US20120132565A1

US20120132565A1 - Asphalt oxidation process using liquid jet ejection

Info

Publication number: US20120132565A1
Application number: US13/304,964
Authority: US
Inventors: Keith Kaluna Aldous
Original assignee: ExxonMobil Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 2010-11-29
Filing date: 2011-11-28
Publication date: 2012-05-31
Also published as: WO2012074961A1; SG190367A1; EP2646526A1; CA2819151A1

Abstract

Provided is a process for increasing the softening temperature of asphalts by use of liquid jet ejector technology, which is used as both an air compressor and an air/oil mixer. The liquid jet ejector motive fluid is hot asphalt and the entrained vapor is air.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a non-provisional application that claims priority to U.S. Provisional Application No. 61/417,747 filed on Nov. 29, 2010, herein incorporated by reference in its entirety.

FIELD

The present disclosure provides a process for increasing the softening temperature of asphalts by use of liquid jet ejector technology, which is used as both air compressor and air/oil mixer. The liquid jet ejector motive fluid is hot asphalt and the entrained vapor is air.

BACKGROUND

Asphalt is one of the world's oldest engineering materials, having been used since the beginning of civilization. Asphalt is a strong, versatile and chemical-resistant binding material that adapts itself to a variety of uses. For example, asphalt is used to bind crushed stone and gravel into firm tough surfaces for roads, streets, and airport runways. Asphalt, also known as pitch, can be obtained from either natural deposits, or as a by-product of the petroleum industry. Natural asphalts were extensively used until the early 1900s. The discovery of refining asphalt from crude petroleum and the increasing popularity of the automobile served to greatly expand the asphalt industry. Modern petroleum asphalt has the same durable qualities as naturally occurring asphalt, with the added advantage of being refined to a uniform condition substantially free of organic and mineral impurities.
Most of the petroleum asphalt produced today is used for road surfacing. Asphalt is also used for expansion joints and patches on concrete roads, as well as for airport runways, tennis courts, playgrounds, and floors in buildings. Another major use of asphalt is in asphalt shingles and roll-roofing which is typically comprised of felt saturated with asphalt. The asphalt helps to preserve and waterproof the roofing material. Other applications for asphalt include waterproofing tunnels, bridges, dams and reservoirs, rust-proofing and sound proofing metal pipes and automotive under-bodies; and sound-proofing walls and ceilings.
The raw material used in modern asphalt manufacturing is petroleum, which is naturally occurring liquid bitumen. Asphalt is a natural constituent of petroleum, and there are crude oils that are almost entirely asphalt. The crude petroleum is separated into its various fractions through a distillation process. After separation, these fractions are further refined into other products such as asphalt, paraffin, gasoline, naphtha, lubricating oil, kerosene and diesel oil. Since asphalt is the base or heavy constituent of crude petroleum, it does not evaporate or boil off during the distillation process. Asphalt is essentially the heavy residue of the oil refining process.
If asphalt is to be used for a purpose other than paving, such as roofing, pipe coating, or as an under sealant or water-proofing material, the asphalt is usually oxidized, typically by air blowing. Oxidation produces an asphalt material that softens at a higher temperature than non-oxidized asphalts. Oxidation is conventionally done by air blowing at the refinery, at an asphalt processing plant, or at a roofing material plant. Air blowing modifies the asphalt by an oxidation process that involves the blowing of air through the asphalt, either on a batch or continuous basis, with a short residue time at a temperature from 175° C. to 300° C.
While processes for oxidizing asphalt have been commercial for many years, there still remains a need in the art for ever more cost effective processes for modifying the physical properties of asphalt by oxidation.

SUMMARY

In accordance with the present disclosure there is provided a process for increasing the softening point of asphalt including the following steps: providing a liquid jet ejector comprising a motive inlet, a motive nozzle, a suction port, a main ejector body, a venturi throat and diffuser, and a discharge connection; conducting a preheated asphalt feed including fresh asphalt and recycled oxidized asphalt, at a temperature from 125° C. to 300° C., as the motive liquid into the motive inlet of the liquid jet ejector, drawing air into the suction port of the liquid jet ejector; mixing the preheated asphalt within the main ejector body with the air from the suction port of the liquid jet ejector to form a mixture, conducting the mixture to a heated and pressurized oxidizer vessel; collecting an off-gas from the overhead of said oxidizer vessel and an oxidized asphalt product stream from the bottoms of said oxidizer vessel, wherein said oxidized asphalt product stream has softening temperature greater than the preheated asphalt feed; and recycling a portion of the oxidized asphalt product stream plus fresh asphalt back to the liquid jet ejector to form the preheated asphalt feed.

BRIEF DESCRIPTION OF THE FIGURES

To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, wherein:

FIG. 1 hereof is a process flow scheme of a conventional asphalt oxidation process (Prior art process).

FIG. 2 hereof is a process flow scheme of the inventive asphalt oxidation process of the present disclosure.

FIG. 3 hereof is a graph of oxidized asphalt penetration versus softening point for asphalt produced via the prior art process and the inventive process disclosed herein.

DETAILED DESCRIPTION

All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.
The instant disclosure is suitable for increasing the softening temperature of any type of asphalt, both naturally occurring and asphalts that result is from the distillation of crude oil. Although it is typically desired to increase the softening temperature of asphalt for uses other than paving, it may be desirable to also increase the softening temperature for asphalts for some paving applications. When the asphalt is to be used for applications such as roofing, pipe coating, or as an under sealant or water-proofing material, it is highly desirable to increase its softening temperature. Such uses typically require the asphalt to have a softening temperature higher than asphalt used for paving roads. The softening temperature is typically increased by oxidizing the asphalt. The softening temperature of asphalts is increased conventionally by an oxidation process that involves the blowing of air through the asphalt, either on a batch or a continuous basis, with the asphalt at a temperature from 175° C. to 300° C.
Conventional air blowing usually involves preheating the asphalt, after which it is introduced into a blowing, or oxidizer column just below the normal liquid level. Air is blown through the asphalt by means of an air distributor located at the bottom of the column. The air serves not only as the reactant, but also serves to agitate and mix the asphalt, thereby increasing the surface area and rate of reaction. Oxygen is consumed by the asphalt as the air ascends through the material. Steam and water are typically sprayed into the vapor space above the asphalt level, the former to suppress foaming and dilute the oxygen content of waste gases and the later cools the vapors to prevent after-burning. The “blown” product flows from the bottom of the blowing column via an external draw-off line and is pumped through heat exchangers to achieve the desired product temperature and to provide an economical means of preheating the incoming asphalt feed. The penetration and softening point of the blown asphalt are affected by such things as: the viscosity of the feedstock, the temperature in the blowing column, the origin of the crude oil used to manufacture the feedstock, the liquid residence time within the oxidizer, and the air-to-feed ratio.
The blowing process dehydrogenates the asphalt, resulting in oxidation and polycondensation, increasing the overall molecular size of the asphaltenes already present in the feed and forming additional asphaltenes from the maltene phase. Because the reaction is exothermic, close temperature control of the process is required, which is typically achieved by regulating the air-to-asphalt ratio in the blowing column.
To produce penetration grade asphalt suitable for certain road construction applications, asphalt manufactured from select crudes requires only a limited amount of air blowing. This process is termed semi-blowing, or air rectification. Used judiciously, semi-blowing can be applied to asphalt to reduce the temperature susceptibility of the asphalt, for example, increasing its penetration index. The penetration index is a measure of the way the binder's (asphalt) consistency (penetration value) changes with temperature. It can be calculated from the penetration at two different temperatures, or from the penetration at one temperature and the softening point.
Fully blown or oxidized asphalts are conventionally produced by vigorous air-blowing of short residue or short residue blended with a heavy distillate. Short residue is the residue left after vacuum distillation. The position of the blowing curve is primarily dependent on the viscosity of the feed; i.e., the softer the feed the higher the curve. The severity of blowing depends on the temperature in the column, the air to feed ratio, and the liquid residence time. Thus, by controlling the viscosity of the feed and the conditions in the column, all the blown grades of asphalts can be manufactured.
Oxidized asphalts are used almost entirely for industrial applications, e.g. roofing, flooring mastics, pipe coatings, paints, etc., and are specified and designated by both softening point and penetration tests, e.g. 85/40 is an oxidized grade asphalt with a softening point of 85° C. plus or minus 5° C. and a penetration of 40 dmm plus or minus 5 dmm.
The aim of the oxidation process is the formation of asphaltenes in which the following three phenomena can be identified:

- Reactions during which the size of the molecules increases. The formation of esters is particularly important and not only account for at least 60% of the oxygen in oxidized asphalt, but also link two different molecules and thus contribute to the formation of a material having a higher molecular weight. This mechanism results in an increase in the asphaltene content and a change in the colloid-chemical constitution and rheological properties of the asphalt,
- Reactions during which the size of the molecule is unchanged. For example, the formation of cyclic hydrocarbons by means of dehydrogenation with H₂O as a side product.
- Reactions during which the size of the molecule decreases. For example, separation of side branches from molecules with blown distillate produced as a side product.

This disclosure can be better understood with reference to the Figures hereof. FIG. 1 hereof is a process flow scheme of a conventional asphalt oxidation process (prior art process). An asphalt feed is passed via line 10 through heat exchanger 1 where it is preheated to a temperature from 125° C. to 300° C., then to oxidizer vessel 2. Air, via line 12, is also introduced to oxidizer vessel 2 by first compressing it by use compressor 3 then passing it through knockout drum 4 to remove any condensed water or other liquids via line 13. The air flows upward through a distributor 15 and countercurrent to down-flowing asphalt. The air is not only the reactant, but also serves to agitate and mix the asphalt, thereby increasing the surface area and rate of reaction. Oxygen is consumed by the asphalt as the air ascends through the down flowing asphalt. Steam or water can be sprayed (not shown) into the vapor space above the asphalt to suppress foaming and to dilute the oxygen content of waste gases that are removed via line 14 and conducted to knockout drum 5 to remove any condensed or entrained liquids via line 17. The oxidizer vessel 2 is typically operated at low pressures of 0 to 2 barg. The low pressure off-gas, which is primarily comprised of nitrogen and water vapor, is often conducted via line 16 to an incinerator 8 where it is burned before being discharged to the atmosphere. The oxidized asphalt product stream is then conducted via line 18 and pumped via pump 6 through heat exchanger 1 wherein it is used to preheat the asphalt feed being conducted to oxidizer vessel 2. The hot asphalt product stream is then conducted via line 20 to steam generator 7 where it is cooled prior to going to storage. While such a conventional process has been commercially successful, there is still much room for improvement.
The practice of the instant disclosure for oxidizing asphalts presents a substantial improvement over conventional air blowing techniques. For example, the use of liquid jet ejector technology of the present disclosure eliminates the need for an air compressor; improves the air/oil mixing compared to that of a conventional oxidizer vessel, thus reducing excess air requirements and reducing the size of the off-gas piping; reduces the excess oxygen in the off-gas allowing it to go to the fuel gas system, thus eliminating the need for an incinerator; and reduces the reaction time, thus reducing the size requirement of the oxidizer vessel.
Liquid jet ejectors have not been used to oxidize asphalts to increase their softening temperatures. Liquid jet ejectors are comprised of the following components: a body having an inlet for introducing the motive liquid, a converging nozzle that converts the motive liquid into a high velocity jet stream, a port (suction inlet) on the body for the entraining in of a second liquid or gas, a diffuser (or venturi), and an outlet wherein the mixed liquid stream is discharged.
In a liquid jet ejector, a motive liquid under high pressure flows through converging nozzles into the mixing chamber and at some distance behind the nozzles forms high-velocity and high-dispersed liquid jets, which mix with entrained gas, speeding up the gas and producing a supersonic liquid-gas flow inside the mixing chamber. Kinetic energy of the liquid jet is transferred to the entrained gas in the mixing chamber producing vacuum at the suction inlet. Hypersonic liquid-gas flow enters the throat, where it is decelerated by the compression shocks. Thus, the low pressure zone in the mixing chamber is isolated from the high pressure zones located downstream.
FIG. 2 hereof is a process flow scheme of the process of the present disclosure for oxidizing asphalts. An asphalt feed via line 100 is preheated in heat exchanger 60 and combined with a portion of the oxidized asphalt product from oxidizer vessel 20 via line 110 and pumped via pump 50 via line 120 to the liquid jet ejector 30 motive inlet and mixed with an effective amount of air via line 130 to liquid jet ejector 30 suction inlet via knockout drum 70. Any liquid collected from knockout drum 70 is drained via line 170. The amount of oxidized asphalt product recycled from the oxidizer will be at least 5 times, preferably at least 10 times, and more preferably at least 20 times that of the volume of incoming asphalt feed. By effective amount of air we mean at least a stoichiometric amount, but not so much that it will cause undesirable results from either a reaction or a process point of view. The stoichiometric amount of air will be determined by the amount of oxidizable components in the particular asphalt feed. It is preferred that a stoichiometric amount of air be used.
Any suitable liquid jet ejector can be used in the practice of the present disclosure. Liquid jet ejectors are typically comprised of a motive inlet, a motive nozzle, a suction port, a main body, a venturi throat and diffuser, and a discharge connection, wherein the hot asphalt, at a temperature from 125° C. to 300° C., is conducted as the motive liquid into said motive inlet and wherein air is drawn into the suction port and mixed with the asphalt within the ejector body. The air drawn into the suction port of the liquid jet ejector may be either atmospheric air or compressed air. The pressurized air/asphalt mixture is then conducted via line 140 to oxidizer/separation vessel 20. The pressure of the mixture exiting the liquid jet ejector will be in excess of the pressure at which the oxidizer is operated and will be further adjusted to allow for the resulting off gas from the oxidizer to be introduced into the fuel gas system of the refinery. The oxidizer vessel 20 is operated at pressures from 0 to 10+ barg, preferably from 0 to 5 barg and more preferably from 0 to 2 barg. The temperature of the oxidizer vessel will be from 150° C. to 300° C., preferably from 200° C. to 270° C., and more preferably from 250° C. to 270° C. It is preferred that the temperature within the oxidizer will be at least 10° C. higher, preferably 20° C., and more preferably 30° C. higher than the incoming asphalt feed temperature. Off-gas is collected overhead via line 150 and passed through a knockout drum 70 where liquids are drained off via line 170 for further processing and the vapor because of its pressure and low oxygen content can be routed into the refinery fuel gas system via line 180. The oxidized product is conducted via line 190 through pump 80, heat exchanger 60 and steam generator 40. An effective amount of steam can be conducted (not shown) to the vapor space 22 above or below the asphalt level 24 in the oxidizer 20 to dilute the oxygen content of the off gas, primarily for safety purposes. By effective amount of steam is meant at least that amount needed to dilute the oxygen content of the resulting off gas to a predetermined value. The oxidized product stream is then routed to product storage via line 190 while a portion of it is recycled via line 110 to line 120 where it is mixed with fresh feed, which functions to provide the necessary motive fluid for the liquid jet ejector.
The following are examples of the present disclosure and are not to be construed as limiting.

Examples

A batch pilot process was constructed to test the feasibility of the use of a liquid jet ejector to entrain the necessary air and mix the air/oil sufficiently for the asphalt oxidation reaction to occur. The results for two experimental runs for the inventive process are shown in Table 1 below.

TABLE 1

Liquid Jet Ejector Batch Pilot Air Blower

Pilot Run #1

temperature	deg C.	251	257	252	252	249
pressure	kpag	28	28	21	103	103
cumulative air	liters/kg	0	24	62	93	100
mixer	rpm	none	none	none	none	none
offgas oxygen	vol. %				1.5%	1.4%
penetration at 25 C.	dmm	194	129		43	38
softening point	deg C.	38.0	42.2		55.2	57.6

Pilot Run #2

temperature	deg C.	189	199	202	202	231	244	249
pressure	kpag	28	28	34	28	28	28	28
cumulative air	liters/kg	0	9	18	36	55	64	73
mixer	rpm	none	none	none	none	none	none	none
offgas oxygen	vol %		17.5%	18.0%	18.2%	15.0%	11.7%	10.4%
penetration at 25 C.	dmm	173		151	130	107		91
softening point	deg C.	38.8		39.8	41.3	43.3		44.8

it should be noted that the liquid distributor within the oxidizer vessel was removed for Pilot Run #2 resulting in significantly higher offgas oxygen content. However, at the end of Pilot Run #1, there was very low offgas oxygen content, which signifies an approach to stoichiometric air. In addition, it was discovered that the asphalt product softening points are greater than the feed softening points.
By comparison, the same feed was run three times on a conventional prior art batch pilot unit and the comparative results achieved are shown in Table 2 below.

TABLE 2

Conventional Stirred Batch Pilot Air Blower

Pilot Run #1

temperature	deg C.	250	250	250
pressure	kpag		0	0	0
cumulative air	liters/kg	0	50	100
mixer	rpm	1750	1750	1750
offgas oxygen	vol %	5.7%	8.1%	9.5%
penetration at 25 C.	dmm	167	67	34
softening point	deg C.	39.1	48.7	59.3

Pilot Run #2

temperature	deg C.	200	200	200	200	200	200
pressure	kpag		0	0	0	0	0	0
cumulative air	liters/kg	0	50	100	150	200	250
mixer	rpm	1750	1750	1750	1750	1750	1750
offgas oxygen	vol %	10.8%	15.1%	15.5%	16.1%	16.3%	16.3%
penetration at 25 C.	dmm	167	91	57	41	30	24
softening point	deg C.	39.1	44.4	49.6	55.0	60.2	66.0

Pilot Run #3

temperature	deg C.	250	250	250	250	250	250
pressure	kpag		0	0	0	0	0	0
cumulative air	liters/kg	0	50	150	250	350	650
mixer	rpm		0	0	0	0	0	0
offgas oxygen	vol %	10.5%	19.4%	19.4%	19.4%	19.5%	19.5%
penetration at 25 C.	dmm	167				98	62
softening point	deg C.	39.1				44.7	49.1

As can be seen, the liquid jet ejector pilot process performed as well as or better than the conventional counterpart. It should be noted that the conventional pilot unit could not achieve the low offgas oxygen content at similar conditions as the liquid jet ejector pilot process signifying the improved efficiency of the liquid jet ejector air blower versus the conventional air blower.
Oxidized asphalt product penetration versus softening point for product produced from the inventive and prior art processes are compared graphically in FIG. 3. The results indicate no differences between the prior art process and the inventive process with regard to these properties.
Applicants have attempted to disclose all embodiments and applications of the disclosed subject matter that could be reasonably foreseen. However, there may be unforeseeable, insubstantial modifications that remain as equivalents. While the present disclosure has been described in conjunction with specific, exemplary embodiments thereof, it is evident that many alterations, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description without departing from the spirit or scope of the present disclosure. Accordingly, the present disclosure is intended to embrace all such alterations, modifications, and variations of the above detailed description.
All patents, test procedures, and other documents cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent with this disclosure and for all jurisdictions in which such incorporation is permitted.
When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.

Claims

1. A process for increasing the softening point of asphalt comprising the following steps:

providing a liquid jet ejector comprising a motive inlet, a motive nozzle, a suction port, a main ejector body, a venturi throat and diffuser, and a discharge connection;

conducting a preheated asphalt feed including fresh asphalt and recycled oxidized asphalt, at a temperature from 125° C. to 300° C., as the motive liquid into the motive inlet of the liquid jet ejector;

drawing atmospheric air or compressed air into the suction port of the liquid jet ejector;

mixing the preheated asphalt within the main ejector body with the air from the suction port of the liquid jet ejector to form a mixture;

conducting the mixture to a heated and pressurized oxidizer vessel;

collecting an off-gas from the overhead of said oxidizer vessel and an oxidized asphalt product stream from the bottoms of said oxidizer vessel, wherein said oxidized asphalt product stream has softening temperature greater than the preheated asphalt feed; and

recycling a portion of the oxidized asphalt product stream back to the liquid jet ejector to form the recycled oxidized asphalt.

2. The process of claim 1 wherein the oxidizer vessel is operated at a temperature from 150° C. to 300° C. with the proviso that it be at least 10° C. greater than the temperature of the preheated asphalt feed being conducted to said motive inlet of the liquid jet ejector.

3. The process of claim 2 wherein the oxidizer vessel is operated at a temperature from 200° C. to 270° C.

4. The process of claim 1 wherein the recycled oxidized asphalt feed rate is at least 5 times greater than that of the fresh asphalt feed rate.

5. The process of claim 4 wherein the recycled oxidized asphalt feed rate is at least 20 times greater than that of the fresh asphalt feed rate.

6. The process of claim 1 wherein the oxidizer vessel is operated at a pressure of from 0 to 10 barg.

7. The process of claim 6 wherein the oxidizer vessel is operated at a to pressure of from 0 to 5 barg.

8. The process of claim 1 wherein the air feed rate is at least a stoichiometric amount based on the preheated asphalt feed rate.

9. The process of claim 1 further including the step of injecting steam from a steam generator to the oxidizer vessel.

10. The process of claim 9 wherein the injecting steam to the oxidizer vessel is above or below the liquid mixture in the oxidizer vessel.

11. The process of claim 1 wherein the air is compressed.

12. The process of claim 1 wherein the air is atmospheric.

13. Oxidized asphalt produced by the process of claim 1.