Separation of different paraffin wax grades using two comparative deoiling techniques

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1 Fuel Processing Technology 88 (2007) Separation of different paraffin grades using two comparative deoiling techniques Magdy T. Zaky, Nermen H. Mohamed, Amal S. Farag Petroleum Refining Division, Egyptian Petroleum Research Institute (EPRI), Nasr City, P. O. Box 11727, Cairo, Egypt Received 26 November 2006; received in revised form 26 April 2007; accepted 30 April 2007 Abstract One stage fractional crystallization and solvent percolation techniques have been used to separate different grades of paraffin es; with different characteristics; from El-Ameria light, middle and heavy es. The two deoiling techniques were performed using ethyl acetate and butyl acetate solvents at ambient temperature of 20 C, at different dilution solvent ratios (S/F by weight) ranging from 2:1 to and constant washing solvent ratio of 2:1 for the first technique and at different percolation solvent ratios ranging from to 1 for the second one. The resulting data revealed that fractional crystallization technique is more suitable for deoiling the heavy using butyl acetate solvent than the percolation technique. While, percolation technology is a preferable technique using ethyl acetate or butyl acetate solvent for separation of paraffin es from light and middle es Elsevier B.V. All rights reserved. Keywords: Paraffin es; Fractional crystallization; Solvent percolation; Deoiling techniques; Slack es 1. Introduction Generally, paraffin es are derived from low-boiling distillate fractions (light and middle ones). They consist mainly of n-paraffins ranging from C 16 to C 30 and possibly higher. Varying proportions of slightly branched-chain paraffins (C 18 C 36 )and naphthenes are present. Fully, semi- and scale refined paraffin es are produced from es. Slack es separated from lubricating oil feedstocks by deing operation, usually contain from 2 to 45 wt.% oil. Low oil content paraffin es with a specific melting point and needle penetration are produced by selective removal of the oil and low melting es from the es. This process is called deoiling or fractionation. The commercial fractionation processes are the sweating, the re-crystallization, the warm-up and the spray deoiling ones [1,2]. The most predominant process is the re-crystallization which was developed as a replacement for the sweating Corresponding author. Tel.: ; fax: address: [email protected] (M.T. Zaky). process. It is sometimes called fractional crystallization process and can be used to fractionate or deoil all types of es. The cake from the primary or the secondary deing filters is heated until the is totally dissolved in the solvent. Additional warm solvent is blended with the cake solution. The mixture is cooled in double pipe scraped surface equipment to a predetermined temperature to crystallize the desired fractions. The mixture is filtered through a rotary vacuum filter and the cake receives a final wash. The filtration temperature of the in the third stage is conducted at a higher temperature than that used in the first or second deing filtrations and the temperature used is selected to adjust melting point and penetration. This process can be operated in series with the solvent deing unit of similar design, which uses double or incremental dilution and single or two-stage filtration [2]. The characteristics of an ideal deing or deoiling solvent include the following: low solvent power of, high solvent power for oil, low freeze point, low viscosity, low in cost, nontoxic and have chemical and thermal stability [2]. In our previous study, n-hexane, dioxane, ethyl acetate and butyl acetate solvents were compared with methyl isobutyl /$ - see front matter 2007 Elsevier B.V. All rights reserved. doi: /j.fuproc

2 914 M.T. Zaky et al. / Fuel Processing Technology 88 (2007) ketone (MIBK) solvent and methyl ethyl ketone (MEK), benzene (B) and toluene (T) (60:20:20 by weight respectively) solvent mixture; the conventional solvents generally used in refineries as deing and deoiling solvents. The study indicated that, the most suitable solvents for separating paraffin es; with the standard specifications; from light, middle and heavy es are MIBK, ethyl and butyl acetates and the mixture of MEK, B & T. Moreover, butyl acetate and MIBK solvents and MEK, B & T solvent mixture can give paraffin es having nearly the same congealing points, needle penetrations and mean molecular weights range. However from the economical point of view, ethyl acetate and butyl acetate solvents are the most popular fractionating solvents due to their lower prices than MIBK solvent and their advantages of saving energy in the solvent distillation step over the solvent mixture of MEK, B &T [3]. Other authors carried out a study deals with the application of solvent percolation technique to separate oil from commercial microcrystalline flakes produced from tank bottom sludges. Wax deoiling has been accomplished by percolating industrial hexane through a packed bed of the flakes at ambient temperature and removing the solvent from the and oil phases to get hard and foot oil respectively. In this technology, mechanical mixing and filtration operation have been substituted with percolation of solvent through flakes, thereby eliminating mixed phase in the process and the need of expensive scraped surface crystallizers, rotary drum filters and refrigeration equipment as required in conventional solvent deoiling [4]. Table 1 molecular type composition of isolated es by one stage fractional crystallization of light using ethyl acetate solvent at fractionating Light Waxes isolated at different (L 1 ) (L 2 ) (L 3 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) TAPPI-ASTM equation Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cyclo-paraffins Iso- and cyclo-paraffins/n-paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Degree of branching (% CH 3 content) Table 2 molecular type composition of isolated es by one stage fractional crystallization of light using butyl acetate solvent at fractionating Thus, the present study deals with the differentiation between the fractional crystallization and solvent percolation techniques using ethyl acetate and butyl acetate solvents by variation the solvent feed ratios, for separation of various grades of paraffin es of different specifications from light, middle and heavy es. 2. Experimental 2.1. Materials Three appropriate crude es; light, middle and heavy es; from El-Ameria Refining Company with different characteristics are used in this study for isolation of different grades of paraffin es. Ethyl and butyl acetate solvents are used for separation of paraffin es by both fractional crystallization and solvent percolation techniques Isolation of paraffin es Light Waxes isolated at different 2:1 (L 4 ) (L 5 ) (L 6 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) TAPPI-ASTM equation Ultraviolet absorbance at 290 nm The three es were subjected practically to one stage fractional crystallization and solvent percolation techniques using ethyl and butyl acetate solvents at ambient temperature of 20 C and at different solvent feed ratios (S/F, by weight) ranging from 2:1 to at fixed washing solvent ratio of 2:1 for the former technique and from to 1 for the latter technique to produce different grades of paraffin es Fractional crystallization technique A known weight of was dissolved in the corresponding amount of solvent or solvent mixture in a beaker and heated till the mixture becomes homogenous. Then the mixture was cooled gradually at room temperature. The beaker and the buchner funnel were transferred to a controlled temperature unit and gradually cooled to the desired temperature. The beaker contents were transferred to the funnel and filtered through a Whatman filter paper No. 43 by using gentle suction. The cake was washed with additional solvent at the same temperature and added at small increments. Solvents were removed from the cake by distillation Solvent percolation technique A known weight of flakes was random packed in a jacketed glass column (diameter 3 cm, length 130 cm). A certain quantity of solvent was percolated under gravity over the packed bed of flakes from the top,

3 M.T. Zaky et al. / Fuel Processing Technology 88 (2007) Table 3 Effect of percolation solvent ratio on the physical characteristics and type of isolated es by solvent percolation of light using ethyl acetate solvent at percolating temperature of 20 C maintaining the temperature of the column at 20 C. After the percolation run, and oil solution phases were made free from the solvent by distillation to get hard and soft, respectively Methods of analysis Light The three es and the isolated paraffin es were physically characterized according to American Society for Testing and Materials (ASTM) standard methods [5]. The type of the isolated paraffin es was specified according to Technical Association of the Pulp and Paper Industry (TAPPI) ASTM equation [6,7]. The aromatic contents of the es and the isolated paraffin es were determined using liquid - solid column chromatography technique [8]. n-paraffin contents were determined for the es and the isolated paraffin es using GC technique. The GC apparatus used was model 6890 plus Aglient, equipped with a hydrogen flame ionization detector and fused silica capillary column (30 m 0.25 mm i.d.), packed with poly (dimethyl siloxane) HP-1 (non-polar packing) of 0.5 μm film thickness. The peak area of each resolved component (consisting of either n- and iso-paraffin) is determined individually. However, the unresolved complex mixtures (humps); composed of non n-paraffins presumably mainly cyclo-paraffins and aromatics with long side chains; were determined only as a total. The degree of branching (%CH 3 content) of the es and the isolated paraffin es was determined using proton nuclear magnetic resonance (Varian Mercury H-NMR spectrometer-danemark) at 300 MHz in deutrated chloroform [9]. Ultraviolet absorbance for the fully refined paraffin es was determined at 290 nm by using UV-Visible Spectrophotometer. 3. Results and discussion Waxes isolated at different percolation solvent to feed (PL 1 ) (PL 2 ) (PL 3 ) (PL 4 ) 1 (PL 5 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Ultraviolet absorbance at 290 nm 3.1. Fractional crystallization and solvent percolation of crude es Effect of dilution and percolation solvent ratios The dilution and the amount of solvent used in fractional crystallization and percolation respectively, have an obvious effect upon the yield and quality of the es isolated from light, middle and heavy es by using ethyl and butyl acetate solvents at ambient temperature of 20 C. Data are represented in Tables The yield decreases with increasing of dilution or percolation solvent ratios (Fig. 1), with the improvement of quality in terms of increasing the congealing point and mean molecular weight and lowering the needle penetration as a result of the decrease of oil content for the separated es. It can be noticed also that, the improvement in the quality is more pronounced with lower yield by using butyl acetate solvent than those obtained by ethyl acetate solvent for both techniques. This may be due to the higher solvent power of butyl acetate towards the oil inherent to such es (Tables 1 11). It is interest to note that the decrease in the oil content is accompanied with an increase in the viscosities and refractive indices of the es separated from light and middle es by increasing the dilution or percolation solvent ratios (Tables 1 8) while for the heavy, the decrease in the oil content is accompanied with the decrease in the viscosities and refractive indices of the separated es (Tables 9 11). This may be attributed to the type of the entrained oil which is mainly iso-paraffins having lower refractive indices and viscosities in the former case and aromatic constituents for the Table 4 Effect of percolation solvent ratio on the physical characteristics, type and molecular type composition of isolated es by solvent percolation of light using butyl acetate solvent at percolating temperature of 20 C Light Waxes isolated at different percolation solvent to feed (PL 6 ) (PL 7 ) (PL 8 ) (PL 9 ) (PL 10 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cycloparaffins Iso- and cyclo-paraffins/ n-paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Degree of branching (% CH 3 content)

4 916 M.T. Zaky et al. / Fuel Processing Technology 88 (2007) Table 5 molecular type composition of isolated es by one stage fractional crystallization of middle using ethyl acetate solvent at fractionating Middle Slack Wax Waxes isolated at different ratios (S/F) by using 2:1 (M 1 ) (M 2 ) (M 3 ) Congealing point, C Kinematic viscosity at 98.9 C, mm 2 s 1 Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cyclo-paraffins Iso- and cyclo-paraffins/ n-paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Degree of branching (% CH 3 content) latter case as they have higher refractive indices and viscosities than the other constituents of the. Data of molecular type composition confirm the above findings as the iso- and cyclo-paraffins contents of the es separated from the three es are decreased by increasing the dilution or percolation solvent ratios (Tables 1, 4 and 5 10) and the decrease is more pronounced by using butyl acetate solvent than ethyl acetate solvent (Compare Tables 5 and 6 or 7 and 8). Meanwhile there is a valuable decrease in the mono-aromatic constituents accompanied with the absence of di-aromatic ones for the es separated from the heavy (Tables 9 and 10). Moreover, the degree of branching decreases with increasing dilution or percolation solvent ratios, is mainly due to the decrease of iso-paraffins content for the es separated from the three es (Tables 1, 4 and 5 10) beside the decrease of aromatics content which is mainly mono-aromatic constituents attached with long side chain for the es separated from the middle and heavy es (Tables 5, 7, 9 and 10). Comparing the effect of increasing the quantity of solvent used in fractional crystallization technique; solvent feed ratios of dilution and washing; with those in solvent percolation technique, it can be noticed that, the two techniques behave the same trend upon increasing the solvent feed ratio as the isoand cyclo-paraffins and mono-aromatic constituents of lower melting points and mean molecular weights decrease in the paraffin es isolated from the three es. But, the solvent percolation technique needs higher quantity of solvent necessary for deoiling to obtain paraffin with nearly the same specifications as those obtained by fractional crystallization. Thus, to obtain paraffin with penetration value of nearly 19 by percolation and fractional crystallization techniques, the quantities of butyl acetate required per unit are & respectively (compare PL 8 in Table 4 with L 5 in Table 2). Also, the quantities of butyl acetate required per unit are & to obtain paraffin with penetration value of 13 by percolation and fractional crystallization techniques respectively (compare PM 9 in Table 8 with M 6 in Table 6). It is interest to note that fractional crystallization technique is more suitable for deoiling the heavy by butyl acetate solvent than the percolation technique (Tables 10 and 11 respectively). Whereas by increasing the quantity of the solvent in fractional crystallization technique, the heavy ( and entrained oil within and oil outside the crystals) is totally dissolved in the solvent by heating till the mixture becomes homogenous. Then the is recrystallized by gradual cooling to the desired fractionating temperature (20 C), while in percolation technique the solvent dissolves only the oil outside the crystals at the desired percolating temperature Table 6 molecular type composition of isolated es by one stage fractional crystallization of middle using butyl acetate solvent at fractionating Middle Slack Wax Waxes isolated at different 2:1 (M 4 ) (M 5 ) (M 6 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cyclo-paraffins Iso- and cyclo-paraffins/ n-paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Degree of branching (% CH 3 content)

5 M.T. Zaky et al. / Fuel Processing Technology 88 (2007) Table 7 Effect of percolation solvent ratio on the physical characteristics, type and molecular type composition of isolated es by solvent percolation of middle using ethyl acetate solvent at percolating temperature of 20 C (20 C) but it can't penetrate them to dissolve the entrained oil. Oil content data confirm the previous findings. Comparing H 6 in Table 10 with PH 3 in Table 11, it was found that both paraffin es are obtained with the same quantity of butyl acetate per unit () by fractional crystallization and percolation techniques having oil contents of 0.05 & 2.5 wt.% respectively. Generally, paraffin es with different specifications can be produced from different es by fractional crystallization or percolation technique using ethyl or butyl acetate solvent at different solvent feed ratios and at ambient temperature of 20 C. Thus, paraffin es of the same needle penetration of 22, 19 and 15 and having different mean molecular weights and congealing points can be obtained. Compare H 2 in Table 9 with both L 4 in Table 2 and PL 7 in Table 4, compare L 2 in Table 1 with both M 2 in Table 5 and PM 6 in Table 8 and compare also PL 10 in Table 4 with PM 8 in Table 8 respectively Isolated type Middle Waxes isolated at different percolation solvent to feed (PM 1 ) (PM 2 ) (PM 3 ) (PM 4 ) (PM 5 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cyclo-paraffins Iso- and cyclo-paraffins / n paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Degree of branching (% CH 3 content) Examining the isolated type in Tables 1 11 on the basis of, it can be noticed that all the studied es isolated from the three es lie in the category of macro-crystalline es; as they characterized by refractive indices lower than those obtained by the equation and by viscosities at 98.9 C lower than 7.4 mm 2 s 1 ; except the es (PH 1 and PH 2 ) isolated from heavy by using butyl acetate at percolation solvent ratios of and by weight (Table 11) lie in the category of semi-microcrystalline es as they characterized by refractive indices higher than those obtained by the equation and by viscosities at 98.9 C lower than 10 mm 2 s 1. According to petroleum specifications, all the tested macro-crystalline es lie also in the category of macrocrystalline es, except the needle penetration for the separated es L 1 in Table 1, PL 1 -PL 3 in Table 3, PL 6 in Table 4, M 1 in Table 5 and H 1 in Table 9 are higher than the macro-crystalline group limit (22). Different grades of paraffin es can be produced from the three es by using fractional crystallization and solvent percolation techniques at ambient temperature of 20 C and at various solvent to feed ratios. Eleven of fully refined food grade paraffin es were separated from the light as they are white in color Table 8 Effect of percolation solvent ratio on the physical characteristics, type and molecular type composition of isolated es by solvent percolation of middle using butyl acetate solvent at percolating temperature of 20 C Middle Waxes isolated at different percolation solvent to feed (PM 6 ) (PM 7 ) (PM 8 ) (PM 9 ) (PM 10 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) TAPPI-ASTM equation Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cyclo-paraffins Iso- and cyclo-paraffins/ n-paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Degree of branching (% CH 3 content)

6 918 M.T. Zaky et al. / Fuel Processing Technology 88 (2007) Table 9 molecular type composition of isolated es by one stage fractional crystallization of heavy using ethyl acetate solvent at fractionating Heavy Waxes isolated at different (H 1 ) (H 2 ) (H 3 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cyclo-paraffins Iso- and cyclo-paraffins/n-paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Di-aromatics, wt.% Degree of branching (% CH 3 content) Table 10 molecular type composition of isolated es by one stage fractional crystallization of heavy using butyl acetate solvent at fractionating Heavy Waxes isolated at different (H 4 ) (H 5 ) (H 6 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Ultraviolet absorbance at 290 nm Total saturates, wt.% n-paraffins Iso- and cyclo-paraffins Iso- and cyclo-paraffins/n-paraffins ratio Total aromatics, wt.% Mono-aromatics, wt.% Di-aromatics, wt.% Degree of branching (% CH 3 content) [7], their oil contents less than 0.5 wt.% and their ultraviolet absorbance at 290 nm less than 0.12 [2]. They are as follows: - Five paraffin es (L 2 L 6 ) were produced by fractional crystallization technique at ethyl acetate dilution solvent ratios of & for L 2 &L 3 respectively (Table 1) and at butyl acetate dilution solvent ratios of 2:1, & for L 4, L 5 &L 6 respectively (Table 2). - Six paraffin es (PL 4,PL 5 &PL 7 PL 10 ) were produced by solvent percolation technique at ethyl acetate percolation solvent ratios of & 1 for PL 4 &PL 5 respectively (Table 3) and at butyl acetate percolation solvent ratios of to for PL 7 to PL 10 respectively (Table 4). Six of fully refined grade and nine of semi-refined grade paraffin es were isolated from the middle. They are as follows: - Six paraffin es (M 3,M 6,PM 4,PM 5,PM 9 &PM 10 ) are classified as fully refined grade paraffin es as their oil contents are less than 0.5 wt.%. M 3 &M 6 were produced by fractional crystallization technique using ethyl and butyl acetate solvents respectively at dilution solvent ratio of (Tables 5 and 6). Meanwhile PM 4 PM 5 &PM 9 PM 10 were obtained by solvent percolation technique using ethyl and butyl acetate solvents respectively at percolation solvent feed ratios of & (Tables 7 and 8). - Nine paraffin es (M 2,M 4,M 5,PM 1 PM 3 &PM 6 PM 8 ) are classified as semi-refined grade paraffin es as their oil contents are higher than 0.5 and less than 1.5 wt.% [1]. M 2,M 4 &M 5 were obtained by fractional crystallization technique at ethyl acetate dilution solvent ratio of for M 2 (Table 5) and at butyl acetate dilution solvent ratios of 2:1 & Table 11 Effect of percolation solvent ratio on the physical characteristics and type of isolated es by solvent percolation of heavy using butyl acetate solvent at percolating temperature of 20 C Heavy Waxes isolated at different percolation solvent to feed ratios (S/F) (PH 1 ) (PH 2 ) (PH 3 ) (PH 4 ) Congealing point, C Kinematic viscosity Refractive index at 98.9 C Mean molecular weight Oil Needle penetration at 25 C Color (ASTM-D 1500) Semimicrocrystalline Macrocrystalline

7 M.T. Zaky et al. / Fuel Processing Technology 88 (2007) Fig. 1. Effect of solvent feed ratio on the yield of es isolated from light (A), middle (B) and heavy (C) es. FC: Fractional crystallization technique, P : Percolation technique, EA: solvent, BA: solvent. for M 4 &M 5 respectively (Table 6). Meanwhile PM 1 PM 3 &PM 6 PM 8 were separated by solvent percolation technique using ethyl acetate solvent for PM 1 PM 3 (Table 7) and butyl acetate solvent for PM 6 PM 8 (Table 8) at percolation solvent feed ratios of to for both solvents. Two of fully refined grade and five scale grade paraffin es were isolated from the heavy. They are as follows: - Two paraffin es (H 5 &H 6 ) are classified as fully refined grade paraffin es (ceresins) as their oil contents are 0.15 & 0.05 wt.% and having congealing points of 70.5 & 71.5 C respectively [10]. They were separated by fractional crystallization technique with butyl acetate solvent at dilution solvent feed ratios of & respectively (Table 10). - Five paraffin es (H 2 H 4,PH 3 &PH 4 ) are classified as scale grade paraffin es as their oil contents are more than 1.5 and less than 3 wt.%. H 2 H 4 were obtained by fractional crystallization technique at ethyl acetate dilution solvent ratios of & for H 2 &H 3 respectively (Table 9) and at butyl acetate dilution solvent ratio of for H 4 (Table 10). Meanwhile PH 3 & PH 4 ; with nearly the same physical

8 920 M.T. Zaky et al. / Fuel Processing Technology 88 (2007) characteristics; were separated by solvent percolation technique with butyl acetate solvent at percolation solvent feed ratios of & respectively (Table 11). 4. Conclusions The study shows that fractional crystallization and solvent percolation techniques using ethyl acetate and butyl acetate solvents could be employed for separation of paraffin es from light and middle es. While, solvent percolation technology is preferable due to it eliminates the need of crystallization and filtration steps and saving of time required in solvent fractional crystallization. Also, it was found that fractional crystallization technique is more suitable for deoiling the heavy by butyl acetate solvent than the percolation technique as by increasing the quantity of the solvent, the solvent dissolves the entrained oil within and oil outside the crystals during the re-crystallization step while in percolation technique, the solvent dissolves only the oil outside the crystals. [3] N.H. Mohamed, M.T. Zaky, A.S. Farag, A.F.M. Fahmy, Separation of Paraffin Wax Using Solvent Fractionation. Accepted at 17/3/2006 to be published in Pet. Sci. and Technol. [4] K.M. Agrawal, Y. Kumar, Deoiling of Hard Microcrystalline Wax by Solvent Percolation Technique, Res. Ind. 39 (1994) [5] Annual Book of ASTM-Standards (American Society for Testing and Materials), Petroleum Products, Lubrications, West Conshohocken, Sect. 5. [6] S.W. Ferris, Petroleum Waxes, Characterization, Performance and Additives, Technical Association of the Pulp and Paper Industry, Special Technical Association Publication, New York, STAP No. 2, 1963, pp [7] R.I. Gottshall, C.F. McCue, Petroleum es including petrolatums, in: J.P. Allinson (Ed.), Criteria for Quality of Petroleum Products, Applied Science Publishers Ltd., on behalf of The Institute of Petroleum, London, 1973, pp [8] L.R. Snyder, in: E. Heftmann (Ed.), Chromatography, Van Nostrand Reinhold Company, New York, [9] K.M. Agrawal, G.C. Joshi, Microcrystalline Waxes. 1. Investigation on the Structure of Waxes by Proton Nuclear Magnetic Resonance Spectroscopy, J. Chem. Tech. Biotechnol., vol. 31, 1981, pp [10] L.P. Kazakova, Investigation and application of solid hydrocarbons from petroleum, Chem. Technol. Fuels Oils 16 (1980) References [1] F. Richter, in: G. Alan (Ed.), Modern Petroleum Technology, vol. 2, Lucas, John Wiley and sons Ltd., on behalf of The Institute of Petroleum, New York, [2] A. Sequeria Jr., Lubricant Base Oil and Wax Processing, Marcel Dekker, Inc., New York, 1994.