After a thorough review of existing studies of clinoptilolite zeolites, three areas for potential investigation of the Saudi Arabian zeolites were found. They are the characterizations, the catalytic activity, active sites, and uses of natural clinoptilolite zeolites. First, no analysis is available worldwide to compare the percentage weight of local zeolites with those sourced from other countries, nor does one exist for the establishment on the zeolite conversion of MBOH with water on acidic catalysts at lower temperatures. Secondly, a review of current literature on the topic revealed that basic and active sites of Saudi Arabian zeolites have yet to be examined. Future investigation of zeolite catalytic activity can be achieved by methyl butynol test reaction (MBOH) and absorption-desorption of ammonia. In the characterization of a range of international materials, the methyl butynol test reaction was utilized, including on natural zeolites, natural clays, and synthesized hydrotalcites. However, the catalytic performance of natural Saudi Arabian clinoptilolite zeolites by test reaction of MBOH conversion has not been yet investigated. Therefore, this article also includes an outline of the general testing conditions and parameters required to execute the accurate characterization of local Saudi clinoptilolite under optimal test conditions. Likewise, knowledge of the important active acidic centers of local materials is prescribed. This can be ascertained by determining the conditions together with the test parameters for the application of the “temperature-programmed desorption of ammonia” method in order to obtain an accurate determination of local Saudi clinoptilolite acidic centers. Additionally, an outline of the catalytic activity of worldwide clinoptilolite is given in this article together with kinetic investigations of other sources for the clinoptilolite zeolite in order to form the basis for the testing of local Saudi clinoptilolite. The percentage average of chemical composition (Wt.%) of natural clinoptilolite from various countries is also included. Finally, a future research plan is proposed here. This will form the basis for a complete study or survey to be compiled detailing the modifications needed to increase the surface areas for Saudi natural clinoptilolite zeolites using different methods of modifications. This could enhance its application as acid catalysts for use in the retardation of coke formation and for membrane separation on cationic exchange.
In general, zeolites are of great interest to researchers working in the various fields such as energy recovery technology [
There are a number of definitions; though not dissimilar, the most widely accepted is by Breck [
Since zeolite NaA is the preferred substitute for calcium and magnesium ions; it has proven to be an adequate substitute [
Due to zeolites’ well-defined pore structure and their acidity, scientific and industrial interest in them is very high. The main fields of application are ion exchange in detergents, adsorption for the separation and purification of substances, and as catalysts zeolites, which are mainly used, in the petrochemical industry [
Additionally, coke formation is another challenge for refinery industry. Since this challenge exists, investigation on local material is beneficial. Suggested characterizations, when are applied, would also provide information about active centers and how they might be modified precisely, including data on their selective adsorption capability. Two methods, namely, the catalytic test reaction of methyl butynol (MBOH) and the temperature program desorption of ammonia method are suggested in this paper as an effective characterization tools to abstract more information about catalytic activity and active acidic centers of the local zeolite. Note that both suggested methods have yet to be implemented on the local Saudi zeolite in particular. Hence, the conditions and parameters for both methods are summarized in the current paper. Results from both analysis will be reported and contribute to the field of knowledge. From this point, the paper presents literature review on that case and then proposes a research approach for the local Saudi zeolite where the conversion of MBOH with water can be applied for local zeolites as acidic catalyst using conversion of MBOH with water at lower reaction temperature of 120°C.
Though there is an ample amount of published works in the general field of zeolites, much less is available related to local natural Saudi Arabian zeolite. Hence, this work, focuses on local sources and discusses its significance and potential use in a variety of industrial applications. In the general published works, samples and examples of reaction provide the bases on which investigation into local clinoptilolite zeolite may be further developed, synthesized, and modified in order to produce an increase in efficiency and reduction in costs. Different factors impact the development of the zeolite material in between: the ratio of silica to alumina and the level of impurities determined by geographical source. Attention is also given in this review to comparing the close similarities of the chemical composition of local clinoptilolite zeolite with that given in the general literature and its modification, also considering geographical sources internationally.
The zeolite ZSM-5 is a synthetic 10-ring zeolite and the formula for describing the composition is [
The ZSM-5 belongs to the group of pentasils, which can reach a Si/Al ratio of 10 to infinity. The high silicon content results in high thermal stability, hydrophobicity, and strength, but it leads to fewer active sites [
The zeolite-Y belongs to the group of faujasites whose unit cell represents the following formula [
The connection of cuboctahedra as a tertiary unit via six-membered rings leads to the three-dimensional structure of the Y zeolite. The arrangement of the polyhedra leads to the formation of large cavities, which are called super cages due to their diameter of 1.2 nm [
Clinoptilolite is closely associated with the series of zeolite tectonic-silicate minerals named Heulandite (HEU). The structural makeup of HEU is a framework of tetrahedral SiO4 and AlO4 units and is formed by the intersection of three sets of channels, A, B, and C. The first two, A and B, run parallel to the
Furthermore, natural clinoptilolite from China (Jiutai, Jili) [
However, treating natural clinoptilolite with acids improved and increased the channel openings [
Additionally, the catalytic activity over clinoptilolite was examined utilizing the advantageous methanol to dimethyl ether [
In addition, synthesized palladium nanoparticles on natural clinoptilolite was achieved [
To date, no Saudi Arabian zeolite deriving from any type of natural clinoptilolite has reportedly been synthesized. Further investigations to clarify this matter are paramount. In addition to the insight into catalytic activity reactions of local natural and sourced clinoptilolite presented in Section 2, Section 3 details the various research methods and approaches adopted for investigating the different types of zeolite. Given that comparatively little work has been conducted so far on the local Saudi clinoptilolite resource, a new database, based on past and current studies, should be created in order to investigate them further.
More recently, research [
The dehydration reaction using zeolites has long been well understood [
The reaction is both highly dependent on the conditions as well as the constitution of the alcohol used. Increased temperatures are usually required for the acid-catalyzed reaction. Furthermore, the ease of dehydration increases with increasing degree of substitution of the hydroxyl-bearing carbon atom. Primary alcohols are difficult to assess for dehydration. In general, the readiness of water elimination increases in the order of primary, secondary, and tertiary alcohol [
Formation of an alkyl oxonium ion [
In the alkyl oxonium ion, the carbon-oxygen bond is weakened compared to that of the alcohol. In Figure
Heterolytic cleavage of the alkyl oxonium ion followed by olefin formation [
Disassociation is a reversible reaction because the water as a Lewis base can recombine with the carbenium ion, which is a Lewis acid. The tendency to form the carbenium ion increases from primary to tertiary alcohol. The reason for stabilizing the ion is its chemical environment. Alkyl groups have a greater positive inductive effect compared to hydrogen atoms, which have a stabilizing effect on the carbenium ion. Furthermore, it leads to hyper conjugation. This can be regarded as a kind of electron thrust of an alkyl substituent in the direction of an electron-deficient center [
Substitution as a competitive reaction [
In Figure
Ether formation as a competing reaction to olefin formation [
Catalytic dehydration of hexylene glycol (HG) results in the formation of 2-methylpenta-1,3-dienes (1,3-dienes) and its isomer 2-methylpenta-2,4-dienes (2,4-dienes). 4-Methylpent-4-en-2-ol (pentenol) is formed as an intermediate in this reaction. Figure
Reaction of HG dehydration under catalytic influence [
For industrial purposes, the 1,3-diene can be used in Diels-Alder reactions. It acts as a diene that undergoes a [4 + 2] cycloaddition with a dienophile. The product is a substituted cyclohexane derivative which has gained great importance, for example, in the production of fragrance compositions [
Heterogeneously catalyzed dehydration reactions have been known since the end of the eighteenth century. The initial attempts [
Review of the literature on the natural clinoptilolite zeolites [
In addition, clinoptilolite zeolites have framework (cage-like) interconnected channel structures with ability to exchange M Cations for various cations from solution [
The US clinoptilolite has 3.9 × 5.4 (Å) channel dimension and relatively high thermal stability. The formula used to represent the unit cell of the US clinoptilolite is (Na3K3) (Al6Si30O72) · 24H2O [
Table
Average of chemical composition (wt.%) of natural clinoptilolite from various countries.
Components | Chemical composition of natural clinoptilolite from different countries (wt.%) | ||||||
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Japan [ |
Serbia [ |
Greece [ |
China [ |
KSA [ |
Ukraine [ |
Mexico [ | |
SiO2 | 77.96 | 72.20 | 68.25 | 66.45 | 65.40 | 64.95 | 62.36 |
Al2O3 | 14.02 | 12.20 | 13.19 | 13.30 | 11.60 | 12.23 | 13.14 |
Fe2O3 | 1.30 | 5.70 | 1.41 | 1.49 | 1.88 | 1.06 | 1.63 |
TiO2 | — | 0.90 | 0.17 | 0.19 | 0.15 | 0.20 | 0.39 |
MgO | 0.46 | 1.0 | 1.14 | 0.92 | 1.75 | 1.21 | 0.92 |
CaO | 1.23 | 5.0 | 0.75 | 3.97 | 3.30 | 3.22 | 2.72 |
Na2O | 1.15 | 0.50 | 4.12 | 1.02 | 1.50 | 0.70 | 3.99 |
K2O | 3.88 | 2.50 | 1.66 | 1.54 | 0.98 | 2.35 | 1.20 |
FeO | 0.22 | ||||||
P2O5 | 0.11 | ||||||
S | 0.03 | ||||||
CO2 | 1.03 | ||||||
H2O | 12.33 |
Recently, local studies in Saudi Arabia, on the natural material were carried out with the aim of determining its potential use in energy producing applications [
On low cost, simple zeolite-based solution for the treatment of wastewater from an olive mill, M cations, and water molecules was examined on the US clinoptilolite zeolites [
In general, zeolite materials show excellent application in fine chemical industries because of their advantage in hydrocarbon conversions [
The result of depositing natural local zeolite with nonporous titania resulted in a novel biomimetic coat material. The new modified zeolite is fabricated to produce a potential anticorrosion application. Other forms of zeolite modifications are presented in the literature through modification of Y zeolites with TiO2 fine particles and intercalating with Ag, which resulted in high performance of photocatalysts [
Similar investigative procedures might also be employed with local Saudi Zeolite. Recently, local researchers from King Saud University [
The fact of the existence of impurities in natural zeolites composition still presents a challenge and has wide implementation for the continuing use of zeolites material employed in industrial applications. Additional investigations focused on designing hierarchical zeolites for petroleum refinery [
Conditions and parameters for characterization of different materials like natural zeolites by methyl butynol catalytic test reaction [
Conditions | Parameters |
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1.1. Oxidation in air: |
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Heating rate: 1 h to 5400°C (4 K/min) airflow | |
1.2. Inertisation: | |
N2 flow |
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Temperature |
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Duration |
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1.3. Cooling to |
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N2 flow |
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Percentage volume of MBOH : hexane | 95 : 5 vol% |
Liquid feed flow through the capillary |
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i.e., pressure over liquid feed |
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Pressure of the reactor system |
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Temperature start | 50°C |
Temperature rate ( |
10°C/min |
Reached up to temperature |
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Holding time |
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Type | Optima wax |
Length | 30 m |
Film thickness | 0.25 |
Maximum temperature |
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A good understanding of the operating parameters like reaction temperatures, reaction mechanisms, the conversion, selectivity, and the activation energy and more results about Thiele modulus are crucial factors in deciding on diffusion limitation and subsequently, will lead to a greater knowledge of zeolite coke formation during reaction [
Collected conditions and parameters for the temperature-programmed desorption of ammonia analysis, over natural zeolite [
Conditions | Parameters |
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Thermal conductivity detector (TCD) | — |
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Helium with a mixture of NH3 in argon | 5 vol.% NH3/Ar |
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0.4 g |
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Temperature start |
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Temperature rate (dT/dt) | 20°C/min |
Reached up to temperature |
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Holding time |
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7 vol.% NH3/Ar |
Steam: helium with a mixture of NH3 in argon temperature of sample saturation |
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Holding time |
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To 100°C |
Temperature rate | 20°C/min, |
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In the long run, greater knowledge will inevitably result in the design of effective operational reaction conditions for local zeolite and in turn the optimum calibration of reaction temperatures and rate for coke formation. Correct theory using Saudi zeolite resource can lead to a better understanding of its behaviour when applied on industrial scales. This in turn will help to create the optimum operational conditions for the variety of industrial applications and greatly assist local product development in Saudi Arabia. The use of a combination of techniques for Saudi zeolite characterization and its coke formation during methanol conversion is recommended [
The benefit of utilizing local Saudi zeolite has a number of advantages. Firstly, it will likely reduce industrial operational production costs and secondly such use will add greater value and benefit local enterprise and the economy. In terms of production costs, Saudi zeolite is of course cheaper to source locally, and huge savings can be made on transportation and on the cost of importing zeolite from overseas. Additionally, using local zeolite in production will encourage greater interest in its research in academic institutions in Saudi Arabia together with the collaborative projects, which may potentially be established with institutes worldwide. Such future research should lead to the discovery of novel, beneficial methodologies and procedures for zeolite modification such as those suggested in this article [
Another pioneering work [
The local Saudi natural zeolite exhibits low surface area and their modification to nanosize increases its surface properties [
Notably, zeolite was employed on membrane applications for the purpose of water desalination and another newer study directed a modified zeolite for carbon capture [
In recent years, researchers [
Currently, the potential use of polymer-zeolite composite in the manufacture of plastics is realistically viable since recycling plastics is problematic and costly. In this way, its use would likely lead to a further reduction in the volume of waste plastic worldwide together with a positive impact on the environment. In order to become effective, comprehensive methods for combining zeolite with plastics in the promotion of efforts in recycling plastics need to be established. Recent investigation [
Heterogeneously catalyzed dehydration reactions have long been investigated. However, the mechanism of these reactions is not fully understood. Pines and Pillai [
Overall, studies conducted on the properties of natural Saudi zeolites have shown huge potential for its use in industrial applications in energy production as a catalyst due to its excellent absorbency. The potential broad application of Saudi zeolite will prove to be of great value in a variety of local industrial settings for example in the production of photocatalyst pollutants degradation and environmental eco-friendly polymer applications. Therefore, based upon the wider literature review [
The effects of the treatment of MFI (H-ZSM-5) with acid (H3PO4) or basic (KOH) was examined, and the catalytic performance was compared with the structural and catalytic aspects of the zeolite after treatment with the help of cracking of 1-butene under steam for a period of five hours [
Moreover, Konno et al. [
In the literature [
An ion exchange method was proposed to modify local Saudi samples [
On other hand, in the literature [
Moreover, further study and exploration is proposed for our proper understanding of new forms such as 2D/3D zeolites [
Local zeolite that has been modified has more uses in commercial applications over and above those already proposed in the literature energy [
Today, a number of polymeric applications have commercial viability and have produced good results. The advantage is that such applications are based on polymeric membranes. The examples are producing nitrogen from air, recovering H2 from ammonia purge gas, removing carbon dioxide from natural gas, and separating hydrocarbons in the process of enhanced oil recovery (EOR) [
The limitation of using conventional polymeric membranes is to compromise productivity with efficiency and vice versa in that solution-diffusion mechanism results in concessions to either permeability (limiting productivity) or selectivity (affecting selectivity) [
Development of the local zeolite to a higher surface area, for removing carbon dioxide from natural gas and separating hydrocarbons in the process of enhanced oil recovery (EOR) [ Treatment of local zeolite with acid (H3PO4) or basic (KOH) is one option for the future examination of local zeolite. After that, it will be fruitful to study the effect of treatment on their catalytic performance and products selectivity using MBOH test reaction [ Comparison of the results of investigations with other findings is necessary, as proposed in Figure Based on previous studies [ Conversion of MBOH with water on an acidic catalyst could be established at a lower temperature. The conversion of MBOH with water [ Moreover, it is believed that metal oxide zeolites composites [
Proposed test protocol for modification, treatment, and characterization of natural Saudi clinoptilolite zeolite for environmental application.
In sum, results of this review shows that kinetics modeling for the clinoptilolite zeolite is needed in order to establish the objective for minimizing coke formation during steam reactions. The chemical weight percentage compositions of natural local Saudi zeolite compared with natural clinoptilolite sourced worldwide have also been reviewed. It was found that the percentage weight chemical compositions of the clinoptilolite zeolite are close to that of other international sources. There is a good correlation of silica to alumina ratio. However, the Japan sample of natural clinoptilolite zeolite is the highest and contains additional elements namely P2O5, S, CO2, and H2O. Moreover, various modification methods of zeolites were presented in the literature [
Catalytic cracking
Methanol-to-gasoline
Ethylenediaminetetraacetic acid
Hexylene glycol
Ultraviolet-visible spectroscopy
X-ray fluorescence
Methyl butynol
Thermal conductivity detector
Differential thermal analysis
Thermal gravimetric analysis
Scanning electron microscopy
X-ray diffraction
Temperature-programmed desorption of pyrrole
Energy dispersive X-ray spectroscopy.
The author declares no conflicts of interest.
The author is grateful to Professor Frank Roessner of Carl Von Ossietzky University, Germany, and Professor Elaref Ratemi of Jubail Industrial College, Saudi Arabia, for valuable scientific discussion. Also, the author gratefully acknowledges the efforts and support of Mr. Mohammed Francis and Mr. Edwin Obra. Author's appreciations extend to Jubail Industrial College for the cooperation and encouragement.