evaluation of feasible ways for refinery naphtha streams processing_stratiev

EVALUATION OF FEASIBLE WAYS FOR REFINERY NAPHTHA STREAMS PROCESSING

Dicho Stratiev1, Todor Tzingov, Ivelina Shishkova, Antoaneta Pavlova,

Pavlina Ivanova

1 Lukoil Neftochim Bourgas- R&D Department, 8104 Bourgas, Bulgaria, e-mail: [email protected]

KEY WORDS: naphtha ,catalytic reformer, isomerization

ABSTRACT

Naphtha streams from crude distillation of Ural crude, middle distillate hydrotreaters, vacuum gas oil hydrotreater and visbreaker have been characterized with the aim to evaluate the most appropriate way for their processing in the refinery. It was found that their octane ratings (RON) varied between 42 and 72. Their sulphur content varied between 370 and 3300 ppm. The middle distillate hydrotreater naphthas contained the highest level of sulphur and the relative part of H2S from their total sulphur varied in the range 33 – 100%. The content of aromatics in the investigated naphtha streams varied between 4.5 and 17.6 vol. %. It was found that the mixed heavy wild naphtha fraction had higher characteristic index 2А+N = 68.2 than the straight run heavy naphtha (fraction 100 – 1800C) 2А+N =54.9. This is an indicator that the naphtha streams from the middle distillate hydrotreaters and the vacuum gas oil hydrotreater are more suitable as a feedstock for catalytic reforming than the straight run heavy naphtha from Ural crude. However, the mixed light wild naphtha fraction contained less C5 and C6 hydrocarbons (17.2%) than the straight run light naphtha, fraction 40 – 1000C, (47.7%). Therefore, the straight run light naphtha from Ural crude is more suitable as a feedstock for C5C6 isomerization. The addition of visbreaker naphtha to the mixed heavy wild naphtha fraction has led to a reduction of the characteristic index 2А+N from 68.2 to 64.1 and an increase of olefins content from 0.5 to 7.7 wt.%. The analysis of metal content in the investigated naphtha streams showed a higher content of lead (27 ppb) in the secondary naphtha streams than the straight run naphtha streams (< 1 ppb). The higher content of lead in the secondary naphtha streams could prohibit their use as a feedstock for catalytic reformer because the typical limit of lead content for catalytic reformer feed is 5 ppb.

INTRODUCTION

Low octane naphtha fractions are produced except by crude oil straight run distillation also by secondary processes as middle distillate fractions and heavy vacuum gas oils hydrotreatment and heavy residues conversion processes like Visbreaker unit. It is well known that two processes of low octane number naphtha upgrading exist. These are low octane number naphtha (C5C6) isomerization and heavy low octane number naphtha (fraction C7- C11) catalytic reforming. It is not desirable low octane naphtha fractions with initial boiling point below 80.6 oC according TBP to be subject to catalytic reforming by reason of standard motor naphtha benzene content limitation not more than 1.0 % v/v. That is why, low octane naphtha fractions of typical boiling range of 30 – 180 oC have to be fractionated to light naphtha fraction of the range 30 – 81 oC and heavy naphtha fraction of the range 81 – 180 oC as

44th International Petroleum Conference, Bratislava, Slovak Republic, September 21-22, 2009 1

the light naphtha has to be turn to isomerization and the heavy one to catalytic reforming. The present work furnishes one study on the properties of primary and secondary low octane naphtha streams at LNB refinery and evaluation of the optional trends for their further processing. RESULTS

Physical and chemical properties of straight run naphtha fractions (light and heavy low octane naphtha) produced by Ural crude oil atmospheric distillation are presented at Table I. Physical-chemical properties of secondary low octane naphtha fractions produced at middle distillate fractions and heavy vacuum gas oil hydrotreatment units and vacuum residue Visbreaker unit are presented in Table II. Physical-chemical properties of feeds and stable hydrogenates produced of them at LNB middle distillate hydrotreatment units are presented in Table III. The PIONA analyses of primary and secondary naphtha produced at LNB refinery are presented in Table IV. In Table V are shown compositions of mixed naphtha samples which PIONA analyses are shown in Table IV. In Table VI are included physical-chemical properties of Visbreaker unit naphtha with different end boiling points. The Visbreaker unit naphtha with different end boiling points PIONA analysis is presented in Table VII. In Table VIII is shown PIONA analysis of LNB hydrotreatment units mixed wild naphtha, Visbreaker unit naphtha, 50 % mixed wild naphtha / 50 % Visbreaker unit naphtha before and after hydrotreatment. Hydrocarbon composition is shown in Table IX and sulfur compounds composition of C5 fraction produced at LNB Gas Fractionation Unit are indicated in Table X. RESULTS DISCUSSION

Data in Tables I and IV shows that light straight run low octane naphtha (LON) is fraction boiling in the range of 37 – 91oC and consists mainly of C5- C8 hydrocarbons and contains minimum quantities of C4 and C9 hydrocarbons. Heavy straight run LON is fraction boiling in the range of 103 – 179 oC and consists mainly of C7 – C11 hydrocarbons and contains minimum quantities of C6 hydrocarbons. It may be noted from this data that Ural petroleum straight run LON produced at crude oil atmospheric distillation units is not adequately accurate fractionated and the effectiveness of benzene precursors (mainly C6 naphthenes) separation from heavy LON is not sufficiently high and may be this is due to the fact that the fractionator separating naphtha to light and heavy fractions has not been design to achieve high separation accuracy. Thus, this data allows also to make a conclusion that distillation characteristics of both naphtha fractions could not be used as reference whether heavy LON contains or not any benzene precursors (C6 hydrocarbons), which shall be converted to benzene at Catalytic Reforming Unit.

Table II data shows that secondary LON are unstable and contain C2 – C4 hydrocarbons and considerable quantity hydrogen sulfide. The total sulfur content of the different secondary LON varies between 370 and 8800 ppm and hydrogen sulfide percentage is between 19 and 100 %. 92 % of total sulfur content is hydrogen sulfide in wild naphtha sample obtained as result of hydrotreatment units wild naphtha mixing in ratio indicated in Table V and it is removed by sample stripping with nitrogen (Table IV). Arenes content according to FIA method in hydrotreatment units wild naphtha varies between


4.5 and 17.6 % v/v as the HT-4 wild naphtha has the highest arenes content because in it FCC light catalytic gas oil is processed. That is why HT-4 feed has the highest arenes content (Table III) as compared to all other LNB middle distillate fraction hydrotreatment units. It is obvious from the presented data that arenes content in the wild naphtha of the different middle distillate fraction hydrotreatment units (HT-1 ÷ HT-4) not always correlates to arenes content in these units feed. Thus, for example feeds for HT-2 and HT-3 units contain between 27.5 and 30 % arenes but arenes content of these units wild naphtha is about 4.5 % while HT-1 unit feed arenes content is 21 % but this unit wild naphtha contains 5.7 % v/v arenes. Similarly, feed for heavy vacuum gas oil (HVGO) hydrotreatment contains about 40 % arenes but this unit wild naphtha contains 8.3 % v/v arenes which are less than HT-4 wild naphtha arenes content which feed contains 38.4 % arenes. Table I Physical-chemical properties of light and heavy low octane naphtha (LON) produced at Ural crude oil atmospheric distillation unit

Properties

Light LON

Heavy LON

Density, d420 0.6733 0.753

Total sulfur content, % 0.0910 0.0748

Distillation, ASTM D-86 IBP., 0С 37 103 5 % 47 112 10 % 49 115 20 % 54 118 30 % 58 123 40 % 61 127 50 % 65 132 60 % 68 137 70 % 71 143 80 % 78 150 90 % 81 159 EBP, 0С 91 179


Table II Physical - chemical properties of secondary low octane naphtha produced at LNB.

Properties HT-1 HT-2 HT-3 HT-3* HT-4

FCC Hydrotreater (FCC HT)

Thermal Cracking (TC)

Catalytic Reforming (CR1)

Density at 15 oC, g/cm

3 0.7350 0.7195 0.7142 0.6961 0.7740 0.7418 0.7201 0.6700

Sulfur ррm % of total S ррm

% of total S ррm

% of total S ррm

% of total S ррm

% of total S ррm

% of total S ррm

% of total S

Total 930 3300 2100 370 0 2500 8800 1300

Mercaptans 3200 37

Hydrogen sulfide 460 49.46 1100 33.33 1500 71.43 370 100 2500 100 1700 19 270 20.8

Others 470 50.54 2200 66.67 600 28.57 3900 44 1030 79.2

Group hydrocarbon composition (ASTM D-1319 – FIA method), % v/v

Saturates 92.87 94.25 94.55 97.00 81.36 91.68 53.37

Olefins 1.40 1.00 0.92 0.90 1.04 37.94

Arenes (Aromatics) 5.73 4.75 4.53 2.10 17.60 8.32 8.69

Distillation, oC

IBP 39 33 32.5 32.5 72 48 32 29

5% v/v 96 64 59 55.0 98 78 52 47

10% v/v 103 72 67 62.0 115 86 60 53

20% v/v 108 82 78 71.0 128 93 74 59

30% v/v 110 89 85 77.5 139 97 83 63

40% v/v 112 94 90 82.0 150 102 92 65

50% v/v 114 99 95 85.0 159 106 100 67

60% v/v 117 103 99 88.0 169 110 107 69

70% v/v 120 107.5 103 91.5 176 114 114 71

80% v/v 123 113 108.5 94.0 185 120 123 75

90% v/v 130 121 117.5 97.5 197 127 162 84

EBP/Recovery, % v/v 143 139/96 123/95 109.5/97.5 219 141/97 293/95 104

*Diesel fraction and Visbreaker unit naphtha fraction have been processed at HT-3.


Table III Characteristics of the diesel fraction hydrotreatment unit feeds and stable hydrogenates at LNB

HT-1

HT-2

HT-3

HT-4

Properties Feed Hydrogenate Feed Hydrogenate Feed Hydrogenate Feed Hydrogenate

Density at 15 0С, ISO

3675

0.801

0.796

0.840

0.833

0.858

0.847

0.840

0.836

Distillation, 0C, ASTM D

86

IBP 176 180 191 202 194 210 179 182 5% 197 196 215 213 250 247 198 200 10% 199 200 225 225 270 262 210 209 50% 210 208 260 257 308 301 243 240 90% 231 230 315 314 348 344 272 269 95% 235 233 335 333 358 352 281 278 EBP 247 246 353 349 369 366 296 294

Sulfur, % mass, ASTM D 2622

0.25

0.0015

0.8

0.0031

1.1

0.0048

0.47

0.001

Nitrogen content, wt ppm, ASTM D 4629

2

228

135

Bromine number, g Br2/100 g, ASTM D 1159

1.1

7-9

3

5

Arenes, % mass, EN 12916 including Mononuclei Polynuclei

21.0

15.0 6.0

27.5

18.2 9.3

27.5

21.9 5.6

30.0

19.5 10.5

30.0

23.7 6.3

38.4

23.2 15.2

38.4

29.8 8.6

Cetane index ASTM D-4737

50.1

51.9

50.2

52.5

55.5

58.4

43.8

44.6


Table IV PIONA analysis of primary and secondary naphtha produced at LNB Composition, wt%

Mixture 1 (Wild naphtha from HT -

1,2,3,4, CR1, FCC HT)

Mixture 2 (Wild naphtha from HT-1,2,3,4, CR1, FCC HT, TC),

LON, IBP-100 oC

LON 100-180 oC

n-Paraffins n-C2 0.04 0.04 n-C3 0.6 0.68 n-C4 1.65 1.8 0.27 n-C5 2.91 2.96 14.62 n-C6 5.82 5.28 11.93 0.41 n-C7 5.31 5.67 7.17 4.67 n-C8 4.67 4.87 1.35 7.74 n-C9 0.97 0.82 0.02 6.24 n-C10 0.6 0.46 2.78 n-C11 0.47 0.36 0.19 n-C12 0.15 0.12 n-C13 0.06 0.06 n-C14 0.02 0.05 n-C15 0.04 Total n-Paraffins 23.27 23.21 35.36 22.03

iso-Paraffins i-C4 0.55 0.49 0.01 i-C5 1.85 1.8 7.56 i-C6 6.61 6.02 13.63 0.08 i-C7 3.22 4.48 8.48 3.10 i-C8 6.28 5.36 6.72 7.76 i-C9 3.53 2.83 0.13 6.62 i-C10 0.66 0.56 6.62 i-C11 0.51 0.35 0.41 i-C12 0.08 0.14 i-C13 0.14 0.05 i-C14 0.07 Total iso-Paraffins 23.43 22.15 36.53 24.59

Olefins O4 0.61 O5 0.1 0.99 O6 1.92 O7 1.99 O8 0.15 1.23 O9 0.21 0.97 0.55 Total n-Olefins 0.46 7.71 0 0.55

Naphthenes N5 0.68 1.04 1.4 N6 8.46 6.8 10.53 1.15 N7 13.82 12 10.27 8.75 N8 12.13 13.18 3.41 13.59 N9 1.8 1.73 0.14 5.79 N10 0.49 0.35 1.85 N11 Total naphthenes 37.38 35.1 25.75 31.13


Composition, wt%

Mixture 1

Mixture 2

LON, IBP-100 oC

LON 100-180 oC

Aromatics А6 0.99 1.1 0.87 0.08 A7 3.64 3.11 0.85 1.58 A8 2.6 2.44 0.33 6.22 A9 0.97 0.76 3.99 A10 1.82 1.2 A11 0.52 0.6 А12 0.14 0.15 A13 0.04 Total aromatics 10.68 9.4 2.05 11.87

2A+N 58.74 53.9 29.85 54.87

Unknowns 4.78 2.43 Total 100 100 nP (C7+) 17.5 18.2 iP(C7+) 20.6 20.2 O(C7+) 0.5 6.1 N7+ 40.4 39.8 A7+ 13.9 12.1 2A+N 68.2 64.1

Pb, ppb 23 24 < 0.1 < 0.1 As, ppb < 1.3 49 45.8 Cu, ppm 0.3 0.4 Na, ppm 1.4 1.1 1.3 S, % 0.086 0.36 S, % (after nitrogen purge) 0.007 0.22 % H2 S vs total Sulfur 91.9 38.9 RON 53.7 54.2 63.2 42 MON 60.6

The different hydrotreatment units wild naphtha fractions has been

mixed in ratio that they are produced at the refinery (Table V) and Visbreaker unit naphtha has been added to them in ratio shown n Table V. The obtained mixtures analysis is shown in Table IV. Table IV data shows that wild naphtha fractions contain more naphthenes and almost equal arenes content as straight run НV/V. Characteristic index 2A + N determining the quality of a given naphtha fraction as Catalytic Reforming fraction feed for С7+ fraction of wild naphtha fractions and their mixture with Visbreaker unit naphtha is higher (68.2 and 64.1) than that of straight run heavy LON (54.9) and consequently wild naphtha fractions are higher quality feed for Catalytic Reforming unit than straight run heavy LON. Unlike straight run naphtha fractions wild naphtha fractions contain lead – 23 ppb but do not contain arsenic while straight run naphtha and wild naphtha fractions and Visbreaker unit naphtha (28.5 % Visbreaker unit naphtha) mixture contains between 45.8 and 49 ppb. It is well known that these metals are catalysts poison and it should be provide guard layer at Catalytic Reforming feed hydrotreatment unit when such type feeds are processed. In view of the fact that in wild naphtha fractions and Visbreaker unit naphtha mixture the Visbreaker unit naphtha percentage is 28.5 % (Table


V) and that wild naphtha fractions do not contain arsenic hence 100 % Visbreaker unit naphtha should contain 172 ppb arsenic. Table V Compositions of the investigated secondary low octane naphtha fraction mixtures, shown in Table IV

Mixture 1

Mixture 2

% %

HT-1 8.9 HT-1 6.4

HT-2 15.1 HT-2 10.8

HT-3 19.9 HT-3 14.2

HT-4 13.3 HT-4 9.5

CR1 13.3 CR1 9.5

FCC HT 29.5 FCC HT 21.1

100 TC 28.5

100

Table VI data shows that as the Visbreaker unit naphtha end boiling point increases its density and arenes content also increase and olefins content decreases. Table VI Physical-chemical properties of Visbreaker unit naphtha fraction with different end boiling point Properties Visbreaker unit

naphtha with EBP = 215 0С

Visbreaker unit naphtha with EBP = 1430С

Visbreaker unit naphtha with EBP = 125 0С

Density, d420 0.6933 0.6969

Distillation, ASTM D-86 IBP, С 40 36.0 35.0 5 % 52.5 55.5 10 % 60.0 61.0 20 % 74.0 69.0 30 % 83.0 75.0 40 % 90.0 80.0 50 % 98.0 85.0 60 % 104.0 89.0 70 % 111.0 93.0 80 % 119.0 99.0 90 % 129.0 106.0 EBP, С 215 143.0 125.0 Recovery 97 95.5

Group hydrocarbon composition (ASTM D-1319 – FIA method), v/v% Saturates 50.1 52.2 47.6 Olefins 36.9 44.7 49.1 Arenes (Aromatics) 13.0 3.2 3.3

Table VII data indicates that as the end boiling point decreases the

normal paraffins content increases, iso-parrafins content decreases, olefins


content increases, naphthene content does not materially change and that of arenes decrease.

Table VII PIONA analysis of Visbreaker unit naphtha with different end boiling points

Composition, wt% Visbreaker unit naphtha with EBP =215 0С



n-C2 0.02 0.03 0.06

n-C3 0.56 0.05 0.87

n-C4 1.42 0.61 2.19

n-C5 2.6 4.99 5.03

n-C6 3.08 9.61 7.54

n-C7 3.77 12.8 10.41

n-C8 3.36 0.12 0.65

n-C9 2.72 0.01

n-C10 2.4

n-C11 1.58

n-C12 0.13

Total n-Paraffins 21.64 28.21 26.76

i-C4 0.19 0.26 0.29

i-C5 1.02 1.74 1.83

i-C6 2.16 6.61 4.99

i-C7 2.1 7.83 5.94

i-C8 3.64 0.65 2.32

i-C9 3.46

i-C10 3.53

i-C11 1.35

i-C12 0.47

i-C13 0.03

Total iso-Paraffins 17.95 17.09 15.37

O4 1.25 0.2 1.9

O5 3.29 5.01 6.33

O6 5.5 14.76 12.92

O7 6.62 18.25 17.03

O8 6.51 0.91 3.72

O9 3.87

O10 1.61

O11 0.8

O12 0.85

Total n-Olefins 30.3 39.13 41.9

N5 0.3 0.66 0.64

N6 1.26 5.02 2.8

N7 1.58 5.12 4.06

N8 2.18 1.34 1.7

N9 2.58 0.03

N10 2.55

N11 0.44

Total naphthenes 10.89 12.14 9.23

А6

A7 0.6 1.19 1.48


A8 2.3 0.03

A9 2.6

A10 3.38

A11 0.28

А12

A13

Total aromatics 9.16 1.19 1.51

Unknowns 10.06 2.24 5.23

Total 100 100 100

It is presented (in Table VIII) PIONA analysis of mixture - mixed wild

naphtha of all LNB hydrotreatment units – 50 % and Visbreaker unit naphtha fraction – 50 % before and after hydrotreatment in order to compare wild naphtha- Visbreaker unit naphtha mixture quality as feed for Catalytic Reforming unit. These data shows that after hydrotreatment of mixture wild naphtha - Visbreaker unit naphtha C7+ fraction characteristic index 2A + N is 54.4 that is closed to that of the straight run heavy LON (54.9) and after fractionation of naphtha fraction to light and heavy ones the last may be successfully used as Catalytic Reforming feed. Here, it should be noted higher lead and arsenic content of the feed containing Visbreaker unit naphtha fraction. Table VIII PIONA analysis of mixed wild naphtha from LNB hydrotreatment units, Visbreaker unit naphtha, 50 % mixed wild naphtha / 50 % Visbreaker unit naphtha before and after hydrotreatment Composition, wt%

Mixture 1 VBN 50 HTN / 50

VBN

After Hydrotreatment 50 HTN / 50

VBN

n-C2 0.04 0.02 0.03 0.04 n-C3 0.6 0.56 0.58 0.73 n-C4 1.65 1.42 1.535 1.94 n-C5 2.91 2.6 2.755 3.48 n-C6 5.82 3.08 4.45 5.62 n-C7 5.31 3.77 4.54 5.73 n-C8 4.67 3.36 4.015 5.07 n-C9 0.97 2.72 1.845 2.33 n-C10 0.6 2.4 1.5 1.89 n-C11 0.47 1.58 1.025 1.29 n-C12 0.15 0.13 0.14 0.18 n-C13 0.06 0.03 0.04 n-C14 0.02 0.01 0.01 Total n-Paraffins 23.27 21.64 22.5 28.4

i-C4 0.55 0.19 0.37 0.48 i-C5 1.85 1.02 1.435 1.85 i-C6 6.61 2.16 4.385 5.67 i-C7 3.22 2.1 2.66 3.44 i-C8 6.28 3.64 4.96 6.41 i-C9 3.53 3.46 3.495 4.52 i-C10 0.66 3.53 2.095 2.71


i-C11 0.51 1.35 0.93 1.20 i-C12 0.08 0.47 0.275 0.36 i-C13 0.14 0.03 0.085 0.11 i-C14 Total iso-Paraffins 23.43 17.95 20.7 26.7

O4 1.25 0.625 O5 0.1 3.29 1.695 O6 5.5 2.75 O7 6.62 3.31 O8 0.15 6.51 3.33 O9 0.21 3.87 2.04 O10 1.61 0.805 O11 0.8 0.4 O12 0.85 0.425 Total n-Olefins 0.46 30.3 15.4 0

N5 0.68 0.3 0.49 0.56 N6 8.46 1.26 4.86 5.54 N7 13.82 1.58 7.7 8.78 N8 12.13 2.18 7.155 8.16 N9 1.8 2.58 2.19 2.50 N10 0.49 2.55 1.52 1.73 N11 0.44 0.22 0.25 Total naphthenes 37.38 10.89 24.1 27.5

А6 0.99 0.495 0.5 A7 3.64 0.6 2.12 2.1 A8 2.6 2.3 2.45 2.5 A9 0.97 2.6 1.785 1.8 A10 1.82 3.38 2.6 2.6 A11 0.52 0.28 0.4 0.4 А12 0.14 0.07 0.1 Total aromatics 10.68 9.16 9.9 9.9

2A+N 58.74 29.21 44.0 47.4

Unknowns 4.78 2.43 7.4 7.5 Total 100 100 100 100

nP (C7+) 17.5 18.0 16.7 22.5 iP(C7+) 20.6 18.8 18.4 25.5 O(C7+) 0.5 26.2 13.1 0.0 N7+ 40.4 11.5 23.6 28.8 A7+ 13.9 11.8 12.0 12.8 2A+N 68.2 35.2 47.6 54.4

Pb, ppb 23 24 As, ppb < 1.3 49 Cu, ppm 0.3 0.4 Na, ppm 1.4 1.1 S, % 0.086 0.36 S, % (after nitrogen purge) 0.007 0.22 % H2S vs total Sulfur 91.9 38.9 RON 53.7 72.6

Wild naphtha fractions octane number is 53.7 (RON) while that of Visbreaker unit naphtha is 72.6. Nevertheless of the higher Visbreaker unit naphtha octane number its addition in quantity of 28.5 % to hydrotreatment


units wild naphtha fraction results to negligible increase of mixture octane number (RON = 54.2). On the base of these data it may be calculated that the Visbreaker unit naphtha mixed octane number is 55.5. The following mixtures have been additionally prepared and their octane numbers has been determined:

The light straight run LON RON is equal to 64.9 when determined

Visbreaker unit naphtha mixed RON is 55.5. The mixed C5 RON is equal to 88.1 when IBP – 100 oC fraction RON is 64.9.

The C5 fraction, produced at LNB refinery GFU, hydrocarbon composition is included in Table IX.

Table IX Hydrocarbon composition of C5 fraction from Gas Fractionation Unit (GFU)

Hydrocarbon % wt.

Hydrocarbon % wt.

Iso-butane 0.01 n- Heptane 0.74

n-Butane 4.21 Olefins С7 0.03

2,2-DMPropane 0.14 Toluene 1.60

Butenes 1.18 Isomers С8 1.40

Iso-Pentane 39.16 Naphthenes С8 0.31

n- Pentane 24.95 n-Octane 0.14

Cyclopentane 2.09 Olefins С8 0.001

Olefins С5 0.27 Aromatics С8 1.33

Isomers С6 10.15 Isomers С9 0.09

Naphthenes С6 2.46 Naphthenes С9 0.04

n-Hexane 3.55 n-Nonane 0.03

Olefins С6 0.06 Aromatics С9 0.57

Benzene 1.35 Hydrocarbons С10 0.03

Isomers С7 2.79 Aromatics С10 0.09

Naphthenes С7 1.23 Hydrocarbons С11+higher 0.002

As it is mentioned above mixed research octane number of this fraction

is 88.1 and it may be used at motor gasoline production but after hydrotreatment as it contains 500 ppm sulfur. The C5 fraction Reid vapor pressure (RVP) is 95 kPa and its addition to motor gasoline may be limited because of the motor gasoline standard requirement of 60 kPa RVP as per EN 228. In order to evaluate the effect of C5 content in motor gasoline on their RVP we have prepared several mixtures of basic gasoline with 49.1 kPa RVP and C5 fraction and have determined mixtures RVP. This study results are shown on Figure 1.

No sample RON MON

1 18 % TC naphtha - 08.06.09 + 82% IBP – 100 oC fraction 63.2 60.6

2 50% GFU C5 fraction + 50 % IBP – 100 oC fraction 76.5 68


Table X Sulfur compounds content of C5 fraction produced at Gas Fractionation Unit

Fraction C5 Components

Sulfur, ppm

Sulfur compounds, ppm

1. Mercaptans: 399 827

Ethylmercaptan 293 568

n-Propylmercaptan 8 19

Isopropylmercaptan 83 198

Tertiary –butylmercaptan 4 11

Secondary-butylmercaptan 11 31

2. Sulfides: 58 120

Dimethylsulfide 40 77

Methylethylsulfide 18 43

3. Disulfides: 46 98

DMDS 0

MEDS 0

DEDS 13 25

Unknowns 33 73

4. Hydrogen sulfide 3 4

Others 506 1048

Fig.1 Motor gasoline RVP (Reid vapor pressure) relationship of C5 fraction content in it

RVP = 1.3527xC5(%) + 49.1

R2 = 0.9969

40

45

50

55

60

65

70

75

80

0 5 10 15 20 25

Съдържание на фракция C5 в бензиновата смес,%

RV

P

C5 fraction content in gasoline mixture, %


Data on Figure 1 show that gasoline Reid vapor pressure increases lineally as C5 fraction content increases. When gasoline Reid vapor pressure prior mixing with C5 fraction is 49.1kPa required standard limitation of 60 kPa is reached as C5 fraction content in the mixture is 8 %. At higher Reid vapor pressure of the basic gasoline the quantity of C5 fraction that may be added shall be less. CONCLUSIONS

The analyses of wild naphtha fractions produced at LNB hydrotreatment units show that after stabilization they are better feed for Catalytic Reforming unit than straight run heavy LON of Ural crude oil. The Visbreaker unit naphtha after hydrotreatment is more suitable for pyrolysis because of higher paraffin’s content and low naphthene’s content. The Visbreaker unit naphtha end boiling point decrease upgrades the Visbreaker unit naphtha quality as potential feed for pyrolysis and worsens its quality as potential feed for reforming after the light fraction (up to C6 hydrocarbons) removal. The mixture of 50 % wild naphtha – 50 % hydrotreated Visbreaker unit naphtha after stabilization is suitable feed for catalytic reforming as its characteristic index 2A+N is identical to that of straight run heavy LON of Ural crude oil.


evaluation of feasible ways for refinery naphtha streams processing_stratiev

Documents

n7 a7 2a

middle distillate hydrotreaters

middle distillate fractions

unit wild naphtha

visbreaker unit naphtha

wild naphtha fractions

secondary naphtha streams

mixed wild naphtha