EFFECT OF PRECIPITATION TEMPERATURE ON THE COMPOSITION OF N-HEPTANE ASPHALTENES Part 2

ABSTRACT

Petroleum asphaltenes precipitated by n-heptane at temperatures between ambient and 80^°C from two crude oils have been characterized regarding hydrocarbon structures using ¹H and ¹³C nmr, and fluorescence spectroscopy. This indicates a very complex and apparently very small change in structural features except for a molecular weight increase as more material stays in solution at elevated temperature. Aromaticity increase and apparently alkyl chains diminish. The latter trend is however affected by the structural equation used. According to the fluorescence spectroscopy the content of large and complex chromophores increases but a significant effect of the presence of porphyrins on the spectra is also observed. The data is analyzed in combination with previous characterizations of the same asphaltenes presented in the first part of this work (Andersen, 1994). This indicates that as smaller molecules are extracted at elevated temperature the precipitated asphaltenes tend to associate more. This implys that these small molecules block association sites which therefore become available for further association at elevated temperature. For Boscan part of the smaller easy to extract porphyrins may have this behavior.     

EFFECT OF PRECIPITATION TEMPERATURE ON THE COMPOSITION OF N-HEPTANE ASPHALTENES

Petroleum asphaltenes were separated from Boscan and Kuwait crude oils by n-heptane at constant temperatures ranging from -2 to 80 ° C. A decreased yield with increase in temperature was observed. The precipitated material was characterized using infrared spectroscopic functional group analysis, HPLC-size exclusion chromatography, vapor pressure osmometry, and elemental analysis. The change in vanadium porphyrin content was estimated for Boscan using UV-Vis. With elevated temperature the asphaltenes are more aromatic (lower H/C) and have higher apparent molecular weight, whereas the pattern of changes in functional groups and heteroatoms (NSO) are more complex and apparently dependent on the crude oil. Porphyrins and low molecular weight types were seen to stay in solution at increased temperature, and a specific extraction of these takes place above 40 ° C. Asphaltene solubility is seen to approximate the Flory-Huggins theory as small molecules go into solution before large molecules. Several other mechanisms may, however, be involved in the phase separation. The molecular size distribution curves obtained by HPLC-SEC were found to explain the trends found in the molecular weights by VPO.     

EFFECT OF EXPERIMENTAL CONDITIONS AND SOLVENTS ON THE PRECIPITATION AND COMPOSITION OF ASPHALTENES

The ASTM D 3279 test method for “n-Heptane Insolubles” is being currently used to determine the asphaltene content of fuel oils as defined by insolubility in normal (n) heptane solvent. Precipitation of n-heptane insolubles can produce sediments which vary in color, morphology and composition. The SEM analysis of n-heptane insolubles indicated that the sediments were heterogeneous containing some large particles >300 μ and the majority of particles to be small, <10 μ, “chained” together forming agglomerates. Significant fractions of n-heptane insolubles were found insoluble in toluene indicating their non-asphaltenic nature (“solids”). FTIR and XRF analyses of “solids” indicated the presence of multiring aromatics, Ni and carboxylate and sulfate salts. FTIR analysis of toluene soluble asphaltenes showed the presence of multiring aromatics. GC/MS analysis of toluene soluble asphaltenes indicated desorption of alkylbenzenes and O-containing molecules but no desorption of N- and S-containing molecules was observed. The tendency for N- and S-containing molecules to remain in the nonvolatile residue during the GC/MS analysis indicates that the N- and S-containing compounds have higher stability. The XRF analysis of the toluene soluble asphaltenes indicated that the molecules are similar to asphaltenes found in crude oils in terms of C, H, N and S contents, however, no presence of V- and Ni-containing molecules was found.     

INFLUENCE OF TEMPERATURE AND SOLVENT ON THE PRECIPITATION OF ASPHALTENES

Asphaltenes has been precipitated from a Kuwait flash residue using different n-alkanes (n-C5 to n-C8) at various temperatures ranging from 4^°C to reflux temperatures of the used precipitants. Structures in the asphaltene fractions has been revealed using U.V. fluorescence spectroscopy, elemental analysis and to some extent 1H-nmr. These analysis shows that asphaltenes precipitated in the same amount but at different temperature and with different solvents have merely the same composition. For all n-alkanes the curves of precipitated amount versus temperature show maxima at about 25^°C, implying a shift in the solubility of the asphaltenes.The impact of alkane chain length on the aggregation of asphaltenes through hydrogen bonds is discussed using the alkane-alcohol system as a model. The asphaltene solubility is discussed with the help of the Scatchard-Hildebrand equation.     

实验温度对沥青质热解的影响

本项研究主要是通过不同温度条件下的沥青质热解实验,研究热解温度对生物降解原油中生物标志物的恢复可能产生的影响。研究结果表明 340℃时,沥青质组分具有最大的产油率。另外,300℃之前,热解温度对沥青质热解产物中生物标志物的组成分布影响较小。因此,对于采用生物标志物恢复的方法来进行油/油对比时,300℃是沥青质热解实验较合适的温度。     

AN EXPERIMENTAL STUDY OF THE EFFECT OF PARAFFINIC SOLVENTS ON THE ONSET AND BULK PRECIPITATION OF ASPHALTENES

Asphaltene onset concentration and bulk deposition were measured for a typical live reservoir oil titrated with n-C₆H₁₄, n-C₅H₁₂, n-C₄H₁₀, C₃H₈, C₂H₆, CH₄ and CO₂ at 100° C (212 ° F) and 29.9 MPa (4340 psia). The concentration of titrant at asphaltene onset was observed to decrease approximately in a linear fashion with decreasing molecular weight of the paraffinic solvent; CH₄ did not induce any asphaltene precipitation. Bulk deposition experiments were performed using a solvent: oil volume ratio of 10:1; the results indicated that the weight percent of asphaltenes precipitated increased exponentially with decreasing molecular weight of the paraffinic solvents. More importantly, the asphaltene molecular weight showed a maximum for n-C₄H₁₀ precipitated asphaltenes. Possible explanations for this unusual result are presented.     

AN EXPERIMENTAL STUDY OF THE EFFECT OF PARAFFINIC SOLVENTS ON THE ONSET AND BULK PRECIPITATION OF ASPHALTENES

ABSTRACT

Asphaltene onset concentration and bulk deposition were measured for a typical live reservoir oil titrated with n-C₆H₁₄, n-C₅H₁₂, n-C₄H₁₀, C₃H₈, C₂H₆, CH₄ and CO₂ at 100° C (212 ° F) and 29.9 MPa (4340 psia). The concentration of titrant at asphaltene onset was observed to decrease approximately in a linear fashion with decreasing molecular weight of the paraffinic solvent; CH₄ did not induce any asphaltene precipitation. Bulk deposition experiments were performed using a solvent: oil volume ratio of 10:1; the results indicated that the weight percent of asphaltenes precipitated increased exponentially with decreasing molecular weight of the paraffinic solvents. More importantly, the asphaltene molecular weight showed a maximum for n-C₄H₁₀ precipitated asphaltenes. Possible explanations for this unusual result are presented.     

THE EFFECT OF ASPHALT COMPOSITION ON THE FORMATION OF ASPHALTENES AND THEIR CONTRIBUTION TO ASPHALT VISCOSITY

ABSTRACT

Interactions among asphalt components have significant effects on the performance of asphalt binder. To understand those interactions, four asphalts, SHRP AAA-I, AAD-I, AAF-I, and AAG-I, were fractionated into three generic fractions according to Corbett's procedure and reblended into asphaltenes/aromatics/saturates ternary mixtures in various ratios. Mixtures were oxidatively aged with atmospheric air at temperatures of 87.7, 93.3, and 98.8°C for 5 to 33 days. The changes in chemical composition and physical properties were monitored using fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical rheometry

The formation of asphaltenes is a major factor in the hardening of asphalt with aging. The data collected in this study indicate that the saturate content in the maltene phase has a profound impact on the contribution that asphaltenes have on the viscosity of aged asphalt. The data also suggest that the aromatics fraction is solely responsible for the formation of asphaltenes as an asphalt oxidizes.     

THE EFFECT OF ASPHALT COMPOSITION ON THE FORMATION OF ASPHALTENES AND THEIR CONTRIBUTION TO ASPHALT VISCOSITY

Interactions among asphalt components have significant effects on the performance of asphalt binder. To understand those interactions, four asphalts, SHRP AAA-I, AAD-I, AAF-I, and AAG-I, were fractionated into three generic fractions according to Corbett's procedure and reblended into asphaltenes/aromatics/saturates ternary mixtures in various ratios. Mixtures were oxidatively aged with atmospheric air at temperatures of 87.7, 93.3, and 98.8°C for 5 to 33 days. The changes in chemical composition and physical properties were monitored using fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical rheometry

The formation of asphaltenes is a major factor in the hardening of asphalt with aging. The data collected in this study indicate that the saturate content in the maltene phase has a profound impact on the contribution that asphaltenes have on the viscosity of aged asphalt. The data also suggest that the aromatics fraction is solely responsible for the formation of asphaltenes as an asphalt oxidizes.     

THE INFLUENCE OF PRESSURE ON THE ASPHALTENES CONTENT AND COMPOSITION IN OILS

The objective of this work was to investigate the effect of pressure on the concentration of the dissolved asphaltenes in a heavy oil. The asphaltenes content was determined in oil samples, produced at reservoir temperature and different pressures ranging from the initial reservoir pressure to the atmospheric one, using the standard IP143/90 method. Additionally, the content of nine trace metals in the asphaltenes, produced at each pressure step was studied by Total Reflection X-Ray Fluorescence (TXRF). It was found that the amount of the dissolved asphaltenes in oil decreases as pressure falls from the initial reservoir pressure down to bubble point pressure and subsequently increases as the pressure is reduced further. A positive correlation was observed between the concentration of several metals (Ni, V, Cr, Mn) and the dissolved asphaltenes content.     

THE INFLUENCE OF PRESSURE ON THE ASPHALTENES CONTENT AND COMPOSITION IN OILS

The objective of this work was to investigate the effect of pressure on the concentration of the dissolved asphaltenes in a heavy oil. The asphaltenes content was determined in oil samples, produced at reservoir temperature and different pressures ranging from the initial reservoir pressure to the atmospheric one, using the standard IP143/90 method. Additionally, the content of nine trace metals in the asphaltenes, produced at each pressure step was studied by Total Reflection X-Ray Fluorescence (TXRF). It was found that the amount of the dissolved asphaltenes in oil decreases as pressure falls from the initial reservoir pressure down to bubble point pressure and subsequently increases as the pressure is reduced further. A positive correlation was observed between the concentration of several metals (Ni, V, Cr, Mn) and the dissolved asphaltenes content.     

THE EFFECT OF LOW TEMPERATURE OXIDATION ON THE CHEMICAL AND PHYSICAL PROPERTIES OF MALTENES AND ASPHALTENES DERIVED FROM HEAVY OIL

The chemical changes that occur when the maltene and asphaltene fractions (separated from heavy oil) are subjected to low temperature oxidation (LTO) in the presence and absence of water have been investigated by a combination of classical separation techniques and analytical pyrolysis. In general, it is observed that water has a mitigating effect on the destructive nature of LTO. A detailed analysis of the pyrolytic products suggests that the presence of water reduces the ease with which oxygen reacts with sulfides to give sulfones and thereby supresses the formation of coke. An analysis of the data indicates that most of the coke produced results from LTO of the asphaltenes; only a small portion originates in the maltenes.     

THE EFFECT OF LOW TEMPERATURE OXIDATION ON THE CHEMICAL AND PHYSICAL PROPERTIES OF MALTENES AND ASPHALTENES DERIVED FROM HEAVY OIL

Abstract

The chemical changes that occur when the maltene and asphaltene fractions (separated from heavy oil) are subjected to low temperature oxidation (LTO) in the presence and absence of water have been investigated by a combination of classical separation techniques and analytical pyrolysis. In general, it is observed that water has a mitigating effect on the destructive nature of LTO. A detailed analysis of the pyrolytic products suggests that the presence of water reduces the ease with which oxygen reacts with sulfides to give sulfones and thereby supresses the formation of coke. An analysis of the data indicates that most of the coke produced results from LTO of the asphaltenes; only a small portion originates in the maltenes.     

EFFECT OF DISPERSANTS AND FLOCCULANTS ON THE COLLOIDAL STABILITY OF ASPHALTENES

Since the traditional deasphalting process is expensive, a more economical approach would be to use dispersants or flocculants to control the colloidal stability of asphaltenes. The asphaltene content of fuel oils is defined by testing the n-heptane insolubles following the ASTM D 3279 method. In the presence of dodecylbenzenesulfonic acid, a decrease in n-heptane insolubles precipitation was observed indicating an increase in their colloidal stability. No significant change in n-heptane insolubles precipitation was observed in the presence of dodecylphenol and nonylphenol. Poly(maleic anhydride-1-octadecene) polymer was found to be an effective flocculant. The flocculation of n-heptane insolubles varied depending on the polymer-to-asphaltenes weight ratios. The FTIR results indicate that the flocculation occurs through the H-bonding between the asphaltenes and the polymer molecules. Maleic anhydride was found to continuously increase the n-heptane insolubles precipitation with an increase in its treat rate. The FTIR analysis showed the presence of an acidic C=O group and no presence of an anhydride functional group. The results indicate that the presence of an anhydride and unsaturation makes the maleic anhydride too reactive leading to chemical changes and the precipitation of asphaltenes and other aromatic molecules found in fuel oils.     

EFFECT OF DISPERSANTS AND FLOCCULANTS ON THE COLLOIDAL STABILITY OF ASPHALTENES

Since the traditional deasphalting process is expensive, a more economical approach would be to use dispersants or flocculants to control the colloidal stability of asphaltenes. The asphaltene content of fuel oils is defined by testing the n-heptane insolubles following the ASTM D 3279 method. In the presence of dodecylbenzenesulfonic acid, a decrease in n-heptane insolubles precipitation was observed indicating an increase in their colloidal stability. No significant change in n-heptane insolubles precipitation was observed in the presence of dodecylphenol and nonylphenol. Poly(maleic anhydride-1-octadecene) polymer was found to be an effective flocculant. The flocculation of n-heptane insolubles varied depending on the polymer-to-asphaltenes weight ratios. The FTIR results indicate that the flocculation occurs through the H-bonding between the asphaltenes and the polymer molecules. Maleic anhydride was found to continuously increase the n-heptane insolubles precipitation with an increase in its treat rate. The FTIR analysis showed the presence of an acidic C=O group and no presence of an anhydride functional group. The results indicate that the presence of an anhydride and unsaturation makes the maleic anhydride too reactive leading to chemical changes and the precipitation of asphaltenes and other aromatic molecules found in fuel oils.     

电解质溶液局部组成模型的温度效应

将电解质溶液的局部组成模型中的粒子间作用能看作常数 ,与温度无关 ,使得模型参数与温度成简单的倒数关系 ,利用 2 5℃的模型参数值 ,关联计算了在不同温度下NaCl KCl H2 O三元体系溶解度数据 ,结果表明在 0～ 1 2 0℃的范围内 ,关联计算结果很好 ,解决了局部组成模型在计算电解质溶液溶解度时缺乏其他温度下模型参数的问题     

石蜡纳米乳液的制备及温度因素的影响

为研究石蜡纳米乳液制备中的温度影响,先以58#石蜡为原料,采用非离子型复合乳化剂司潘-40、吐温-40制备了石蜡纳米乳液,并利用单因素法确定了配方组成和乳化条件:水/58#石蜡/司潘-40/吐温-40(质量比)=70/21/3.6/5.4,乳化时间为10 min,搅拌速率为1400 r/min.考察了乳化温度、降温速率...     

EFFECT OF ATTAPULGITE CLAY ON THE COMPOSITION OF JET FUELS

To identify the chemistry of polar molecules affecting the stability of jet fuels, spent Attapulgite clays collected from the top, middle and the bottom of the clay treater, were analyzed. The GC/MS analysis allowed for the selective desorption of polar organic molecules. At the low temperature range of 50–200°C, the GC/MS analysis showed desorption of C₉–C₁₆ hydrocarbons which are typical jet fuel molecules. At the higher temperature range of 50–400°C, the GC/MS analysis of spent clays showed desorption of water, amines, pyridines, quinolines, thiophenes, sulfides, thiols and alkylbenzenes. At the high temperature range of 50–600°C, the GC/MS analysis showed desorption of water, phenols, pyridines, quinolines, alkylbenzenes and other unidentified N compounds. No desorption of S compounds was observed above 400°C. Desorption of water above 200°C indicated that the water molecules were held inside the crystalline structure of the clay. The Attapulgite clay was found to be effective in adsorbing a wide range of polar molecules from jet fuel. Desorption of pyridines, quinolines and alkylbenzenes below and above 400°C indicated that their chemistry was different and required different energy to desorb from the clay. The high adsorbent capacity clays capable of adsorbing different chemistry polar molecules are required to assure stability of jet fuels.     

EFFECT OF ATTAPULGITE CLAY ON THE COMPOSITION OF JET FUELS

To identify the chemistry of polar molecules affecting the stability of jet fuels, spent Attapulgite clays collected from the top, middle and the bottom of the clay treater, were analyzed. The GC/MS analysis allowed for the selective desorption of polar organic molecules. At the low temperature range of 50-200°C, the GC/MS analysis showed desorption of C₉-C₁₆ hydrocarbons which are typical jet fuel molecules. At the higher temperature range of 50-400°C, the GC/MS analysis of spent clays showed desorption of water, amines, pyridines, quinolines, thiophenes, sulfides, thiols and alkylbenzenes. At the high temperature range of 50-600°C, the GC/MS analysis showed desorption of water, phenols, pyridines, quinolines, alkylbenzenes and other unidentified N compounds. No desorption of S compounds was observed above 400°C. Desorption of water above 200°C indicated that the water molecules were held inside the crystalline structure of the clay. The Attapulgite clay was found to be effective in adsorbing a wide range of polar molecules from jet fuel. Desorption of pyridines, quinolines and alkylbenzenes below and above 400°C indicated that their chemistry was different and required different energy to desorb from the clay. The high adsorbent capacity clays capable of adsorbing different chemistry polar molecules are required to assure stability of jet fuels.     

ELEMENTAL COMPOSITION OF ASPHALTENES FROM COAL LIQUEFACTION

The elemental composition (C, H, N, S, O) of asphaltenes isolated from coal liquefaction experiments carried out at different temperatures and tetralin/coal ratios has been determined. The liquefaction experiments were conducted in a 250 ml autoclave, with 10 g of a Spanish subbituminous A coal, for 1 hour, and at 17 ± 1 MPa operating pressure and 400 rpm stirring speed. The liquefaction products were fractionated into oils, asphaltenes and preasphaltenes using pentane, toluene and THF as extractive solvents. The % S and % O are lower in asphaltenes than in coal, while the % C and % N are higher and % H depends on the temperature and tetralin/coal ratio used. On the other hand asphaltenes % C decreases, and % H and % O increase as the tetralin/coal ratio is raised at every temperature except 475 °C, while % S and % N do not have a clear variation.