**4. Historical perspective**

*Legume Crops – Characterization and Breeding for Improved Food Security*

and intensive genetic and cytogenetic investigations. These legumes have a strategic position in Southeast Asian countries for nutritional security and sustainable crop production. Due to rich in quality protein, minerals and vitamins, they are inseparable ingredients in the diets of a vast majority of Indian population. When supplemented with cereals, they provide a perfect mix of essential amino acids with high biological value. Mungbean has the ability to fix atmospheric nitrogen in symbiotic association with Rhizobium bacteria, which enables them to meet their own nitrogen requirement and also benefit the succeeding crops [1]. These crops have also been reported to smother weed flora appreciably (20–45%) when intercropped with tall cereals and consequently, reduce the cost incurred on weed control [2]. On account of short duration and photo-thermo insensitivity, they are considered excellent crops for crop intensification and diversification. A seed of mungbean is highly nutritious containing 24–28% protein, 1.0–1.5% fat, 3.5–4.5% fibre, 4.5–5.5% ash and 59–65% carbohydrates on dry weight basis [3] and provide 334–344 kcal energy [4]. Mungbean protein is considered to be easily digestible. The dried grains of mungbean can be split or eaten whole after cooking and made into a soup or dhal. The iron availability in mungbean improves substantially to 7.2–11.3% through cooking practices such as soaking, fermenting and sprouting [5]. Mungbean is also widely relished as sprouts. The germinated grains have higher nutritional value as compared with asparagus or mushroom [6, 7]. Green pods and seeds can be cooked as vegetables. These pulses are frequently fed to children, convalescents and geriatrics or used when "breaking" a long fasting period owing to their ease of digestibility. The haulms are used for fodder and the beans husks and small broken pieces are useful as a feed concentrate. The crops are also grown for hay, green manure and cover crop. Mungbean makes better hay than urad bean as the stems and leaves are less hairy.

Mungbean is of Indian origin as is evidenced by their occurrence at archeological sites in the continent. *Vigna radiata* is native to north eastern India-Myanmar regions of Asia [8, 9]. *Vigna radiata var. sublobata* Verdc. is the closest wild relatives of the cultivated mungbean, respectively, and are regarded as their putative progenitors [10–13]. Based on morphological evidence alone, many researchers have considered var. sublobata as progenitor of mungbean [14, 15]. The detailed morpho-chemotaxonomic studies on wide collections of var. sublobata [12, 13, 16, 17], cross ability and chromosome pairing evidence [11, 18–20] have led to the conclusion that var. sublobata is a polymorphic taxon; two distinct morphological groups of it are the wild progenitors of mungbean and can be designated as *V. radiata* var. sublobata. The wild collections have characteristics conducive to domestication like annual growth habit, erect plant type, photoperiod insensitivity, more pods with high number of seeds, and smaller leaves. The present day cultivars of mungbean might have originated from new combinations of the already existing variants, changes in growth habit and seed size have been brought about by possible accumulation of recessive mutant genes [21]. Moreover, during domestication the dehiscent nature of pods and seed hardness of the wild progenitors have been selected out.

Mungbean is tropical grain legumes widely grown in the sub-tropical countries of South and Southeast Asia [22, 23]. These legumes are grown at low to

**50**

**3. Ecology**

**2. Origin and domestication**

Pure lines continued even during the early 40s to mid from these landraces were isolated on the basis of colour of stem, foliage, flower, unripe and ripe pods, seed colour and texture and other morphological features. The types selected were best suited in their respective regions mostly under low management. In mungbean, the first promising variety released was Type 1 for cultivation in Uttar Pradesh in 1948. It is a local selection from Muzaffarpur (Bihar). A large number of varieties were developed afterwards through selection from local materials and were released in different states between 1948 and 1970. Some of the important varieties developed through selection are Co 1 and ADT 1 (Tamil Nadu), Jalgaon (Maharashtra), Khargone 1, Krishna (Madhya Pradesh), and G 65 (Punjab). Jawahar 45 (Hybrid 45) released in 1971 in Madhya Pradesh and Type 44 released in Uttar Pradesh in 1972 was perhaps the first varieties developed through hybridization. Afterwards, a number of varieties were developed mainly through selection from the germplasm [24, 25]. Earlier a variety Virat has been released from ICAR—Indian Institute of Pulses Research, Kanpur, Uttar Pradesh; it is mature by 55 days only and fitted to rice wheat cropping system. This has resulted in development of appropriate production technologies and improved varieties besides basic knowledge on these crops.


**4. Dielectric properties**

## **4.1 Local field**

occurs under the influence of an internal process in a dielectric, without the effect of external factors. A ferroelectric crystal generally consists of regions called domains of homogeneous polarization, within each of which the polarization is in the same direction, but in the adjacent domains, the polarization is in different directions so that the net polarization of the specimen is equal to zero in the beginning when no electric field (*E* ¼ 0) is applied. The polarization varies in a non-linear configuration with an electric field (*E*). This non-linear relation exhibits the closed curve called the hysteresis loop in the polarization when an electric field is applied, as shown in **Figure 5** [2–6]. When the electric field (*E* ¼ 0) is zero, the spontaneous polarization (*Ps*Þ in a single domain specimen is either positive or negative in sign. As an applied electric field strength gradually increases in the direction of spontaneous polarization (*Ps*Þ, the polarization (*P*) increases due to induced polarization such as electronic, ionic and dipolar types. As the electric field is increased further, more and more domains rotate along the direction of the electric field (*E*) until the polarization

At this stage, the whole specimen represents a single domain. This is usually accompanied by a distortion in the crystal along the polarization direction. The extrapolation of the saturation value to zero field gives the magnitude of the spontaneous polarization (*Ps*Þ. This value of *Ps* is the same as possessed by each domain before the application of the electric field. However, if the applied electric field decreases, the polarization also decreases but follows another path and does not become zero for zero electric field. The remaining polarization at this stage is called remnant polarization ð Þ �*Pr* and the intercept on the E-axis, where *Pr* refers to the whole crystal block. In order to destroy the remnant polarization (*Pr*Þ, the polarization of nearly half of the crystal is to be reversed by reversing the direction of the field, the electric field required to make the polarization zero is called the coercive field (*Ec*Þ. Furthermore, an increase in the reverse field results in the saturation of polarization in the reverse direction. Reversing the electric field again, the hysteresis curve will be obtained. The relation between polarization (*P*) and applied electric field ð Þ *E* is thus represented by a hysteresis loop (BDFGHB) which is the most important characteristic of the ferroelectric crystals. The most important feature of a ferroelectric is thus not the fact that it has a spontaneous polarization (*Ps*Þ but rather the fact that this spontaneous polarization can be reversed by means of an

reaches a maximum value called the saturation value.

*Multifunctional Ferroelectric Materials*

electric field [2–14].

**Figure 5.**

**12**

*Ferroelectric (P-E) hysteresis loop [13].*

The electric field acting at the site of atom or molecule is, in general, significantly different from the macroscopic filed *E* and is known as the local field ð Þ *Eloc* . This field is responsible for the polarization of each atom or molecule of a material [5, 6]. For an atomic site with cubic crystal symmetry, the local field ð Þ *Eloc* is expressed by the Lorentz-relation as

$$E\_{\rm loc} = E\_0 + E\_P + \frac{P}{\mathfrak{B}\varepsilon\_0} = E + \frac{P}{\mathfrak{B}\varepsilon\_0} \tag{2}$$

where *E* ¼ *E*0 þ *EP*. The field *EP* is called the polarization field as it tends to oppose the external applied field *E*0. Thus, apart from the macroscopic field Eð Þ, the local field also contains a term called Lorentz field ð Þ *Eloc* . The difference between the macroscopic field ð Þ *E* and the Lorentz field ð Þ *Eloc* may be understood as follows. The macroscopic field is macroscopic in nature, is an average value and is constant throughout the medium. On the other hand, the Lorentz field ð Þ *Eloc* is a microscopic field and is periodic in nature. This is quite large at molecular sites representing that the molecules are more effectively polarized than they are under the average field.

#### **4.2 Polarization and dielectric susceptibility**

Generally, at ordinary electric fields, the magnitude of polarization (*P*) is directly proportional to the macroscopic electric field Eð Þ at a given point of a dielectric [5–15]. It is expressed as

$$P \propto E \Rightarrow P = \varepsilon\_0 \chi\_e E \tag{3}$$

where *ε*0 is the permittivity of free space and *χe* is the dielectric susceptibility. Thus, except for a constant factor ð Þ *ε*0 , the dielectric susceptibility is a measure of the polarization produced in the material per unit electric field. If the dielectric material slab is placed in a uniform electric field (*E*) with its normal parallel to the field. The dielectric displacement vector (*D*) for an isotropic or cubic medium relative to vacuum is defined in terms of the macroscopic field ð Þ *E* as

$$D = \varepsilon\_0 \varepsilon\_r E = \varepsilon E = \varepsilon\_0 E + P \tag{4}$$

where *εr* is called the relative permittivity or dielectric constant of medium and *ε*0 is the permittivity or dielectric constant of free space, and *P* is the polarization. It is a scalar quantity for an isotropic medium and is always dimensionless. The dielectric constant (also called as permittivity of medium) is a measure of the degree to which a medium can resist the flow of charge, defined as the ratio of the dielectric displacement *D* to the macroscopic field intensity ð Þ *E* as

$$
\varepsilon\_r = \frac{D}{\varepsilon\_0 E} = \frac{\varepsilon\_0 E + P}{\varepsilon\_0 E} = \mathbf{1} + \frac{P}{\varepsilon\_0 E} = \mathbf{1} + \chi\_e \tag{5}
$$

Eq. (5) gives the dielectric constant of an isotropic medium or cubic medium. This is represented by a scalar quantity. The dielectric susceptibility (*χe*Þis related to the dielectric constant defined as

$$\chi\_{\varepsilon} = \frac{P}{\varepsilon\_0 E} = e\_r - \mathbf{1} \tag{6}$$

Solving for P

polarization [2–17] given as

tively shown in **Figure 6**.

**Figure 6.**

**15**

*Atomic contributions to electric polarization [18].*

*j*

*DOI: http://dx.doi.org/10.5772/intechopen.97720*

*General Introduction to Ferroelectrics*

*N jα j* we get

*n*2 � 1 *n*2 þ 2 ¼ 1

constant (*εr*Þ by the relation

3*ε*0 X *j*

where *n* being the refractive index which is related to the dielectric

ii. Ionic polarizability (*αi*Þ: The ionic polarizability (*αi*Þ arises due to the relative displacement of positive and negative ions from their equilibrium positions to a distance less than the distance between adjacent ions. The cations are displaced parallel to the Lorentz field, and the anions are displaced in the opposite direction, as shown in **Figure 6b** [5–18].

*εr* � 1 *εr* þ 2 ¼ 1

3*ε*0 X *j*

This is known as the Clausius-Mossotti relation. It relates the dielectric constant to the atomic polarizability, but only for crystal structures for which the Lorentz field Eq. (2) obtains. The total polarization (*α*Þ can be expressed as the sum of three types of basic polarizability representing the most important contributions to the

where *αe*, *αi* and *αd* are the electronic, ionic and dipolar polarizabilities, respec-

i. Electronic polarizability (*αe*Þ: The electronic polarizability (*αe*Þ arises due to the displacement of electrons in an atom relative to the atomic nucleus in the external electric field, as shown in **Figure 6a**. The polarization, as well as the dielectric constant of a material at optical frequencies, results mainly from the electronic polarizability (*αe*Þ. The optical range Eq. (13) reduces as

*N jα j* (13)

*α* ¼ *αe* þ *αi* þ *αd* (14)

*N jα j*ð Þ electronic (15)

*n*2 ¼ *εr* (16)

Thus, like susceptibility, the dielectric constant (*εr*Þ is also a measure of the polarization (*P*) of the material. The larger the polarization per unit resultant macroscopic field, the greater will be the dielectric constant of the dielectric medium. However, for anisotropic medium, the dielectric response (*εr*or *χe*Þ depends on the direction of the field and described by the components of the susceptibility tensor or of the dielectric tensor of the second rank

$$P\_{\mu} = \chi\_{\mu\nu}\varepsilon\_0 \varepsilon\_\nu; \varepsilon\_{\mu\nu} = \delta\_{\mu\nu} + \chi\_{\mu\nu} \tag{7}$$

#### **4.3 Dielectric constant and polarizability**

The polarizability ð Þ *α* of an atom is defined in terms of the local electric field (Lorentz field) at the atom. The induced dipoles of moments (*p*) are proportional to the local field (*Eloc*Þ can be expressed as

$$p = aE\_{loc} \tag{8}$$

where *α* is known as the polarizability of an atom. For a non-spherical atom or isotropic medium, *α* will be a tensor quantity [6–16]. Thus, polarizability is an atomic property, whereas dielectric constant is a macroscopic property that depends upon the arrangement of atoms within the crystal. If all the atoms have the same polarizability (*α*Þ and there are *N* number of atoms per unit volume, the total polarization of the crystal may be expressed as the product of the polarizabilities of the atoms times the local field

$$P = \sum\_{j} N\_{j} p\_{j} = \sum\_{j} N\_{j} a\_{j} E\_{\text{loc}}(j) \tag{9}$$

where the summation is over all the atoms or atomic sites. *N j* is the concentration and αj is the polarizability of atom *j* and *Eloc*ð Þ*j* is the local field at atom sites *j*. For an isotropic dielectric medium, the local field given by the Lorentz relation Eq. (2) inside the crystal is everywhere the same so that it can be taken out of the summation sign from Eq. (9). Substituting the value of the local field from Eq. (2), the Eq. (9) becomes

$$P = \left(E + \frac{P}{3\varepsilon\_0}\right) \sum\_{j} N\_j \alpha\_j \tag{10}$$

On rearranging the terms and making use of Eq. (5) gives

$$\chi\_{\varepsilon} = \frac{P}{\varepsilon\_{0}E} = \frac{\sum\_{j} N\_{j}a\_{j}}{\left(\varepsilon\_{0} - \frac{1}{3}\sum\_{j} N\_{j}a\_{j}\right)}\tag{11}$$

Using Eq. (6), we get

$$\varepsilon\_r = \mathbf{1} + \frac{\frac{\sum\_j N\_j a\_j}{c\_0}}{\mathbf{1} - \frac{1}{3c\_0} \sum\_j N\_j a\_j} = \frac{\mathbf{1} + \frac{2}{3c\_0} \sum\_j N\_j a\_j}{\mathbf{1} - \frac{1}{3c\_0} \sum\_j N\_j a\_j} \tag{12}$$

*General Introduction to Ferroelectrics DOI: http://dx.doi.org/10.5772/intechopen.97720*

Solving for P *j N jα j* we get

*χe* ¼ *P*

susceptibility tensor or of the dielectric tensor of the second rank

*P* ¼ X *j*

*P* ¼ *E* þ

P *j N jα j ε*0

1 � 1 3*ε*0 P *j N jα j*

On rearranging the terms and making use of Eq. (5) gives

*χe* ¼ *P ε*0*E* ¼

*εr* ¼ 1 þ

**4.3 Dielectric constant and polarizability**

*Multifunctional Ferroelectric Materials*

the local field (*Eloc*Þ can be expressed as

the atoms times the local field

the Eq. (9) becomes

Using Eq. (6), we get

**14**

Thus, like susceptibility, the dielectric constant (*εr*Þ is also a measure of the polarization (*P*) of the material. The larger the polarization per unit resultant macroscopic field, the greater will be the dielectric constant of the dielectric medium. However, for anisotropic medium, the dielectric response (*εr*or *χe*Þ depends on the direction of the field and described by the components of the

The polarizability ð Þ *α* of an atom is defined in terms of the local electric field (Lorentz field) at the atom. The induced dipoles of moments (*p*) are proportional to

where *α* is known as the polarizability of an atom. For a non-spherical atom or isotropic medium, *α* will be a tensor quantity [6–16]. Thus, polarizability is an atomic property, whereas dielectric constant is a macroscopic property that

depends upon the arrangement of atoms within the crystal. If all the atoms have the same polarizability (*α*Þ and there are *N* number of atoms per unit volume, the total polarization of the crystal may be expressed as the product of the polarizabilities of

*N jp j* ¼ X

*j*

where the summation is over all the atoms or atomic sites. *N j* is the concentration and αj is the polarizability of atom *j* and *Eloc*ð Þ*j* is the local field at atom sites *j*. For an isotropic dielectric medium, the local field given by the Lorentz relation Eq. (2) inside the crystal is everywhere the same so that it can be taken out of the summation sign from Eq. (9). Substituting the value of the local field from Eq. (2),

> *P* 3*ε*0 � �X

*j*

¼ 1 þ 2 3*ε*0 P *j N jα j*

1 � 1 3*ε*0 P *j N jα j*

P *j N jα j*

*ε*0 � 1 3 P *j N jα j*

*ε*0*E* ¼ *εr* � 1 (6)

*Pμ* ¼ *χμνε*0*Eν*; *εμν* ¼ *δμν* þ *χμν* (7)

*p* ¼ *αEloc* (8)

*N jα jEloc*ð Þ*j* (9)

*N jα j* (10)

(12)

� � (11)

$$\frac{\varepsilon\_r - 1}{\varepsilon\_r + 2} = \frac{1}{3\varepsilon\_0} \sum\_j N\_j a\_j \tag{13}$$

This is known as the Clausius-Mossotti relation. It relates the dielectric constant to the atomic polarizability, but only for crystal structures for which the Lorentz field Eq. (2) obtains. The total polarization (*α*Þ can be expressed as the sum of three types of basic polarizability representing the most important contributions to the polarization [2–17] given as

$$a = a\_{\epsilon} + a\_{i} + a\_{d} \tag{14}$$

where *αe*, *αi* and *αd* are the electronic, ionic and dipolar polarizabilities, respectively shown in **Figure 6**.

i. Electronic polarizability (*αe*Þ: The electronic polarizability (*αe*Þ arises due to the displacement of electrons in an atom relative to the atomic nucleus in the external electric field, as shown in **Figure 6a**. The polarization, as well as the dielectric constant of a material at optical frequencies, results mainly from the electronic polarizability (*αe*Þ. The optical range Eq. (13) reduces as

$$\frac{m^2 - 1}{m^2 + 2} = \frac{1}{3\epsilon\_0} \sum\_{j} N\_j a\_j (\text{electronic}) \tag{15}$$

where *n* being the refractive index which is related to the dielectric constant (*εr*Þ by the relation

$$m^2 = \varepsilon\_r \tag{16}$$

ii. Ionic polarizability (*αi*Þ: The ionic polarizability (*αi*Þ arises due to the relative displacement of positive and negative ions from their equilibrium positions to a distance less than the distance between adjacent ions. The cations are displaced parallel to the Lorentz field, and the anions are displaced in the opposite direction, as shown in **Figure 6b** [5–18].

**Figure 6.**

*Atomic contributions to electric polarization [18].*

**Figure 7.** *Frequency dependence of the various contributions to the polarizability [6].*

If the relative displacement of the positive and negative ions is *d* and the charge on each ion is *q*, then the dipole moment per molecule is *p* ¼ *qd* and the ionic polarization becomes

$$P\_{\rm ion} = \mathcal{N}qd \tag{17}$$

**5. Classification of ferroelectrics**

*DOI: http://dx.doi.org/10.5772/intechopen.97720*

*General Introduction to Ferroelectrics*

niobate (LiNbO3) etc.

etc.

of two types.

salt.

etc.

Ferroelectric crystals have been classified into the following types [1–6].

a. Hydrogen bonded and its isomorphs such as KH2PO4 (KDP), triglycine sulphate (TGS), Rochelle salt (RS) and lead hydrogen phosphate (LHP)

b. Double oxides such as BaTiO3, potassium niobite (KNbO3) and lithium

2.Based on the number of directions allowed to the spontaneous polarization are

3.According to the existence or lack of centre of symmetry in non-polar phase.

a. Non-centre of symmetrical non-polar phase such as KDP and Rochelle

b. Centre of symmetrical non-polar phase such as BaTiO3 and TGS crystals,

a. Order–disorder type such as KDP, RS, TGS, LHP and CsH2PO4 (CDP) etc.

In the order–disorder group of ferroelectrics, the ferroelectric phase transition is associated with an individual ordering of ions. These are the crystals that contain H-bonds and in which the motion of protons is related to the ferroelectric properties. The examples are KH2PO4, RS, TGS, CsH2PO4, PbHPO4 and RbH2PO4, etc. The displacive group of ferroelectrics is the one in which the ferroelectric phase transition is associated with the displacement of a whole sublattice of ions of one type relative to a sublattice of another type. The displacive type ferroelectrics possess perovskite ABO3 type structures. Examples are BaTiO3, LiNbO3 and KNbO3, etc. Consider the case of BaTiO3 crystal, as shown in **Figure 8**. The unit cell is cubic with *Ba*2þ ions occupying at the corners, *O*2� ions occupying the face centres and *Ti*4þ ion occupying the body centre of the cube. Thus, each *Ti*4þ ion is surrounded by six *O*2� ions in an octahedral configuration. Above the Curie temperature (*T* >*Tc*Þ, the prototype crystal structure is cubic, the centres of gravity of positive and negative charges exactly coincide with each other to produce a net dipole moment is zero. Below the Curie temperature (*T* < *Tc*Þ, the structure is slightly deformed with *Ti*4þ at the body centre while *Ba*2þ ions at cube corners slightly move upwards, and the structure becomes tetragonal with centres of the positive (þ) and negative (�Þ

b. Displacive type such as BaTiO3, LiNbO3 and KNbO3 etc.

a. Single-axis of polarization such as Rochelle salt, KDP etc.

b. Several-axes of polarization such as BaTiO3 etc.

4.According to the nature of the phase change.

charges not coinciding with each other.

**17**

1.According to the chemical composition of the crystal.

where *N* is the number of atoms per unit volume.

iii. Dipolar polarizability (αdÞ: The dipolar polarizability, also called orientational polarizability, is important only in materials that contain complex ions having permanent dipole moment. In the absence of an external electric field, the dipoles have random orientations, and there is no net polarization. However, when the electric field is applied, the dipoles orient themselves along the direction of the field and produce dipolar or orientational polarization, as shown in **Figure 6c**. Such an orientation is opposed by the thermal agitation which tends. According to Debye's quantum theory, dipolar polarizability (*αd*Þ per dipole is given by

$$a\_d = \frac{\bar{p}}{E} = \frac{p^2}{3kT} \tag{18}$$

where *k* is the Boltzmann's constant, *T* is the absolute temperature, and *p* is the dipole moment of the atom. The polarization contributed by electronic polarizability (*αe*Þ and ionic polarizability (*αi*Þ is called distortion polarization. Since *αe* and *αi* are temperature independent, the part of dielectric constant depending on them is essentially independent of the temperature. The contribution to the polarization made by dipolar polarizability (*αd*Þ which is a function of temperature in accordance with Eq. (18). The contributions to the total polarizability (polarizability versus frequency curve) are shown in **Figure 7** [2–17].

We find that in the optical frequency range, the dielectric constant (*ε*0) arises entirely due to the electronic polarizability. The ionic and dipolar contributions are small at high frequencies because of the inertia of the ions and molecules.


*2.3. Data Extraction*

Data extraction was performed by two reviewers (J.P. and M.A.-J.). From the studies that met the inclusion eligibility criteria, the following data were extracted into a predefined Microsoft Excel spreadsheet (Microsoft Corp., Redmond, WA, USA): (a) study characteristic (i.e., first author, year of publication, country, study design, inclusion and exclusion criteria, primary outcomes, findings; intervention and control group); (b) participant characteristics (i.e., number of participants, age, sex); (c) main study outcomes (i.e., blood volume loss, operative time, adverse events, hospital length of stay). Potential disagreements were resolved by discussion with a third reviewer (L.S.).


**3. Potential application of kaolin-based ZSM-5**

#### **3.1 Catalytic oligomerisation**

The performance of the zeolites as catalysts was tested in the transformation of 1-hexene, used as a model compound for the oligomerisation of alkenes; reaction was performed at the following conditions: T = 350°C, pressure = 1 atm, WHSV = 8 h−1 . The activities of the catalysts were determined by assuming all

**89**

**Figure 7.**

*Synthesis and Application of Porous Kaolin-Based ZSM-5 in the Petrochemical Industry*

activity as a function of time on stream is shown in **Figure 7**.

the influence of quartz on the performance of the catalyst.

further and correlated with their physicochemical properties.

1-hexene present in the product was due to unconverted feed. The graph showing

The catalytic tests were conducted over a time period of 420 min. All catalysts showed some deactivation over the total time on stream although some were more rapidly deactivated than others. All catalysts had a conversion not less than 90% in the first hour on stream. The highest conversion achieved was approximately 98%. It is clearly noticed that the conversion of the catalysts is highly dependent on the acidity, in particular the Bronsted acidity. Si-Al 42 RK and Si-Al 70 BK with similar acidities and possessing the highest acidities of the catalysts had the highest conversions and both showed only slight deactivation as the conversion remained above 90% for the duration of the reaction. Si-Al 70 RK and Si-Al 150 BK having identical amounts of strong acid sites and tetrahedral alumina (**Tables 3** and **4** respectively) have the same conversion and deactivation for the time on stream. Si-Al 42 BK which had the least amount of Bronsted sites showed the lowest conversion and the most rapid deactivation. Interestingly, Si-Al 150 RK having a much lower acidity compared to Si-Al 42 RK and Si-Al 70 BK has a very similar activity and shows even better stability (**Figure 7**). This was attributed to the effect of quartz coating the surface of the ZSM-5 which prevents deactivation. Therefore it is seen that this catalyst functions better than catalysts with more than double its acidity and further validates

The catalysts tested in the transformation of 1-hexene all possess a wide product distribution. The products are grouped accordingly: (C2–C5) range, (C6–C9) gasoline range and (C10+) diesel range. This indicates multiple types of reactions may occur at the set reaction conditions such as oligomerisation, cracking, isomerisation and alkylation to name a few. The selectivities to these ranges however change with time on stream and it is noticed that small changes in conversion can have large changes in selectivity to products. The selectivities of the catalysts are discussed

Si-Al 150 BK and Si-Al 70 RK are compared to each other since they have similar

acidities as well as conversions over time on stream as shown in **Figure 7**. The selectivities however differ from each other. The selectivities to gasoline (C6–C9)

and diesel (C10+) ranges are shown in **Figure 8(a)** and **(b)** respectively.

*Graph showing hexane conversion over different catalysts (P = 1 atm, T = 350°C, WHSV = 8 h−1*

*).*

*DOI: http://dx.doi.org/10.5772/intechopen.81375*

#### *Synthesis and Application of Porous Kaolin-Based ZSM-5 in the Petrochemical Industry DOI: http://dx.doi.org/10.5772/intechopen.81375*

1-hexene present in the product was due to unconverted feed. The graph showing activity as a function of time on stream is shown in **Figure 7**.

The catalytic tests were conducted over a time period of 420 min. All catalysts showed some deactivation over the total time on stream although some were more rapidly deactivated than others. All catalysts had a conversion not less than 90% in the first hour on stream. The highest conversion achieved was approximately 98%. It is clearly noticed that the conversion of the catalysts is highly dependent on the acidity, in particular the Bronsted acidity. Si-Al 42 RK and Si-Al 70 BK with similar acidities and possessing the highest acidities of the catalysts had the highest conversions and both showed only slight deactivation as the conversion remained above 90% for the duration of the reaction. Si-Al 70 RK and Si-Al 150 BK having identical amounts of strong acid sites and tetrahedral alumina (**Tables 3** and **4** respectively) have the same conversion and deactivation for the time on stream. Si-Al 42 BK which had the least amount of Bronsted sites showed the lowest conversion and the most rapid deactivation. Interestingly, Si-Al 150 RK having a much lower acidity compared to Si-Al 42 RK and Si-Al 70 BK has a very similar activity and shows even better stability (**Figure 7**). This was attributed to the effect of quartz coating the surface of the ZSM-5 which prevents deactivation. Therefore it is seen that this catalyst functions better than catalysts with more than double its acidity and further validates the influence of quartz on the performance of the catalyst.

The catalysts tested in the transformation of 1-hexene all possess a wide product distribution. The products are grouped accordingly: (C2–C5) range, (C6–C9) gasoline range and (C10+) diesel range. This indicates multiple types of reactions may occur at the set reaction conditions such as oligomerisation, cracking, isomerisation and alkylation to name a few. The selectivities to these ranges however change with time on stream and it is noticed that small changes in conversion can have large changes in selectivity to products. The selectivities of the catalysts are discussed further and correlated with their physicochemical properties.

Si-Al 150 BK and Si-Al 70 RK are compared to each other since they have similar acidities as well as conversions over time on stream as shown in **Figure 7**. The selectivities however differ from each other. The selectivities to gasoline (C6–C9) and diesel (C10+) ranges are shown in **Figure 8(a)** and **(b)** respectively.

**Figure 7.** *Graph showing hexane conversion over different catalysts (P = 1 atm, T = 350°C, WHSV = 8 h−1 ).*

*Nanofluid Flow in Porous Media*

possible that BK forms more Al rich ZSM-5 than RK for two reasons. The first being that RK causes a higher degree of depolymerisation due to the presence of quartz (as discussed above) of the remaining Na-silicate which is broken down to silicate species. This then forms more networked silicate and aluminosilicate and has less formation of close Al atoms resulting in higher ratios. Second for the BK samples, which were prepared with a smaller amount of additional Na-silicate, was not well depolymerised due to a lower alkalinity i.e. the silicate remained non-transformed

the highly reactive Al species resulting in aluminosilicate with a much lower

The performance of the zeolites as catalysts was tested in the transformation of 1-hexene, used as a model compound for the oligomerisation of alkenes; reaction was performed at the following conditions: T = 350°C, pressure = 1 atm,

. The activities of the catalysts were determined by assuming all

of aluminosilicate species with close Al atoms [37].

*27Al MAS NMR spectra of the RK and BK samples with different Si/Al ratios.*

**3. Potential application of kaolin-based ZSM-5**

Si/Al ratio having also more Alefr and in the case of Si-Al 42 BK, in a high probability

and only a much lower concentration of Si was available for

**88**

WHSV = 8 h−1

and balanced by the Na+

**Figure 6.**

**3.1 Catalytic oligomerisation**

*Selectivity of Si-Al 150 BK and Si-Al 70 RK to gasoline (C6–C9) (a) and diesel (C10+) (b) range products over time on stream.*

Both catalysts have a similar trend to selectivity of diesel range products as noticed in the graph and decrease with time as the conversion decreased. However Si-Al 150 BK has a slightly higher selectivity throughout the reaction. Both show good selectivity (40–55%) to gasoline products with the selectivity of Si-Al 70 RK possessing a steady increase over the reaction time. Si-Al 150 BK was more unstable and the selectivity varied over time and was slightly less than Si-Al 70 RK. It was thought Si-Al 70 RK was more selective to reactions pertaining to chain growth such as oligomerisation and alkylation but a closer look at the product selectivity of the gasoline range revealed that Si-Al 70 RK was highly selective to C6 hydrocarbons as compared to Si-Al 150 BK as shown in **Figure 9**. An increase from ~12% to above 30% was observed. The C2–C5 selectivity trend is also shown and decreases over time for the Si-Al 70 RK catalyst but shows an overall increase in the C2–C5 products

**Figure 9.**

*Selectivity of Si-Al 150 BK and Si-Al 70 RK to C6 (black curves) and C2–C5 (blue curves) range products over time on stream.*

**91**

**Figure 10.**

*RK, Si-Al 70 BK and Si-Al 42 BK as a function of time.*

*Synthesis and Application of Porous Kaolin-Based ZSM-5 in the Petrochemical Industry*

synthesised from RK are shown to affect its catalytic performance.

**Figure 10** shows the selectivity of Si-Al 150 RK, Si-Al 42 RK, Si-Al 70 BK and Si-Al 42 BK to diesel and gasoline range hydrocarbons. The three catalysts with similar conversions i.e. Si-Al 150 RK, Si-Al 42 RK and Si-Al 70 BK can be compared

From **Figure 10** it is noticed that after the first hour on stream the selectivity to C10+ is the highest for the catalyst Si-Al 42 RK showing ~16% selectivity. This may indicate that oligomerisation to long chain hydrocarbons largely depends on the acidity since Si-Al 42 RK which has a high Bronsted acidity had the highest selectivity. The more acidic catalysts have better selectivity over the first 3 h on stream. As the reaction proceeds however, all catalysts show a large decrease in selectivity to C10+ hydrocarbons except Si-Al 150 RK which shows a greater stability. The decrease for Si-Al 42 RK is almost linear over the reaction time and drops to ~3%. The decrease in selectivity to C10+ suggests the deactivation of certain acid sites which are most likely strong Bronsted acid sites as oligomerisation reactions are favoured at these catalytic centres [65]. Si-Al 70 BK which has similar acidity to Si-Al 42 RK shows a slightly better selectivity to C10+ hence less deactivation of Bronsted sites. This is most likely due to the higher surface area and increased mesoporosity which may inhibit the build-up of carbonaceous deposits usually responsible for deactivation and hence further highlights the effects of the physicochemical properties of the zeolites on its catalytic behaviour. As mentioned in our previous work [30], the effect of quartz deposits on

*Selectivities to diesel range (C10+) and gasoline range (C6–C9) hydrocarbons of catalysts Si-Al 150 RK, Si-Al 42*

for Si-Al 150 BK. Thus there may be a greater selectivity to isomerisation reactions over cracking reactions for the Si-Al 70 RK catalyst whereas Si-Al 150 BK has a better selectivity to chain growth reactions as its total selectivity to C7+ hydrocarbons is higher. This may suggest a slight difference in strength of acid sites available as oligomerisation and cracking occur on stronger acid sites than isomerisation reactions which occur on sites of intermediate acidity [65]. The main difference between the two catalysts however is the crystal morphology and size. The Si-Al 70 RK possessing nanocrystals as shown in HRSEM, this may reduce the effects of diffusion limitation. As shown by Buchanan et al. [66] larger crystals showed a higher selectivity to C3/C4 products and a lower isomerization/cracking of olefin ratio due to diffusion limitation. Therefore it is possible that as the strength of the acidic sites are reduced over time due to deactivation which happens more in Si-Al 70 RK, isomerization reactions which occur faster than cracking reactions [66], increase and due to the nanocrystals, the isomers which form are able to diffuse out before any secondary cracking leading to more C6 isomers, less cracked C2–C5 products and a better gasoline selectivity. Therefore the physical properties of the catalyst

*DOI: http://dx.doi.org/10.5772/intechopen.81375*

in terms of selectivity.

#### *Synthesis and Application of Porous Kaolin-Based ZSM-5 in the Petrochemical Industry DOI: http://dx.doi.org/10.5772/intechopen.81375*

for Si-Al 150 BK. Thus there may be a greater selectivity to isomerisation reactions over cracking reactions for the Si-Al 70 RK catalyst whereas Si-Al 150 BK has a better selectivity to chain growth reactions as its total selectivity to C7+ hydrocarbons is higher. This may suggest a slight difference in strength of acid sites available as oligomerisation and cracking occur on stronger acid sites than isomerisation reactions which occur on sites of intermediate acidity [65]. The main difference between the two catalysts however is the crystal morphology and size. The Si-Al 70 RK possessing nanocrystals as shown in HRSEM, this may reduce the effects of diffusion limitation. As shown by Buchanan et al. [66] larger crystals showed a higher selectivity to C3/C4 products and a lower isomerization/cracking of olefin ratio due to diffusion limitation. Therefore it is possible that as the strength of the acidic sites are reduced over time due to deactivation which happens more in Si-Al 70 RK, isomerization reactions which occur faster than cracking reactions [66], increase and due to the nanocrystals, the isomers which form are able to diffuse out before any secondary cracking leading to more C6 isomers, less cracked C2–C5 products and a better gasoline selectivity. Therefore the physical properties of the catalyst synthesised from RK are shown to affect its catalytic performance.

**Figure 10** shows the selectivity of Si-Al 150 RK, Si-Al 42 RK, Si-Al 70 BK and Si-Al 42 BK to diesel and gasoline range hydrocarbons. The three catalysts with similar conversions i.e. Si-Al 150 RK, Si-Al 42 RK and Si-Al 70 BK can be compared in terms of selectivity.

From **Figure 10** it is noticed that after the first hour on stream the selectivity to C10+ is the highest for the catalyst Si-Al 42 RK showing ~16% selectivity. This may indicate that oligomerisation to long chain hydrocarbons largely depends on the acidity since Si-Al 42 RK which has a high Bronsted acidity had the highest selectivity. The more acidic catalysts have better selectivity over the first 3 h on stream. As the reaction proceeds however, all catalysts show a large decrease in selectivity to C10+ hydrocarbons except Si-Al 150 RK which shows a greater stability. The decrease for Si-Al 42 RK is almost linear over the reaction time and drops to ~3%. The decrease in selectivity to C10+ suggests the deactivation of certain acid sites which are most likely strong Bronsted acid sites as oligomerisation reactions are favoured at these catalytic centres [65]. Si-Al 70 BK which has similar acidity to Si-Al 42 RK shows a slightly better selectivity to C10+ hence less deactivation of Bronsted sites. This is most likely due to the higher surface area and increased mesoporosity which may inhibit the build-up of carbonaceous deposits usually responsible for deactivation and hence further highlights the effects of the physicochemical properties of the zeolites on its catalytic behaviour. As mentioned in our previous work [30], the effect of quartz deposits on

#### **Figure 10.**

*Selectivities to diesel range (C10+) and gasoline range (C6–C9) hydrocarbons of catalysts Si-Al 150 RK, Si-Al 42 RK, Si-Al 70 BK and Si-Al 42 BK as a function of time.*

*Nanofluid Flow in Porous Media*

**90**

**Figure 9.**

**Figure 8.**

*time on stream.*

*time on stream.*

*Selectivity of Si-Al 150 BK and Si-Al 70 RK to C6 (black curves) and C2–C5 (blue curves) range products over*

Both catalysts have a similar trend to selectivity of diesel range products as noticed in the graph and decrease with time as the conversion decreased. However Si-Al 150 BK has a slightly higher selectivity throughout the reaction. Both show good selectivity (40–55%) to gasoline products with the selectivity of Si-Al 70 RK possessing a steady increase over the reaction time. Si-Al 150 BK was more unstable and the selectivity varied over time and was slightly less than Si-Al 70 RK. It was thought Si-Al 70 RK was more selective to reactions pertaining to chain growth such as oligomerisation and alkylation but a closer look at the product selectivity of the gasoline range revealed that Si-Al 70 RK was highly selective to C6 hydrocarbons as compared to Si-Al 150 BK as shown in **Figure 9**. An increase from ~12% to above 30% was observed. The C2–C5 selectivity trend is also shown and decreases over time for the Si-Al 70 RK catalyst but shows an overall increase in the C2–C5 products

*Selectivity of Si-Al 150 BK and Si-Al 70 RK to gasoline (C6–C9) (a) and diesel (C10+) (b) range products over*

**Figure 11.** *Selectivity to C6 hydrocarbons and C2–C5 selectivity of Si-Al 42 RK (blue curve) as a function of time.*

the external surface of the crystals in Si-Al 150 RK plays a major role in inhibiting the formation of carbonaceous material causing deactivation. Thus even when compared to catalysts with greater acid site density and strength (almost double its acidity), Si-Al 150 RK possesses greater stability and selectivity is almost double that of the more acidic catalysts. This clearly suggests that the acid sites are prevented from being deactivated by the deposition of quartz and continue to catalyse oligomerisation reactions for the duration of the reaction. Si-Al 42 BK had the lowest selectivity to C10+. This is most likely due to its low Bronsted acidity but also the high content of extra-framework aluminium may cause pore blockage and prevent access to acid sites for oligomerisation. The closeness of Al atoms in the structure may also have an effect on the acidity and types of catalytic reactions that are favoured.

All catalysts showed good selectivity to the gasoline range. Si-Al 42 RK shows the opposite trend for selectivity to gasoline as this increase over the reaction time. The selectivity spikes in the last 2 h from 45 to 74%. **Figure 11** shows the selectivity to C6 and C2–C5 products.

The spike in gasoline activity is again due to an increase in C6 selectivity. This further confirms our observations with the Si-Al 70 RK catalyst. The decrease in C10+ selectivity indicates deactivation of strong acid sites. Thus isomerisation reactions are then favoured when only less acidic site are available and due to Si-Al 70 RK and Si-Al 42 RK possessing the same morphology the isomerisation products diffuse out before cracking. **Figure 11** clearly shows the contrasting selectivities between isomerisation (C6) and cracking reactions (C2–C5) for the Si-Al 42 RK catalyst. Si-Al 42 BK also shows good isomerisation activity which further indicates the reaction occurring on weaker acid sites.

#### **4. Conclusion**

In conclusion, this chapter discusses some of the key factors affecting the synthesis of kaolin-based ZSM-5 such as kaolin crystallinity, kaolinite content,

**93**

*Synthesis and Application of Porous Kaolin-Based ZSM-5 in the Petrochemical Industry*

crystallisation parameters and Si/Al ratio. Additionally, the catalytic performance of the ZSM-5 derived from kaolin was evaluated. These factors are important considerations when attempting to synthesise ZSM-5 with high purity and crystallinity. However, ZSM-5 can also be synthesised from impure kaolin sources and these impurities may act as poisons or promoters during synthesis and catalytic application. The requirements to develop synthesis conditions that are optimised for specific sources of kaolin are established. The physicochemical properties such as porosity, morphology and acidity of ZSM-5 can be controlled by choosing the right synthesis procedures. Kaolin-based ZSM-5 zeolites are promising as catalysts for petrochemical reactions such as oligomerisation. High activity and selectivity to gasoline and diesel range hydrocarbons was attainable. The activity of the catalysts correlated well with the acidity of ZSM-5 samples. The catalytic performance of the zeolites also correlated well with the physical properties such as morphology and surface area which were shown to influence selectivity to certain products by favouring isomerisation and oligomerisation reactions respectively. Impurities in the kaolin precursor may also have positive effects on catalytic performance, in this case quartz deposition on ZSM-5 inhibiting deactivation and increasing catalyst stability. Therefore, ZSM-5 zeolites can be successfully synthesised from cheaper, more environmentally friendly alternative starting materials that have satisfactory

The authors would like to thank the Petroleum, Oil and Gas Corporation of South Africa (PetroSA) for their financial support and technical discussions, the National Research Foundation (NRF) for granting Ebrahim Mohiuddin a scholarship, Makana Brick for supplying the raw kaolin, the electron microscope unit, Physics department, University of the Western Cape for the SEM images, Mrs. E. Antunes, Chemistry department, University of the Western Cape and Dr. D.J. Brand, University of Stellenbosch for the solid state NMR work and Ithemba

*DOI: http://dx.doi.org/10.5772/intechopen.81375*

performances in catalytic application.

**Acknowledgements**

labs for the XRD work.

*Synthesis and Application of Porous Kaolin-Based ZSM-5 in the Petrochemical Industry DOI: http://dx.doi.org/10.5772/intechopen.81375*

crystallisation parameters and Si/Al ratio. Additionally, the catalytic performance of the ZSM-5 derived from kaolin was evaluated. These factors are important considerations when attempting to synthesise ZSM-5 with high purity and crystallinity. However, ZSM-5 can also be synthesised from impure kaolin sources and these impurities may act as poisons or promoters during synthesis and catalytic application. The requirements to develop synthesis conditions that are optimised for specific sources of kaolin are established. The physicochemical properties such as porosity, morphology and acidity of ZSM-5 can be controlled by choosing the right synthesis procedures. Kaolin-based ZSM-5 zeolites are promising as catalysts for petrochemical reactions such as oligomerisation. High activity and selectivity to gasoline and diesel range hydrocarbons was attainable. The activity of the catalysts correlated well with the acidity of ZSM-5 samples. The catalytic performance of the zeolites also correlated well with the physical properties such as morphology and surface area which were shown to influence selectivity to certain products by favouring isomerisation and oligomerisation reactions respectively. Impurities in the kaolin precursor may also have positive effects on catalytic performance, in this case quartz deposition on ZSM-5 inhibiting deactivation and increasing catalyst stability. Therefore, ZSM-5 zeolites can be successfully synthesised from cheaper, more environmentally friendly alternative starting materials that have satisfactory performances in catalytic application.

### **Acknowledgements**

*Nanofluid Flow in Porous Media*

the external surface of the crystals in Si-Al 150 RK plays a major role in inhibiting the formation of carbonaceous material causing deactivation. Thus even when compared to catalysts with greater acid site density and strength (almost double its acidity), Si-Al 150 RK possesses greater stability and selectivity is almost double that of the more acidic catalysts. This clearly suggests that the acid sites are prevented from being deactivated by the deposition of quartz and continue to catalyse oligomerisation reactions for the duration of the reaction. Si-Al 42 BK had the lowest selectivity to C10+. This is most likely due to its low Bronsted acidity but also the high content of extra-framework aluminium may cause pore blockage and prevent access to acid sites for oligomerisation. The closeness of Al atoms in the structure may also have an effect

*Selectivity to C6 hydrocarbons and C2–C5 selectivity of Si-Al 42 RK (blue curve) as a function of time.*

All catalysts showed good selectivity to the gasoline range. Si-Al 42 RK shows the opposite trend for selectivity to gasoline as this increase over the reaction time. The selectivity spikes in the last 2 h from 45 to 74%. **Figure 11** shows the selectivity to C6

The spike in gasoline activity is again due to an increase in C6 selectivity. This further confirms our observations with the Si-Al 70 RK catalyst. The decrease in C10+ selectivity indicates deactivation of strong acid sites. Thus isomerisation reactions are then favoured when only less acidic site are available and due to Si-Al 70 RK and Si-Al 42 RK possessing the same morphology the isomerisation products diffuse out before cracking. **Figure 11** clearly shows the contrasting selectivities between isomerisation (C6) and cracking reactions (C2–C5) for the Si-Al 42 RK catalyst. Si-Al 42 BK also shows good isomerisation activity which further indicates

In conclusion, this chapter discusses some of the key factors affecting the synthesis of kaolin-based ZSM-5 such as kaolin crystallinity, kaolinite content,

on the acidity and types of catalytic reactions that are favoured.

**92**

and C2–C5 products.

**Figure 11.**

**4. Conclusion**

the reaction occurring on weaker acid sites.

The authors would like to thank the Petroleum, Oil and Gas Corporation of South Africa (PetroSA) for their financial support and technical discussions, the National Research Foundation (NRF) for granting Ebrahim Mohiuddin a scholarship, Makana Brick for supplying the raw kaolin, the electron microscope unit, Physics department, University of the Western Cape for the SEM images, Mrs. E. Antunes, Chemistry department, University of the Western Cape and Dr. D.J. Brand, University of Stellenbosch for the solid state NMR work and Ithemba labs for the XRD work.

*Nanofluid Flow in Porous Media*