Prevention of the emission of hydrogen sulphide in the production of hot bitumen or asphalt

Abstract

The present application relates to a method to prevent the emission of hydrogen sulphide in the production of hot bitumen or asphalt having a temperature of between 150 and 200° C., wherein the method comprises the steps of providing a bituminous or asphalt mixture, heating the mixture until a temperature of between 150-200° C. and adding an aqueous calcium nitrate solution or a calcium nitrate powder while mixing the bituminous or asphalt mixture. The present application furthermore relates to the use of an aqueous calcium nitrate solution or a calcium nitrate powder during mixing of a bituminous or asphalt mixture in the production of a hot bitumen or asphalt having a temperature of between 150 and 200° C. to prevent the emission of hydrogen sulphide.

Claims

1. A method to reduce the emission of hydrogen sulphide in the production of hot bitumen or asphalt, wherein the method comprises the steps of: providing a bituminous or asphalt mixture comprising sulfide; heating the mixture to a temperature of between 150-200° C.; and adding an aqueous calcium nitrate solution or a calcium nitrate powder while mixing the bituminous or asphalt mixture.

2. The method according to claim 1, wherein an amount of calcium nitrate added is between 0.5 and 2.0 mg calcium nitrate per mg sulfide present in the bituminous or asphalt mixture.

3. The method according to claim 2, wherein around 1 mg of calcium nitrate is added per mg sulfide present in the bituminous or asphalt mixture.

4. The method according to claim 1, wherein the calcium nitrate powder has a water content of between 1 and 33 weight %.

5. The method according to claim 1, wherein the aqueous calcium nitrate solution has a concentration of between 45 and 55 weight % of calcium nitrate and between 45 and 55 weight % of water.

6. A method comprising adding calcium nitrate to a bituminous or asphalt mixture while mixing at a temperature between 150 and 200° C., the bituminous or asphalt mixture comprising sulfide, wherein the emission of hydrogen sulphide is prevented, the calcium nitrate being in the form of a calcium nitrate solution or powder, wherein the calcium nitrate powder has a particle size of less than 0.5 mm.

7. The method according to claim 6, wherein an amount of between 0.5 and 2.0 mg calcium nitrate is added per mg sulfide present in the bituminous or asphalt mixture.

8. The method according to claim 7, wherein the amount of calcium nitrate added is around 1 mg calcium nitrate per mg sulfide present in the bituminous or asphalt mixture.

9. The method according to claim 6 wherein the calcium nitrate powder has a water content of between 1 and 33 weight %.

10. The method according to claim 6 wherein the aqueous calcium nitrate solution has a concentration of between 45 and 55 weight % of calcium nitrate and between 45 and 55 weight % of water.

Description

DETAILED DESCRIPTION

(1) A method according to the application to prevent the emission of hydrogen sulphide (H.sub.2S) in the production of hot bitumen or asphalt is described herein. More particularly, the method according to the application aims primarily to counteract the emission of H.sub.2S from a hot bitumen or asphalt mixture, rather than to cure the emission. The method comprises the following steps: Producing or providing a bituminous or asphalt mixture, heating the bituminous or asphalt mixture to a temperature of between 150 to 200° C., and adding an aqueous calcium nitrate solution or a calcium nitrate powder while mixing the bituminous or asphalt mixture.

(2) More in particular, an amount of between 0.5 and 2.0 mg calcium nitrate, and most in particular, an amount of around 1 mg calcium nitrate is added per mg sulphide present in the bituminous or asphalt mixture.

(3) In the context of the present invention, the term “bituminous or asphalt mixture” is the residue and heaviest fraction obtained during refining of crude oil. It comprises very long chain hydrocarbon compounds, which do not evaporate during the refining process, and in addition mineral impurities and sulphur compounds. It is understood that the bituminous or asphalt mixture is not made up of a homogenous single hydrocarbon compound.

(4) Suitable assays and ASTM standard methods to determine the sulphide content of petroleum products are known. For asphalt and bitumen, a so-called and well-known “can test” method is typically used, wherein a sample, e.g. an asphalt or bitumen sample, is put into a metal container, and following heating of the container, the H.sub.2S emission of the sample is determined by measuring the H.sub.2S content of the head space in the metal container. The measurement of hydrogen sulfide in the vapor phase may be, for instance, performed according to ASTM D5705-15.

(5) More in particular, the hydrogen sulphide concentration in asphalt or bitumen may be determined via the so-called Baker Hughes field can test method (see e.g. Draper and Stark, 2012, incorporated herein by reference http://www.digitalrefining.com/article/10000336#.WWxveYSGPRY), which allows for a more reproducible means of establishing the vapour phase in the sample container. In this method, quart-sized metal cans are used which are half-filled with asphalt, which is most appropriately sampled on-site with fresh asphalt directly from the unit into the sampling container. The metal cans are then sealed and shaken using a specially designed container that allows adequate agitation of the sample while protecting the operator from accidental leakage of hot asphalt. Samples are tested immediately using gas detection tubes and after storage at relevant temperatures and time periods.

(6) When calcium nitrate powder is used, the calcium nitrate powder has preferably a water content of between 1 and 33 weight %. The particle size of the calcium nitrate powder is of no importance.

(7) When an aqueous calcium nitrate solution is used, the concentration of calcium nitrate therein is preferably between 45 and 55 weight % and the rest is water, being between 45 and 55 weight %.

(8) The present application furthermore relates to the use of an aqueous calcium nitrate solution of a calcium nitrate powder in the production of the hot bituminous or asphalt mixture during mixing of a bituminous or asphalt mixture, wherein the hot bituminous or asphalt mixture has a temperature of between 150 and 200° C., to prevent the emission of hydrogen sulphide.

(9) In particular, an amount of between 0.5 and 2.0 mg of calcium nitrate, and more in particular, an amount of around 1 mg calcium nitrate per mg of sulphide present in the bituminous or asphalt mixture is used.

(10) When calcium nitrate powder is used, the calcium nitrate powder has a water content of between 1 and 33 weight %. When as an alternative an aqueous calcium nitrate solution is used, the solution has a concentration of between 45 and 55 weight % of calcium nitrate and between 45 and 55 weight % of water.

Example

(11) An experiment was performed using a bituminous emulsion called Elastopaz, an aqueous calcium nitrate solution and an aqueous sulphide solution, and Dräger Tubes®. Elastopaz is a single component bitumen polymer liquid membrane commercialised by the Israelian company Pazkar Ltd. Dräger Tubes® are gas detection tubes commercialized by the US Company Dräger.

(12) Approximately 100 ml of Elastopaz was added to a 600 ml beaker. A watch glass was placed on top of the beaker and the beaker was placed on a heating plate with a magnetic stirrer. The Elastopaz was heated to the boiling point of approximately 100° C. and an aqueous calcium nitrate solution in a concentration of 1 g/l and an aqueous solution of sodium sulphide nonahydrate in a concentration of 1 g/l were added to the hot Elastopaz. To ensure proper mixing, the aqueous calcium nitrate solution and the aqueous solution of sodium sulphide nonahydrate were added in the vortex that was created by the magnetic stirrer. A Dräger-Tube® was placed in the headspace over the beaker under the watch glass using an extension hose to measure the amount of hydrogen sulphide produced. The amount of hydrogen sulphide was measured three times consecutively in each sample. The time between each measurement was between 8 and 10 minutes. The samples were kept a boiling point throughout all measurements.

(13) A total of 12 samples were analysed. Three parallels each of four different calcium nitrate additions, i.e. 0 ml, 2.5 ml, 5 ml and 10 ml, equal to 0, 25, 50 and 100 mg calcium nitrate/litre Elastopaz respectively. 5 ml of the aqueous solution of sodium sulphide nonahydrate, equal to 50 mg S.sup.2−/litre Elastopaz was added to each sample.

(14) TABLE-US-00001 TABLE 1 Amount of Amount of Amount of Amount of aqueous CN- H.sub.2S in H.sub.2S in H.sub.2S in Measurement solution sample sample sample moment added (ml) 1 (ppm) 2 (ppm) 3 (ppm) 1 0 15.0 7.0 3.0 2 12.0 10.0 6.5 3 4.0 5.0 3.0 1 2.5 9.0 7.0 2.0 2 10.5 10.0 4.0 3 3.2 2.0 2.0 1 5.0 3.0 1.0 1.0 2 2.0 1.0 2.0 3 1.0 6.0 5.0 1 10.0 8.0 8.0 2.0 2 10.0 3.0 0.5 3 3.5 4.0 1.0

(15) As the results show in table 1, there is an indication that adding calcium nitrate to hot bitumen or asphalt during the mixing process prevents the emission of hydrogen sulphide. When 2.5 and 5.0 ml of the aqueous calcium nitrate solution is added, the hydrogen sulphide is reduced. Adding 10.0 ml of the aqueous calcium nitrate solution seems to be an overdose.