12 SULZER TECHNICAL REVIEW 3/2008 4243

PETER FÄSSLERSULZER CHEMTECHAUREO CELEGHIN

CELEGHIN

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minesmizemine

Sulzer Chemtech has over 30 years of experience inthe field of ethanolamine technology. Its expertiseincludes the provision of comprehensive engineeringservices for the modernization of existing plants, as well as the manufacturing of key components forplants such as distillation column internals (Fig. 1).Sulzer Chemtech and Celeghin ConsultantsCorporation of Houston, TX, USA, teamed up tocreate an innovative new ethanolamine techno-logy solution that optimizes product quality andprocess flexibility while lowering energy con-sumption during production. This complete solution reduces the investment and operating costs related to the production of ethanolamines.

Cost-efficient productionof ethanolamines

A new approach to an established product coth(NIdetenpcoapucatrinteasis

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SULZER TECHNICAL REVIEW 3/2008 1343

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t Ethanolamines are flamma-ble, corrosive, colorless, vis-

cous liquids that are produced bythe reaction between ammonia(NH3) and ethylene oxide (EO).Identified many years ago,ethanolamines are a key ingredi-ent in a number of importantproduct formulations such ascosmetics and personal hygieneapplications, agricultural prod-ucts, wood-preservation chemi-cals, soaps and detergents, gastreatments. They can also be usedin the production of non-ionic de-tergents, emulsifiers, and soaps, as well as in emulsion paints, pol-ishes, and cleansers.

Flexible ethanolamineproduction technologyThere are 3 types of ethanolamines:monoethanolamines (MEA), di-ethanolamines (DEA), and tri-ethanolamines (TEA). The for-mation of MEA, DEA, or TEAdepends on whether an ammoniamolecule reacts with 1, 2, or 3 ethylene oxide molecules (Fig. 2). Unlike conventional ethanolamineproduction technology, which isoften limited in terms of the ratioof ammonia to ethanolamine thatcan be handled, the flexible SulzerChemtech solution offers the op-tion of altering the amounts of thefinal product generated. The com-position of the resulting mixture isdetermined by the ratio betweenthe raw materials, which can bevaried in accordance with require-ments. The higher the proportionof ammonia, the more mono-ethanolamine is formed (Fig. 3).The Sulzer Chemtech process canhandle ammonia to ethanolamineratios up to or exceeding 6:1 andoffers the customer a high level ofMEA or DEA distribution while

minimizing the volume of TEAproduced (Fig. 4).

Lower costsThe volume of water used inethanolamine production canvary: if the water content remainslow during the process, it is neces-sary for the reaction to be conduct-ed under high pressure—resultingin high investment costs. These re-actions consume a low level of en-ergy. In order to lower investmentcosts, a high water content may beused under low pressure, but therelated energy consumption willconsequently be higher. The newethanolamine technology solutionoffered by Sulzer Chemtech com-bines the advantages of the high-pressure ammonia route with thebenefits of the low-pressureprocess. The process allows theuse of a relatively low-pressurereaction and incorporates veryadvanced heat integration, whichsaves costs across the board.The Sulzer Chemtech water recov-ery system, which uses the energyintegration concept, thermally tiesthe water evaporator to the ammo-nia stripper column and mini-mizes the size of the drying col-umn. It thus enables the plant to

operate economically even at am-monia to ethylene oxide ratios of6:1 or above. Furthermore, thepresence of water as a catalyst inthe synthesis of ethanolamine en-sures a rational and economical re-actor setup. The use of water pro-vides the greatest control over thetemperature rise in the reactor sys-tem and allows a reduction in thevolume of the reactor. The averagereaction temperature can be low-ered and adjusted to minimize sec-ondary side reactions that couldcompromise the quality of theresulting ethanolamine.

Ammonia recoveryThe key to saving energy in theproduction of ethanolamine lies inthe design and operating pressureof the main ammonia absorber.The ammonia stripper is integrat-ed directly with the absorber byfeeding the stripper overhead va-pors into the bottom of the ammo-nia stripper. In other words, thereis a direct connection between thetwo columns. In addition, theoverhead vapors from the mainwater distillation columns areused as a heat source for the am-monia stripper reboiler. The pressure at the top of the main

1 Jilin ethanolamineproduction plant in China.

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14 SULZER TECHNICAL REVIEW 3/2008

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water evaporation column is lim-ited by the maximum permissibletemperature at the bottom of thecolumn. Hence, the boundary op-erating conditions of the ammoniaabsorber, ammonia stripper, andmain water evaporation columnare basically fixed. The only de-gree of flexibility in the design isin the selection of the column op-erating conditions, column inter-nals, and the heat exchanger. Sulzer Chemtech has added ther-mal and energy integration to theammonia absorber, the ammoniastripper, and the water distillationcolumn. As a direct consequenceof this thermal and process heat in-tegration, the energy required bythe improved process is compara-ble to the high-pressure route(Fig. 5).The increase in the ammonia con-centration in the ammonia ab-sorber is a direct result of theprocess heat integration and has asignificant impact on overall ener-gy consumption. The higher theoperating pressure in the ammo-nia absorber, the higher the ammo-nia concentration. The higher theammonia content, the less waterhas to be handled in the system.Since the water must be recycledback into the system by means ofevaporation, each percentagepoint increase in the ammonia con-centration leads to an approximateenergy saving of between 1.5 and2%—which represents a signifi-cant reduction in absolute terms.The ammonia concentration canalso be set to allow for the efficientand economical recovery of theresidual ammonia from the reac-tion loop. This recovery occurs ata pressure that is sufficiently lowto ensure that the ammonia strip-ping takes place at a low tempera-

ture, thus reducing the possibledegradation of the product andminimizing the corrosion of equip-ment.The high ammonia concentrationallowed by the Sulzer Chemtechprocess further reduces the size ofthe ammonia stripper and ammo-nia scrubber and eliminates theneed for an additional auxiliary re-boiler heated by an external heat-ing source. These features signifi-cantly reduce investment costs.

A clear advantageEthanolamines are sensitive toheat and therefore tend to degradeand must be separated with greatcare. The higher the temperature(respectively the pressure), themore colored the ethanolaminesbecome. Color is, however, themost important characteristic de-termining their quality and value;the more colorless the substancesare, the higher their market value.The use of high-efficiency pack-ings from Sulzer Chemtech andthe rational design of the distilla-tion train minimizes the packingvolume and enables the column tobe operated at a lower tempera-ture, with narrow residence timedistribution and minimum per-manent holdup. The separation ofethanolamines at these carefullymaintained conditions improvesthe product color and reduces the corrosion at the bottom of thecolumn.

Accelerated production withoutethanolamine recyclingThe ethanolamines produced areoften recycled back into the mainreactor system in order to adjustthe desired MEA:DEA:TEA ratio.If the reaction is performed in theprimary reactor, the recycling not

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2 Mono-, di-, andtriethanolamines areproduced by reacting

ethylene oxide with ammonia.

Ethanolamine (EA) product distribution (reaction 1)

NH3/EO ratio

Ethanolamine (EA) product distribution (reaction 2)

MEA/EO ratio

3 The ratio of MEA, DEA, and TEA produced canbe varied by altering the ratio of the reactants.

4 The second reaction is requiredto produce a higher level of DEA.

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SULZER TECHNICAL REVIEW 3/2008 15

designs. Any adjustments that arerequired, e.g. relating to productcapacity and product distribution,can be implemented relativelyquickly and with a high degree ofreliability.In addition, the accumulation ofunwanted byproducts or feed im-purity products trapped in theprocess loops can be detected andeliminated through purging atspecific locations.Since such complex design ap-proaches are very time consuming,they are only justified for selectedprocess steps in ethanolamine pro-duction—an area in which SulzerChemtech has extensive experi-ence, supported by a diversifiedrange of market applications.

Product stress ~ A×(residence time)T

where:Residence time = the time inminutes during which theaverage bottom product molecule stays in the bottomof the column.T = the absolute temperatureof the hot stream at the bottom of the column.A = a proportionality factor.

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ContactSulzer Chemtech AGPeter FässlerSulzer-Allee 488404 WinterthurSwitzerlandPhone +41 52 262 37 29Fax +41 52 262 00 64peter.faessler@sulzer.com

only consumes more energy andrequires a higher residence timebut can also lower the productquality through the developmentof color and an increase in corro-sion. The Sulzer Chemtech conceptavoids the difficulties associatedwith recycling and eliminates re-peated process steps, thus reduc-ing the overall residence time inthe plant and lowering energyconsumption.

Avoiding product stressProduct stress is defined as thetendency of the product to de-grade and carbonize at the bottomof the column. Product stress canbe minimized through the rationalstudy of the temperature profileand the configuration at the bot-tom of the column, resulting in lessproduct degradation. Side reac-tions, such as color precursors, canbe suppressed to a certain extentthrough the smooth execution ofthe process at the lowest tempera-tures possible.The level of product stress is di-rectly related to the hot productresidence time and is exponential-ly related to the temperature of thehot product (see box). The SulzerChemtech process for ethanol-

amine production makes effectiveuse of the product stress conceptto ensure the best handling of thehot product at the bottom of thecolumn.

PurificationThe synthesis and purification ofethanolamines is a relatively com-plex process as the final productquality is determined by the pres-ence of minor impurity streams in the feed, as well as by internalrecycle streams, thermal processintegration, and the reaction ofindividual components includingside reactions.

Integrated approachA fully integrated approachthroughout the plant is a prerequi-site for a successful design. SulzerChemtech and Celeghin havetherefore adopted a single blockfor the entire process simulation.This module has been systemati-cally improved not only by inte-grating the accumulated know-how but also by relying on realplant operating data and perfor-mance characteristics. This type ofcomprehensive simulation tool issophisticated enough to provide asatisfactory description of plantdetails and serves as a powerfultool for the analysis of possibleprocess improvements, for heatintegration, and for new plant

5 Sulzer Chemtechprovides a completeand flexible solutionfor ethanolamine production.

Ammonia absorption

AmmoniastrippingReaction 1 Concen-

tration

Ethanolamine technology: overview

Distillation

Water purge

MEANH3

EO

EO

DEA

TEA

Residue/TEA

Reaction 2

Demi-water

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