CLIAMS:1. A sulphur containing additive for bitumen paving mixtures, said sulphur containing additive comprising:
a. sulphur;
b. a mixture of metal oxides; and
c. optionally at least one metal sulphate,
wherein said mixture of metal oxides comprising calcium oxide, silicon dioxide, aluminum oxide, and ferric oxide .
2. The sulphur containing additive as claimed in claim 1, wherein the composition of said sulphur containing additive is:
a. sulphur in an amount ranging from 85 to 98 weight% of the sulphur containing additive;
b. metal oxides in an amount ranging from 2 to 15 weight% of the sulphur containing additive; and
c. metal sulphate in an amount ranging from 0 to 10 weight% of the sulphur containing additive.
3. The sulphur containing additive as claimed in claim 1, wherein the composition of said mixture of metal oxides comprises:
a. calcium oxide in an amount ranging from 50 weight% to 70 weight%;
b. silicon dioxide in an amount ranging from 10 weight% to 30 weight%;
c. aluminium oxide in an amount ranging from 1 weight% to 10 weight%; and
d. ferric oxide in an amount ranging from 1 weight% to 10 weight%.
4. The sulphur containing additive as claimed in claim 1, wherein the metal sulphate is calcium sulphate used in an amount ranging from 0 to 10 weight%.
5. The sulphur containing additive as claimed in claim 1, wherein said sulphur containing additive is molded into at least one solid article shape selected from the group consisting of pastilles, flakes, extrudates and granules.
6. The process for the preparation of an sulphur containing additive as claimed in claim 1, wherein said process comprises the following steps:
a. providing sulphur;
b. heating said sulphur to obtain molten sulphur;
c. mixing a mixture of metal oxides, optionally metal sulphate and said molten sulphur to obtain a slurry; and
d. cooling said slurry to obtain the sulphur containing additive.
7. The process as claimed in claim 6, wherein the mixture of metal oxides and metal sulphate is added to sulphur before heating to obtain the molten sulphur followed by cooling to obtain sulphur containing additive.
8. The process as claimed in claim 6, wherein sulphur is heated in the temperature range of 70 to 160 °C.
9. A process for the preparation of bitumen paving mixture comprising mixing sulphur containing additive as claimed in claim 1 to the bitumen at a temperature in the range of 80 to 180 °C, preferably in the range of 120 to 135 °C and at a mixing speed ranging from 20 to 100 rpm, preferably ranging from 30 to 70 rpm. ,TagSPECI:FIELD
The present disclosure relates to a sulphur containing additive for making bitumen paving mixtures and method for the preparation thereof.
BACKGROUND
Viscosity grade bitumen is used to coat aggregate material for the construction and/or pavement of roads. Sulphur is mixed with bitumen to enhance properties of bitumen viz. mechanical strength, corrosion and water resistance, marshal stability, fatigue, resilient modulus (MR) and the like. However, use of sulphur in bitumen for making bitumen paving mixtures is restricted due to emission of hydrogen sulphide gas during use of sulphur extended bitumen in paving mixture preparation, its transportation or laying down on the road. The H2S released while mixing of sulphur with bitumen may be derived from several sources. The chemistry of generation of H2S is the reaction that occurs between bitumen and sulphur at temperatures greater than 80 °C. Sulphur has condensing effect upon asphalt under heat resulting in the formation of gaseous hydrogen sulphide as per below given reaction:
CxHy + S ? CxHy-2 + H2S (g)
At temperature 80 to 100 °C, cracking of sulphur containing organic compounds is also responsible for liberation of H2S. H2S emission is hazardous as directly affecting human nervous system and therefore not desired.
Occupational safety and health administration (OSHA) has established a permissible exposure limit (8 hour time-weighted average of 10 ppm and acceptable ceiling concentration of 20 ppm.)
Hence, it is essential to minimize the emission of hazardous H2S gas during paving mixture preparation.
OBJECTS:
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to provide a sulphur containing additive for producing bitumen paving mixture having significant H2S suppressant ability.
It is another object of the present disclosure to reduce the emission of H2S gas below permissible limit during preparation, transportation and application of bitumen paving mixture.
It is still another object of the present disclosure to provide a simple, economic and safe process for the preparation of sulphur containing additive.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
SUMMARY:
The present disclosure provides a sulphur containing additive for making bitumen paving mixtures. The sulphur containing additive comprises of sulphur, a mixture of metal oxides and optionally at least one metal sulphate; said sulphur containing additive comprising:
• sulphur in an amount ranging from 85 weight% to 98 weight%;
• a mixture of metal oxides in an amount ranging from 2 weight% to 15 weight% ;
• at least one metal sulphate in an amount ranging from 0 to 10 weight%.
In accordance with one of embodiments of the present disclosure, the metal sulphate used along with mixture of metal oxides is calcium sulphate.
wherein the mixture of metal oxides comprising calcium oxide, silicon dioxide, aluminum oxide and ferric oxide.
The composition of said mixture of metal oxides includes:
a) calcium oxide in an amount ranging from 50 weight% to 70 weight%;
b) silicon dioxide in an amount ranging from 10 weight% to 30 weight%;
c) aluminium oxide in an amount ranging from 1 weight% to 10 weight%; and
d) ferric oxide in an amount ranging from 1 weight% to 10 weight%.
Present invention also discloses the process for the preparation of the sulphur containing additive and its subsequent use in the bitumen paving mixture.
The sulphur containing additive of the present disclosure reduces the emission of hydrogen sulphide (H2S) gas below permissible level during the preparation of bitumen paving mixture, its transportation and laying on the road.
DETAILED DESCRIPTION:
The present disclosure provides a sulphur containing additive for reducing the emission of H2S gas during the preparation of sulphur extended bitumen paving mixtures.
In accordance with one aspect of the present disclosure there is provided a sulphur containing additive for preparing bitumen paving mixtures, the sulphur containing additive comprising:
• sulphur;
• a mixture of metal oxides; and
• optionally at least one metal sulphate,
The composition of the sulphur containing additive comprises of various proportion of sulphur, a mixture of metal oxides and optionally at least one metal sulphate.
Sulphur content in the sulphur containing additive ranges from 85 weight% to 98 weight%.
The amount of a mixture of metal oxides and metal sulphate in the sulphur containing additive is in the range from 2 weight% to 15 weight%, preferably ranges from 7 weight% to 10 weight %.
The amount of at least one metal sulphate in the sulphur containing additive is in the range from 0 to 10 weight%.
In accordance with one embodiment of the present disclosure, the metal sulphate is calcium sulphate.
The composition of mixture of metal oxides is as follows:
• calcium oxide in an amount ranging from 50 to 70 weight%;
• silicon dioxide in an amount ranging from 10 to 30 weight%;
• aluminium oxide in an amount ranging from 1 to 10 weight%; and
• ferric oxide in an amount ranging from 1 to 10 weight%.
In accordance with another aspect of the present disclosure there is provided a process for the preparation of the sulphur containing additive, the process comprising the following steps:
In the first step sulphur is provided;
In the second step sulphur is heated to obtain molten sulphur;
In the third step, a mixture of metal oxides, optionally at least one metal sulphate and said molten sulphur are mixed and heated to obtain melted slurry.
In the fourth step the melted slurry is cooled to obtain the sulphur containing additive.
In yet another embodiment, sulphur can be molten after addition and homogeneous mixing of metal oxide and metal sulphate in powder form, to obtain melted slurry which is further cooled to obtain sulphur containing additive.
In accordance with one embodiment of the present disclosure sulphur or mixture of sulphur with metal oxide and metal sulphate is heated at the temperature in the range of 70 to 160 °C to obtain the molten sulphur or melted slurry.
The melted slurry is then molded into solid article having at least one of the shapes selected from the group consisting of pastilles, flakes, extrudates and granules.
In accordance with still another aspect of the present disclosure there is provided a process for the preparation of bitumen paving mixtures, said process comprising the following steps:
In the first step bitumen is crushed into pieces of desired size;
In the second step bitumen is heated to melt to obtain molten bitumen;
In the third step, the molten bitumen and the sulphur containing additive are mixed to obtain said bitumen paving mixtures.
It has been found that certain combinations of mixing agitator speed and temperature is more effectively suppressing H2S generation while preparation of bitumen paving mixture having minimum 30 wt% of sulphur containing additive. Preferred mixing speed of sulphur containing additive with bitumen is in the range of 20 to 100 rpm, preferably in the range of 30 to 70 rpm. The mixing temperature is in the range of 80 to 180 oC, preferably in the range of 120 to 135 oC. The bitumen paving mixture from this composition can be applied in places having extreme weather conditions of temperature (-10 to 700C).
Use of a sulphur containing additive in bitumen paving mixtures is useful for reducing the emission of hydrogen sulphide (H2S) gas. Sulphur containing additive when mixed with bitumen, enhances the binding property of the bitumen due to which the quality of roads in terms of marshal stability, mechanical strength, corrosion resistance, water resistance, fatigue resistance, resilient modulus (MR) and the like is improved.
In accordance with one embodiment of the present disclosure, the preparation of bitumen paving mixture comprising mixing sulphur containing additive to the bitumen at a temperature in the range of 80 to 180 oC, more preferably in the range of 120 to 135oC and at a mixing speed ranging from 20 rpm to100 rpm, more preferably from 30 rpm to 70 rpm.
The present disclosure is further illustrated herein below with the help of the following examples. The examples used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
Example-1:
A beaker was charged with a 60 g of crushed sulphur pellets or sulphur powder. The crushed sulphur pellets were then heated at a temperature of 150 °C to obtain molten sulphur. 5 g of a mixture of metal oxides and metal sulphate was added in the beaker under constant stirring of molten sulphur to obtain homogeneous slurry. The slurry was cooled and molded into granules to obtain the sulphur containing additive.
Example-2:
A beaker was charged with 140 g of bitumen. The bitumen was heated at a temperature of 180 °C to obtain the heated bitumen. 60 g of the sulphur containing additive was added under continuous stirring of 50 rpm to obtain the bitumen paving mixture. H2S emission was observed at zero inch level of beaker brim using multi-gas detector at a temperature range within 120 to 180 °C.
Table-1 illustrates the effect of addition of the sulphur containing additive in bitumen on H2S emission
Table-1:
Experiment No. Sulphur containing additive (weight%) Sulphur
(weight%) Bitumen (weight%) Temperature (°C) H2S emission
(ppm)
1 0 30 70 140 200
2 30 0 70 100 non-detectable
3 30 0 70 120 < 2
4 30 0 70 140 < 2
5 30 0 70 160 > 6
6 30 0 70 180 > 10
As shown in Table 1, Exp. No 1 is performed for the comparative purpose, wherein no sulphur containing additive is added. It is observed that on addition of sulphur in bitumen paving mixture at 140 °C results in emission of 200 ppm of hydrogen sulphide (H2S) gas. However, Experiment No’s 2 to 6 shows that the emission of hydrogen sulphide (H2S) gas is reduced by the addition of sulphur containing additive in bitumen paving mixture.
Example-3:
The bitumen paving mixture prepared in Example-2 was cooled down overnight to room temperature to obtain a solid mass. The solid mass was cut into pieces and heated at a temperature of 80 °C. H2S emission was checked at different levels using multi-gas detector.
Table-2 illustrates the effect of addition of the sulphur containing additive in bitumen on H2S emission as given in Example-3
Table-2:
Bitumen paving mixture
(weight%) Temperature
(°C) H2S emission
(ppm)
100 40 non-detectable
100 60 non-detectable
100 80 non-detectable
100 100 < 2
Table-2 clearly reveals that, sulphur containing additive in bitumen paving mixture results in reduction in the emission of hydrogen sulphide gas. Heating the solid mass of bitumen paving mixture at temperature range within 40 to 100 °C shows non-detectable H2S emission or less than 2 ppm of H2S emission.
TECHINCAL ADVANCEMENT:
The present disclosure relates to the sulphur containing additive for making bitumen paving mixtures and the process for preparation thereof. The sulphur containing additive has several technical advancements such as:
• hydrogen sulphide gas (H2S) emission during the preparation of bitumen paving mixture is mitigated; and
• the process for the preparation of the sulphur containing additive is economically viable.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.