Ammonia separation and purification by absorbing pervaporation

Ammonia separation and purification by absorbing pervaporation

Desalination 200 (2006) 379–380 Ammonia separation and purification by absorbing pervaporation Ilya V. Vorotyntseva*, Pavel N. Drozdovb, Dmitry N. Sh...

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Desalination 200 (2006) 379–380

Ammonia separation and purification by absorbing pervaporation Ilya V. Vorotyntseva*, Pavel N. Drozdovb, Dmitry N. Shablikinb, Tatjana V. Gamajunovab a

Chemical Department, Nizhny Novgorod State University, 23 Gagarin Avenue, 603950 Nizhny Novgorod, Russia b Physics and Technology of Materials and Components of Electronic Technique (FTMKET) Department, Nizhny Novgorod State Technical University, 24 Minina Str., 603600 Nizhny Novgorod, Russia email: [email protected] Received 22 October 2005; accepted 4 March 2006

1. Introduction Pure ammonia consumption by microelectronics is increasing every year because the production capacity of light-emitting diodes (LEDs) based on InGaN/GaN/AlGaN is also increasing. Specifically, the performance of GaN LEDs is critically dependent on impurities present in the ammonia process gas. Ammonia separation and purification in this case is the advanced development. The ammonia separation and purification by the new method — the absorbing pervaporation was investigated. 2. Theory and experimental The separation process according to the absorbing pervaporation [1] consists of few stages. First of all, ammonia with its impurities dissolves in absorbent placed on a flat membrane surface. Then, ammonia diffuses through the absorbent and through the membrane.

*Corresponding author.

Finally, it evolves in a low-pressure cavity of a membrane module. Different type of membranes including rubbery and glass polymers were used for the investigation. Pure water, glycol, polyethylene glycol and water solution of polyethylene glycol with different molar mass (up to 2000) were used as absorbents. The Barrier technique was used for the permeability measurement. Because ammonia is a reactive gas all used equipment was made of stainless steel. The combine system of absorbent and membrane was tested by contact angle measurement. The solubility of gases (ammonia and its impurities) was determined by gas chromatography. 3. Results and discussion The results of permeability and selectivity achieved for ammonia separation and purification by absorbing pervaporation was compared to membrane gas separation. It was shown that selectivity of absorbing pervaporation was by >1000 times more efficient.

Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.382

I.V. Vorotyntsev et al. / Desalination 200 (2006) 379–380

The above mentioned different absorbents were compared by the wetting ability, which is characterized by the contact angle measurement. It was shown that water has the biggest solubility of ammonia and the lowest wetting ability that is why other absorbents were tested. The parameters of the penetrating mechanism were determined and calculated. The thickness of selective layer A consisting of static absorbent layer near by membrane surface and selective layer of the membrane was determined by the following equation:

A = 6×Q× D,

0.0084 Q, cm2/(cm2 sec bar)

380

0.0063 0.0042 0.0021 0.0000 0

5

10

15 t, min

20

25

30

Fig. 1. The time dependence of ammonia permeability through the polyethylene glycol (molar mass 400) — polydimethylsiloxane membrane.

(1)

where D is the diffusion coefficient of gas component into absorbent; Q “the time of the gap” which is determined as a segment on the time axis. This segment is cut by the line which we get by the approximation of the experimental data (Fig. 1) corresponding to the process of increasing of permeability up to stationary values. It was shown that the limiting stage of ammonia permeability was penetration through the polymeric membrane and the permeability achieved by absorbing pervaporation was compared to the membrane gas separation. But the simple gases i.e. nitrogen, hydrogen, permeability was limited by solubility into absorbent that is why the achieved selectivity of absorbing pervaporation is much bigger than the membrane gas separation. The surface free energy per unit area of membrane was calculated from the dependence of contact angle and concentration of absorbent.

The solubility and adsorption heat of ammonia were calculated from sorption isotherm. Sorption isotherm was defined from gas chromatography peaks. 4. Conclusion The influence of the absorbent and the membrane on selectivity of the separation process was studied. It was shown that it is possible to achieve a high degree of ammonia purification from most of the impurities by the absorption pervaporation method. Reference [1]

V.M. Vorotyntsev, P.N. Drozdov and E.Yu. Kolotilov, Absorbing pervaporation — a new method of gas separation, Desalination, 149 (2002) 23–27.