WO2014206986A1

WO2014206986A1 - Process for the manufacture of an asphalt composition

Info

Publication number: WO2014206986A1
Application number: PCT/EP2014/063289
Authority: WO
Inventors: Raghu HANUMANTHGARI; Dawid John D'MELO; Gary Fitts; Chantal Soubigou
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2013-06-24
Filing date: 2014-06-24
Publication date: 2014-12-31

Abstract

A process for manufacturing an asphalt composition comprising aggregate, bitumen, sulphur and an anionic surfactant is disclosed. The process uses sulphur pellets wherein from 0.05 wt% to 10 wt% of anionic surfactant, based upon the weight of the sulphur, is coated on the surface of the sulphur pellet.

Description

PROCESS FOR THE MANUFACTURE OF AN ASPHALT COMPOSITION

Field of the Invention

The invention relates to a process for the

manufacture of an asphalt composition, sulphur pellets that are used in the process for the manufacture of the asphalt composition and processes for the manufacture of the sulphur pellets.

Background of the Invention

In the road construction and road paving industry, it is a well-practised procedure to coat aggregate material such as sand, gravel, crushed stone or mixtures thereof with hot fluid bitumen, spread the coated material as a uniform layer on a road bed or previously built road while it is still hot, and compact the uniform layer by rolling with heavy rollers to form a smooth surfaced road.

The combination of bitumen with aggregate material, such as sand, gravel, crushed stone or mixtures thereof, is referred to as "asphalt". Bitumen, also referred to as "asphalt binder", is usually a liquid binder comprising asphaltenes, resins, saturate and aromatics . Bitumen can for example comprise pyrogenous mixtures derived from petroleum residues such as residual oils, tar or pitch or mixtures thereof.

It is known in the art that sulphur can be mixed with bitumen for applications in the road construction and road paving industry. Sulphur-modified bitumen is formulated by replacing some of the bitumen in

conventional binders by elemental sulphur. Sulphur- modified bitumen typically comprises a greater amount of sulphur than bitumen compositions in which sulphur is included as a crosslinking agent for polymer. A problem that may be encountered during the production and paving of sulphur-containing asphalt, especially asphalt prepared using sulphur-modified bitumen, is eye and throat irritation. WO 2012/160116 teaches that eye and throat irritation can be caused by the presence of sulphur vapour. WO 2012/160116 also teaches that by incorporating anionic surfactants such as calcium lignosulphonate into the sulphur-containing asphalt it is possible to reduce the quantity of sulphur vapour and thereby decrease the amount of eye and throat irritation experienced by workers. WO 2012/160116 describes a sulphur pellet comprising 0.05 to 10wt% of anionic surfactant and states that this may be prepared by mixing liquid sulphur with anionic surfactant, and subsequently shaping and/or pelletising the mixture.

Calcium lignosulphonate and other anionic

surfactants can be difficult materials to handle, particularly in connection with dust management. It is desirable to use a sulphur pellet that contains the anionic surfactant but the inventors have found that the manufacture of such pellets can be difficult due to poor miscibility of the surfactants with liquid sulphur. The poor miscibility leads to inhomogeneous distribution of surfactant within the pellet and leads to variation in the concentration of surfactant from pellet to pellet. The present inventors have sought to provide a process for the manufacture of an asphalt composition that avoids the problems of the prior art processes.

Summary of the Invention

The present inventors have found that surfactants such as calcium lignosulphonate are effectively combined with sulphur in a process whereby the surfactant is coated onto the surface of a sulphur pellet .

Accordingly the present invention provides a process for manufacturing an asphalt composition comprising aggregate, bitumen, sulphur and an anionic surfactant, the process comprising the steps of:

(i) heating bitumen;

(ii) heating aggregate;

(iii) mixing the hot bitumen with the hot aggregate in a mixing unit to form an asphalt composition;

wherein sulphur pellets are added in at least one of steps (i), (ii) or (iii); and wherein from 0.05 wt% to 10 wt% of anionic surfactant, based upon the weight of the sulphur, is coated on the surface of the sulphur pellet.

The invention further provides a process for preparing an asphalt pavement, wherein asphalt is prepared by a process according to the invention, and further comprising steps of :

(iv) spreading the asphalt into a layer; and

(v) compacting the layer.

In another aspect, the invention further provides sulphur pellets comprising an anionic surfactant in an amount of from 0.05wt% to 10wt%, based upon the weight of the sulphur, wherein the anionic surfactant is coated on the surface of the sulphur pellet.

In yet another aspect, the invention provides a process for preparing sulphur pellets comprising an anionic surfactant in an amount of from 0.05wt% to 10wt%, based upon the weight of the sulphur, comprising steps of contacting a liquid comprising the anionic surfactant with sulphur pellets and drying the sulphur pellets. Detailed Description of the Invention

The asphalt composition obtainable by the process of the present invention comprises aggregate, bitumen, sulphur and an anionic surfactant .

The aggregate is suitably any aggregate that is used in road applications. The aggregate may comprise coarse aggregate (retained on a 4mm sieve) , fine aggregate (passes a 4mm sieve but is retained on a 63μηι sieve) and/or filler (passes a 63μηι sieve) .

Typically, the asphalt composition comprises at least 1 wt% of bitumen, based on the weight of the asphalt composition. An asphalt composition comprising from about 1 wt% to about 10 wt% of bitumen is preferred, with a special preference for asphalt compositions comprising from about 3 wt % to about 7 wt % of bitumen, based on the weight of the asphalt composition.

The bitumen can be selected from a wide range of bituminous compounds . The bitumen that can be employed may be straight run bitumen, thermally cracked residue or precipitation bitumen, e.g. from propane. Although not necessary, the bitumen may also have been subjected to blowing. The blowing may be carried out by treating the bitumen with an oxygen-containing gas, such as air, oxygen-enriched air, pure oxygen or any other gas that comprises molecular oxygen and an inert gas, such carbon dioxide or nitrogen. The blowing operation may be conducted at temperatures of 175 to 400°C, preferably from 200 to 350°C. Alternatively, the blowing treatment may be conducted by means of a catalytic process.

The bitumen for use herein is preferably a paving grade bitumen suitable for road application having a penetration of, for example, from 9 to lOOOdmm, more preferably of from 15 to 450dmm (tested at 25°C according to EN 1426: 1999, revised in March 2007) and a softening point of from 25 to 100°C, more preferably of from 25 to 60°C (tested according to EN 1427: 1999, revised in March 2007) .

The amount of sulphur in the asphalt composition is preferably from 10 to 200 wt%, based upon the weight of the bitumen, preferably from 20wt%, more preferably from 40wt% and preferably to 100wt%, more preferably to 80wt%. The presence of sulphur in the asphalt paving mixture can improve the strength and rutting resistance of the paving mixture and it is important to include sufficient sulphur to realise these advantages. Additionally, incorporating increased amounts of sulphur can decrease the cost of the paving mixture. However, too much sulphur can decrease the workability of the paving mixture.

The sulphur is incorporated into the asphalt

composition in the form of sulphur pellets. Reference herein to pellets is to any type of sulphur material that has been cast from the molten state into some kind of regularly sized particle, for example flakes, slates or sphere-shaped sulphur such as prills, granules, nuggets and pastilles or half pea sized sulphur. The sulphur pellets typically comprise from 50 to 100wt% of sulphur, based upon the weight of the sulphur pellets, preferably from 60wt% and most preferably from 70wt%; and typically to 99wt%, and preferably to 95wt% or to 100wt%. A more preferred range is from 60 to 100wt%.

These sulphur pellets may contain carbon black and, optionally, other ingredients, such as amyl acetate and wax. Carbon black may be present in amounts up to 5%wt, based on the pellet, preferably up to 2%wt. Suitably, the content of carbon black in the sulphur pellet is at least 0.25%wt. The content of other ingredients, such as amyl acetate and wax, typically does not exceed an amount of 1.0%wt each. When wax is present, it may be in the form of, for example, slack wax or wax derived from a Fischer- Tropsch process. Examples of suitable waxes for use herein are Sasobit (RTM) , a Fischer-Tropsch derived wax commercially available from Sasol, and SX105 wax, a Fischer-Tropsch wax from Shell Malaysia.

An example of a suitable sulphur pellet for use herein is Thiopave (RTM) pellets commercially available from Shell Canada.

The anionic surfactant is suitably chosen from: the group consisting of lignin derivatives such as

lignosulphonates; aromatic sulphonates and aliphatic sulphonates and their formaldehyde condensates and derivatives; fatty acids and carboxylates , including sulphonated fatty acids; and phosphate esters of

alkylphenol-, polyalkylaryl- or alkyl- alkoxylates.

In a preferred embodiment, the anionic surfactant is a lignin derivative, more preferably a lignosulphonate . Lignosulphonates are known and are defined, for example, in Rompp Chemielexikon [Dictionary of Chemistry] , 9th Edition, Volume 3, Georg-Thieme Verlag, Stuttgart, N.Y. 1990, page 2511. Particularly suitable lignosulphonates are the alkali metal salts and/or alkaline earth metal salts and/or ammonium salts, for example the ammonium, sodium, potassium, calcium or magnesium salts of

lignosulphonic acid. The sodium, potassium or calcium salts are preferably used, and the sodium and/or calcium salts are most preferably used.

Lignosulphonates are derived from lignin, which is found in the cellular material of plants, e.g. trees.

Lignins comprise polymeric propylphenol substituted moieties which are interconnected at various positions on the carbon skeleton through a phenoxy group.

Lignosulphonate may be produced from lignin by a sulphite process, in which suitable feedstock such as wood is digested at 140-170°C with an aqueous solution of calcium bisulphite in acidic conditions. A benzylic cation is formed under the stated conditions, which is quenched by the sulphite ion to produce a sulphonated derivative which is separated.

R = H, alkyl, aryl

Ri = H, neighbouring lignin unit

R2 = neighbouring lignin unit

Details of this process are described, for example, in Monomers, Polymers and Composites from Renewable

Resources; M. N. Belgacem, A. Gandini; Elsevier, 2008, 225-241.

Depending on the nature of the reaction conditions the lignosulphonate produced can contain carbohydrate components which are chemically linked to the

lignosulphonate molecular framework. This material finds commercial applications as sugared lignosulphonate, which may for example have a carbohydrate content as high as 35wt% depending on manufacturing conditions. Alcoholic fermentation of a sugared lignosulphonate mixture or selective chemical treatment by ultrafiltration can be used to remove sugar content to produce a de-sugared calcium lignosulphonate. Lignosulphonates useful as anionic surfactants in the context of the invention may be sugared

lignosulphonates or de-sugared lignosulphonates and may be derived from softwood or hardwood feedstocks.

For example, sugared lignosulphonates derived from hardwood and de-sugared lignosulphonates derived from softwood have been found to be of particular use.

Preferably, the carbohydrate content of the

lignosulphonates, as determined by TAPPI test method T 249 cm-85 (involves an acid treatment followed by gas chromatography analysis), may be at most 35wt%, more preferably at most 15wt%, even more preferably at most 5wt% .

In some embodiments of the invention, the

lignosulphonates may have a sulphur content in the range of from 4 to 8 wt%, and/or a sulphur content in the +6 (sulphonate) oxidation state in the range of from 4 to 8wt%. The molecular weight of the lignosulphonates may vary considerably and may lie, for example, in the range of from 7000 to 35000 Daltons, preferably 12,000 to

28, 000 Daltons .

The term lignosulphonates also encompasses mixed salts of different ions such as potassium/sodium

lignosulphonate, potassium/calcium lignosulphonate or the like, in particular sodium/calcium lignosulphonate.

In another embodiment, the anionic surfactant is an aromatic sulphonate. Examples of aromatic sulphonates are alkylnaphthalene sulphonates and condensates thereof; preferably the alkyl group contains 1 to 10 carbon atoms. Typical counter-ions are: proton, sodium, potassium, calcium, isopropropyl ammonium, ammonium, alkanolamine etc. Exemplary alkylnaphthalene sulfonates include metal salts and organic salts of alkylnaphthalene sulfonates such as sodium diisopropylnaphthalene sulfonate,

butylnaphthalene sodium sulfonate, nonylnaphthalene sodium sulfonate, sodium dibutylnaphthalene sulfonate and sodium dimethylnaphthalene sulfonate.

Also, alkylbenzene sulphonates are preferred, in particular wherein the alkyl contains 1 to 20 carbon atoms, such as 1 to 12 carbon atoms. Suitable

alkylbenzene sulphonates may be provided as a mixture of alkylbenzene sulphonates with a range of alkyl carbon atoms, preferably 10 to 16 carbon atoms, with the mean number of carbon atoms preferably being in the range of from 1 to 12. The alkylbenzene sulphonates may be linear or branched, with linear alkyl preferred for enhanced biodegradability . A particularly preferred alkylbenzene sulphonate is dodecyl benzene sulphonate, e.g. as its sodium salt .

Aliphatic sulphonates may, for example, be chosen from sulphonates of the formula R-S0₂-0-R', wherein R is C₈-Ci6 alkyl or alkenyl and R' is a counter-ion selected from: proton, sodium, potassium, calcium, isopropropyl ammonium, ammonium, alkanolamine .

Fatty acids and carboxylates may, for example, be chosen from carboxylic compounds of formula RCOOH, wherein R is C₈-C₂2 alkyl or alkenyl and optionally their carboxylates or salts. Preferably R is an alkyl group. It is preferred that R is a Ci₅-C₂o alkyl or alkenyl group, more preferably a Ci₅-Ci₈ alkyl or alkenyl group, and especially a Ci₅-Ci₈ alkyl group. For example, the fatty acid may be stearic acid. Alternatively, R may be a C₂i^~ C₂2 alkyl group, e.g. the carboxylic additive may be behenic acid. The fatty acids may be sulphonated.

Phosphate esters of alkylphenol-, polyalkylaryl- or alkyl- alkoxylates may, for example, be chosen to comprise in the range of from 1 to 30 carbon atoms, e.g. 5 to 25 carbon atoms or 10 to 20 carbon atoms.

The amount of anionic surfactant is from 0.05 wt% to 10 wt%, based upon the weight of the sulphur. Preferably the amount of anionic surfactant is from 0.1 to 8wt%, more preferably from 0.2 to 5wt% and most preferably from 0.7 to 3wt%. Sufficient anionic surfactant should be incorporated to achieve the desired reduction in sulphur vapour and eye and throat irritation, but larger

quantities will incur greater expense. For the avoidance of doubt, the "anionic surfactant" is described herein as a component which may consist of one or more of the anionic surfactant types or anionic surfactants mentioned herein .

The sulphur pellets comprise from 0.05 wt% to 10 wt% of anionic surfactant, based upon the weight of the sulphur, and the anionic surfactant is coated on the surface of the sulphur pellet. By "coated on the surface of the pellet" the inventors mean that the anionic surfactant is located on the outer surface of the sulphur pellet, rather than being present in the bulk of the sulphur pellet .

The sulphur pellets having anionic surfactant coated on the surface of the pellet are suitably prepared by a process comprising a step of contacting a liquid

comprising the anionic surfactant with sulphur pellets. In a first embodiment of the invention, the sulphur pellets are prepared by a process comprising steps of contacting an aqueous solution comprising the anionic surfactant with sulphur pellets and drying the sulphur pellets. The aqueous solution preferably comprises from 1 to 80wt% anionic surfactant (based upon the weight of the aqueous solution) , more preferably from 5 to 70wt% of anionic surfactant . The aqueous solution preferably comprises from 20 to 99wt% water, more preferably from 30 to 95wt% water. The aqueous solution may comprise additional components and in a preferred embodiment, the aqueous solution comprises a water-soluble polymer such as polyvinyl alcohol. The polymer may assist in providing a more flexible coating of anionic polymer on the surface of the sulphur pellets. The aqueous solution preferably comprises from 1 to 30wt% water-soluble polymer, more preferably from 2 to 10wt% water-soluble polymer. The step of contacting the aqueous solution and the sulphur pellets suitably involves stirring to ensure that the aqueous solution contacts all surfaces of the sulphur pellets. The amount of aqueous solution is chosen such that the solution is able to readily contact all of the sulphur pellets. The sulphur pellets may be dried at ambient temperature, but are preferably dried at

temperatures of from 40 to 90°C, more preferably from 50 to 70°C.

In a second embodiment of the invention, the sulphur pellets are prepared by a process comprising a step of contacting a hot melt with sulphur pellets wherein the hot melt comprises wax and anionic surfactant. The pellets are then cooled such that the wax solidifies and the wax and anionic surfactant are coated on the surface of the sulphur pellets.

The sulphur pellets may also be prepared by a process comprising steps of contacting a carrier material with sulphur pellets and subsequently spraying a powder of anionic surfactant onto the pellets. The carrier material is suitably a base oil or a wax.

The asphalt composition of the invention may suitably comprise additional components. In one embodiment of the invention, the asphalt composition comprises a polymer. A preferred type of polymer is a copolymer comprising one or more vinyl aromatic compounds and one or more conjugated dienes, in an amount of 0.1 to 7 %wt, based upon the weight of the asphalt composition.

More preferably the polymer is a linear styrene- butadiene-styrene block copolymer of formula ABA wherein A is a polystyrene block and B is a polybutadiene block. Another preferred type of polymer is a copolymer formed from monomers including ethylene and glycidyl

methacrylate or glycidyl acrylate, in an amount of 0.1 to 7 %wt, based upon the weight of the asphalt composition. More preferably the polymer is a terpolymer formed from ethylene, alkyl acrylate and glycidyl methacrylate or glycidyl acrylate.

The asphalt composition may comprise an aminic compound selected from carbamides, thiocarbamides, carbamates and thiocarbamates, and mixtures thereof. The asphalt composition preferably comprises from 0.01 wt% to 10 wt% of the aminic compound. Preferred aminic compounds include urea, N, N' - (bishydroxymethyl ) urea, N, N' -dimethyl urea, N, N' trimethyl urea, 1,1-dimethyl urea, 1,3-diethyl urea, 1 , 3-dimethyl-l , 3-diphenyl urea, benzyl urea, tert- butyl urea, phenyl urea, 1, 3-diphenyl urea, 1,3-carbonyl dipiperidine, 1,3-dipropyl urea, 1,3-dibutyl urea, l-[3-

(trimethoxysilyl ) propyl ] urea, methyl carbamate, ethyl carbamate (also known as urethane), tert-butyl carbamate, phenyl carbamate and propyl carbamate.

In step (i) of the processes for manufacturing the present asphalt compositions the bitumen is heated, preferably at a temperature of from 60°C to 200°C, preferably from 80 to 150°C, more preferably from 100°C to 145°C, and even more preferably from 125°C to 145°C. Working above 120°C has the advantage that sulphur is liquid which facilitates the mixing process. Although the skilled person can easily determine the optimal mixing time the mixing time may be relatively short, e.g., from 10 to 600 seconds.

In step (ii) of the process for manufacturing the present asphalt composition the aggregate is heated, preferably at a temperature of from 60 to 200°C,

preferably from 80 to 170°C, more preferably from 100 to 160°C, even more preferably from 100 to 145°C.

In step (iii) of the asphalt manufacturing process, the hot bitumen from step (i) and hot aggregate from step (ii) are mixed in a mixing unit. Suitably, the mixing takes place at a temperature of from 80 to 200°C, preferably from 90 to 150°C, more preferably from 100 to

145°C. Typically, the mixing time is from 10 to 60 seconds, preferably from 20 to 40 seconds.

The sulphur pellets are preferably added as late as possible in the process, preferably in step (iii) .

The sulphur pellets may be added in step (i) , step

(ii) or step (iii) . In a first embodiment, the hot aggregate is mixed with the sulphur pellets. Hot bitumen is then added to the hot aggregate-sulphur pellets mixture. In a second embodiment, hot aggregate is mixed with hot bitumen, and the sulphur pellets are added to the hot bitumen-aggregate mixture. This embodiment offers the advantage of producing a stronger sulphur-asphalt mixture strength. In a third embodiment, hot bitumen is mixed with the sulphur pellets and the resulting hot bitumen-sulphur pellets mixture is mixed with hot aggregate to obtain a sulphur-comprising asphalt mixture.

In one embodiment of the invention sulphur may be added in the form of two types of sulphur pellets; a first type of sulphur pellet that comprises the anionic surfactant and a second type of sulphur pellet that does not comprise the anionic surfactant. This has the advantage that the anionic surfactant is essentially concentrated in the first type of sulphur pellet and conventional sulphur pellets can be used to make up the rest of the sulphur requirement .

(iv) spreading the asphalt into a layer; and

(v) compacting the layer.

The invention further provides an asphalt pavement prepared by the process according to the invention.

The compaction in step (v) suitably takes place at a temperature of from 80 to 200°C, preferably from 90 to 150°C, more preferably from 100 to 145°C. The temperature of compaction is desirably kept as low as possible in order to reduce hydrogen sulphide emissions. However, the temperature of compaction needs to be sufficiently high such that the voids content of the resulting asphalt is sufficiently low for the asphalt to be durable and water resistant .

The invention will now be illustrated by means of the following Examples, which are not intended to limit the invention.

Comparative Example 1

This comparative examples demonstrates the poor miscibility of calcium lignosulphonate and sulphur and the difficulty in forming homogeneous pellets.

Calcium lignosulphonate (2.0 %) was added to molten elemental sulphur (98.0 %) and was observed to float on the surface of the sulphur. When the speed of mixing was increased some mixing was observed. However, when the mixing was stopped to assess the miscibility, the calcium lignosulphonate was observed to separate out and float on the surface of the sulphur. When pellets were formed, a brown coating was observed on the upper surface of the pellet .

The concentration of calcium lignosulphonate was decreased in 0.5% increments to determine the highest concentration which was miscible with sulphur. Some improvement in miscibility was observed at lower calcium lignosulphonate concentrations, but separation was still observed when 0.5% calcium lignosulphonate was added to sulphur. Separation of calcium lignosulphonate was observed in the pellets formed, at all calcium

lignosulphonate concentrations, resulting in an uneven distribution of calcium lignosulphonate in the pellet and a concentration of additive on the upper pellet surface. Example 1

An aqueous solution containing 15wt% calcium lignosulphonate (Borregaard LignoTech) , 5wt% polyvinyl alcohol (Merck) and 80wt% water was prepared. 98g of sulphur pellets were taken in a glass beaker and an amount of the aqueous solution was added, in order to have a calcium lignosulphonate concentration of 2.0wt% on drying (based upon the weight of the sulphur pellet) . The mixture was stirred using a spatula to uniformly coat all the sulphur granules. The coated sulphur pellets were then placed in an aluminium tray and dried for 24 hours at 60°C. The coated sulphur pellets were then visually assessed and appeared to have uniform coatings. Example 2

An aqueous solution containing 60wt% calcium lignosulphonate (Borregaard LignoTech) and 40wt% water was prepared. Sulphur pellets were taken in a glass beaker and an amount of the aqueous solution was added.

The mixture was stirred using a spatula to uniformly coat all the sulphur pellets. The coated sulphur pellets were dried at room temperature for 30 minutes and for 15 minutes at 80°C. The coated sulphur pellets were then visually assessed and observed to have uniform coatings.

The amount of calcium lignosulphonate coated on the pellets was determined by immersing a pre-weighed amount of the coated pellets in water for 8 hours and then filtering. The pellets were then washed with water and filtered until the water collected was clear. The pellets were dried at 80°C, weighed and the amount of calcium lignosulphate coated determined from the decrease in weight .

Example 3

Batches of asphalt were prepared. Each batch weighed approximately 1200 g and included 4% bitumen (PG64-22) and 3% sulphur by weight of the total mixture. The aggregates used were siliceous gravel and natural sand. To induce more fuming, zeolites were blended with the mixture at 0.3% by weight of the total mixture. Before mixing, the aggregates and bitumen had been held in a 300°F (149°C) oven overnight.

A total of four asphalt mixtures were prepared.

Comparative Mixture 1 contained no lignosulphonate additive. Comparative Mixture 2 contained 2% calcium lignosulphonate by weight of the sulphur and the calcium lignosulphonate was added as a dry powder. Comparative Mixture 3 contained 2% calcium lignosulphonate by weight of the sulphur and the calcium lignosulphonate was added as dry granules. Example Mixture 1 contained 2% calcium lignosulphonate and the calcium lignosulphonate had been coated onto the surface of sulphur pellets. The coated sulphur pellets were prepared by contacting sulphur pellets with an aqueous solution of calcium

lignosulphonate and then drying overnight in an oven at 140°F (60°C) .

After observations were made, each mixture was placed in a labelled, sealed plastic bag (used for oven roasting) and set in a 275°F (135°C) oven to see if there was any noticeable difference in fuming while the sulphur was in a molten state.

It was observed that with Comparative Mixture 2 (powdered calcium lignosulphonate), the sulphur smell during mixing was practically eliminated. Comparative Mixture 3 (granules of calcium lignosulphonate) improved the smell of the mixture compared to Comparative Mixture 1 (no calcium lignosulphonate) , but the improvement in smell was not as good as for Comparative Mixture 2

(powdered calcium lignosulphonate) . Example Mixture 1 had a similar effect on odour as for Comparative Mixture 2 and, additionally, visible fume seemed to be reduced.

Claims

C L A I M S

1. A process for manufacturing an asphalt composition comprising aggregate, bitumen, sulphur and an anionic surfactant, the process comprising the steps of:

(i) heating bitumen;

(ii) heating aggregate;

2. A process according to claim 1, wherein the anionic surfactant is a lignosulphonate .

3. A process for preparing an asphalt pavement, wherein asphalt is prepared by a process according to claim 1 or claim 2, and further comprising steps of:

(iv) spreading the asphalt into a layer; and

(v) compacting the layer.

4. Sulphur pellets comprising an anionic surfactant in an amount of from 0.05wt% to 10wt%, based upon the weight of the sulphur, wherein the anionic surfactant is coated on the surface of the sulphur pellet.

5. Sulphur pellets according to claim 4, wherein the anionic surfactant is a lignosulphonate.

6. A process for preparing sulphur pellets comprising an anionic surfactant in an amount of from 0.05wt% to 10wt%, based upon the weight of the sulphur, comprising a step of contacting a liquid comprising the anionic surfactant with sulphur pellets.

7. A process for preparing sulphur pellets according to claim 6, comprising steps of contacting an aqueous solution comprising the anionic surfactant with sulphur pellets and drying the sulphur pellets.

8. A process for preparing sulphur pellets according to claim 7, wherein the aqueous solution comprises a water- soluble polymer.

9. A process for preparing sulphur pellets according to claim 8, wherein the water-soluble water is polyvinyl alcohol.