GB2321645A - Oxidising bitumen in the presence of a catalyst - Google Patents

Abstract

A process is described for the preparation of a bitumen composition which comprises blowing the bitumen with an oxygen-containing gas at 280‹C, at least, in the presence of a catalyst in an amount of less than 5% of the bitumen composition which has a penetration value in the range of 50-100 dmm (ASTM D 5 @ 25‹C). The catalyst is preferably ferric chloride, aluminium chloride, phosphoric acid, boric acid or phosphorous pentoxide. The composition is intended for use in the preparation of road surfaces.

Description

PROCESS FOR PREPARING A BITUMEN COMPOSITION The present invention relates to a process for preparing a bitumen composition and the use of the bitumen composition so obtained in an asphalt mixture for road applications.

Bitumen is used as a binder in road asphalt mixtures, and has developed continually to meet everincreasing performance demands from roadbuilding constructors. In general bitumen performs well in road asphalt, but increasingly heavy traffic loads have led to the premature wear of many roads through rutting and cracking of the surface. Cracking is a serious defect in an asphalt road because it allows water to reach lower layers of the road surface where it causes rapid deterioration, and accelerates the need for premature repairs. Increasing the bitumen content of asphalt or using a softer grade of asphalt improves the crack resistance of asphalt at low temperatures but increases the risk of excessive rutting at higher temperatures because the mixture is effectively softer. Conversely, resistance of rutting can be improved by reducing the amount of bitumen in the asphalt mixture or by using a harder grade of bitumen, at the expense of crack resistance because the mixture becomes less flexible.

In addition to the above performance demands it is nowadays desirable that the bitumen to be used in a road asphalt mixture can be applied satisfactory over a large temperature range.

A well known technique to prepare bitumen compositions meeting the above performance demands and having a large service temperature range is blending bitumens of different quality. By means of such conventional blending processes bitumen compositions can be prepared having pre-selected properties, e.g.

penetration and softening point, which meet today's performance demands. It will be appreciated, however, that such processes have the disadvantage that they require adequate blending equipment and additional storage facilities.

Object of the present invention is to provide a process wherein a bitumen composition meeting today's performance demands can directly be prepared from a bitumen, i.e. without requiring any blending of various bitumen components of different quality.

Accordingly, the present invention provides a process for preparing a bitumen composition comprising blowing a preheated bitumen in the presence of a bitumen blowing catalyst with an oxygen-containing gas for a period of time at a temperature of at least 280 "C, which bitumen has a penetration in the range of from 50 to 500 dmm (as measured by ASTM D 5 at 250C) and the bitumen blowing catalyst is present in an amount of less than 5 %wt, based on bitumen.

Suitably, the present process is carried out at a temperature of at most 350 OC. Preferably, the temperature is in the range of from 285 to 345 OC, more preferably in the range of from 290 to 340 OC, and most preferably in the range of from 300 to 330 OC.

The bitumen to be used in accordance with the present process has a penetration in the range of from 50 to 500 dmm (as measured by ASTM D 5 at 25 C).

Preferably, the bitumen has a penetration in the range of from 100 to 300 dmm, more preferably in the range of from 150 to 250 dmm (as measured by ASTM D 5 at 25 OC).

The preheated mixture is blown with an oxygencontaining gas, such as air, air-containing mixtures (e.g. steam) or pure oxygen. Preferably, use is made of air.

The process according to the present invention may be carried out at ambient pressure or elevated pressure. Normally, however, it will be carried out at ambient pressure.

Suitably, the present invention is carried out over a period of time of less than 4 hours, preferably less than 3 hours, more preferably less than 2.5 hours.

The bitumen may be a residue from a distillation of crude oil, a cracked residue, a residue obtained by blowing a crude oil or residues of crude oil distillation or extracts of crude oils, a bitumen derived from propane bitumen, butane bitumen, pentane bitumen or mixtures thereof. Other suitable bitumens include mixtures of the above bitumens with extenders (fluxes) such as petroleum extracts, e.g. aromatic extracts, distillates or residues.

The preheated bitumen is blown in the presence of a bitumen blowing catalyst. The bitumen blowing catalyst is present in an amount of less than 5%wt, based on bitumen. Suitable bitumen blowing catalysts include those taught in the art such as ferric chloride, phosphorus pentoxide, aluminium chloride, boric acid and phosphoric acid. Preferably use is made of phosphoric acid. Preferably, the bitumen blowing catalyst is present in an amount of less than 2 %wt, more preferably in an amount in the range of from 0.5 to 1 %wt, based on bitumen.

The bitumen to be used in accordance with the present invention is normally, optionally in the presence of the bitumen blowing catalyst, preheated in such a way to establish an initial temperature in the range of from 200 to 300 OC.

The preheated bitumen may in addition contain less than 5 %wt, based on bitumen, of any polymer known in the art to modify bitumens. The process in accordance with the present invention is normally, however, carried out in the absence of such a polymer.

The process in accordance with the present invention is normally carried out in a blowing vessel in which the bitumen to be blown is maintained at a temperature of at least 280 0C into which vessel hot air is injected.

The bitumen composition prepared in accordance with the present invention has suitably a penetration index (PI) in the range of from 0.3 to 1.3, preferably in the range of from 0.4 to 1.2.

The present invention further provides the use in an asphalt mixture for road applications of any bitumen composition as prepared in accordance with the present invention.

The present invention will now be illustrated by means of the following Examples.

Examples Example 1 A process in accordance with the present invention was carried out as follows.

A bitumen feedstock having a penetration of 200 dmm (as measured by ASTM D 5 at 25 OC) and a softening point of 40 OC (as measured by ASTM D 36) was firstly heated to a temperature of 275 OC. The bitumen feedstock had been obtained by vacuum distillation of a crude oil.

Subsequently, the preheated bitumen was blown with air in a blowing vessel at a temperature of 315 "C during 1.5 hours. Phosphoric acid (1.2 %wt, based on preheated bitumen) was continuously introduced in the preheated bitumen from the beginning of the blowing process. The main properties of the blown bitumen composition so obtained are shown in Table 1. These properties include properties of the freshly prepared bitumen composition and those of this product after one week storage.

Example 2 A comparative process was carried out as follows.

The same bitumen feedstock as described in Example 1 was blown with air at a temperature of 275 OC in the presence of 2 %wt phosphoric acid, based on bitumen.

60 pbw of the blown bitumen so prepared were then blended at a temperature of 180 OC with 40 pbw of the bitumen feedstock (non-blown) to obtain the desired product.The main properties of the bitumen composition so obtained are shown in Table 1.

Example 3 A comparative blowing process was carried out in a similar way as described in Example 1 except that the blowing process was carried out at a temperature of 275 OC. The main properties of the blown bitumen composition so obtained are shown in Table 1.

Table 1

Example 1 2 3 Properties freshly prepared compositions: penetration 250C (0.1 mm) 40 53 52 Softening Point, Ring and Ball (OC) 64 59 56 Penetration Index (-) 1.2 1.0 0.5 Properties after 1 week storage: penetration 250C (0.1 mm) 38 51 46 Softening Point, Ring and Ball (OC) 65 60 55 Penetration Index (-) 1.2 1.0 -0.2 From the results shown in Table 1 it will be clear that with the process according to the present invention (Example 1) a bitumen composition can be prepared fulfilling today's performance demands without requiring any conventional blend facilities (Example 2). Moreover, it will be clear that in accordance with the present invention (Example 1) an improved bitumen composition, i.e. a bitumen composition having enhanced stiffness at high temperature and lower stiffness at low temperature, can be obtained when compared with a conventional blowing process (Example 3).

Claims (10)

1. A process for preparing a bitumen composition comprising blowing a preheated bitumen with an oxygencontaining gas in the presence of a bitumen blowing catalyst for a period of time at a temperature of at least 280 "C, which bitumen has a penetration in the range of from 50 to 500 dmm (as measured by ASTM D 5 at 25"C) and the bitumen blowing catalyst is present in an amount of less than 5 %wt, based on bitumen.

2. A process according to claim 1, wherein the temperature is at most 350 "C.

3. A process according to claim 1 or 2, wherein the temperature is in the range of from 285 to 3450C.

4. A process according to any one of claims 1 to 3, wherein the period of time is in the range of from 0.5 to 4 hours.

5. A process according to any one of claims 1 to 4, wherein the bitumen blowing catalyst is present in an amount of less than 2 %wt, based on bitumen.

6. A process according to any one of claims 1 to 5, wherein the bitumen has a penetration in the range of from 100 to 300 dmm (as measured by ASTM D 5 at 25 "C).

7. A process according to any one of claims 1 to 6, wherein the bitumen blowing catalyst is present in an amount in the range of from 0.5 to 1%wt, based on bitumen.

8. A process according to any one of claims 1 to 7, wherein the bitumen blowing catalyst comprises phosphoric acid.

9. A process according to any one of claims 1 to 8, substantially as described hereinbefore with reference to the non-comparative part of the Examples.

10. Use of a bitumen composition as prepared in accordance with a process as defined in any one of claims 1 to 9 in an asphalt mixture for road applications.