcohol
`ether sulfates, dyes and dye intermediates. Figure 6 showsa typical reaction. Note that
`as the reaction moves to completion, hydrochloric acid (HCl) is released. This acid must
`be scrubbed or otherwise recovered. Chlorosulfuric acid is an expensive source of SO,
`althoughit is approximately one half the cost of sulfamic acid. The cost per pound of
`reactive SO, is US$0.255. It is a rapid, stoichiometric reactant. However,itis still more
`expensive than other sources of SO,. It is also corrosive and a hazardous chemical to
`handle and liberates HCl as a by-product during the reaction. The HCl can be recovered
`by scrubbing the off-gas stream with water, or neutralized by scrubbing the off-gas with a
`dilute basic scrubbing solution. In either case, additional equipment and complexity are
`added to the process.
`
`Page 4 of 36
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`© 1997 The Chemithon Corporation
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`

`CHEMITHON
`
`Figure 6. Chlorosulfonic Acid Sulfation
`
`OUl
`H-O-S-Cl + CH,- (CH,),9 - CH, - OH a
`
`I O
`
`Chlorosulfonic
`acid
`
`Lauryl alcohol
`
`Ol
`
`l
`
`CH, - (CH), - CH; - 0 - $ - O° H® + HCl
`
`O
`
`Lauryl alcohol
`sulfuric acid
`
`Hydrochloric
`acid
`
`Figure 7. Sulfuric Acid /Oleum
`
`O
`H-O-S-O-H + ©> (CH,),,-CH, [=
`0
`Sulfuric acid
`
`Alkyl benzene
`
`Sulfuric acid (H,SO,) and oleum (SO; « H,SO,) are widely used as sulfonating agents.
`Oleum is used to sulfonate alkyl benzene and sulfate fatty alcohols for heavy duty
`detergents. The reaction is shown in Figure 7. It is an equilibrium process, as water is
`formed in the reaction and the resultant water dilutes the oleum and/or sulfuric acid. The
`sulfonation reaction stops when
`the sulfuric acid concentration
`drops to approximately 90%. This
`"spent" acid may be separated
`from alkyl benzene sulfonic acid
`to produce a product, which on
`neutralization containsa relatively
`low level (6-10%) of sodium
`sulfate. When fatty alcohols are
`sulfated, the spent acid cannot be
`separated. It must be neutralized
`with the alcohol sulfuric acid to
`make a product containing a high
`level of sodium sulfate. Oleum is
`relatively inexpensive — about
`US$0.153 per pound of reactive
`SO,. Oleum sulfonation can be
`operated as either a batch or continuous process. This process has the dual advantage of
`low SO, cost and low capital equipment cost. However, it has the disadvantage of being
`an equilibrium process whichleaves large quantities of un-reacted sulfuric acid. This
`
`
`
`O
`H®°o0°-s -o)- (CH,),,- CH, + HO
`I
`O
`Alkyl benzene sulfonic acid
`
`Water
`
`Page 5 of 36
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`© 1997 The Chemithon Corporation
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`

`

`CHEMITHON
`
`waste acid must be separated from the reaction mixture and subsequently disposed. In
`North America, the expense of disposing the "spent" sulfuric acid has becomeso high
`that the process economics are now questionable.
`
`Sulfonation with sulfuric acid is a special case of oleum sulfonation. Because the
`sulfonation reaction stops whenthe acid concentration in the reaction mixture drops to
`less than approximately 90%, sulfonation of detergent feedstocks with sulfuric acid is not
`normally practiced. Today sulfuric acid sulfonation is principally used for production of
`hydrotropes by azeotropic reaction with benzene, toluene or xylene. In this special
`process, the water formed during the reaction is removed by azeotropic distillation of the
`water and unreacted feedstock. The water is then separated from the immiscible organic
`feedstock whichis returned to the reaction vessel. Because water is removed, the
`reaction may continue to completion.
`
`The air/SO, sulfonation processis a direct process in which SO,gasis diluted with very
`dry air and reacted directly with the organic feedstock. The source of the SO, gas may be
`either liquid SO, or SO, produced by burning sulfur. As shownin Figure 8, the reaction
`of gaseous SO, with organic is rapid and stoichiometric. It is complicated by the
`possibility of side reactions and therefore tight process control is essential. The cost for
`liquid SO, is US$0.09 per poundofreactive SO,; while SO, from sulfur burningis
`US$0.02 per pound ofreactive SO,. The air/SO, sulfonation processis the lowest SO;
`cost of any sulfonation process and is extremely versatile, producing very high quality
`products. However, it is a continuousprocessbest suited to large production volumes.
`In addition, it requires expensive precision equipment and highly trained operating
`personnel.
`
`Figure 8. Air / SO;
`
`SO, + CH,-(CH,),) - CH,- (O - CH, - CH,);-OH —>
`
`Sulfur
`trioxide
`
`Ethoxylated lauryl alcohol
`
`OI
`
`l
`
`CH; - (CH,);- CH- (O - CH, - CH,);- 0 - S - 0° H®
`
`O
`
`Ethoxylated lauryl alcoholsulfuric acid
`
`Page 6 of 36
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`© 1997 The Chemithon Corporation
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`

`CHEMITHON
`
`Aspreviously mentioned, a commercially successful sulfonation process requires
`reaction of SO, with the organic feedstock undertightly controlled conditions. Figure 9
`illustrates the level of control demandedbythe air/SO, sulfonation process!3!. This
`illustration showsthe production of 1,4-dioxane, an undesirable by-product formed
`during the sulfation of ethoxylated alcohols. The 1,4-dioxane formedis a function of
`mole ratio (kg moles per unit time of SO, fed to the reactor divided by kg molesper unit
`time of feedstock fed to the reactor). As the mole ratio of SO, to organic feedstock
`increases, the level of dioxane in the product remainsrelatively low at 20 to 30 ppm. A
`critical point of over-sulfation occurs at a mole ratio of approximately 1.03. Once over-
`sulfation occurs and the mole ratio exceeds 1.04, dioxane production increasesrapidly to
`values measured in hundredsofparts per million. Similar adverse responses are
`observed with productcolor or levels of unsulfonated or unsulfated (free 011) materials in
`the product. Clearly, the sulfonation process must be controlled to within 1% of the
`desire mole ratio in order to achieve excellent product quality. Other important process
`variables are reaction temperature, SO, gas concentration, time to neutralization,
`neutralization pH andneutralization temperature. These variables also influence product
`quality although the effect is not as dramatic as the effect of mole ratio.
`
`Figure 9. 1,4-Dioxane vs. Mole Ratio
`
`Five minutes acid recycle residence time at
`30°C and 2.5% SO,inlet gas concentration
`
`
`“I6oOooo&
`
`
`
` 1,4-Dioxane,AMBasis(ppm) so
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`600
`
`g
`
`300
`
`200
`
`100
`
`0:
`
`0.97 0.98 0.99
`
`1
`
`1.01 1.02 1.03 1.04 1.05 1.06 1.07
`
`Mole Ratio (SO,/A3EO)
`
`Page 7 of 36
`
`© 1997 The Chemithon Corporation
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`

`

`CHEMITHON
`
`The profound effect of mole ratio on product quality implies that an air/SO, sulfonation
`reactor must be designed to ensure the mole ratio is equally and constantly maintained at
`all points in the reactor.
`I have coined the phrase "micro scale" mole ratio control to
`describe this condition. Micro scale control meansthat the reactor has been designed and
`calibrated so that the same moleratio is held constant at every point at a cross section
`through the linear flow axis of the reactor. All molecules of feed see exactly the same
`quantity of SO,. This is different than the macro moleratio control whichis the overall
`mole ratio of organic feedstock and SO, fed to the reactor. Macro control is determined
`by the plant's control system. It is imperative that the equipment be capable of both
`macro and micro mole ratio control because sulfonation is suchacritical reaction with
`respect to mole ratio control. A 1% variation in the mole ratio can spell the difference
`between world class product and off-specification material.
`
`Choosing a Sulfonation Process
`
`The choice of sulfonation process depends on many factors. One of the most importantis
`the desired products and their required quality. Some processesare very versatile while
`others produce only a few types of products. Each process producesslightly different
`products. For example, the sulfamic acid process produces only ammonium sulfates from
`alcohols or ethoxylated alcohols. Another example is the presence of a minimum of 8%
`sulfate in sodium alkyl benzene sulfonates made with oleum. Someprocesses such as the
`air/SO, process are capable of sulfating or sulfonating a wide variety of feedstocks and
`producing excellent quality products from all of them.
`
`A secondfactor to consider in the choice of sulfonation processis the required
`production capacity. The sulfamic acid processis a batch process suitable for production
`of small quantities of material. The air/SO, processis a large scale continuous process
`best suited to 24 hours per day, seven days per week manufacture of tons per hour of
`product. The chlorosulfuric acid and oleum processescan be runaseither batch or
`continuousprocesses.
`
`Reagent cost may have a major impact on choosing a process. The air/SO, process has
`the lowest cost per pound of SO, reacted while the sulfamic acid process has the highest.
`For large scale commodity production, the air/SO, process clearly has an advantage.
`However, for small scale production of a high value specialty product this advantage may
`be outweighed by other considerations such as initial equipment cost and the necessity
`for continuousoperation.
`
`Page 8 of 36
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`© 1997 The Chemithon Corporation
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`

`CHEMITHON
`
`The process equipmentcost is an important factor to be considered in choice of a
`sulfonation process. You mustlookat the installed cost of the system, tankage and
`required safety systems. The equipmentcost is almost exactly the inverse of the reagent
`cost. Here, the air/SO, processis highest in cost while the simple batch sulfamic process
`is lowest. Other processesare intermediate.
`
`The final factor to consider in the choice of sulfonation processesis the cost of waste
`disposal. The chlorosulfuric acid and oleum sulfonation processes produce large
`by-product streams of either hydrochloric acid or sulfuric acid. These by-products must
`be recovered and sold, or disposed of as a waste. Waste disposal can havea significant
`impact on the profitability of these processes, as the necessary equipmentcan be costly
`and the disposal costs can be high.
`
`Figure 10 showsthe trends in sulfonation plants in the United States!!!. The air/SO,
`processhasrapidly overtaken the oleum processas the predominate choice. This is the
`result of several trends. Thefirst is the waste disposal cost for the spent sulfuric acid
`from the oleum process. The secondis the desire of many processors to avoid storing a
`hazardous material such as oleum. Thethird is the move toward compactdetergent
`products which reducesor eliminates the sodium sulfate content of detergent products.
`The oleum process addsa large quantity of sulfate to the products and for many
`applications this is not acceptable. Finally, the air/SO, process is capable of making a
`broad range of very high quality products.
`
`Figure 10.
`
`Estimated U.S. Sulfonation Plants
`
`1980
`
`1985
`
`1990
`
`Plant Type
`
`No. of
`Plants
`
`Capacity*
`
`No. of
`Plants Capacity*
`
`No. of
`Plants Capacity*
`
`so,
`Oleum
`
`Chlorosulfonic
`
`Acid
`
`Sulfoxidation
`
`44
`51
`
`5
`
`1
`
`630.0
`720.0
`
`35.0
`
`0.45
`
`62
`50
`
`6
`
`2
`
`855
`605
`
`50
`
`1.35
`
`41
`39
`
`6
`
`1
`
`1,016
`548
`
`59
`
`0.45
`
`Totals
`
`101
`
`1385.45
`
`120
`
`1,511.35
`
`87
`
`1,623.45
`
`*Million kg/yr (Information supplied by E.A. Knaggs)
`
`Page 9 of 36
`
`© 1997 The Chemithon Corporation
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`10
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`

`

`CHEMITHON
`
`Commercial Scale Sulfonation Equipment
`
`Sulfamic Acid Sulfation Equipment
`
`Figure 11 illustrates the equipmentused for sulfamic acid sulfation. This batch processis
`run inastainless steel or glass lined,air tight, stirred tank reactor. The reactor has
`heating and cooling coils and provision for weighing in the organic reactant and the
`sulfamic acid. Before the reactionstarts, air is purged from the reactor with dry nitrogen
`and the reaction is run undera blanket of nitrogen. The organic is weighedinto the
`reactor and a 5% molar excess of sulfamic acid is then added. The reactor is purged and
`blanketed with dry nitrogen to remove oxygen. The reactants are heated to 110—160°C
`and held at this temperature for approximately 90 minutes. The products are then cooled
`to 70°C and water or alcohol are added to dilute the product. As previously mentioned,
`an ammoniumsalt is the direct reaction product so no neutralization step is required.
`
`Figure 11. Sulfamic Acid Sulfation
`
`Solid granular
`sulfamic acid
`
`Cooling
`
`Scale Heating/
`
`Organic
`Feed
`
`Product
`
`Loadcell
`
`Page 10 of 36
`
`© 1997 The Chemithon Corporation
`
`11
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`

`CHEMITHON
`
`Chlorosulfonic Acid Sulfation Equipment
`
`Chlorosulfuric acid can be used to sulfonate in either a batch or continuousprocess. For
`the batch process,illustrated in Figure 12, the equipmentis a glasslined,stirred, sealed
`reactor with heating and cooling jackets. The reactor must be fitted with a glass lined
`absorber to remove the HCI gas evolvedin the reaction. A slight vacuum is usually
`pulled on the reaction vessel to enhance HCl removal. The liberated HCI gas is absorbed
`into water to make a dilute HClsolution. In operation, the alcohol or ethoxy alcohol
`feedstock is charged to the reactor and chlorosulfuric acid is gradually added. A good
`refrigeration system is required for heat removal becausethe reaction is exothermic. The
`reaction mass must be kept at approximately 25°C to avoid side reactions and color body
`formation and to minimize foaming. Therate of addition of chlorosulfuric acid is
`adjusted to ensure that this temperature is not exceeded. Immediate neutralization is
`required once the reaction is complete.
`
`Figure 12. Batch Chlorosulfonic Acid Sulfation
`
`Water Vacuum
`
`
`
`
` HCl
`
`Absorber
`
`
`
`
`
`
`Load Cell
`
`Chlorosulfation can also be continuous. Figure 13 showsa typical flow sheet for a
`continuouschlorosulfuric acid sulfation process. In this application the alcohol and
`chlorosulfuric acid are added into a mixing zone, combined and sent to a degasser. A
`slight vacuum is pulled on the degasser to assist separation of HCl from the reaction
`products. The disengaged sulfonic acid is sent through a heat exchanger to removethe
`heat of reaction and recycled back to the mixer to cool the process. A portion of the
`
`Page 11 of 36
`
`© 1997 The Chemithon Corporation
`
`12
`
`Chlorosulfonic
`
`Dilute
`HCl
`Solution
`
`Refrigerated
`Cooling
`
`Product
`
`Acid
`
`

`

`CHEMITHON
`
`reaction mixture is sent to a second degasser where the HCI separation is completed. The
`HClis continuously absorbed into water and the acid mixture is continuously neutralized.
`Several companies including Henkel use continuouschlorosulfation technology for
`making detergent actives. The process is economically viable if a source for the HClis
`available and if the product, which contains someresidual chloride ion, is acceptable.
`
`Oleum and Sulfuric Acid Sulfonation Equipment
`
`Oleum and sulfuric acid can be used to sulfonate aromatics and alcohols in either batch
`or continuous equipment. For detergent alkylates, the batch equipmentis very similar to
`other processes. As shownin Figure 14, the required equipmentis a stirred, sealed, glass
`lined or stainless steel kettle with a provision
`
`Figure 13. Continuous Alcohol Sulfation with Chlorosulfonic Acid
`
`
` 2
`| Ejector
`Degasser
`
`Acid
`
`
`
`First
`Stage
`
`Cooler
`
`
`
`Second
`Stage
`Degasser
`
`Alcohol
`from
`
`Gear Pump
`
`Mixing
`Pump
`
`Ejector
`
`Cool
`ooler
`
`Hydrochloric
`
`Mixing Pump
`Water
`
`|
`Neutralized
`erent
`v
`
`>
`
`Chloro-
`sulfonic
`Acid from
`Storage
`
`Proportioning
`Pump
`
`Gear Pump
`
`Sulfation
`
`Hydrochloric Acid
`Absorption System
`
`for heating and cooling. The detergent alkylate is first added to the reaction vessel then
`the oleum is slowly added overa period of several hours. The reaction is highly
`exothermic and the oleum addition rate is determined by the ability to removethe heat of
`reaction. The temperature should be maintained below 35°C for optimum product
`quality. Frequently the heat of reaction is removed by pumping the reaction mixture
`
`Page 12 of 36
`
`© 1997 The Chemithon Corporation
`
`13
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`

`

`CHEMITHON
`
`through an external heat exchanger. Becauseit is an equilibrium reaction, except for the
`special case of azeotropic sulfonation of hydrotropes with sulfuric acid, a large surplus of
`sulfuric acid forms. When the sulfonation reaction is complete, the sulfuric acid may be
`separated from the sulfonated detergent alkylate by adding water. The water addition
`(typically about 10% by weight of the reaction mixture) causes a phase separation to
`occur betweenthe sulfonic acid and the diluted sulfuric acid. The separation usually
`takes place in a separate, glass lined vessel and occurs overa period of about
`
`Figure 14. Batch Oleum Sulfonation of Detergent Alkylate
`
`Optional
`Sodium
`
`[] Alkyl Benzene
`
`SulfonateL|
`
`
` '
`
`'W
`
`Spent
`Sulfuric Acid
`
`CW
`
`Alkylate
`
`A
`
`A
`
`Oleum 20%
`
`x
`x
`
`Weigh Tanks
`
`Sulfonator
`
`Gravity Acid Separator
`
`Neutralizer
`
`10 hours. Materials of construction are crucial because the dilution process makes
`sulfuric acid whichis in a very corrosive temperature and concentration range. After
`separation, the sulfonic acid may be neutralized with aqueous sodium hydroxide, usually
`in a separate neutralization vessel. Including neutralization, total batch time is 15 to 20
`hours. The product contains about 15% sodium sulfate after neutralization if the acid is
`separated, and about 60% sodium sulfate if not. Without separation, the product's
`application is limited to low active, traditional detergent powders where the large content
`of sodium sulfate is used asafiller.
`
`In the special case of azeotropic sulfonation of toluene, cumeneor xylene with 98%
`sulfuric acid to form hydrotropes, a reflux condenseris addedat the top of the reactor.
`The condenserseparates the unreacted feed from the water produced in the reaction. The
`water is removed from the condenser, and the feed is refluxed back to the reactor.
`Because the water is removed, the reaction proceeds to completion and a large excess of
`sulfuric acid is not required. Typical equipment for hydrotrope sulfonation is shown in
`Figure 15.
`
`Page 13 of 36
`
`© 1997 The Chemithon Corporation
`
`14
`
`

`

`CHEMITHON
`
`The invention of the process for continuous oleum sulfonation was the foundation of The
`Chemithon Corporation in 1954I+.5], Figure 16 showsa flow sheet for continuous oleum
`sulfonation of detergent alkylate. In this process, alkyl benzene is mixed and reacted
`with oleum in a recycle loop wherethe reaction mixture is cooled by recycling it through
`a heat exchanger. Typical reaction temperatures in the recycle loop are 38—54°C. The
`mixedacid products
`
`Figure 15. Batch Azeotropic Sulfonation of Aromatics with Sulfuric Acid
`
`Sulfuric
`Acid
`
`Aromatic
`
`(toluene,
`xylene or
`cumene)
`
`Condenser
`
`(<i
`
`
`
`Steam /
`Hot Water
`
`Product
`
`
`
`
`
`
`
`LoadCell
`
`Page 14 of 36
`
`© 1997 The Chemithon Corporation
`
`15
`
`

`

`CHEMITHON
`
`Figure 16. Continuous High Active Alkylate Sulfonation with Oleum
`
`Alkyl Benzene
`
`
`Settler
`
`From Storage Reaction
`
`Coil
`
`|.
`
`
`
`
`
`Mixing
`Mixing
`Pump
`Pump
`
`Oleum
`From
`Storage ————>
`
`Proportioning
`Pump
`
`Sulfonation
`Cooler
`
`Dilution
`Cooler
`
`Neutralized
`Detergent
`Slurry
`
`
`
`
`Neutralization
`Cooler
`
`
`SpentAcid
`
`
`Alkali
`
`Mixing
`Pump
`
`Sulfonation
`
`Dilution
`
`Sulfonic
`Concentration
`
`Neutralization
`
`are digested in a plug flow reactor and then dilution water (approximately 13% by
`weight) is added in a second mixing loop. A second heat exchanger removesthe heat of
`dilution. The diluted sulfuric acid and alkylbenzene sulfonic acid are separated in a
`continuoussettler. The sulfonic acid is then continuously neutralized with aqueous
`sodium hydroxide solution in a third, cooled mixing loop. Sulfate levels as low as 10%
`in the final product can be achieved in this equipment. Total processing timeis less than
`one hour. The equipmentcan also be used to sulfate detergent range alcohols for use in
`laundry powdersif a high level of sulfate in the product can be tolerated. The sulfates are
`present because the separation process cannot be used when sulfating alcohols. If water
`is added to the alcohol sulfuric acid/sulfuric acid mixture, the alcohol sulfuric acid
`immediately hydrolyzes. Additionally, mixed products containing both alkyl benzene
`sulfonates and alcohol sulfates can be manufactured as shownin Figure 17. In this case
`alkylate is sulfonated first, followed by sulfation of the alcohol. Some of the excess
`sulfuric acid from the sulfonation stage is used to react with the alcohol and the
`combined mixture is immediately neutralized. Because no separation stage is used, the
`resultant productis high in sulfate.
`
`Page 15 of 36
`
`© 1997 The Chemithon Corporation
`
`16
`
`

`

`CHEMITHON
`
`Figure 17. Continuous Tandem Type Sulfonation-Sulfation with Oleum
`
`Alkyl Benzene
`
`
`
`Coil
`
`Neutralized
`Detergent
`
`Slurry
`from Storage Reaction
`
`
`
`
`Sulfation
`Sulfonation
`
`
`Cooler
`Cooler
`
`
`
`Mixing
`
`Proportioning
`Pump
`Pump
`Pump
`
`
`
`Alkali
`
`|
`
`Neutralization
`
`Cooler
`
`Fatty Alcohol
`from Storage
`
`Oleum
`from Storage
`
`Sulfonation
`
`Sulfation
`
`Neutralization
`
`Air/SO; Sulfonation Equipment
`
`Fourpossible sources of SO, gas used for an air/SO, sulfonation system are:
`
`Sulfuric acid plant converter gas
`e
`SO, from boiling concentrated oleum
`e
`e Liquid SO,
`e
`Sulfur burning in equipment specifically designed to produce SO, gas
`for sulfonation
`
`Converter gas from a sulfuric acid plant contains 10-12% SO, and appears to be a
`potential SO, source for sulfonation. There are several problems with using a sulfuric
`acid plant as an SO, source for sulfonation. Nevertheless, such an arrangement has been
`commercially installed and at first glance appears to be an attractive, low cost method of
`supplying SO, gas to a sulfonation plant. Physical locationis a limiting factor; as the
`sulfonation plant must be installed as closely as possible to the sulfuric acid plant
`converter. In addition, the sulfonation plant can run only whenthe sulfuric acid plantis
`running.
`
`There are three other more subtle difficulties when using a sulfuric acid plant as an SO,
`source for sulfonation. First, the SO; gas at approximately 18% concentration must be
`diluted to the normal range for sulfonation (typically 4-7%). An auxiliary air supply
`mustbe installed, which adds expense and complexity. Second, because sulfuric acid
`absorption towersare used forair drying, the air/SO, from a sulfuric acid plant has a
`higher dew point (typically —35°C) than that required in a sulfonation plant (typically —
`
`Page 16 of 36
`
`© 1997 The Chemithon Corporation
`
`17
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`

`

`CHEMITHON
`
`60°C to —80°C). The high dew point causes product quality problems in the sulfonation
`process and accelerates corrosion of the process equipment. Third, the pressure of the
`air/SO, from the sulfuric acid plant is usually not sufficient to overcome the pressure
`drop of the sulfonation system. Compressingthe air/SO, from the converteris nottrivial
`as it requires a high alloy compressor to withstand the corrosive environment created by
`the wet air/SO, stream. This problem can be overcome,butthe solution is not
`inexpensive. Considering all the problemsinherentin utilizing the converter gas stream
`from a sulfuric acid plant, the conclusionisthat it is technically feasible. Howeverthis
`choice addssignificant operational difficulties and does not result in a major cost savings
`overinstalling a complete sulfur burning sulfonation plant.
`
`Anotherpossible source of SO, for sulfonation is produced by boiling oleum to produce
`gaseous SO, whichis then blended with dry air. It is practically limited to locations
`wherefresh oleum can be received, and depleted oleum returned by pipeline. Compared
`to sulfur burning, this process somewhat reduces the equipment requirement. However,
`it still requires an air supply system, an oleum boiler and an SO, metering system.
`Unlike a sulfur burning plant which generates its own heatfor air dryer regeneration,this
`air supply system requires an external source of heat which addsextra utility expenses.
`Also, significant safety hazards are associated with handling concentrated oleum. Such
`an installation may be economical for a few site locations, and at least oneis
`commercially operating in North America.
`
`Someofthe first air/SO, sulfonation plants installed were based on use ofliquid SO.
`These plants require an air supply system identical to the system described below for a
`sulfur burning plant exceptthat it also requires an external heat source for air dryer
`regeneration. In addition, a liquid SO, plant requires an SO, storage system. This
`storage system is usually a large 20,000 to 80,000 kg storage tank located in a heated
`room and maintained at a temperature of about 40-43°C. Heating the SO, storage room
`can beasignificant cost in colder climates. In case of SO, leaks, the room must be
`sealed and should haveprovision for scrubbing any SO, that escapes into the room's
`atmosphere. In the sulfonation process, the liquid SO, is metered from the storage tank
`into a steam heated vaporizer whereit is evaporated and mixedinto the dried air stream
`from the air supply system. From this point on, the processis identical to a sulfur
`burning air/SO, sulfonation plant, described below. A liquid SO, storage and metering
`system is shown in Figure 18. Because of the rigorous storage requirements imposed by
`the hazardousnature ofliquid SO,, the installed cost for a liquid SO, sulfonation facility
`is close to that for a sulfur burning installation.
`
`There are significant safety advantages to a sulfur burning system. With sulfur burning
`air/SO, sulfonation processes, the only SO, onsite is the small quantity of dilute gaseous
`material in the process piping between the converter (SO, to SO,) and the sulfonation
`
`Page 17 of 36
`
`© 1997 The Chemithon Corporation
`
`18
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`

`

`CHEMITHON
`
`reactor. Even in the world's largest sulfonation plant (20,000 kg/hr active production),
`this amounts to only about 100 kg of dilute SO, gas. The sulfur burning process is much
`safer than transporting, storing and handling tank truck (18,000 kg)or rail car (72,000
`kg) quantities of oleum or liquid SO;. Sulfonation equipment based on liquid SO, has
`becomeincreasingly undesirable for the following reasons:
`
`Figure 18. Dilute SO3 Gas from Liquid SO3
`
`
`
`H,SO,
`Absorber
`
`Heated Storage Room
`
`
`
`
`
`|__| Safety Relief
`
`SO,
`Storage
`Tank
`
`SO,
`Metering
`System
`
`1
`I
`I
`
`l
`I
`
`SO,
`Unloading
`Facility
`
`I
`I
`I
`
`I
`I
`
`Dilute
`so
`Vapoizer ——P Gaseous SO,
`to Process
`
`Air Chiller
`
`Air
`Compressor
`
`
`
`
`
`
`
`
`
`
`Air Dryer
`Regeneration
`
`Heater
`
`e
`
`e
`
`e
`
`Safety concerns
`
`Liquid SO, is unavailable in manyparts of the world
`
`Sulfur is readily available worldwide
`
`Sulfur is relatively inexpensive
`
`The remainderofthis section, therefore, is confined to the