adsorption literature

8/13/2019 Adsorption Literature

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Adsorptionis a process that occurs when a gas or liquidsolute accumulates on the surface ofa solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (theadsorbate). It is different fromabsorption,in which a substance diffuses into a liquid or solidto form a solution. The termsorptionencompasses both processes, whiledesorption is thereverse process.

Adsorption is operative in most natural physical, biological, and chemical systems, and iswidely used in industrial applications such as activated charcoal, synthetic resins and water

purification. Adsorption,ion exchange andchromatography are sorption processes in whichcertain adsorptives are selectively transferred from the fluid phase to the surface of insoluble,rigid particles suspended in a vessel or packed in a column.

Similar tosurface tension,adsorption is a consequence ofsurface energy.In a bulk material,all the bonding requirements (be theyionic,covalent ormetallic)of the constituentatoms ofthe material are filled. But atoms on the (clean) surface experience a bond deficiency, becausethey are not wholly surrounded by other atoms. Thus it is energetically favourable for them to

bond with whatever happens to be available. The exact nature of the bonding depends on thedetails of the species involved, but the adsorbed material is generally classified as exhibiting

physisorption orchemisorption.

Adsorption is usually described through isotherms, that is, functions which connect theamount of adsorbate on the adsorbent, with its pressure (if gas) or concentration (if liquid).

The first isotherm is due to Freundlich and Kster (1894) and it is a purely empirical formula

valid for gaseous adsorbates: , wherexis the adsorbed quantity, mis the mass of

adsorbent,Pis the pressure of adsorbate and kand nare empirical constants for eachadsorbent-adsorbate pair at each temperature. The function has an asymtotic maximum. Asthe temperature increases, the adsorbed quantity rises more slowly and more pressure isrequired to achieve the maximum.

Langmuir

In 1916,Irving Langmuirpublished a new isotherm for gases adsorbed on solids, whichretained his name. It is an empirical isotherm derived from a proposed kinetic mechanism. Itis based on four hypotheses:

1. The surface of the adsorbent is uniform, that is, all the adsorption sites are equal.2. Adsorbed molecules do not interact.3. All adsorption occurs through the same mechanism.4. At the maximum adsorption, only a monolayer is formed: molecules of adsorbate do

not deposit on other, already adsorbed, molecules of adsorbate, only on the freesurface of the adsorbent.

These four points are seldom true: there are always imperfections on the surface, adsorbedmolecules are not necessarily inert, the mechanism is clearly not the same for the very firstmolecules as for the last to adsorb. The fourth condition is the most troublesome, as oftenmore molecules can adsorb on the monolayer, but this problem is solved by theBETisotherm.
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Langmuir suggests that adsorption takes place through this mechanism: A(g)+ SAS, whereA is a gas molecule and S is an adsorption site.

The direct and inverse rate constants are k and k-1. If we define surface coverage, , as thefraction of the adsorption sites occupied, in the equilibrium we have

or

For very low pressures and for high pressures

is difficult to measure experimentally; usually, the adsorbate is a gas and the adsorbedquantity is given atstandard temperature and pressure (STP) volume per gram of adsorbent.Therefore, if we call vmonthe STP volume of adsorbate required to form a monolayer on the

adsorbent (per gram of adsorbent too), and we obtain an expression for a straightline:

Through its slope andy-intercept we can obtain vmonandK, which are constants for eachadsorbent/adsorbate pair at a given temperature. vmonis related to the number of adsorptionsites through theideal gas law.If we assume that the number of sites is just the whole area of

the solid divided into the cross section of the adsorbate molecules, we can easily calculate thesurface area of the adsorbent. Surface area of adsorbents depends on their structure, the morepores they have, the greater the area, which has a big influence onreactions on surfaces.

If more than one gas adsorbs on the surface, we call Ethe fraction of empty sites and wehave

and

where iis each one of the gases that adsorb.
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Langmuir equation

Langmuir isotherm. Value of constant increases from blue, red, green and brown

The Langmuir equationor Langmuir isothermor Langmuir adsorption equationrelatesthe coverage oradsorption of molecules on a solid surface togas pressure orconcentration ofa medium above the solid surface at a fixed temperature. The equation was developed byIrving Langmuir in 1916. The equation is stated as:

ortheta is the percentage coverage of the surface, Pis the gas pressure or concentration, alpha is a constant.

The constant is the Langmuir adsorption constantand increases with an increase in thestrength of adsorption and with a decrease in temperature. The equation is derived startingfrom theequilibriumbetween empty surface sites, particles and filled particle sites

equilibrium between empty surface sites S*and particles P and filled surface sites S-P

Because the fraction of filled surface sites is equal to and the fraction of unfilled sites equal

to 1- and because P is proportional to the gas pressure or concentration the equation can berewritten to
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Other equations relating to adsorption exist such as theTemkin equation or theFreundlichequation.The Langmuir equation (as a relationship between the concentration of a compoundadsorbing to binding sites and the fractional occupancy of the binding sites) is equivalent totheHill equation.

Inchemistry,Henry's lawis one of thegas laws,formulated byWilliam Henry.It states that:

At a constant temperature, the amount of a given gas dissolved in a given type andvolume of liquid is directly proportional to thepartial pressureof that gas inequilibrium with that liquid.

A formula for Henry's Law is:

where:thepartial pressure of thesolute above thesolutiontheconcentration of the solute in the solution (in one of its many units)the Henry's Law constant, which has units such as Latm/mol, atm/(mol fraction) or

Pam3/mol.

Taking thenatural logarithm of the formula, gives us the more commonly used formula:[1]

Some values for kinclude:

oxygen (O2) : 769.2 Latm/molcarbon dioxide (CO2) : 29.4 Latm/molhydrogen (H2) : 1282.1 Latm/mol

when these gases are dissolved inwater at 298kelvin.

Note that in the above, the unit of concentration was chosen to bemolarity.Hence thedimensional units:Lis liters of solution, atmis the partial pressure of the gaseous solute

above the solution (in atmospheres of absolute pressure), and molis the moles of the gaseoussolute in the solution. Also note that the Henry's Law constant, k, varies with the solvent andthe temperature.

As discussed in the next section, there are other forms of Henry's Law each of which

defines the constant kdifferently and requires different dimensional units. The form of

the equation presented above is consistent with the given example numerical values for

oxygen, carbon dioxide and hydrogen and with their corresponding dimensional units.
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Other Forms

There is various other forms Henry's Law which are discussed in the technical literature.[2][3]

Table 1: Some forms of Henry's law and constants (gases in water at 298K), derived from [3]

equation:

dimension

:

O2 769.23 1.3 E-3 4.259 E4 3.180 E-2

H2 1282.05 7.8 E-4 7.099 E4 1.907 E-2

CO2 29.41 3.4 E-2 0.163 E4 0.8317

N2 1639.34 6.1 E-4 9.077 E4 1.492 E-2

He 2702.7 3.7 E-4 14.97 E4 9.051 E-3

Ne 2222.22 4.5 E-4 12.30 E4 1.101 E-2

Ar 714.28 1.4 E-3 3.955 E4 3.425 E-2

CO 1052.63 9.5 E-4 5.828 E4 2.324 E-2

where:

=moles of gas perliter of solution

= liters of solution=partial pressure of gas above the solution, inatmospheres ofabsolute pressure

=mole fraction of gas in solution = moles of gas per total moles moles of gasper mole of water= atmospheres of absolute pressure
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As can be seen by comparing the equations in the above table, the Henry's Law constant kH,pcis simply the inverse of the constant kH,cp. Since all kHmay be referred to as the Henry's Lawconstant, readers of the technical literature must be quite careful to note which version of theHenry's Law equation is being used.

It should also be noted the Henry's Law is a limiting law that only applies for dilute enoughsolutions. The range of concentrations in which it applies becomes narrower the more thesystem diverges from non-ideal behavior. Roughly speaking, that is the more chemicallydifferentthe solute is from the solvent.

It also only applies for solutions where the solvent does notreact chemically with the gasbeing dissolved. A common example of a gas that does react with the solvent iscarbondioxide,which rapidly forms hydrated carbon dioxide and thencarbonic acid (H2CO3) withwater.

Temperature dependence

When the temperature of a system changes, the Henry constant will also change. This is whysome people prefer to name it Henry coefficient. There are multiple equations assessing theeffect of temperature on the constant. A simple example is[3],which is a form of thevan'tHoff equation:

where

kfor a given temperature is the Henry's Law constant (as defined in the first section of

this article), identical with kH,pcdefined in Table 1,Tis in kelvins,the index (Theta)refers to the standard temperature (298K).

The above equation is an approximation only and should be used only when no betterexperimentally derived formula for a given gas exists.

The following table lists some values for constant C (dimension of kelvins) in the equationabove:

Table 2: Values of C

Gas O2 H2 CO2 N2 He Ne Ar CO

C 1700 500 2400 1300 230 490 1300 1300

Because solubility of gases is decreasing with increasing temperature, the partial pressure agiven gas concentration has in liquid must increase. While heating water (saturated withnitrogen) from 25C to 95C the solubility will decrease to about 43% of its initial value. Thiscan be verified when heating water in a pot. Small bubbles evolve and rise, long before thewater reaches boiling temperature. Similarly, carbon dioxide from acarbonated drink escapesmuch faster when the drink is not cooled because of the increased partial pressure of CO2in

higher temperatures. Partial pressure of CO2in seawater doubles with every 16 K increase intemperature.[4]
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Deriving Raoult's Law (Raoult's Equation)

We define anideal solution as asolution for which thechemical potential of component iis:

,where the reference state is the pure substance.

If the system is atequilibrium,then thechemical potential of the component imust be thesame in the liquid solution and in thevapor above it. That is,

Assuming the liquid is an ideal solution, and using the formula for the chemical potential of agas, gives:

(1)

where

is thefugacity of thevapor of i.

If we study the component iin its pure state, we have:

where * indicates that we study a pure component.

But now, = 1, so

Subtracting both equations gives us

which can be written as
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or

This equation is valid for the ideal solution.

Now, suppose thevapor of the solution behaves as anideal gas.In this case,fugacity andpressure are identical, and we get

At equilibrium we have = 0, and then

Finally,

This last equality is what is known asRaoults Law.

Henry vs Raoult

Both Henry's law andRaoult's law relate the vapor pressure of a component to itsconcentration. It is possible (and sometimes more convenient) for either law to write theconcentration in terms of mole fractionsx. Note however that the numerical value of kas wellas its dimensions change when mole fractions are used rather than molarity (as seen in theTable 1).

Henry's law:

Raoult's law:

The difference is thatp*is the equilibrium vapor pressure of the pure component whereas theHenry constant kHis a value that differsfromp*. It must be determined experimentally fromthe mixtures, not the pure compound.

If the solution is ideal (which it seldom is), both components follow Raoult's law over theentire composition range. In most systems, the laws can only be applied in a very limitedconcentration range at extreme ends of the range. In that case, the minority component (thesolute)follows Henry's law, but the solvent still follows Raoult's law. TheGibbs-Duhemequation can be used to prove that this is so.
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Ideal/Non-Ideal Mixing

Ideal

An ideal solution can be said to follow Raoult's Law but it must be kept in mind that in the

strict sense ideal solutions do not exist. The fact that the vapor is taken to be ideal is the leastof our worries. Interactions between gas molecules are typically quite small especially if thevapor pressures are low. The interactions in a liquid however are very strong. For a solution to

be ideal we must assume that it does not matter whether a molecule A has another A asneighbor or a B molecule. This is only approximately true if the two species are almostidentical chemically. We can see that from considering theGibbs free energy change ofmixing:

This is always negative, so mixing is spontaneous. However the expression is -apart from afactor -T- equal to the entropy of mixing. This leaves no room at all for an enthalpy effect andimplies that Hmixmust be equal to zero and this can only be if the interactions U between themolecules are indifferent.

It can be shown using theGibbs-Duhem equation that if Raoult's law holds over the entireconcentration range x=0 to 1 in a binary solution that for the second component the samemust hold.

If the deviations from ideality are not too strong, Raoult's law will still be valid in a narrowconcentration range when approaching x=1 for the majority phase (thesolvent). The solute

will also show a linear limiting law but with a different coefficient. This law is known asHenry's law.

The presence of these limited linear regimes has been experimentally verified in a greatnumber of cases.

Non-Ideal

Raoult's Law may be adapted to non-ideal solutions by incorporating two factors that willaccount for the interactions between molecules of different substances. The first factor is acorrection for gas non-ideality, or deviations from theideal-gas law.It is called the fugacitycoefficient (). The second, the activity coefficient (), is a correction for interactions in theliquid phase between the different molecules.

This modified or extended Raoult's law is then written:

Adsorbents

The adsorbents are used usually in the form of spherical pellets, rods, moldings or monoliths

with hydrodynamic diameter between 0.5 and 10 mm. They must have high abrasionresistance, high thermal stability and small micropore diameter, which results in higher
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exposed surface area and hence high capacity of adsorption. The adsorbents must also have adistinct macropore structure which enables fast transport of the gaseous vapours.

Different types of industrial adsorbents generally fall into three classes:

Oxygen-containing compoundsAre hydrophilic and polar, including materials suchassilica gel andzeolites. Carbon-based compoundsAre hydrophobic and non-polar, including materials such

as activated carbon. Polymer-based compounds - Are polar or non-polar functional groups in a porous

polymer matrix.

Silica gel

Silica gel is a chemically inert, nontoxic, polar and dimensionally stable (< 400 C)amorphous form of SiO2. It is prepared by the reaction between sodium silicate and sulphuric

acid, which is followed by a series of after-treatment processes such as aging, pickling, etc.These after treatment methods results in various pore size distributions on its surface.

Silica is also used for drying of process air (e.g. oxygen, natural gas etc) and adsorption ofhigher (polar) hydrocarbons from natural gas.

Zeolites

Zeolites are natural or synthetic aluminum silicates which form a regular crystal lattice andrelease water at high temperature. Zeolites are polar in nature.

They are manufactured by hydrothermal synthesis of sodium aluminosilicate in an autoclavefollowed by ion exchange with certain cations (Na+, Li+, Ca++, K+). The channel diameterof zeolite cages usually ranges from 2 to 9 (200 to 900pm). This process is followed bydrying of microcrystals, which are palletized with a binder, to form macropores and thermallyactivated at a temperature of 6500 C.

Zeolites are applied in drying of process air (only traces), CO2removal from natural gas, COremoval from reforming gas and air separation.

Non-polar zeolites are synthesized by dealumination of polar zeolites. This is done by treating

the zeolite with steam at elevated temperatures, greater than 500 C (1000 F). This hightemperature heat treatment breaks the aluminum-oxygen bonds and the aluminum atom isexpelled from the zeolite framework.

Non-polar zeolites are mostly used in non-polar organics removal.

Activated carbon

They are highly porous, amorphous solids consisting of microcrystallites with a graphitelattice. They are non-polar and cheap. One of their main drawbacks is that they arecombustible.

Activated carbon can be manufactured from carbonaceous material, including coal(bituminous, subbituminous, and lignite), peat, wood, or nutshells (i.e., coconut). The
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manufacturing process consists of two phases, carbonization and activation. Thecarbonization process includes drying and then heating to separate by-products, including tarsand other hydrocarbons, from the raw material, as well as to drive off any gases generated.The carbonization process is completed by heating the material at 400600 C in an oxygen-deficient atmosphere that cannot support combustion.

The carbonized particles are activated by exposing them to an activating agent, such assteam at high temperature. The steam burns off the decomposition products from thecarbonization phase to develop a porous, three-dimensional graphite lattice structure. The sizeof the pores developed during activation is a function of the time that they are exposed to thesteam. Longer exposure times result in larger pore sizes. The most popular aqueous phasecarbons are bituminous based because of their hardness, abrasion resistance, pore sizedistribution, and low cost, but their effectiveness needs to be tested in each application todetermine the optimal product.

Activated carbon is used for adsorption of organic substances and non-polar adsorptives and it

is also usually used for waste gas (and waste water) treatment. It is the most widely usedadsorbent. Its usefulness derives mainly from its large micropore and mesopore volumes and

Test questions

1.) Draw the typical diagrams to determine the coefficients of the Langmuir-, Freundlich- andDubinin-Isotherm by linear regression (linear form)!

LnV = lnV0(1/E) x

Coefficients: V0 x E slope

Original Dubinin

V

Ln Vabs

E


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LnV = lnV0(1/E) x

Coefficients: V0 x E slope

Freundlich isotherm

Coeff: KLx Qmax from

Q = Qmax1/KL x Q/[]

V0

Ln Vabs

E

Qmax

Q/[ ]

-1/KL

Q


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2.) Drawthe concentration profiles of SO2 in a drop of water falling through the flue gas of apit coal power unit in case of a very good external mass transfer coefficient!Explain the Enhancement-factor in case of an aqueous solution of calcium hydroxide insteadof pure water!

Where A = SO2 B = water

3.) Design a typical stripping column for regeneration of washing agents! Draw an X/Y-diagram with the equilibrium line and the operation line for stripping!

4.) Draw the concentration profiles in a spherical pellet of activated carbon for different timesin a non-steady state adsorption process! Explain the jump-function on the surface of the

pellet!

8.) Draw the concentration profiles in a spherical pellet of activated carbon for differentinternal diffusion coefficients and a very good external mass transfer coefficient in a non-steady state adsorption process! Explain the jump-function on the surface of the pellet!

16.) Draw the concentration profiles of water in a spherical pellet of silica gel for different

pore size distributions (different internal diffusion coefficients) in case of a very good externalmass transfer coefficient in a non-steady state adsorption process! Explain the jump-function on the surface of the pellet!

5.) How can you get information about the capacity of an adsorbent from a break throughcurve? Which information could we take from the curve at a concentration ratio of 0,5?

[A]g

[A]Leq

[A]L

[B]L

[A]geq


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6.) What are the differences between an absorption cooling process with water andlithiumbromide and a process with water and ammonia? How to separatewater/lithiumbromide and water/ammonia?

Water-cooled absorption systems use water as the refrigerant and a lithium bromide solution as theabsorbent material. Air-cooled systems use ammonia as the refrigerant and water as the absorbent.

An ammonia water absorption system works like any absorption chiller except that ammoniais the refrigerant and water is the absorbent.Ammonia is boiled out of water by heat from agas-fired burner and condensed in an outdoor air coil. The liquid ammonia is then evaporatedat low pressure, producing cooling, and reabsorbed into the water.

Ammonia makes a great refrigerant. With 2.5 times the heat of vaporization of fluorocarbons,ammonia is highly effective, has no ozone depletion potential, and no significant globalwarming potential.

Advantages of ammonia-water

Ammonia/water has advantages over the more common lithium bromide/water absorbers. Ammonia is a high-pressure refrigerant, meaning that it can be directly air cooled in acompact coil. No cooling tower is required. There is no salt to crystallize in an ammonia water system. The system is under positive pressure, making components more compact and eliminatingthe need for air purge systems.

Ammonia/water has a quirk that doesnt exist in lithium bromide absorption systems. When

the water reabsorbs the ammonia, it releases heat. But unlike bromide systems, this heat ispartly released at a high temperature. This high temperature heat can actually be recycled toreplace some of the gas firing and reduce fuel input.

How Absorption Cooling Works

Like the compressor in an electric vapour compression cycle, the absorption system uses its "thermal"compressor (consisting of the generator, absorber, pump and heat exchanger) to boil water vapour(refrigerant) out of a lithium bromide/water solution and compress the refrigerant vapour to a higherpressure. Increasing the refrigerant pressure also increases its condensing temperature.

The refrigerant vapor condenses to a liquid at this higher pressure and temperature. Because thiscondensing temperature is hotter than the ambient temperature, heat moves from the condenser tothe ambient air and is rejected. The high-pressure liquid then passes through a throttling valve thatreduces its pressure. Reducing its pressure also reduces its boiling point temperature. The low-pressure liquid then passes into the evaporator and is boiled at this lower temperature and pressure.

Because the boiling temperature is now lower than the temperature of the conditioned air, heat movesfrom the conditioned air stream into the evaporator and causes this liquid to boil. Removing heat fromthe air in this manner causes the air to be cooled.

The refrigerant vapour then passes into the absorber where it returns to a liquid state as it is pulledinto the lithium bromidesolution (the absorption process). The diluted lithium bromidesolution is

pumped back to the generator. Because lithium bromide (the absorbent) does not boil, water (therefrigerant) is easily separated by adding heat. The resultant water vapor passes into the condenser,the absorbent solution returns to the absorber, and the process repeats.


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Simplified diagram of a single-effect absorptioncycle

Although the process is similar to conventional electric vapor compression systems, absorption coolingsubstitutes a generator and absorber, called a thermal compressor, for an electric compressor.Efficiency and lower operating costs are achieved through the use of a pump rather than acompressor and a heat exchanger to recover and supply heat to the generator. Double-effect

absorption cooling adds a second generator and condenser to increase the refrigerant flow, andtherefore the cooling effect, for a fraction of the heat input of a single-effect system.

Absorption Cooling Technology

Absorption cooling operates similarly to conventional electric vapor compression chillers with somevery important differences. The major differences are seen in the components of the system and therefrigerant used in the cycle. Absorption systems use what is called a thermal compressor in placeof the conventional systems compressor.

Additionally, absorption systems use distilled water and either nontoxic lithium bromide or ammonia,

thereby eliminating harmful chlorofluorocarbons (CFCs) common to mechanical systems.

Other significant differences include the use of heat, rather than a compressor, as the driving force,and lower pressure/vacuum conditions. Heat for the absorption process can be supplied directly by agas burner or indirectly from the recovered waste heat of a cogeneration system, hot water or steam.

The number of heat exchangers distinguishes the system as either single-effect or double-effect andserves to improve efficiency and lower operating costs. Indirect-fired single-effect absorption systemsattain coefficients of performance (COP) of 0.60 to 0.70 while comparable double-effect systems canachieve a COP of 1.20.

Three types of double-effect absorption chillers are commercially available and all offer comparable

performance. The three types, series-flow cycle,parallel-flow cycleand reverse-flow cycle, aredifferentiated by the path that the absorbent/refrigerant solution flows to the primary and secondarygenerators.


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7.) Draw an X/Y-diagram with equilibrium line and explain the differences in calculationbetween gaseous phase resistance and liquid phase resistance!

9.) Explain the words volume-filling-theory and potential-theory! Can we use both

theories simultaneously?

10.) What is the main difference between absorption of oxygen in water and absorption ofammonia in water? How do the equilibrium lines look like?

The polarity of NH3molecules and their ability to form hydrogen bonds explains to some extent thehigh solubility of ammonia in water. However, a chemical reaction also occurs when ammoniadissolves in water. In aqueous solution, ammonia acts as a base, acquiring hydrogen ions from H2O toyield ammonium and hydroxide ions.

NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

The production of hydroxide ions when ammonia dissolves in water gives aqueous solutionsof ammonia their characteristic alkaline (basic) properties. The double arrow in the equation indicatesthat an equilibrium is established between dissolved ammonia gas and ammonium ions. Not all of thedissolved ammonia reacts with water to form ammonium ions. A substantial fraction remains in themolecular form in solution. In other words, ammonia is a weak base. A quantitative indication of thisstrength is given by its base ionization constant:

11.) Draw the typical diagrams to determine the coefficients of the Dubinin-Isotherm bylinear regression (linear form) Explain the meaning of the two coefficients

12.) Draw the concentration profiles in an absorption process with chemical reaction. Inwhich cases is the Enhancement-factor required to describe the kinetic behavior correctly?

13.) Why is the tray efficiency always less than 100% Make proposals how to increase it!

14.) Sketch the flow-sheets of an adsorption cooling or an adsorption heat pumpingprocess! What are the advantages of adsorption processes related to absorption processes?

15.) Design a typical adsorption column for the reduction of SO2 in flue gases with water.Explain the reason for taking solutions of calcium hydroxide in water instead of pure water.What are the disadvantages in both cases?

17.) Explain the words pressure swing adsorption and temperature swing adsorption!

Draw the difference between constructions of the 2 adsorbers!

Pressure Swing Adsorption(PSA) is a technology used to separate some gas species from amixture of gases under pressure according to the species' molecular characteristics andaffinity for anadsorbent material. It operates at near-ambient temperatures and so differs fromcryogenicdistillation techniques ofgas separation.Special adsorptive materials (e.g.,zeolites)
http://en.wikipedia.org/wiki/Adsorbenthttp://en.wikipedia.org/wiki/Cryogenichttp://en.wikipedia.org/wiki/Distillationhttp://en.wikipedia.org/wiki/Gas_separationhttp://en.wikipedia.org/wiki/Zeoliteshttp://en.wikipedia.org/wiki/Zeoliteshttp://en.wikipedia.org/wiki/Gas_separationhttp://en.wikipedia.org/wiki/Distillationhttp://en.wikipedia.org/wiki/Cryogenichttp://en.wikipedia.org/wiki/Adsorbent


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are used as amolecular sieve,preferentially adsorbing the target gas species at high pressure.The process then swings to low pressure to desorb the adsorbent material.

Using two adsorbent vessels allows near-continuous production of the target gas. It alsopermits so-called pressure equalisation, where the gas leaving the vessel being depressured is

used to partially pressurise the second vessel. This results in significant energy savings, and iscommon industrial practice.

Applications of the PSA technology

One of the primary applications of PSA is in the removal ofcarbon dioxide (CO2) as the finalstep in the large-scale commercial synthesis ofhydrogen (H2) for use inoil refineries and intheproduction of ammonia (NH3). Another application of PSA is the separation of carbondioxide frombiogas to increase themethane (CH4) content. Through PSA the biogas can beupgraded to a quality similar tonatural gas.

Research is currently underway for PSA to capture CO2in large quantities fromcoal-firedpower plantsprior togeosequestration,in order to reducegreenhouse gasproduction fromthese plants.[1]

PSA is an economic choice for small-scale production of reasonable purityoxygen ornitrogenfromair.PSA technology has a major use in the medical industry to produce oxygen,

particularly in remote or inaccessible parts of the world where bulk cryogenic or compressedcylinder storage are not possible.

PSA has also been discussed as a future alternative to the non-regenerable sorbent technology

used inspace suitPrimary Life Support Systems,in order to save weight and extend theoperating time of the suit.[1]

18.) What is the main difference between mixture behavior of water/lithiumbromide andwater/sodium chloride regarding process cooling processes! Can we use water as a coolingagent in both cases for an absorption cooling process?

19.) Explain Henrys law and Raoults law! Draw the difference in a T = const. -diagramof a binary mixture.
http://en.wikipedia.org/wiki/Molecular_sievehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Oil_refineryhttp://en.wikipedia.org/wiki/Ammonia_productionhttp://en.wikipedia.org/wiki/Biogashttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Fossil_fuel_power_planthttp://en.wikipedia.org/wiki/Fossil_fuel_power_planthttp://en.wikipedia.org/wiki/Geosequestrationhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://www.co2crc.com.au/RESEARCH/research_c_2_4.htmlhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Space_suithttp://en.wikipedia.org/wiki/Primary_Life_Support_Systemhttp://en.wikipedia.org/wiki/Pressure_swing_adsorption#_note-0#_note-0http://en.wikipedia.org/wiki/Pressure_swing_adsorption#_note-0#_note-0http://en.wikipedia.org/wiki/Pressure_swing_adsorption#_note-0#_note-0http://en.wikipedia.org/wiki/Pressure_swing_adsorption#_note-0#_note-0http://en.wikipedia.org/wiki/Primary_Life_Support_Systemhttp://en.wikipedia.org/wiki/Space_suithttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://www.co2crc.com.au/RESEARCH/research_c_2_4.htmlhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Geosequestrationhttp://en.wikipedia.org/wiki/Fossil_fuel_power_planthttp://en.wikipedia.org/wiki/Fossil_fuel_power_planthttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Biogashttp://en.wikipedia.org/wiki/Ammonia_productionhttp://en.wikipedia.org/wiki/Oil_refineryhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Molecular_sieve

adsorption literature

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