Economics of producing unleaded gasoline blends with Oxinol and MTBE

Energy Vol. I I, No. 3. pp. 253-260.

1986

0360-5442/86 $3.00 + 00 0 1986 Pergamon Press Ltd

Printed in Great Britam.

ECONOMICS OF PRODUCING UNLEADED GASOLINE BLENDS WITH OXINOL AND MTBE F. K. MAK Department of Chemical Engineering, University of Queensland. St. Lucia, Qld. 4067 (Received 8 January 1985; receivedfir

publicahn

11 .4pril 1985)

Abstract-A combined model of the oil refining-transportation sector has been used to quantify the economics of producing unleaded gasoline blends with Oxinol and MTBE as octane enhancers. The value of the additives was determined in the liquid-fuel market. Several scenarios were included to assess blending options, capital investment for refining capacity, crude oil, and transport-fuel slates.

INTRODUCTION

We studied the octane improvement of unleaded gasoline by addition of the octane-enhancers, viz. Oxinol and MTBE (methyl tri-butyl ether). Oxinol is an ARC0 (US) product containing equal proportions of methanol and tertiary butanol. In the US, Oxinol may be blended up to 9.6% volume in the unleaded gasoline, according to limits set by the Environmental Protection Agency. MTBE, on the other hand, may be added up to 11% volume. However, MTBE is not a readily available octane enhancer because its current production capacity is small. The blending characteristics are close to those of hydrocarbons, especially toluene. METHOD

OF INVESTIGATION

A model of the combined refining-transportation sector was used to quantify the minimum total cost associated with various scenarios which were chosen to evaluate the blending options, capital investment in processing capacity, crude oil, and transport-fuel slates. The model optimised both the refinery operation and transport fleet by allowing it to choose its feed from a given set of crudes, thus determining the relative usage of the three transport fuels. The constraints of product and transport demands (the latter is expressed as VKTsvehicle-km travelled) were met. Four classes of vehicles (cars/wagons, utilities/vans, rigid trucks, and articulated trucks) and three transport fuels (gasoline, automotive distillate and automotive lpg) were considered in the transportation sector. The gasoline grades used were 98/81,89/82 and 92/82 (expressed as RON/MON). The first two are currently available in the leaded form, while the last is the likely unleaded substitute in the implementation of the lead phase-out in Australia. We examined the blending with MTBE and Oxinol in the 98/87 and 92/82 grades, but kept a clear gasoline of 89/82. A base year of 1979/80 was chosen as a matter of convenience since it provided a complete set of the data required. National consumption of refinery products’ and vehiclekm travelled (VKT)2 are given in Table 1, refining capacity’ in Table 2, and assumed crude oil prices in Table 3. The new processing facilities are the hydrocracker and heavy-end processing units (visbreaking, delayed coking and distillate dewaxing). The blending properties of Oxinol and MTBE are given by Unzelman et ~1.~ OXINOL-GASOLINE

BLENDS

Oxinol is added in 5 and 10% volume in the gasoline blend. Table 4 summarises the blending options. Option A

Oxinol-gasoline blends of 98187 octane and a clear gasoline of 89182 are available for the optimisation. Figure 1 shows that the 10% blend was uneconomical to produce when the Oxinol price is above $8/bbl. For the 5% blend, the corresponding limit is $lS/bbl. 253

F. K. MAK

254

Table l(a). National consumption of refinery products, 1979/80. Consumptix,

Aviation p,asoli::eC56

kt/d

3.776

serosenr: '1.523 2..+6;r 3.c4u 1. 139 2.632 Indusfriai fuel oil: inland bunker

13.99 4.66

;:abe oil Yitumen Sas CZ-(.rClE) Non automobile distillate Non a-tomobile LPG Refinery Fuel, High S fuel oil

l.i64

1.585 3.153 11.723 1.383 float

Table l(b). National vehicle-kilometres travelled, 1979. Vehicle Class Cars and wagons and motor CyCieS

VKT, km/day 237.4 x :06

Utilities and vans

43.64 x lo6

Rigid trucks and cathe trucks

17.24 x lo6

Articulated

trucks

7.1L x lo6

Table 2. National aggregate refining capacity. Processing Unit

kt/d

Crude unit

90.3

Vacuum tower

29.50

Catcracker

2b.86

h'igh pressure reformer

13.71

Low pressure reformer

9.15

Alkylation unit

2.75

Isomeriser

1.03

Desulphuriser Deas?halter

18.84 1 .a5

Unleaded gasoline blends with Oxinol and MTBE Table 3. Assumed crude oil prices, 1979/80.

Crude Oil

I

Prices,

S/t

(1979/80)

Gippsland

170.9

Arab light

162.8

Arab heavy

1511.1

Berri

181.3

Attaka

201.2

Minas

176.3

I

Lead

$3.5/kg 1

Table 4. Oxinol-blend options. OPTION

CAPACITY CONSTRAINTS

2 grades of gasoline

A(i) A(ii)

10% Oxinol in 98/87, clear 89/82 5% Oxinol in 98/87, clear 89/82

with incremental capacity for existing processing units

1

1 grade of gasoline

B

10% Oxinol in 92/82

C(i)

10% Oxinol in 98/87

C(ii.1 5% Oxinol in 98/87

7

with new units and incremental capacity for all units

J

4.8-

4

46-

>

’

B

2 8 4.uIlY 0 5 4.2-

4.0'

T

.

5

*

10

15

20

25

30

35

40

Wbbl Oxlnol

Fig. I. Total costs for the Oxinol-blend options.

255

256

F. K.

-

MAK

A(i)-98/87 Blend

40

15

5

10

15

20

25

30

35

40

Vbbl Oxlnol

Fig. 2(a). Gasoline yields for the Oxinol-blend options.

3

12 10

a 1 6 4

A(1) 5

10

15


, 25

30

35

40

Ubbl Oxlnol

Fig. 2(b). Automotive distillate yields for the Oxinol-blend options.

*. 8.4. : 8.2._ ;

8.0-

a

7.87.67.4.

A(11)

v(1)

7.2 7.0

5

10

15

20

25

30

35

40

t/bbl Oxlnol

Fig. 2(c). Automotive Ipg yields for the Oxinol-blend options.

Unleaded gasoline blends with Oxinol and MTBE

257

Above these prices, only the clear 89/82 gasoline was produced. Figure 2(a) shows that the total gasoline yield at low Oxinol prices is higher with the 10 than the 5% addition, as is to be expected. Figs. 2(b) and (c) show that the automotive distillate (ADO) and automotive lpg (ALP) yields for both Oxinol levels are comparable, around 5% for ADO and 7.4% for ALP. The gasoline components are the high-octane reformates, catcracked gasolines, isomerate and alkylate. Hydrocracking and incremental capacity for existing units were not required, although the catcracker, crude distillation unit, high-pressure reformer, isomerisation, alkylation, and desulphurisation units ran on high rates. Option B The production of a lo%-92182 blend required hydrocracking and heavy-end processing facilities which maximised the ADO yield. A comparison of the optimal yields of gasoline, ADO and ALP is given in Figs. 2(a), (b), (c), respectively. Option C The production of a 98/87 gasoline with 5 and 10% Oxinol addition required significant uprate in isomerisation capacity, in contrast to Options A and B. The use of hydrocracking and heavy-end processing gave rise to a relatively high ADO yield. As with the other options, the optimal refinery configuration stayed constant above $2O/bbl for Oxinol, indicating that increases in the total cost were due entirely to Oxinol price increases. Summary of main findings in Oxinol-gasoline blending The 5%-98/87 blend was the most economical option with Oxinol price below $50/bbl and new processing capacities available. This is followed by the 10% addition in the 98/87 and 92/82 blends with capacity constraints similar to the stated. The corresponding Oxinol price is $25-30/bbl. Above these prices, it is cheaper to produce the clear 89/82 gasoline. The economics of producing only the unleaded gasolines of equivalent octane were included for comparison. Thus, in Fig. 1, point X is the cost of producing the combined 98/87 and 89/82 grades, both being clear gasolines, without incremental capacity for the existing refinery. Point Y is the cost of producing the clear 92/82 grade with new units available. Thus, it is cheaper to produce the clear gasoline than its equivalent blend, under similar capacity constraints. MTBE-GASOLINE

BLENDS

MTBE-gasoline blends at the 5 and 10% levels were studied. Table 5 shows the blending options. Figure 3 shows that the 5%-98/87 blend of Option A was not viable above the MTBE price of $20/bbl. Options B(ii) and C(i) share the same total costs. However, costs rose significantly when these blends were produced without the heavy-end processing units, or at the 10% level of MTBE addition. For example, the difference in total cost between B(i) and (ii) (i.e. the effect of heavy-end processing) is 0.16-0.20 c/VKT, or about $220 X 106/yr for MTBE prices between $5 and 35/bbl. The difference between C(i) and (iii) (i.e. the effect of MTBE levels) is 0.40-0.54 Q/VKT, or about $500 X 106/yr. The presence of 10% of MTBE displaced some middle components from the gasoline base, in this case, the alkylate, so that alkyl feed was diverted to refinery fuel. The main components of gasoline are the high-octane reformates and catcracked gasolines. The refinery was locked into a very costly configuration, with the alkylation unit running at very low rates (and supplying part of the refinery fuel) while the hydrocracker, visbreaker and lowpressure reformer were shut down. Additional capacity was required in isomerisation, vacuum distillation and high-pressure reforming. The optimal yields of the transport-fuels for the various options are compared in Figs. 4(a) to (c). Summary of main findings in MTBE-gasoline blending The 5% blends of 98187 or 92182 octanes were the most economical options with new processing capacities available and MTBE price below $50/bbl. Without heavy-end pro-

F. K. MAK

258

Table 5. MTBE-blend options. CAPACITY CONSTRAINTS

OPTION 2

grades of gasoline

A

With incremental capacity for existing processing units

5% MTBE in 98/87, clear 89/82

1 grade of gasoline

B(i)

(ii)

C(i)

With hydrocracking and incremental capacity for all processing units

5% MTBE in 92/82

5% MTBE in 92/82 With hydrocracking, heavy-end processing and incremental capacity for all processing units

5% MTBE in 98/87

(ii) 10% MTBE in 98/87

cessing, the 5%98187 blend increased in cost, and became unviable above $20/bbl for MTBE. Above these prices, only the clear 89/82 gasoline production was viable. The most expensive option was the 1OS-98/87 blend. In Fig. 3, points X, Y, Z are the costs of producing the clear gasolines of the following grades: 98/87 combined with 89/82 (without heavy-end processing) and 98/87 and 92/82 (both with heavy-end processing), respectively. It is obvious that the clear gasolines are cheaper to produce than the MTBE-blends of equivalent octane, under similar capacity constraints. OPTIMAL

TRANSPORT-FUEL

SLATES

It is interesting to compare the optimal transport-fuel slates obtained in the various options with the actual distribution.* Table 6 provides the comparison. The slates were determined at $20/bbl for the additive, which figures were considered representative of the blends. There is significant variation in the relative proportions of the transport-fuels with the scenarios. Compared with the 1979/80 distribution, the optimal slate contains a high proportion of ALP, especially where the clear gasolines were produced without heavy-end processing capacity. However, the gasoline proportion decreased significantly when the latter facility was on-line. Consequently the ADO yield increased to levels comparable with gasoline.

&

5

10

15

20

25

30

35

40

t/bbl MTBE

Fig. 3. Total costs for the MTBE-blend options.

C(1)

45

Unleaded gasoline blends with Oxinol and MTBE

45 40 bp

A - 89182 Clear

. 35 z z 30 2

25

: s

20 15 10

- 98/87 Blend

5 0

5

15

10

20

25

30

35

40

45

thbi MTBE

Fig. 4(a). Gasoline yields for the MTBE-blend options.

I

1

10

5

15

20

25

30

35

40

b/t&l F?TBE

Fig. 4(b). Automotive distillate yields for the MTBE-blend options.

6

I 5

10

15

20

25

30

Wbbl

MTBE

35

40

Fig. 4(c). Automotive Ipg yields for the MTBE-blend options.

259

F. K. MAK

260

Table 6. Optimal transport-fuel slates. Gasoline

: ADO :

ALP

5% MTBE in 98/87 (b)

1.01

1.00

0.45

10% Oxinol in 98/87 (b)

1.04

1.00

0.45

5% MTBE in 92/82 (b)

1.04

1.00

0.45

5% MTBE in 92/82 (a)

2.67

1.00

0.55

ODtion

clear 92/82

(a)

6.10

1.00

1.30

clear 92/82

(b)

1.30

1.00

0.54

clear 89/82

(a)

7.20

1.00

1.50

clear 98/87 with 89/82 (a)

8.00

1.00

1.50

1979/80 situation2

6.20

1.00

0.014

(a)

With hydrocracking and incremental capacity on all processing units

(b)

With hydrocracking, heavy-end processing and incremental capacity on all processing units

This behaviour is observed for the blends and clear gasoline. In all cases the users of ALP and ADO are cars and wagons, while gasoline supplies all four classes of vehicles. REFERENCES

1. Australian Institute of Petroleum Ltd., “Oil and Australia, the Figures Behind the Facts,” Melbourne, Victoria, Australia (198I). 2. Australian Bureau of Statistics, “Survey of Motor Vehicle Usage-Twelve Months Ended 30th September, 1979,” Canberra, ACT, Australia (February 198 I). 3. G. H. Unzelman, D. D. Hombeck, and R. M. Labruyere, “Oxygenated Compounds as Blending Agents in Gasoline-Octane Value and Current Economics,” Paper presented at the Session on Alternative Fuels of the Joint Session of osterreichische Gesellschaji fir Erdtilwissenschaften and Deutsche Gessellschaji ftir Mineraliilwissenschaji and Kohlechemie E. V. (DGMK). Munich, West Germany (October 1980).