3110
Ind. Eng. Chem. Res. 1997, 36, 3110-3115
Separation and Characterization of Paraffins and Naphthenes from FCC Feedstocks A. A. Lappas,* D. Patiaka, D. Ikonomou, and I. A. Vasalos Chemical Process Engineering Research Institute (CPERI) and Department of Chemical Engineering, University of Thessaloniki, P.O. Box 361, 57001 Thermi, Thessaloniki, Greece
A separation technique was developed for the characterization and identification of the nonaromatic fraction of a light and a heavy FCC feedstock (gas-oil). The separation of the paraffins was based upon the selective reaction of n-paraffins with urea and branched paraffins with thiourea. One more method based on the molecular sieves adsorption was also applied for n-paraffin separation, but the urea method was found to be more satisfactory. The total recovery of the method was about 70%. All the fractions were characterized using a system of GC/MS under the specific conditions presented in this work. The hydrocarbons in the n-paraffinic and isoparaffinic fractions were identified satisfactorily, while for the naphthenic fraction this identification was more difficult. A quantitative analysis was attempted of all the paraffinic compounds in the FCC feedstock. Using a standard sample of n-paraffins, the relative wt % concentrations of the n-paraffinic and isoparaffinic compounds were determined. For the cycloparaffins, the method of ASTM D2786 was applied and the concentrations of naphthenes were approximately estimated according to the number of rings in these compounds. 1. Introduction The most important processing unit in an integrated refinery is the fluid catalytic cracking (FCC) wherein petroleum gas-oil is catalytically cracked toward valuable light products (LPG, gasoline and light cycle oil). The chemical composition of the FCC feedstocks is one of the key variables to predict the industrial performance of a FCCU concerning product yields and qualities. A complete hydrocarbon-type analysis of the paraffins (normal, branched, and cyclo) and the aromatics from an FCC feedstock can provide sufficient data to permit the engineer to find correlations between the feed composition and product distributions. In addition, the feed characterization can assist in the development of reliable kinetic and fluid dynamic models in order to optimize the FCC reactors (Liguras and Allen, 1989; Avidan and Shinar, 1990; Weekman, 1979; Froment and Bischoff, 1979). The isolation, identification, and characterization of the constituents in heavy oil fractions is a very complicated task (Dooley et al., 1974). For this reason, the standard analysis usually performed in refinery laboratories is not sufficient to give a good quantitative and qualitative prediction of chemical composition of a given feedstock. In order to analyze thoroughly the components of the FCC feedstock, a separation procedure has to be applied. For the separation of the aromatics and nonaromatics, the elution chromatography procedure (using many absorbents) was used from the literature (Lipkin et al., 1948; Hirsh et al., 1972; Dooley et al., 1974; Struppe et al., 1987; Standard Test Method D-2549-85, 1985). The techniques of applying these absorbents to petroleum samples usually consist of separating the oil into a saturate portion and an aromatic portion by adsorption on silica or on alumina (or on both of them). The further separation of the aromatic portion is followed by adsorption on alumina. Both steps utilize elution chromatography with solvents of different polarity. An integrated method for this * Author to whom inquires about the paper should be addressed. S0888-5885(96)00586-6 CCC: $14.00
separation was developed in CPERI and was described by Lappas et al. (1997). In contrast to the separation of aromatics and nonaromatics, the further separation of the nonaromatics is more complicated. The available literature is limited, and this separation was applied only in some standard mixtures or in some light petroleum fraction (Altgelt and Gouw, 1979; Marsh and Smith, 1984; Nwadinique and Nwobobo, 1994). The two common approaches for isolating n-paraffins from other hydrocarbons are urea adduction (Ijam and Al-Zaid, 1977; Marquart et al., 1968; Nwadinique and Sunday, 1990) and adsorption in molecular sieves (Fitzerald et al., 1970; Mortimer and Luke, 1967; Washall et al., 1970). Urea crystallizes from solutions in a matrix where the n-paraffins, but not the branched or cyclic compounds, are included within urea’s cylindrical pores. For this process, various reaction temperatures have been used in the literature. Thus, some investigators use room temperature (Ijam and Al-Zaid, 1977; Nwadinique and Nwobobo, 1994) but others use higher temperatures (55-60 °C) in order to adduct heavier paraffins (Altgelt and Gouw, 1979). For the recovery of the lighter paraffins (C11-C13), lower temperatures must be used (Marquart et al., 1968). Subsequent recovery of the n-paraffins is by decomposition of the urea clathrate by heat or by simply adding water. In this way, the urea reverts to its original form. For effecting complex formation, the presence of a polar compound (activator) such as water, aliphatic alcohol, or ketone expedites the complex formation (Weedman and Haddleston, 1955; Hess, 1954). Thiourea has been shown to form similar adducts with branched paraffins (Ijam and Al-Zaid, 1977) under a similar procedure. Molecular sieves (synthetic zeolites) can also be used for paraffin separation. Molecules with diameters small enough to invade into the zeolite channels are absorbed, but large molecules are excluded. In this way, 5A molecular sieves selectively adsorb n-paraffins from hydrocarbons. For the recovery of the n-paraffins, the 5A molecular sieves are decomposed mainly with hydrofluoric acid or allowed to stand with n-pentane for a number of days to enable n-paraffins to desorb into the solvent (Nwadinique and Nwabobo, 1994). © 1997 American Chemical Society
Ind. Eng. Chem. Res., Vol. 36, No. 8, 1997 3111 Table 1. Recovery of Total Paraffins feedstock
LGO, wt %
HGO, wt %
paraffins aromatics recovery
48 52 100
69 30 99
Table 2. Recovery of the Paraffinic Fractions n-paraffins branched paraffins naphthenes total recovery
Figure 1. Schematic view of the total paraffin separation procedure.
The aim of this research is to apply an integrated method for the complete separation of saturate fraction of FCC feed in order to characterize the feed quantitatively and quantitatively. The identification of the paraffinic compounds was carried out using a mass spectrometer. GC/MS is the most widely accepted technique for this characterization (Lumpkin, 1956; Melpolder et al., 1956; Altgelt and Gouw, 1979; Allgood et al., 1990). However, for the quantitative analysis, some methods from the literature were used (Wang and Fingas, 1994; Allgood et al., 1990; Standard Test Method D-2786-86, 1986). This analysis will be described later in this study, and although the relative concentration of all compounds is presented, it gives an understanding of the distribution of all compounds in FCC feedstocks. 2. Separation and Characterization of FCC Feedstock 2.1. Feed Preparation and Characterization. A FCC feedstock (gas-oil) from a Greek refinery (Hellenic Aspropyrgos Refinery, HAR) was used in this study. The characterization of feedstock was determined using standard ASTM procedures. The feed had the following physical properties: boiling range 216-560 °C, sulfur content 0.3 wt %, density and refractive index d20 ) 0.9033 and n70 ) 1.4802, respectively. In order to achieve a better characterization, the gas-oil was firstly separated in two fractions: a light gas-oil (LGO, with boiling range the IBP-343 °C) and a heavy-gas oil (HGO, 343 °C-EP of GO). This separation was carried out in our laboratory using the ASTM D-2892 distillation method. 2.2. Gas-Oil Separation Procedures. A methodology was developed in order to separate the original LGO and HGO into aromatic and non-aromatic fractions. The entire methodology is based on a modified version of ASTM D-2549, and it was described by Lappas et al. (1997). In this study, a further separation of nonaromatics in paraffins and naphthenes has taken place. Separation of n-Paraffins by Urea Adduct Formation. The entire separation procedure for the nonaromatic fraction is described in Figure 1. The typical removal procedure of the strain-chain hydrocarbons (nparaffins) from heavy or light gas-oil is (i) 15 g of urea and 5 g of HGO (or LGO) aliphatic hydrocarbons (isolated by elution chromatography-ASTM D-2549) are
LGO, wt %
HGO, wt %
22 9 43 74
24 5 40 69
placed in a 250-mL flask and stirred for 0.5 h at 55-60 °C by adding 25 mL of methanol and (ii) the mixture is stirred for 1.5 h in room temperature and for 0.5 h at 10 °C. The solid adduct is washed with hexane (60 mL) and filtered off. The filtrate is kept for further treatment with thiourea. The precipitate is decomposed in hot distilled water (150 mL). Subsequently, the organic layer is extracted with hexane (4 × 35 mL), dried with granular calcium chloride, and evaporated in order to give the n-paraffins (Figure 1). Separation of Branched Paraffins by Thiourea Adduct Formation. The hexane is removed from the filtrate (which was produced from the procedure with urea) by evaporation, and the remainder is stirred with thiourea (15 g), activated with methanol (25 mL), for 2 h at room temperature (Figure 1). The obtained adduct is filtered and washed with hexane (60 mL), and subsequently, the precipitate is decomposed in hot distilled water (150 mL). The organic layer is removed by extraction with hexane (4 × 35 mL), dried with calcium chloride, and evaporated, giving the branched paraffins. The filtrate which contains cycloparaffins is also evaporated. Separation of n-Paraffins with 5A Molecular Sieves. The second method for the separation of n-paraffins using 5A molecular sieves was applied as follows: 1 g of the saturate fraction with 25 g of 5A molecular sieves (activated at 800 °F for 5 h) were mixed with 150 mL of isooctane. The mixture was refluxed for 16 h, and after this time, it was filtrated. The filtrate, which contained the non-n-paraffins, was evaporated and weighed. The molecular sieves were broken down by pouring hydrofluoric acid at a slow rate. A soap slurry was formed, and the n-paraffins were resolved with three extractions with 50 mL of ether. After that, the n-paraffins were evaporated and weighed. 2.3. Separation Results and Discussion. The recovery of the total saturates with the ASTM D-2549 method was 99 and 100% for HGO and LGO, respectively. The results are presented in Table 1. Further separation of paraffins, concerning all steps, has a recovery of 74 wt % for the LGO and 69 wt % for the HGO (Table 2). The recovery does not seem to be very high, but the complexity of the feed must be taken into account. For this reason, the most simple feed (LGO) presents a higher recovery than the more complex (HGO). As it is clear from Figure 1, the separation procedure involves many steps of filtration, evaporation, etc., and thus, this loss of recovery is owed to small losses of paraffins in all these steps. As was mentioned in the Introduction, higher recoveries have been mentioned in the literature only for artificial feeds or light petroleum fractions. Comparing the procedures for the separation of LGO and HGO paraffins, it can be concluded that exactly the same procedure can be applied for both fractions. Moreover, it must be men-
3112 Ind. Eng. Chem. Res., Vol. 36, No. 8, 1997 Table 3. GC/MS Operating Conditions conditions
LGO
HGO
electron energy, eV source temp, °C emission, V scan rate He flow rate, mL/min split ratio injector temp, °C transfer line temp, °C oven program initial temp, °C rate
70 200 300 1 scan/min from 40-400 amu 0.7 100:1 250 280
70 220 300 1 scan/min from 50-550 amu 0.7 100:1 250 300
70 2 °C/min up to 200 °C 8 °C/min up to 300 °C 300 °C for 5 min
100 5 °C/min up to 180 °C 180 °C for 1 min 2 °C/min up to 310 °C 310 °C for 10 min
tioned here that this method was applied in our laboratory with the same success for paraffin separation of a vacuum gas-oil with resid. The key factor which affects the entire procedure is the effective contact between urea (or thiourea) and the paraffinic substances. This contact is influenced by the amount of excess urea and methanol. The following excesses are necessary for satisfactory separation: 25 mL of methanol and 15 g of urea for n-paraffin separation and 25 mL of methanol and 15 g of thiourea for naphthene separation. The stirring of mixtures at some specific temperatures is also very important. The initial heating must be at 55 °C for a period of 30 min. This serves to increase the rate of adduction of the heavier n-paraffins (through increased solubility and diffusion) to the methanol-urea phase. By decreasing the final adduction temperature to 10 °C, the recovery of compounds such as C15 and above is improved. Comparing the two methods for the removal of nparaffins (by urea and molecular sieves) for both gasoils, it was concluded that the urea method has more advantages than that of molecular sieves. In the molecular sieves method, the required time is longer, while the procedure for the destruction of the molecular sieves using a high amount of hydrofluoric acid can crack the n-paraffins. Moreover, the sequential reflux requires a high excess of solvents, and this results in a lower n-paraffins recovery (especially for HGO) in relation to the urea method. This conclusion is in accordance with the literature where some authors tested the two methods for crude oil separation and they found similar advantages for the urea method (Nwadiniqwe and Nwobobo, 1994). According to this comparison, the paraffinic fraction obtained by the molecular sieves method has not been used for further separation, and thus, the characterization of the n-paraffins obtained by this method is not included in the paragraph which follows. 3. Characterization of FCC Feedstock 3.1. Identification of Saturate Fractions Using GC/MS. Efforts were made for the analysis of all the resulting fractions with GC/MS. All the fractions obtained from the ASTM D-2549 elution chromatography method and the urea-thiourea method were analyzed. The analysis was performed in a HP 5989 MS engine with a HP 5890 Series II gas chromatograph. The capillary column was an 50-m HP Ultra-1 with inside diameter of 0.20 mm. The GC/MS operating conditions are presented in Table 3. For the analysis 1-µL solution of each sample in n-hexane (at known concentrations) was injected into the GC in a split mode
Table 4. Estimation of Relative Sensitivities (RS) C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23
RS(C14)
RS(C24)
2.203803 1.776177 1.385065 1.442398 0.98486 1.487204 1.243602 1 0.779091 0.991189 0.788161 0.547421 0.50082 0.454219 0.43 0.41 0.39
5.826844 4.689162 3.660354 3.807028 2.601325 3.929834 3.287909 2.645985 2.062511 2.618466 2.084925 1.444757 1.321671 1.198586 1.18 1.12 1.06
C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40
RS(C14)
RS(C24)
0.378704 0.384 0.389 0.392 0.398229 0.41 0.44 0.48 0.512637 0.57 0.63 0.69 0.711868 0.773 0.74 0.75 0.76
1 1.01 1.03 1.04 1.047865 1.1 1.16 1.24 1.34857 1.48 1.62 1.75 1.870935 1.86 1.88 1.9 1.92
1:100. The qualitative analysis of the various fractions was obtained using the component library of the instrument. A quantitative analysis of the samples is very difficult to perform in the GC/MS. The present mixtures are very complicated, and standards of each one of the components are needed. For this reason, the absolute values of the concentrations for the recovered paraffins cannot be given. However, a quantitative analysis of each sample in a wt % relative basis can be carried out. This analysis is based on the following assumption (Wang and Fingas, 1994; Allgood et al., 1990): if there is no significant mass discrimination (as in the present study), the total sample ion abundance measured at the detector is proportional to the amount of total sample ionization in the source of MS. The total ion abundance was recorded, and the relative sensitivities were obtained by integrating the total ion abundance across the chromatographic peak for each compound. All integrated values are reported relatively to n-C24 for the HGO fractions and n-C14 for the LGO fractions. For the quantitative calculations, a calibration standard was used. This standard (provided by Hewlett-Packard) contains the majority of the n-paraffins from C6 to C40 at known concentrations. The relative sensitivities of the standard analysis are quoted in Table 4. From the values of Table 4 and the integration of the chromatographic peaks of the compounds in the n-paraffinic fraction of HGO and LGO, the relative wt % concentrations of the n-paraffins in these fractions were estimated, and they are presented in Tables 5 and 6. The term “relative concentration” is used since there are no calibration standards for all the n-paraffins present in the two fractions. Since standard mixtures for branched paraffins were not available, it was assumed that the
Ind. Eng. Chem. Res., Vol. 36, No. 8, 1997 3113 Table 5. Relative Quantitative Analysis of HGO n-paraffins
isoparaffins
comp
area %
%RWT
comp
area %
%RWT
C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 total
0.02 0.02 0.05 0.07 0.06 0.10 0.26 0.62 3.58 3.59 14.34 14.65 13.68 10.44 7.71 4.30 2.34 1.20 0.68 0.40 0.25 0.16 0.11 0.09 0.06 0.02 0.03 0.02 0.02 79
0.09 0.07 0.15 0.17 0.18 0.25 0.44 0.96 5.05 4.99 18.90 18.28 16.11 12.41 9.35 5.26 2.89 1.55 0.93 0.59 0.39 0.28 0.20 0.18 0.14 0.04 0.07 0.05 0.04 100
C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 total
0.01 0.22 0.39 0.35 0.30 0.47 1.00 4.06 5.02 8.33 8.94 10.76 10.54 8.86 5.73 5.16 3.90 3.76 2.70 2.00 1.97 1.17 1.00 1.12 0.83 0.63 0.53 0.20 0.03 90
0.05 0.69 0.99 0.68 0.76 0.94 1.38 5.10 5.72 9.35 9.53 10.85 10.02 8.51 5.61 5.10 3.89 3.94 2.98 2.35 2.52 1.65 1.55 1.87 1.48 1.11 0.94 0.37 0.05 100
Table 6. Relative Quantitative Analysis of LGO n-paraffins
isoparaffins
comp
area %
%RWT
comp
area %
%RWT
C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22
0.08 0.18 0.67 1.90 2.95 4.23 6.14 9.39 11.24 12.79 10.05 2.36
0.23 0.73 2.31 5.23 6.33 11.56 13.34 14.17 15.52 16.01 11.91 2.67
total
62
C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 total
0.14 0.47 1.26 1.76 1.67 3.62 5.73 6.63 8.95 11.08 18.34 13.41 8.58 81.5
0.52 1.50 3.23 3.52 4.23 7.31 8.04 8.51 10.43 12.21 19.28 13.41 8.33 100
100
relative sensitivities of Table 4 are valid for the isoparaffins as well. With this assumption and following the same procedure as above, the relative concentrations of the iso compounds are presented in Tables 5 and 6. Cycloparaffin quantitative analysis was studied based on the ASTM D-2786 method (Standard Test Method D-2786-86, 1986). This method was applied since no appropriate standards of cycloparaffins were available as well. According to the method, the repeller settings of the instrument were adjusted to optimum based on a m/e 226 ion of n-hexadecane and the ∑69/71 ratio for n-hexadecane was 0.19. 3.2. Identification Results and Discussion. The rules (Ijam et al., 1981) upon which the identification of paraffins was based in this study are (i) the relative intensities of the parent peaks are the highest for straight-chain hydrocarbons and they decrease as the degree of branching increases, (ii) the relative intensities of the parent peaks decrease with increasing molecular weight in a homologous series, and (iii) the presence of a large peak at mass is usually accompanied by a homologous series of peaks (at masses 57, 71, 85, etc.),
Figure 2. GC/MS analysis of total paraffinic fraction from HGO (a) and LGO (b).
suggesting ions of the type CnH2n+1+. In general, the molecular ion peaks of the n-paraffins are stronger than those of branched-chain hydrocarbons. Based on the above rules, the GC/MS operating conditions, and the assumptions made for the quantitative results, all the saturate fractions have been analyzed and characterized. The chromatogram of the HGO total paraffins is presented in Figure 2a. It shows the characteristic large peaks for the n-paraffins and a great deal of other peaks related to iso- and cycloparaffins, which cause the baseline to rise. The n-paraffins seem to begin from C18 up to C34. There are traces of C35-C38 as well. The chromatogram of the LGO total paraffinic fraction (Figure 2b) shows the characteristic peaks of C12-C21 (and some traces of C11 and C22) n-paraffins. Testing these two samples for the presence of aromatic compounds, it can be concluded that there are no aromatics penetrated in both of the saturate fractions. The characteristic ions of 105, 115, 131, 167, 168, 178, and 198 for alkyl-aromatic rings are absent from the total scan. This means that the ASTM D-2549 method was applied satisfactorily. Figure 2 reveals that the further separation of nonaromatics is necessary in order to characterize thoroughly the two paraffinic fractions. From this figure, only some information from the n-paraffins can be concluded, while as will be shown later no quantitative calculations can be performed. Figure 3a presents the chromatogram of HGO nparaffins. The characteristic large peaks for the nparaffins are now more clear. In relation to the total paraffinic fraction (Figure 2a), the baseline of this chromatogram seems to be constant, and this means that the majority of the compounds in this fraction are n-paraffins. The identification shows n-paraffins from C18 to C34. However, some tracers of compounds from C12 to C17 can be detected. These compounds are coming from the overlap of the distillation procedure. Tracers of C35-C40 can also be detected, but there are no n-paraffins with more than 40 carbons atoms. These results are more clear from the quantitative analysis of the sample. Table 5 reveals the relative wt %
3114 Ind. Eng. Chem. Res., Vol. 36, No. 8, 1997
Figure 3. GC/MS analysis of HGO n-paraffins (a), isoparaffins (b), and cycloparaffins (c).
concentration of all the n-paraffins, and it seems that the bulk of the n-paraffins are in the C20-C29 range. Table 5 also shows that about 20% of this fraction contains other paraffins which are mainly isoparaffins. The analysis of LGO n-paraffins (Figure 4a) shows the characteristic large peaks for the n-paraffins from C11 to C22. The quantitative analysis is presented in Table 6. LGO n-paraffins are mainly in the range C13-C22. In this fraction, about 38% of other paraffins have been penetrated (Table 6). The analysis of HGO isoparaffins (Figure 3b) shows some peaks for the isoparaffins but the characteristic large peaks of the n-paraffins are also present. The wt % relative concentrations of this fraction show that the bulk of isoparaffins are in the range C18-C37 (Table 5). Branched paraffins up to C40 are also included. Table 5 presents that this fraction contains 90% isoparaffins and only 10% of n-paraffins are included. In the LGO isoparaffinic fraction (Figure 4b), the bulk of the n-paraffins seem to disappear and there are only small amounts of normal C17-C21. However, as the quantitative analysis shows (Table 6), 18.5 wt % of other paraffins are present. Table 6 also declares that isoparaffins up to C24 are present. The bulk of this fraction contains branched paraffins from 13 to 24 carbon atoms. Generally, the isoparaffinic fractions seem to be better separated than the n-paraffinic for both gas-oils (Tables 5 and 6). The cycloparaffins give chromatograms (Figures 3c and 4c) with a bad resolution of peaks. The chromatogram (Figure 3c) of HGO cycloparaffins shows a large curve with small separated peaks related to the large number of cycloparaffins. Only small amounts of n-
Figure 4. GC/MS analysis of LGO n-paraffins (a), isoparaffins (b), and cycloparaffins (c).
paraffins are included in this fraction. For LGO cycloparaffins, the chromatogram (Figure 4c) shows cycloparaffins (Figure 4c) which are not well isolated from each other. For both chromatograms, even a qualitative analysis is very difficult, and for this reason, the ASTM D-2854 method (as was mentioned in section 3.1) was applied. The method estimates only the wt % of naphthenic compounds with one, two, three, four, and five rings. The results of this method for these compounds respectively are (i) for HGO 22.83, 18.14, 13.50, 13.89, and 14.85 and (ii) for LGO 28.43, 21.46, 15.34, 14.34, and 2.05. Moreover, the method predicts the presence of 11.99 wt % noncyclic paraffins and 4.8 wt % monoaromatics in HGO naphthenes (for LGO naphthenes, the values are 13.31 and 5.06, respectively). From these results, it is concluded that naphthenes up to five rings are present in the HGO, while the bulk of LGO naphthenes contain compounds with one to four rings. The method shows a very small amount of monoaromatics present in these fractions. As was discussed before, these amounts are not detectable in the other paraffinic fractions. It must be pointed out that the ASTM D-2786 method which was applied for the quantitative analysis of cycloparaffins depends highly on many parameters, the type of instrument and tune and ion source parameters, while some other variables of the method should be checked with pure standard naphthenic compounds. So these results give only a preliminary study of the quantitative analysis of the naphthenes, and a more detailed study is necessary.
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4. Conclusions A method was developed for the separation of the nonaromatic fraction of an FCC gas-oil into normal and branched paraffinic and naphthenic fractions. The method was based on the urea adduct formation for the separation of n-paraffins. The use of 5A molecular sieves for this separation has more disadvantages in relation to the urea. The urea method is faster and more convenient. The further separation of the branched paraffins was performed with the method of thiourea. The entire method gives separation recovery of 70%. The important parameters for a correct separation were found to be the contact time between urea and nparaffins, the excess of urea, and the appropriate temperature control. The most important result from the above separation was the ability to characterize all paraffinic fractions quantitatively and qualitatively. For the identification, a GC/MS method was applied under specific column conditions. From the characterization, it was concluded that the HGO contains mainly n-paraffins from C20 to C29. C40 is the heavier detectable n-paraffin in the HGO. HGO also contains isoparaffins from 18 to 37 carbon numbers. LGO contains n-paraffins from C13 up to C22 and isoparaffins from C13 up to C24. A complete relative quantitative analysis of all the components in these fractions is presented in this study. The naphthenic mixture is very complicated for a detailed characterization. Applying method ASTM D-2786, some preliminary results were concluded which concern the wt % concentration of the naphthenes according to their ring numbers. Literature Cited Allgood, C.; Orlando, R.; Munson, B. Correlations of Relative Sensitivities in Gas Chromatography Electron Ionization Mass Spectrometry with Molecular Parameters. J. Am. Soc. Mass Spectrom. 1990, 1, 397. Altgelt K. H.; Gouw T. H. Chromatography in Petroleum Analysis; Marcel Decker: New York, 1979. Avidan, A. A.; Shinar, R. Development of Catalytic Cracking Technology. A Lesson in Chemical Reactor Design. Ind. Eng. Chem. Res. 1990, 29, 9. Dooley, J. E.; Thompson, C. J.; Hirsh, D. E.; Ward, C. C. Analyzing Heavy Ends of Crude. Hydrocarbon Proc. 1974, April, 93. Fitzerald, M. E.; Moirano, J. L.; Morgan, H.; Cirillo, V. A. Characterization of Gas Oil Stocks: An Integrated Analysis. Appl. Spectrosc. 1970, 24, 1. Froment, G. F.; Bischoff, K. B. Chemical Reactor Analysis and Design; Willey: New York, 1979. Hess, H. Process for Effecting Complex Formation with Urea and Thiourea. U.S. Patent 2, 686, 755, 1954. Hirsh, D. E.; Hopkins, R. L.; Coleman, H. J. Separation of High Boiling Petroleum Distillates Using Gradient Elution Through Dual Packed Silica-Gel Alumina Adsorption Column. Anal. Chem. 1972, 44, 915. Ijam, M. J.; Al-Zaid, K. A. H. Isolation and Identification of Paraffinic Hydrocarbons from Light Kerosene Obtained from Kuwait Oil. Ind. Eng. Chem. Prod. Res. Dev. 1977, 16, 1.
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Received for review September 27, 1996 Revised manuscript received March 6, 1997 Accepted March 9, 1997X IE960586R
Abstract published in Advance ACS Abstracts, June 15, 1997. X
