Crystallization of inorganic compounds [Elektronische Ressource] : scaling in seawater desalination / von Ali Mousa Al-Atia

Crystallization of inorganic compounds [Elektronische Ressource] : scaling in seawater desalination / von Ali Mousa Al-Atia

-

English
97 Pages
Read
Download
Downloading requires you to have access to the YouScribe library
Learn all about the services we offer

Description

Crystallization of Inorganic Compounds – Scaling in Seawater Desalination Eingereicht am Zentrum für Ingenieurwissenschaften Martin-Luther-Universität Halle-Wittenberg zur Erlangung des akademischen Grades Doktor-Ingenieur (Dr.-Ing.) genehmigte Dissertation von M.Sc. Chem. Eng. Ali Mousa Al-Atia geboren 6. Mai 1977 in Bagdad, Irak Gutachter: 1. Prof. Dr.-Ing. habil. J. Ulrich 2. Prof. Dr. Schulte Halle (Saale), 08. December 2008 urn:nbn:de:gbv:3-000014874[http://nbn-resolving.de/urn/resolver.pl?urn=nbn%3Ade%3Agbv%3A3-000014874] Dedication I dedicate this work to my father, who passed away while I am far away from him busy with this work, may God bless his soul, and to my mother who is proud of me as I am proud of her. Dad... You are always in my thoughts! Acknowledgment I wish to express my deepest gratitude and sincere appreciation to my supervisor Prof. Joachim Ulrich, for his supervision, guidance and helpful suggestion throughout the research work. I would like to acknowledge the financial support by the DAAD for my PhD work in Germany. Also, special thanks to the staff of department of thermal separation processes who offered great help and cooperation. I would like to thank Dr.

Subjects

Informations

Published by
Published 01 January 2008
Reads 31
Language English
Document size 1 MB
Report a problem



Crystallization of Inorganic Compounds – Scaling in Seawater
Desalination






Eingereicht am Zentrum für Ingenieurwissenschaften
Martin-Luther-Universität Halle-Wittenberg



zur Erlangung des akademischen Grades
Doktor-Ingenieur (Dr.-Ing.)
genehmigte



Dissertation



von

M.Sc. Chem. Eng. Ali Mousa Al-Atia
geboren 6. Mai 1977 in Bagdad, Irak



Gutachter:
1. Prof. Dr.-Ing. habil. J. Ulrich
2. Prof. Dr. Schulte

Halle (Saale), 08. December 2008

urn:nbn:de:gbv:3-000014874
[http://nbn-resolving.de/urn/resolver.pl?urn=nbn%3Ade%3Agbv%3A3-000014874]


Dedication


I dedicate this work to my father, who passed away while I am far away from
him busy with this work, may God bless his soul, and to my mother who is proud of
me as I am proud of her.

Dad... You are always in my thoughts!









































Acknowledgment


I wish to express my deepest gratitude and sincere appreciation to my
supervisor Prof. Joachim Ulrich, for his supervision, guidance and helpful suggestion
throughout the research work.
I would like to acknowledge the financial support by the DAAD for my PhD work in
Germany.

Also, special thanks to the staff of department of thermal separation processes
who offered great help and cooperation. I would like to thank Dr. Matthew Jones,
Helmut Weißbarth, Severine Dette, Kathrin Jäger, Isolde Trümper, Nadine Pachulski
and Caner Yürüdü.
Last but not least, I am very grateful to my entire family for their moral support.
To each and every one of you - thank you!

Halle (Saale), August 2008
Table of content


1 Introduction ……………………………………………………………….. 1

2 State of the Art.................................................................................... 2

Effects of Additives on the MSZ Width

2.1 Electrolyte solutions…………………………………………………………... 2
2.2 Thermodynamics of ion solvation…………………………………………… 2
4 2.3 Solubility and nucleation ……………………………………………………..
2.4 Metastable zone width and influence of the additive……………………… 8
2.5 Induction time………………………………………………………………..... 9

Scale Reduction in Seawater

2.6 Seawater composition and saturation state………………………….......... 11
2.7 Chemical definition of scales………………………………………………… 13
2.7.1 The alkaline scale……………………………………………………... 13
2.7.2 The non alkaline scale………………………………………………... 13
2.8 Desalination methods………………………………………………………… 14
15 2.9 Problems caused by scaling.…………………………………………………
2.9.1 Thermal technologies…………………………………………………. 15
2.9.2 Membrane technologies……………………………………………… 15
2.10 Methods of scale reduction; disadvantages………………………………... 15
2.11 Aims of research work………………………………………………………... 16
2.12 Present work methodology ………………………………………………….. 17
2.12.1 Suggested rule to select the additives……………………………… 17
2.12.2 Suggested methods to reduce scaling in seawater desalination… 18


3 Experimental Work………………………………………………………. 20

3.1 Polythermal and isothermal methods……………………………………….. 20
3.1.1 The effect of inorganic impurities on the width of the metastable
zone…………………………………………………………………….. 20
22 3.1.2 Induction time of calcium carbonate in artificial seawater…………
3.2 Fluidized bed crystallizer……………………………………………………... 23
3.2.1 Seeds of natural calcite………………………………………………. 23
3.2.2 The hot finger technique……………………………………………… 25
3.3 Ultrasonic irradiation………………………………………………………….. 26



4 Table of content

4 Results………………………………………………………….................... 28

MSZ Width Results

4.1 The effect of selected inorganic additives on the MSZ width of inorganic
compounds…………………………………………………………………….. 28
4.1.1 The effects of Al (SO ) , FeSO , BaCl , Li SO and K SO on the 2 4 3 4 2 2 4 2 4
MSZ width of ZnSO ……….…………………………………………. 4 28
4.1.1.1 The effect of Al (SO ) on the MSZ width of ZnSO …………. 29 2 4 3 4
31 4.1.1.2 The effect of FeSOi …………….. 4 4
32 4.1.1.3 The effect of BaCl on the MSZ width of ZnSO ……………… 2 4
34 4.1.1.4 The effect of Li SOi …………….. 2 4 4
4.1.1.5 The effect of K SOidth of ZnSO …………….. 35 2 4 4
4.1.2 The effects of AlCl , FeCl , MgCl and BaCl on the MSZ width of 3 2 2 2
LiCl……………………………………………………………………… 37
4.1.2.1 The effect of AlCl on the MSZ width of LiCl…………………. 37 3
4.1.2.2 The effect of FeCli 38 2
4.1.2.3 The effect of MgClidth of LiCl………………… 40 2
4.1.2.4 The effect of BaCl on the MSZ wi 41 2
4.1.3 The effects of CuSO , BaCl and Li SO on the MSZ width of 4 2 2 4
K SO …………………………………………………………………… 2 4 43
4.1.3.1 The effect of CuSO on the MSZ width of K SO .................... 43 4 2 4
4.1.3.2 The effect of BaCl on the MSZ wi SO ...................... 44 2 2 4
4.1.3.3 The effect of Li SO on the MSZ width of K SO .................... 46 2 4 2 4
4.2 Determination the induction time of CaCO in artificial seawater………... 48 3
4.2.1 Induction time at 35 g/kg salinity…………………………………….. 49
4.2.1.1 Effect of NaHCO addition on the induction time of CaCO .. 49 3 3
4.2.1.2 Induction time of CaCO as a function of supersaturation 3
and temperatures (30, 40, 50 and 70 °C)………………………. 50
4.2.2 Induction time at 55 g/kg salinity…………………………………….. 51
4.2.2.1 Effect of NaHCO addition on the induction time of CaCO .. 51 3 3
4.2.2.2 Induction time of CaCO as a function of supersaturation 3
and temperatures (30, 50 and 70 °C)…………………………… 52

Scale Reduction Results

4.3 Reduction of CaCO by seeding; without chemical addition…………….. 53 3
4.4 by a hot finger; without chemical addition………… 53 3
4.5 by precipitation; supersaturation modified by 3
NaHCO ………………………………………………………………………... 3 54
4.5.1 Reduction of calcium ion versus NaHCO addition……………….. 54 3
5 Table of content

56 4.5.2 Reduction of calcium ion versus operational temperature………...
4.5.3 Reduction of calcium ion versus operational time, power of
58 ultrasound and salinity………………………………………………...


5 Discussion………………………………………………………………….. 60

5.1 The effect of additives on the MSZ width………………………………….. 60
5.1.1 ZnSO -H O solution………………………………………………...… 60 4 2
5.1.1.1 Effect of Al (SO ) …………………………………………………. 60 2 4 3
5.1.1.2 Effect of FeSO …………………………………………………….. 61 4
5.1.1.3 Effect of BaCl ……………………………………………………… 61 2
5.1.1.4 Effect of Li SO 62 2 4
5.1.1.5 Effect of K SO ........................................................................... 63 2 4
5.1.2 LiCl-H O solution……………………………………………………… 64 2
5.1.2.1 Effect of AlCl ………………………………………………………. 64 3
5.1.2.2 Effect of FeCl ……………………………………………………… 65 2
5.1.2.3 Effect of MgCl …………………………………………………….. 65 2
5.1.2.4 Effect of BaCl 66 2
5.1.3 K SO -H O solution…………………………………………………… 67 2 4 2
5.1.3.1 Effect of CuSO 67 4
5.1.3.2 Effect of BaCl 67 2
68 5.1.3.3 Effect of Li SO 2 4
5.2 The induction time of CaCO in artificial seawater………………………… 69 3
5.2.1 Effect the mass addition of NaHCO at 35 and 55 g/kg salinity 3
(Sa.) ……………………………………………………………………. 71
5.2.2 Interfacial tension (surface energy) of CaCO in ASW……………. 73 3
5.3 Scale reduction of CaCO in seawater desalination………………………. 75 3
5.3.1 Crystal growth…………………………………………………………. 75
75 5.3.2 Precipitation…………………………………………………………….
5.3.2.1 Calcium ion reduction as a function of NaHCO mass and 3
temperature………………………………………………………… 76
5.3.2.2 Operational time of ultrasound, power of ultrasound and
salinity change…………………………………………………….. 77
5.3.3 An environmentally friendly and economically solution to reduce
77 scaling…………………………………………………………………..

6 Conclusion………………………………………………………………….. 80
7 Summary…………………………………………………………………….. 82
8 Nomenclature……………………………………………………………… 84
9 References 86
6 Introduction

1. Introduction

There is a big effort in developing techniques to improve the seawater
desalinisation. That means to reduce the costs of fresh water and to reduce the
impacts on environment.

One of the most important factors that contribute to high production costs of
fresh water from seawater in desalination is scale formation (encrustation). Scale
formation e.g. CaCO in seawater desalination is a crystallization phenomenon. This 3
phenomenon can be defined as crystallization of inorganic compounds in a multi-
component solution (seawater). This type of crystallization is considered to be
complicated, since the crystallization process is influenced by the compounds which
exist in seawater and the complex plant operational conditions.
Most known techniques that are used to reduce the encrustation in seawater
desalination are not based on crystallization processes as will be shown in the next
chapters. On this account, the motivation of this work is to find alternative
technologies to reduce the encrustation by applying the principles of crystallization.

It would be desirable therefore first to study the effect of inorganic compounds
on the nucleation step of crystallization in inorganic solutions. In order to fill the gap
in the literature in terms of finding an interpretation to the effect of additives
concerning suppression, enhancement or non of both of these effects on the
metastable zone width of inorganic solutions. This study will indeed be helpful in a
better understanding of crystallization processes.
Reducing the scale formation in seawater desalination can be achieved by a pre-
treatment process where a precipitation and a separation of CaCO is taking place. A 3
spontaneous precipitation of CaCO in seawater can not occur without modifying the 3
degree of supersaturation of CaCO in seawater as it will be presented. 3
The aspects of using a pre-treatment process as alternative method by means of an
environmental friendly and economical solution will be discussed.









1 State of the Art
2. State of the Art

2.1 Electrolyte solutions

Compounds that exist as ions, as cations and anions, when dissolved in water
are called electrolytes and thus, the mixture of cations, anions and water molecules
is called an electrolyte solution. This electrolyte solution can be formed pure or as
mixture according to the number of dissolved substances (solute) in water (solvent).
Further, the electrolyte solutions are divided into week and strong solution, this is due
to the ionization process of electrolytes that dissolve in water. There are references
which are dealing with types, properties, structures and the thermodynamics of
electrolyte solutions [MUR84], [ZEM86], [LOB89].
In solution and under special conditions (supersaturation), a solid phase can
form from the dissolved compounds. This phase separation process is called
crystallization. Generally speaking, crystallization from solutions can be achieved by
two steps, nucleation and crystal growth. Both steps are controlling the crystalline
products in terms of crystal shape, size distribution, purity and morphology.
Furthermore, they could strongly affect the product yield.
Decades ago, many researchers started to investigate and interpret the effect
of additives on nucleation and crystal growth processes. The methodology of their
research was so far concentrated on the conditions accompanied to the solid phase
formation (crystals in bulk solutions) [DAV74], [KUB97], [HEN98], [SAN04]. The liquid
phase structure changes of the bulk solutions [ONO68], [KUB95] and [NYV98] were
hardly be considered. Especially, when they studied the effect of impurities on the
nucleation process.
Thereby, the present study will show how the change in the structure of solutions can
play a big role in interpreting the effect of impurities on the nucleation process.

2.2 Thermodynamics of ion solvation

Solvation is defined as the attraction and association of molecules of a solvent
with molecules or ions of a solute [DOG85]. As salts dissolve in a solvent they spread
out and become surrounded by solvent molecules. There are different types of
intermolecular interactions: ion-ion, ion-dipole and dipole-dipole attractions or van der
Waals forces which occur only in polar solvents. Figure 2-1 shows the sequence of
thermodynamic steps for a general case of salt dissolution in water.






2 State of the Art


Figure 2-1: The enthalpy change of ion-dipole formation during the dissolution process
according to Norton [CTS08]

The dissolution process can be thermodynamically summarized as follows:

1. Breaking of solute ionic bonds, i.e. lattice enthalpy.
2. The spherical symmetrical field of individual ions may tear water dipoles out the
liquid structure (Breaking of hydrogen bonds in solvent, i.e. enthalpy of solvent).
3. A certain number of water molecules in the immediate vicinity of the ion are
trapped. And water dipole charged ends are oriented towards the center of ions
to form a hydration shell (primary solvation shell) of ion-dipole. It can have a
positive or a negative charge as shown in e.g. figure 2-2. The energy required to
form the shell of hydration is called the enthalpy of hydration. This energy
represents the ion-dipole intermolecular force interaction, which is the value
which depends on the ionic radius and charge [BUR88]. Further, it depends on
the temperature, pressure and number of water molecules in the hydration shell.

The enthalpy of hydration values for different inorganic compounds in terms of
cations and anions have been calculated through thermodynamic models as can be
found by Marcus [MAR87]. These values will be the factor of setting up a new rule to
study and interpret the effect of inorganic additives on the nucleation of inorganic
compounds, as will be described later.


3 State of the Art


Figure 2-2: Hydration shell represented by ammonium nitrate dissolved in water [CTS08]

Accordingly, ion-ion intermolecular forces can be understood through the
following concepts:
1. Each solvated ion, i.e. ion-dipole may be assumed to undergo random motion
in solution.
2. The positive and negative charges of solvated ions may be trapped in the
columbic field of each other, the electrostatic force (F) between these ions can
be represented by the following equation [SAN07]:

2z ⋅z ⋅e1 2F = (2-1) 2ε ⋅r
With: z valence of ion (-) i
-19e elementary charge (1.6022*10 c)
r distance between the ions (nm)
ε dielectric constant of the solvent ( ε = ε ε ) r o
ε relative dielectric constant (relative permittivity) of solvent (water r
[DAV95])
-12 2 2 ε vacuum permittivity (8.854187*10 c /N.m ) o
In concentrated electrolyte solutions, the electrostatic force is very strong between
the positive and negative ion-dipole in the bulk water.
From all of above, the intermolecular forces namely ion-ion and ion-dipole
interaction are the key factors to study the effect of additives on nucleation.

2.3 Solubility and nucleation

One of the basic requirements in crystallization process design is to find the
phase diagram of solute-solvent equilibrium. Generally speaking, the phase diagram
4