Mohammad Nahid Siddiqui

Studies on the aging behavior of the Arabian asphalts

In this study the rheological, physical, and chemical properties of asphalts procured from Ras Tanura, Riyadh, Kuwait, and Bahrain refineries were evaluated. The rolling thin-film oven (RTFO), termed as short-term aging, and the pressurized aging vessel (PAV), termed as long-term aging, tests were used to simulate asphalt aging. Viscosity, penetration, softening point, and weight loss tests were applied to investigate the rheological properties of fresh and aged Arabian asphalts. The Corbett method was used to separate asphalts into asphaltene, polar aromatic, naphthene aromatic, and saturate fractions. Asphaltene contents and Gaestel index (Ic) were found to increase linearly with aging process. It was found that PAV has more severe effects on the rheological and chemical properties of asphalt than RTFO test method. Using infrared spectroscopy, it was found that on aging the weight percent of oxygen as carbonyl and sulfur as sulfoxide group types increased in asphaltenes. Significant differences were observed between the structure and composition of fresh and aged asphaltenes of Ras Tanura (RT) asphalt.

Use of X-ray diffraction in assessing the aging pattern of asphalt fractions

The X-ray diffraction (XRD) method was employed to investigate and compare some of the crystallite parameters and aromaticity of asphaltenes obtained from fresh and aged Arabian asphalts, procured from Ras Tanura (RT) and Kuwait (KW) refineries. A few crystallite parameters in the polar aromatics, naphthene aromatics and saturate fractions of these Arabian asphalts were also determined. The results obtained by XRD method for both the types of asphaltenes and other fractions were evaluated and compared. Significant differences were observed between the structure and the aging patterns of fresh and aged asphaltenes of RT and KW asphalt. The results indicate that the source and chemistry of asphalt are responsible for the aging behavior of its components. The rolling thin-film oven and the pressurized aging vessel tests were used to simulate asphalt aging in this research.

Investigation of chemical transformations by NMR and GPC during the laboratory aging of Arabian asphalt

In this work, the chemical properties of a commercial grade Saudi Arabian asphalt procured from Ras Tanura refinery were evaluated. The rolling thin film oven (RTFO), termed as short-term aging, and pressurized aging vessel (PAV), termed as long-term aging, tests were used to simulate the laboratory aging of this asphalt. It was found that PAV has more severe effects on the chemical properties of asphalt than RTFO method. The Corbett fractionation procedure was used to separate fresh and aged asphalts into four generic fractions namely; asphaltenes, polar aromatics, naphthene aromatics, and saturates and various analytical techniques were applied to evaluate the chemical changes that occurred during the aging processes. High pressure-gel permeation chromatography (HP-GPC) molecular weight and size distributions suggested that molecular rearrangement occurs predominantly on aging. Carbon and proton NMR measurements of generic fractions showed that isomerization, internal cross-linking, and dehydrogenation were the main chemical reactions of hydrocarbon groups following aging. Coupling the results from the GPC and NMR techniques have led to some interesting information concerning the chemical reaction types during the aging processes. Significant differences were observed between the structure and composition of fresh and aged generic fractions of Ras Tanura asphalt.

Identification of different kinds of plastics using laser-induced breakdown spectroscopy for waste management

Laser-Induced Breakdown Spectroscopy (LIBS) was applied for the identification of various kinds of plastics for management and recycling of plastic waste. In order to fingerprint these plastics, a laser-produced plasma emission was recorded for spectral analysis of various kinds of plastics. The plasma was generated by focusing a Nd:YAG laser radiation at wavelength = 1064 nm having laser energy = 40 mJ. The 6 main family of plastics tested are: Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Polypropylenes (PP), Polystyrene (PS), Polyethylene Terephthalate (PET) and Polyvinyl chloride (PVC). The capability of this technique is demonstrated by the analysis of the major constituents carbon and hydrogen present in polymer matrices. The LIBS signal intensity measured for carbon and hydrogen was detrimental for the fingerprinting of various kinds of plastics. The C/H line intensity ratio was 1.68, 1.51, 1.42, 1.16, 1.01 and 0.91 for HDPE, LDPE, PS, PP, PET and PVC respectively. The detection limits of carbon and hydrogen were found to be approximately 6 μ g/g by applying 20 laser shots. The unique features of LIBS are: it is a simple, rapid, remote, real-time analysis without sampling requirements. The study demonstrated that LIBS could be applied as a best tool for sorting out different kinds plastics on a fast scale for waste management. The health hazards of different kinds of plastics are also described.

Conversion of hazardous plastic wastes into useful chemical products.

Azoisobutylnitrile (AIBN) initiator was used in the treatment of most widely used domestic plastics in lieu of catalysts. The pyrolysis of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), poly-ethylene terephthalate (PET) and polystyrene (PS) plastics with azoisobutylnitrile was carried out individually under nitrogen atmosphere. A series of single (plastic/AIBN) and binary (mixed plastics/AIBN) reactions were carried out in a 25-cm(3) micro-autoclave reactor. The optimum conditions selected for this study were: 5% AIBN by weight of total plastics, 60 min, 650 psi and 420 degrees C. It was found that HDPE, LDPE, PP underwent to a maximum cracking and produced highest amounts of liquid and gaseous products. Pyrolysis of PET and PS plastics with AIBN afforded comparatively significant amount of insoluble organic materials. In other reactions, fixed ratios of mixed plastics were pyrolyzed with AIBN that afforded excellent yields of liquid hydrocarbons. This result shows a very significant increase in the liquid portions of the products on using AIBN in the pyrolysis of plastics. The use of AIBN in the pyrolysis of plastics is seems to be feasible and an environmental friendly alternative to catalytic process for maximizing the liquid fuels or chemical feed stocks in higher amounts.

Metal–organic framework-guided growth of Mo2C embedded in mesoporous carbon as a high-performance and stable electrocatalyst for the hydrogen evolution reaction

Large-scale production of H2 by electrochemical water splitting is discerned as one of the most economical and viable approaches and designing Pt-less electrocatalysts remains at the forefront of this technology development. Herein, in situ transformation of metal–organic frameworks (MOF), impregnated with a molybdenum precursor, into a porous and rigid carbon support and molybdenum carbide (Mo2C) was demonstrated to fabricate highly active and stable β-Mo2C/C heterostructure for electrocatalytic H2 evolution. The two-step synthesis approach involved the impregnation of molybdenum source into frameworks of MOF (namely MIL-53(Al)) followed by nucleation and growth of Mo2C nanocrystals into confined porous texture through carburization. Characterization revealed the formation of mesoporous carbon embodied with crystalline nanoparticles of β-Mo2C (between 5 and 10 nm). A probable mechanism for the formation of Mo2C/C nanocomposite is proposed. The propensity of the catalyst was tested towards the electrocatalytic H2 evolution reaction (HER) under alkaline aqueous media (1 M KOH). The electrocatalyst showed a remarkable HER activity as compared to the benchmark electrocatalyst Pt/C and Mo2C/XC72 black catalysts at 10 mA cm−2 and stability for 20 h at the same current density. Electrochemical impedance spectroscopy results of Mo2C/C were construed by two time constants, porosity and charge transfer, and the HER reaction followed the Volmer–Heyrovsky mechanism.

Morphology and antifungal effect of nano-ZnO and nano-Pd-doped nano-ZnO against Aspergillus and Candida

The present work was aimed to study the activity of nano-particulated ZnO and nano Pd doped nano-ZnO against Aspergillus and Candida species, commonly contaminating the water supply systems. Micro-ZnO was purchased from the market (Aldrich, USA) while nano ZnO were synthesized using sole gel and precipitation methods and their morphology was determined using XRD and TEM techniques. The average grain size of nano-ZnO estimated by these techniques was 30 nm and 20 nm, respectively. The doping of nano-ZnO with 5 % Pd was achieved by a thermal decomposition method and its morphology; as characterized by XRD, TEM and FESEM techniques; gave an average grain size of 35 nm. Serial dilutions of nano-ZnO doped with 5 % Pd, pure nano-ZnO and micro-ZnO (as a control) were prepared from 10 mg/mL stock solution of each in dermasel agar (OXOID), inoculated with standard strains of Candida albicans and Aspergillus niger and incubated at 37°C for 24 and 48 hours, respectively. Their antimicrobial effect was compared by the minimal inhibitory concentration (MIC), determined as the dilution giving a negligible growth of microorganism. Nano-ZnO doped with 5 % nano-Pd, pure nano-ZnO and micro-ZnO, showed antifungal activity against Aspergilus niger with an MIC of 1.25, 2.5 and 5mg/mL, respectively. However, Candida albicans yeasts were relatively resistant to these compounds, with an MIC of 2.5, 5 and 10 mg/mL for Pd doped nano-ZnO, nano-ZnO and micro-ZnO, respectively. Thus nano-ZnO was twice as potent in killing Aspergillus, as compared to its non-nano-counterpart and loading of nano-ZnO with 5 % nano-Pd further increased its activity, four times that of micro-ZnO. Further investigations are needed to confirm the potential use of nano-ZnO and its doping with nano-Pd in the treatment of water supply systems and food preservation.

Regiochemistry of mercury(II) oxide oxidation of unsymmetrical N,N-disubstituted hydroxylamines

Abstract Mercury(II) oxide oxidation of N,N-disubstituted hydroxylamines with the α and α′ carbon atoms containing one and two hydrogen atoms, respectively, gave aldonitrones in a highly regioselective manner. Removal of the α proton is involved in the rate determining step as shown by primary kinetic isotope effect.

Alkylation and oxidation reactions of Arabian asphaltenes

Infrared and NMR spectroscopy and thermogravimetric analysis were employed to investigate the structural changes in the Arab heavy and Arab medium asphaltenes following the Friedel–Crafts alkylation and permanganate oxidation reactions. The results provided significant and in-depth information regarding the nature of chemical reactive sites present in asphaltenes. This work gave clear indication that the aromatic C–H group had undergone alkyl substitution reaction in presence of strong Lewis acid AlCl3. The CH2/CH3 groups oxidized to carboxylic acids and other carbonyl functional groups during the oxidation process. Since asphaltenes possess long aliphatic chains, condensed aromatic rings, heteroatoms and metals, information obtained from the structural changes during these reaction processes is considered very significant. The combinations of IR and NMR spectroscopy and TGA have proven to be very useful tools in assessing the structural changes occurred in the asphaltenes on subjecting to oxidation and alkylation reactions.

Infrared Study of Hydrogen Bond Types in Asphaltenes

Abstract The structural characteristics of asphaltenes are important to refiners for determining the yields from the residual fraction of crude oils and the operating parameters of the process units for deep conversion processes. In this article, we studied the hydrogen bonding distribution of four Saudi Arabian crude-oil-derived asphaltenes against the phenol solutions of various concentrations in carbon tetrachloride. In an attempt to explain relative hydrogen bonding capabilities of asphaltenes, OH peak intensity of phenol and enthalpies of hydrogen bond formation were used in combination with the content of heteroatoms (N, O, and S) in asphaltenes. The OH peak intensity of phenol depends on the presence of acidic and basic moieties or functional groups on the surface of asphaltenes. The results obtained show that the asphaltenes with high oxygen and low nitrogen contents have poor interaction with phenol, which indicates that oxygen might be incorporated as acidic hydroxyl groups in asphaltenes. In a similar way, asphaltenes with low oxygen and high nitrogen contents give high phenol interaction values. Piperidine was also tried to evaluate the hydrogen bonding capabilities of NH group with the asphaltenes. The trace metal and GPC molecular weight measurements showed that the Arab heavy asphaltenes possess highest molecular weights and maximum V and Ni contents.Abstract The structural characteristics of asphaltenes are important to refiners for determining the yields from the residual fraction of crude oils and the operating parameters of the process units for deep conversion processes. In this article, we studied the hydrogen bonding distribution of four Saudi Arabian crude-oil-derived asphaltenes against the phenol solutions of various concentrations in carbon tetrachloride. In an attempt to explain relative hydrogen bonding capabilities of asphaltenes, OH peak intensity of phenol and enthalpies of hydrogen bond formation were used in combination with the content of heteroatoms (N, O, and S) in asphaltenes. The OH peak intensity of phenol depends on the presence of acidic and basic moieties or functional groups on the surface of asphaltenes. The results obtained show that the asphaltenes with high oxygen and low nitrogen contents have poor interaction with phenol, which indicates that oxygen might be incorporated as acidic hydroxyl groups in asphaltenes. In a ...