Study of Phase Transition in Hard Microcrystalline Waxes and Wax Blends by Differential Scanning Calorimetry

Phase transition temperature and associated energies in hard high melting microcrystalline waxes and its various blend with paraffin wax (melting range from 60 to 97°C) have been determined by DSC in both heating and cooling mode. The dependence of these on the composition and properties of waxes have been analyzed. The solid liquid transition temperature obtained by DSC has been compared with ASTM drop melting point of these wax samples. The present study has demonstrated that DSC can be of great use in identifying whether the wax sample is blend of different waxes or not.     

Composition and Properties of Some Petroleum Waxes

Abstract

Structural composition of paraffin waxes and soft wax fraction derived from microcrystalline wax were determined. Waxes were fractionated by multistage solvent crystallization at different temperatures. The n-alkane components of the waxes were separated by urea adduction. The average structural parameters of parent waxes, their fractions, and urea adductables were estimated by ¹h and ¹³C NMR spectroscopy. The thermal parameters viz. phase transition temperature and the associated energy during phase transitions were determined by using DSC and correlated with the penetration temperature behavior of waxes. The carbon number distribution determined by GC for these waxes and their n-alkane components were also correlated with physical properties and thermal parameters.     

Characterization and Classification of Some Egyptian Petroleum Crude Waxes Using Different Techniques

Abstract

In order to characterize and identify some crude waxes, derived from various Egyptian petroleum distillates and residues, suitable for production of different types of petroleum waxes, many standard test procedures have been used for measurement the physical characteristics of crude waxes and wax products. Moreover, some analytical techniques such as gas chromatography (GC), Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (H-NMR), urea adducting analysis, and solid-liquid chromatography have been used to characterize the crude waxes. Finally, one stage fractional crystallization has been done to separate the hard waxes from El-Ameria and Suez heavy slack waxes and Alexandria and Suez crude petrolatums using ethyl acetate solvent at an ambient temperature of 20^○C and at fixed dilution and washing solvent ratios of 7:1 and 6:1 by weight, respectively. The resulting wax products are evaluated according to TAPPI-ASTM equation and petroleum wax specifications.     

Fractionation and Characterization of Waxes

By using short path molecular distillation (SPD) and supercritical fluid extraction (SFE) techniques, petroleum waxes have been fractionated into different fractions. These wax fractions were analyzed for their composition and phase transitions by gas chromatography (GC) and differential scanning calorimetry (DSC). GC data and the DSC thermograms indicated that the waxes vary significantly in their properties and composition.     

STUDY OF THE TEMPERATURE AND ENTHALPY OF WAX CRYSTALLIZATION FROM MIDDLE DISTILLATE BY DSC

ABSTRACT

The temperature and enthalpy of the wax crystallization as well as of melting have been studied in the middle distillate (boiling range: 250–375°C) obtained from the indigenous Bombay-High (Off-Shore) crude oil by using a differential scanning calorimeter (DSC). In order to have better understanding of the gel formation processes the broad distillate fraction was fractionated into five narrow fractions of 25°C interval each. From these narrow subfractions the saturates were separated from aromatics by column chromatography, and from saturates the n-paraffins were separated from iso-and cyclo-paraffins by urea adduction, to obtain the n-paraffins concentrates (urea adductables)–-the wax- and the saturated solvent portion–-the UNA. The thermal behaviour of narrow subfractions alongwith their urea adductables and the solvent portions have been studied and the wax appearance temperature (WAT) thus measured has been compared with those obtained by optical microscopy and with the ASTM cloud point, wherever possible. To obtain a clearer picture of the solidification process, further study has been done by preparing synthetic blends of urea adductables in different concentrations in the respective aromatic and iso- and cyclo-paraffinic solvents (UNA) and studying the thermal behaviour of each blend. It is found that the variation in WAT with wax concentration as measured by DSC is identical with that measured by optical microscopy and the ASTM cloud point. However, DSC values are lower than microscopic values and higher than ASTM cloud point. The enthalpy of the blends with the same amount of wax in the aromatic and iso- and cyclo-parffinic solvents indicated that it is higher in the saturated solvent in comparison to aromatic solvent. This confirms the fact that in an aromatic solvent the solubility of the wax is greater, and hence a comparatively lower WAT. The results are further discussed.     

CHARACTERIZATION OF TOTAL WAXES DERIVED FROM SOME INDIAN CRUDE OILS BY FRACTIONATION

ABSTRACT

Characterization of total refined waxes separated from Indian origin Ratna & BorhoHa crude oils have been made by fractionation. Solvent crystallization and vaccum distillation technique have been used for the fractionation of the waxes. The study indicated that each wax had different melting point distribution characteristics.     

CHARACTERISATION OF PARAFFIN WAXES BY DSC AND HIGH TEMPERATURE GC

ABSTRACT

Paraffin waxes of different crude oil sources were characterised using Differential Scanning Calorimetry, and High Temperature Capillary GC techniques. The carbon number distribution of the waxes were determined by calibrating the GC with standard n-paraffins blend. The δH_s?s transition obtained in DSC. thermogram of the waxes were correlated with its normal paraffin content. This correlation was further validated by obtaining n-paraffins content through High Temperature GC technique.     

费-托合成蜡溶剂精制及其结构性质的研究

采用甲乙酮-甲苯溶剂对含油量较高的费-托合成蜡进行脱油精制,研究蜡脱油前后在不同溶剂中的溶解性能。结果表明：甲乙酮-甲苯溶剂可以作为费-托合成蜡脱油精制的溶剂。使用X射线衍射仪对蜡样品的晶体结构进行分析研究,用差示扫描量热法（DSC）测定脱油精制蜡样品的熔点为90.68 ℃。对蜡样品的DSC曲线分析表明：费-脱合成蜡仅有一个熔融峰,没有明显的固-固晶体转变,这与石油蜡区别明显。     

Separation of Paraffin Wax Using Solvent Fractionation

Abstract

In order to separate and characterize some grades of paraffin waxes from El-Ameria crude waxes (slack waxes), a one-stage fractional crystallization technique has been done to separate the paraffin waxes with different characteristics by using different solvents and solvent mixtures at ambient temperature of 20°C and fixed dilution and washing solvent ratios (S/F) of 4:1 and 2:1 by weight, respectively. The fractionating solvents used are n-hexane, methyl isobutyl ketone (MIBK), dioxane, ethyl acetate, and butyl acetate as a single solvent and a mixture of methyl ethyl ketone (MEK) containing benzene (B) and toluene (T) as a mixed solvent. The resulting data revealed that dioxane and n-hexane solvents are not suitable for fractional crystallization of slack waxes, and the most suitable solvents for separating paraffin waxes with the standard specifications are ethyl and butyl acetates, MIBK, and the mixture of MEK, B, and T (60:20:20 by weight, respectively).     

PHASE TRANSITIONS IN PETROLEUM WAXES DETERMINED BY INFRARED SPECTROSCOPY

In the present paper attempts have been made to study the phase transition temperatures in petroleum waxes by infrared spectroscopy and the resulting data were correlated with phase transition temperatures obtained by differential scanning calorimetry (DSC).     

Composition and Properties of Some Petroleum Waxes

Structural composition of paraffin waxes and soft wax fraction derived from microcrystalline wax were determined. Waxes were fractionated by multistage solvent crystallization at different temperatures. The n-alkane components of the waxes were separated by urea adduction. The average structural parameters of parent waxes, their fractions, and urea adductables were estimated by ¹h and ¹³C NMR spectroscopy. The thermal parameters viz. phase transition temperature and the associated energy during phase transitions were determined by using DSC and correlated with the penetration temperature behavior of waxes. The carbon number distribution determined by GC for these waxes and their n-alkane components were also correlated with physical properties and thermal parameters.     

STUDY OF THE TEMPERATURE AND ENTHALPY OF THERMALLY INDUCED PHASE-TRANSITIONS IN n-ALKANES,THEIR MIXTURES AND FISCHER-TROPSCH WAXES

ABSTRACT

A precise determination of the temperatures and enthalpies of thermally induced various phases of n-alkanes, especially those having the molecular weights in the petroleum wax range, have been done by using a differential scanning calorimeter (DSC). These phase transitional parameters are shown to be dependent on the rate of heating/cooling, particularly on the faster rates. Also, the parameters measured during heating cycle (melting) differ from those obtained during the cooling cycle (crystallization). The typical shape of the solid-solid transition curve in the DSC thermograms(cooling cycle) of even n-alkanes readily distinguishes these from the odd n-alkanes, which is greately influenced by the increase in the carbon numbers in the chain (n-C₃₄ and beyond) and the purity of the sample.High molecular weight n-alkanes also showed instability in the structures at the phase transitions

The formation of solid solutions of n-alkanes have been studied by measuring phase transitional parameters and studying nature of the DSC thermograms of various binary and multicomponent mixtures of n-tetracosane (n-C₂₄) with other n-alkanes. It is observed that the immiscibility between two n-alkanes of the binary mixture begins when chain-length difference between them is more than four carbon atoms. In between the two extremes of solid solution and eutectic formations, there also existed the partial miscibility of two n-alkanes, particularly at high temperatures

The DSC thermograms of multicomponent n-alkane mixtures and Fischer-Tropsch waxes revealed that perfect solid solution is formed when the involved n-alkanes have carbon number very close to each other or the carbon number distribution is in a narrow range with smaller chain n-alkanes dominating.     

EFFECT OF ASPHALTENE AND RESINS ON THE STABILITY OF WATER-IN-WAXY OIL EMULSIONS

ABSTRACT

Asphaltene, resins and paraffin waxes, their mutual interactions and their influence on the stability of water-in-oil emulsions have been studied. 20 wt % paraffin wax dissolved in decalin was used to model the waxy crude oil. Asphaltene and resins separated from a crude oil were used to stabilize the water-in-oil emulsions. Synthetic formation water was utilized as the aqueous phase of the emulsion. The emulsion stability increased with increasing the concentration of asphaltene with a subsequent decrease in the average particle size distribution of the emulsion. Resins alone are not capable of stabilizing the emulsion, however, in the presence of asphaltene they form very stable emulsions. Dynamic viscosity and pour point measurements provided evidence for resins-paraffin waxes interactions. Asphaltene in the form of solid aggregates form suitable nuclei for the wax crystallites to build over with a mechanism similar to that of paraffin wax crystal-modifiers. As asphaltene are polar in nature they are derived at the oil/water interface which was proved by the ability of asphaltene to reduce oil/water interfacial tension. Consequently, nucleation of the wax crystallites by asphaltene and resins at the interface will add to the thickness of the oil-water interfacial film and hence increase the stability of the emulsion.     

COMPOSITIONAL ANALYSIS OF PETROLEUM WAXES BY ZEOLITE MOLECULAR SIEVE-GCMS

ABSTRACT

To investigate the composition of petroleum waxes, studies were carried out on the extraction of normal paraffins from petroleum waxes by zeolite molecular sieve type 5A. Time required for adsorption of different molecular weight n-paraffins from standard mixture and petroleum waxes has been ascertained. Un-adsorbed part of the waxes has been investigated by GC-MS technique. Recovery of adsorbed hydrocarbon from molecular sieve was done by supercritical fluid extraction.     

Understanding wax appearance temperature in light crude oils by DSC,NMR, and HT-GC

The wax precipitated from oil mixtures primarily consists of C18 to C36 (macro crystalline waxes) or C30 to C60 (micro crystalline waxes), both made of aligned paraffinic and naphthenic molecules. Paraffins have significant impact on wax deposition characteristics as paraffin waxes react and respond easily to temperature changes due to its straight chain structure. In this paper, 12 light crudes of different origin were analyzed by DSC. Method was standardized for the determination of WAT in light crudes and these were found to have WAT ranging from 10 to 30°C. Wax content is proportional to enthalpy of crystallization (ΔH) and the ΔH ranges from 3 to 9 J/g. WAT and wax content do not follow the same trend which is understandable as these parameters depends not only on the concentration and molecular weight of the waxes but also on the chemical nature of both waxy and non waxy part of the crude oil. To understand the trend in WAT, these crudes were also analyzed for paraffinic carbon (Cp), Saturates and CH₂/CH₃ ratio by NMR spectroscopy and carbon number distribution by HT-GC. It was observed that WAT correlates fairly well with CH₂/CH₃ ratio which is in an indicator of normal paraffin content as WAT depends primarily on the nature / type of paraffins. The anomalies can be explained through carbon–wise n-paraffin content by HT-GC.     

Determination of wax content in crude oil

Wax deposition is one of the chronic problems in the petroleum industry. The various crude oils present in the world contain wax contents of up to 32.5%. Paraffin waxes consist of straight chain saturated hydrocarbons with carbons atoms ranging from C18 to C36. Paraffin wax consists mostly with normal paraffin content (80–90%), while, the rest consists of branched paraffins (iso-paraffins) and cycloparaffins. The sources of higher molecular weight waxes in oils have not yet been proven and are under exploration. Waxes may precipitate as the temperature decreases and a solid phase may arise due to their low solubility. For instance, paraffinic waxes can precipitate out when temperature decreases during oil production, transportation through pipelines, and oil storage. The process of solvent dewaxing is used to remove wax from either distillate or residual feedstocks at any stage in the refining process. The solvents used, methyl-ethyl ketone and toluene, can then be separated from dewaxed oil filtrate stream by membrane process and recycled back to be used again in solvent dewaxing process.     

STUDY OF THE TEMPERATURE AND ENTHALPY OF WAX CRYSTALLIZATION FROM MIDDLE DISTILLATE BY DSC

The temperature and enthalpy of the wax crystallization as well as of melting have been studied in the middle distillate (boiling range: 250-375°C) obtained from the indigenous Bombay-High (Off-Shore) crude oil by using a differential scanning calorimeter (DSC). In order to have better understanding of the gel formation processes the broad distillate fraction was fractionated into five narrow fractions of 25°C interval each. From these narrow subfractions the saturates were separated from aromatics by column chromatography, and from saturates the n-paraffins were separated from iso-and cyclo-paraffins by urea adduction, to obtain the n-paraffins concentrates (urea adductables)--the wax- and the saturated solvent portion--the UNA. The thermal behaviour of narrow subfractions alongwith their urea adductables and the solvent portions have been studied and the wax appearance temperature (WAT) thus measured has been compared with those obtained by optical microscopy and with the ASTM cloud point, wherever possible. To obtain a clearer picture of the solidification process, further study has been done by preparing synthetic blends of urea adductables in different concentrations in the respective aromatic and iso- and cyclo-paraffinic solvents (UNA) and studying the thermal behaviour of each blend. It is found that the variation in WAT with wax concentration as measured by DSC is identical with that measured by optical microscopy and the ASTM cloud point. However, DSC values are lower than microscopic values and higher than ASTM cloud point. The enthalpy of the blends with the same amount of wax in the aromatic and iso- and cyclo-parffinic solvents indicated that it is higher in the saturated solvent in comparison to aromatic solvent. This confirms the fact that in an aromatic solvent the solubility of the wax is greater, and hence a comparatively lower WAT. The results are further discussed.     

SOLUBILITY STUDIES OF PARAFFIN WAXES IN SELECTED PETROLEUM FRACTIONS AND TOLUENE

ABSTRACT

Solubility studies of paraffin waxes with melting point range of 43^°C to 57^°C in two undefined petroleum fractions and Toluene have been carried out. An Attempt was made to develop a correlation for predicting the solubility of the waxes in these solvents. The one parameter ideal solubility law expression has been successfully used to represent the experimental data.     

Separation of Microcrystalline Waxes from Local Crude Petrolatums using Solvent–Antisolvent Mixtures

Abstract

In order to separate and characterize the microcrystalline waxes from Suez and Alexandria crude petrolatums, multistage fractional crystallization technique has been used to fractionate Suez crude petrolatum by using n-hexane as a single solvent at different fractionating temperatures ranging from 20 to ?20°C and at two different dilution and washing solvent ratios. Suez and Alexandria crude petrolatums were subjected also to multistage fractional crystallizations with solvent mixture at ambient temperature of 20°C and at fixed dilution and washing solvent ratios of 4:1 and 2:1 by weight, respectively. The solvent mixture composed of n-hexane as the main solvent and different percentages of absolute ethyl alcohol (ranging from 10 to 50 wt.%) as antisolvent. The solvent to feed ratios of dilution and washing were studied in the range of 2:1 to 8:1 and 2:1 to 6:1 by weight, respectively. Finally, one stage fractional crystallization has been done at the most suitable conditions to separate the microcrystalline waxes from Suez and Alexandria crude petrolatums followed by finishing via percolation in molten state through an activated bauxite column. The resulting finished microcrystalline waxes are evaluated according to the standard specifications of microcrystalline waxes, molecular type composition, degree of crystallinity, and scanning electron microscope (SEM).     

Physical Properties of Petroleum Waxes. I. Effect of Oil Content

Abstract

The effect of oil content on the physical properties of five microcrystalline waxes having widely different oil content have been investigated. It has been observed that the physical properties are affected to a great extent by the variation in oil content. Oil content has a profound effect on viscosity, hardness, and crystallinity of waxes. The effect is not so profound in the case of melting point.