GB2108998A - Modified asphalts - Google Patents

Abstract

An asphalt is modified by oxidation (with for example air, oxygen or hydrogen peroxide at 140-170 DEG C for up to 1 hour), such that the softening point of the asphalt is not materially altered whilst its reactivity toward sulfur is substantially reduced. Such a mildly oxidised asphalt can be stored hot and subsequently treated with sulfur, for example at a road-making site, without the high hydrogen sulfide evolution encountered with known products.

Description

1

GB 2 108 998 A 1

SPECIFICATION Modified asphalts

This invention relates to modified asphalts, to processes for preparing them and to uses thereof.

It is known that the addition of sulfur to asphalt leads to modified binders having improved 5 workability and mechanical characteristics. However, the blending operation, which must take place above 120°C (fusion point for sulfur), is generally accompanied by the evolution of significant amounts of H2S. This is due to the reaction of sulfur with some molecules of the asphalt blend which are especially prone to it.

It is an object of the present invention to provide an improved asphalt, which when treated with 10 sulfur gives rise to decreased, or no, H2S evolution.

According to one aspect of the present invention there is provided a process for modifying asphalt by contacting the asphalt with an oxidant, optionally in the presence of a catalyst, wherein the oxidant and conditions of contact thereof with the asphalt are such that (i) the softening point of the asphalt is not materially altered, and (ii) the reactivity of the asphalt toward sulfur is decreased. 15 The oxidant can be a suitable non-gaseous oxidant, for example hydrogen peroxide; however it has been found that ammonium nitrate, chromium trioxide and phosphorus pentasulfide are not suitable oxidants for the process of this aspect of the invention.

Preferably the oxidant is oxygen or air. It is then preferred that the temperature of contact, the rate of feeding of the oxygen or air and the residence time of the oxygen or air in contact with the asphalt are 20 such that the softening point of the material is not significantly altered. Preferably the temperature of contact is in the range 140° to 170°C, more especially 145 to 155°C. It is further preferred that the duration of the contact is not. more than one hour, typically 10 to 20 minutes depending on the feedstock being processed.

The product of such a process may be described as a mildly oxidized asphalt and is quite different 251 from the well-known oxidized or blown types which are normally prepared by oxidation for from 4 to 8 hours at 240°C to 290°C.

Whilst it can have other uses, the product is especially suitable for the preparation of asphalt/suifur materials, preferably with sulfur which is not chemically bound or combined.

According to another aspect of the invention, a sulfur-modified asphalt is obtained by blending the 30 product of the aforedescribed process with sulfur at a temperature in the range 120°Cto 170°C. The steps of contacting with the oxidant and with the sulfur are preferably conducted at substantially the same temperature in the range 140 to 170°C, more especially 145°C to 1 55°C.

The sulfur may be employed in amount from upto 45 wt% based on the asphalt, preferably 20 to 35 wt%, suitably 25 to 35 wt%, more especially 30 wt%.

35 The asphalt feedstock employed in processes of the invention may be any one of the known non-oxidized materials, for example the penetration grade asphalts such as 40/60 to 180/220, preferably 80/100. However, much softer residua can be employed, for example those with penetrations of about 600, or higher, including the light 600—800 grade (ASTM D 5).

The invention will now be illustrated by reference to the following Examples:—

40 EXAMPLE 1

In this example ten different asphalt types were tested with respect to their reactivity with sulfur. The reactivity was quantified by the cumulative quantity of H2S evolved during the first ten minutes of treatment of the asphalt with elemental sulfur at 150°C.

Table 1 shows for each material its crude oil origin, its penetration and the said H2S quantity 45 evolved.

The first six materials show essentially the same reactivity to sulfur, independent of the crude oil origin. Moreover, as indicated by Tests 2 and 3, the reactivity is substantially independent of the penetration, so that short and long run vacuum residua produced from the same crude oil behave substantially similarly when treated with the sulfur.

50 Test Nos 7 and 8 were conducted with two different blends of straight run vacuum residua and oxidized vacuum residua, that is to say normally oxidized material. The blends show less reactivity with sulfur under the stated conditions.

Finally, Tests 9 and 10 were conducted with two mildly blown materials made in accordance with the invention. Both materials show a considerably reduced reactivity with sulfur under the stated 55 conditions, the origin of crude oil being unimportant. It will be seen that the reactivity is appreciably less than even the blends 7 and 8; indicating that the results obtainable by means of the invention cannot be achieved by mere blending of known blown and un-blown materials.

EXAMPLE 2

In order to illustrate suitable conditions for conducting the mild oxidation, a series of air blowing 60 experiments was conducted on some asphalt materials at 150°C or 1 65°C and for oxidation times in the range 5 to 60 minutes. The asphalts employed were (1) a straight run vacuum residuum from an Arabian Light crude (2) a blend of straight run vacuum residuum having a penetration 80 to 100 and (3)

5

10

15

20

25

30

35

40

45

50

55

60

2

GB 2 108 998 A 2

a straight run vacuum residuum of penetration 80 to 100 from an Arabian Heavy crude oil.

Fig. 1 is a plot of relative reactivity of the various oxidized materials thus produced with sulfur,

against oxidation time. With all materials H2S is reduced by 50% after only 15 mins air blowing, and by 75% after 1 hour.

5 Similar results were obtained employing hydrogen peroxide as the oxidant. By contrast NH4N03, 5

Cr03 and P2Os do not produce similar results.

EXAMPLE 3

This example illustrates that the mildly oxidized product of the invention retains its low reactivity to sulfur over a storage period at 1 50°C of ten or more days. This is very important in practice in that the 10 oxidized product can be made and hot-stored in one location and thereafter blended with sulfur at 10

another location days later.

Fig 2 shows the results obtained with an asphalt of penetration 80 to 100 from an Arabian Heavy crude and a residue from the vacuum distillation of an Arabian Light crude. The figure clearly shows that even after 10 days storage, both products are still considerably less reactive with sulfur than the 15 corresponding unblown materials. 15

The sulfur-modified, mildly oxidized asphalts of the invention have considerable importance as binding agents in road-making and road-surfacing operations, among other uses. H2S evolution has hiterto presented problems which sometimes rule out the possibility of using sulfur-modified asphalts even though they have desirable properties. By means of the invention H2S evolution can be reduced, 20 thereby widening the practical scope of use of sulfur-modified asphalts, since the important properties 20 of those are not significantly affected in the products according to the present invention.

TABLE 1

H2S Evolved in

Test

Penetration

First 10 Mins

No.

Crude Oil Origin

Asphalt Type

(ASTM D5)

(ML /KG) *

1

Arab Light

All Are

600

255

2

Arab Heavy

Straight

90

295

3

Arab Heavy

Run Vacuum

45

305

4

Tia Juana

Residua

90

255

5

Crude Oil Blend

90

340

6

Crude Oil Blend

45

303

7

Arab Heavy

Both are Blends

70

207

of Straight Run

8

Arab Heavy and Oxidized

50

225

Vacuum Residua

9

Arab Light

Vacuum Residua

90

185

Mildly Blown

10

Arab Light J

Per Invention

45

165

* After Treatment with 20 wt % S at 150°C.

Claims (11)

1. A process for modifying asphalt by contacting the asphalt with an oxidant, optionally in the

25 presence of a catalyst, wherein the oxidant and conditions of contact thereof with the asphalt are such 25 that (i) the softening point of the asphalt is not materially altered, and (ii) the reactivity of the asphalt toward sulfur is decreased.

2. A process as claimed in claim 1, wherein the oxidant is oxygen or air.

3. A process as claimed in claim 1 or claim 2, wherein the temperature of the contact is in the

30 range 140°C to 170°C. 30

3

GB 2 108 998 A 3

4. A process as claimed in claim 2 or claim 3, wherein the contact is continued for not more than one hour.

5. A modified asphalt whenever prepared by any one of the preceding claims.

6. A process for preparing a sulfur-modified asphalt, comprising contacting the modified asphalt

5 claimed in claim 5 with non-chemically-combined or bound sulfur, in the temperature range 120°C to 5 170°C.

7. A process for preparing a sulfur-modified asphalt comprising conducting the steps defined in any one of claims 1 to 4 and then contacting with the sulfur in the temperature range 120°C to 170°C.

8. A process as claimed in claim 7, wherein the steps of contacting with the oxidant and with the

10 sulfur are conducted at substantially the same temperature in the range 140 to 170°C. 10

9. A process as claimed in claim 8, wherein said temperature is in the range 145 to 155°C.

10. A sulfur-modified asphalt whenever produced by the process claimed in any one of claims 7 to

9.

11. The use of a sulfur-modified asphalt claimed in claim 10 as a, or the, binder in road-making or

15 road surfacing. 15

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.