WO2022266733A1 - Process for obtaining an asphalt binder modified with waste tyre rubber powder - Google Patents

Abstract

The present invention relates to a process for obtaining an asphalt binder modified with waste tyre rubber powder, characterized by involving combining, in a single step, in a process of grinding in a high-shear dispersion reactor, the waste tyre rubber powder with the asphalt cement subjected to heating at a temperature ranging from 175ºC to 200ºC, with the rubber powder falling within the following grain size range: 0%-5% of the particulate material can pass through a #200 (0.075 mm) sieve, 10%-35% can pass through a #80 (0.180 mm) sieve, 40%-80% can pass through a #50 (0.300 mm) sieve, 60%-100% can pass through a #40 (0.420 mm) sieve and 100% can pass through a #30 (0.600) sieve; and the rubber powder having a minimum volatile polymer material content of 60%, a maximum carbon black content of 36% and a maximum ash content of 9%.

Description

“PROCESS FOR OBTAINING MODIFIED ASPHALT BINDER WITH RUBBER POWDER FROM UNSERVED TIRES”

TECHNICAL FIELD

[001] The present invention is applied to the technical field of modifying asphalt binders used in the construction of flexible pavement highways, by adding waste tires with their own characteristics in a high shear process also known as terminal blend, generating a stable binder and with better characteristics to absorb the efforts generated by the action of traffic and weather on the highways.

STATE OF THE TECHNIQUE

[002] Asphalts modified by dust from waste tires are already known in the state of the art because they have characteristics that increase the performance of the pavement, reducing the harmful effects of traffic and bad weather, such as elastic recovery, high softening point and high rotational viscosity.

[003] Current techniques for inserting rubber powder into the asphalt binder are dry and wet. In the dry process, the rubber is mixed with the binder in partial replacement of the aggregate, generating modified asphalt concrete with the addition of rubber. In the wet process, the rubber is ground finer than in the dry process and is incorporated into the heated binder, resulting in the rubber-modified or rubber-asphalt binder. The wet process can be done in two different ways, which are usually designated by the expressions “continuous blend” and “terminal blend”. The continuous blend does not involve the grinding of the binder/modifier and is intended for the production of the mixture on site for immediate application due to its instability. The blend terminal is intended for the production of the mixture for storage and is characterized by mixing the finely ground rubber with the hot binder in a process that promotes the grinding, agitation and circulation of the mixture. In this process, a fusion occurs between petroleum asphalt cement (PAC) and rubber powder, through heating (180 ^Q C at 190 ^° C) and mechanical movement promoted by low or high shear agitators. The result is a stable modified binder that can be stored without separating the phases of the mixture. This process enables even greater quality control, since it is carried out in industrial plants.

[004] In general, processes that incorporate rubber into asphalt binders can be done by mixing by stirring at high or low shear. To enable the incorporation of rubber into the asphalt, various mixing processes by agitation in high shear existing in the state of the art make use of additives, such as solvents or stabilizers, or even subject the mixture to longer processes or multiple agitation processes.

[005] Document ^EP439232B1 , for example, adopts mixing the particles in three stages, at temperatures above 150 ° C. In this document, the components mentioned for mixing are rubber, bitumen and oils. The first stage comprises mixing and heating under high shear the rubber particles and oil to ^150-160 °C. ^Q C. In the third step, the temperature is reduced to ^190-210 ° C and the mixture remains for about two hours to mature and optionally the other components of the asphalt are added.

[006] Document CN108659556A presents a method of preparing high viscosity and high elasticity rubber-modified asphalt composed of SBS polymer (Styrene-Butadiene-Styrene), basic asphalt, natural asphalt, sulfur, rubber, stabilizer, mixing agent warm and anti-aging. These components are mixed in two steps: (i) preheating the base asphalt to ^170-180 °C in a colloidal high shear mill and adding the rubber; (ii) passage of the mixture from step (i) to a development tank for cyclic stirring for about 2 hours and subsequent passage of the mixture through the high shear mill, with the addition of stabilizer and reaction for about 3 hours. This process is followed by the addition of the hot mixing agent, further heating and mixing and further cooling to obtain high elasticity.

DISCLOSURE TECHNICAL PROBLEM

[007] The process of incorporating rubber into asphalt binders involves mixing for long periods, with the insertion of additives and, in general, more than one process or mixing steps. These additional variables imply higher costs for the process. In conventional processes there are problems with the dispersion of rubber powder, generating non-homogeneous mixtures and with a greater amount of solid residue at the end. This difficulty occurs because some rubber particles do not undergo shearing because they adhere to the walls of the reactors and stirring blades.

[008] The mixture of rubber from tires to asphalt cement also generates another liability: the high emission of FLS due to the reaction of the rubber with the CAP at high temperatures.

TECHNICAL SOLUTION

[009] To overcome the obstacles and problems described above and other disadvantages not mentioned here, according to the purposes of the invention, as described herein, a basic aspect of the present invention relates to a process for obtaining asphaltic binder modified with pneumatic rubber powder characterized by combining in a single pass, in a grinding process in a high shear dispersion reactor, the rubber powder with the asphalt cement subjected to heating at a temperature of 175 ^° C to 200 ^° C.

ADVANTAGEOUS EFFECTS

[010] When combining the rubber powder with the asphalt cement subjected to heating at a temperature of 175 ^Q C to 200 ^Q C in a single pass, in a grinding process in a high shear dispersion reactor, there is a series of advantageous effects, such as: total absorption of existing polymers in the rubber powder; decrease in the thermal load applied to the binder during the modification period, lower energy consumption for modification, high productivity, storage stability and better performance.

[011] The process differs from the solutions proposed in the state of the art by obtaining a homogeneous mixture and with little residue at the end, which results from the grinding of the rubber by the high shear mill, during the mixture, in a single pass. In addition, it has the advantage of not using dispersants or other additives to homogenize the mixture and providing a process with less mixing time, as it is more efficient, allowing the mixture to pass through the high-shear mill only once.

[012] Unlike document EP439232B1, this application proposes mixing rubber with asphalt cement in a single pass in the high-shear mill, resulting in a lower overall cost of the process.

[013] This application also differs from CN108659556A by using tire rubber for insertion in asphalt cement, while the prior art document uses SBS polymer. This polymer is already widely used for insertion in asphalt to improve mechanical properties and durability. Its addition in asphalt cement differs from rubber from tires, as it is easier to disperse. Therefore, it is not trivial to replace the polymer source in asphalt mixtures, as proposed by the present application. Furthermore, by proposing the use of waste tires, the present invention brings an environmental benefit, not explored by document CN108659556A.

DETAILED DESCRIPTION OF THE INVENTION MODES OF THE INVENTION

[014] This invention is not limited in its application to the constructive details and arrangement of components determined in the following description or illustrated in the drawings. The invention is realizable in other configurations and can be practiced or carried out in a variety of ways. Furthermore, the wording and terminology used herein is for the purpose of description and should not be considered restrictive. The use of "including", "comprising", "having", "containing" or "involving", and variants of these terms, is intended to encompass the items listed after said terms and their equivalents, as well as additional items.

[015] In one of the exemplary modes of implementation of the present invention, the disclosed process begins with loading the rubber powder into a passing silo. The powder then passes through a magnetic drawer to remove the metallic filings present in the raw material. Then the rubber is pumped automatically to a storage silo and then to the high shear mill. Before entering the mill, the rubber powder passes through an auxiliary metal detector to remove possible metallic residues. A dosing screw controls the entry of rubber powder into the mill according to the dosage established in proportion to the CAP. The insertion of raw materials into the shear mill is adjusted through the rotation of the feed pump motor and the dosing screw, which simultaneously control the entry of rubber dust and asphalt cement into the mill.

[016] The high shear mill used in the process disclosed in the present invention is a high shear dispersion reactor type mill for continuous processes, consisting of three stages. The first stage consists of a rotor and stator assembly, where asphalt and rubber powder are mixed. The mixture is pushed to the edges where there is a row of stator teeth, giving rise to the first grind. The second stage of the mill has a rotor and stator assembly with four rows of teeth, two on the rotor and two on the stator, which promote a new grinding in a process called medium shear. In the third stage, the rotor and stator set has six rows of teeth, three on the rotor and three on the stator, promoting a third grinding, known as fine shearing. After going through these three stages, the final product is pumped into the storage tank. The application of the high shear mill, combined with the use of rubber in the appropriate granulometry and chemical composition guarantee a more homogeneous mixture, with a smaller amount of residues at the end of the process when compared to other methods of the state of the art, for example the use of high or low shear agitators. Furthermore, due to the greater mixing effectiveness, the combination of raw materials can be done in a single pass in the high shear mill, resulting in a significant saving in mixing time. In order to obtain the desired result, the rubber dust from waste tires must fit into the following granulometric range: 0% to 5% of the particulate material passing through the #200 sieve (0.075 mm), 10% to 35% passing through the #80 sieve (0.180 mm), 40% to 80% passing the #50 sieve (0.300 mm), 60% to 100% passing the #40 sieve (0.420 mm) and 100% passing the #30 sieve (0.600), as well as having a content of polymeric and volatile material minimum 60%, carbon black content maximum 36% and ash content maximum 9%.

[017] In an exemplary embodiment of the present invention, rubber-modified asphalt has a softening point of at least 50 ^Q C, penetration (25 ^Q C, 100 g, 5 s, 0.1 mm) from 3 mm to 7 mm, elastic recovery (25 ^Q C, 10 cm) min 50%, dynamic viscosity (175 ^Q C, spindle 3, 20 rpm) min 800 cP and max 2000 cP, flash point min 235 ^Q C.

[018] In an exemplary embodiment of the present invention, the proportion of added rubber powder is in the range of 15% to 20%, and the proportion of added asphalt cement is in the range of 85% to 80%.

[019] In an exemplary way of implementing the present invention, the rubber powder passes through magnets to remove waste steel filings, before being inserted into the high shear mill.

[020] In an exemplary way of implementing the present invention, the inlet temperature of the asphalt binder in the high shear mill is between 150 ^° C and 180 ^° C.

[021] In an exemplary way of carrying out the present invention, a high shear homogenizing mixer with three dispersion stages is used, composed of three sets of rotors and stators having teeth at an angle of approximately 45 ^Q and drive shaft speed 1100 rpm.

[022] In an exemplary mode of the present invention the high shear dispersion reactor type mill used is the model Dispax Reactor DR-PB 2000/50 from the manufacturer IKA.

[023] In an exemplary way of carrying out the present invention, an H ₂ S emission reducer is added to the mixture in the high shear mill.

[024] In an exemplary mode of the present invention, the hhS emission reducing additive used is from the manufacturer ArrMaz, marketed under the name of deScent TBP and acts in the reincorporation, to the binder, of the hhS emitted during the modification.

[025] Table 1 shows an example of the production process of the state of the art and Table 2 shows an example of the production process according to the present invention, for the same amount of modified asphalt.

Table 1 - State of the Art

Table 2 - Example of the Invention

Claims

01. Process for obtaining modified asphalt binder with rubber powder from waste tires characterized by combining in a single pass, in a grinding process in a high shear dispersion reactor, the rubber powder from waste tires with asphalt cement subjected to heating at a temperature in the range of 175 ^° C to 200 ^° C, where: the rubber powder falls within the following granulometric range: 0% to 5% of the particulate material passing through the #200 sieve (0.075 mm), 10% to 35% passing #80 sieve (0.180 mm), 40% to 80% passing #50 sieve (0.300 mm), 60% to 100% passing #40 sieve (0.420 mm) and 100% passing #30 sieve (0.600 mm) ; and the rubber powder has a minimum polymeric and volatile material content of 60%, a maximum carbon black content of 36% and a maximum ash content of 9%. 02. Process according to claim 01, characterized in that rubber-modified asphalt has a softening point of at least 50 ^° C, penetration (25 ^° C, 100 g, 5 s, 0.1 mm) from 3 mm to 7 mm , elastic recovery (25 ^Q C, 10 cm) of at least 50%, dynamic viscosity (175 ^Q C, spindle 3, 20 rpm) of at least 800 cP and a maximum of 2000 cP, flash point of at least 235 ^Q C . 03. Process according to claim 01, characterized by the proportion of added rubber powder being in the range of 15% to 20%, and the proportion of added asphalt cement being in the range of 85% to 80%. 04. Process according to claim 01, in which the rubber powder passes through magnets, to remove steel filings residues, before being inserted into the high shear mill. 05. Process according to claim 01, characterized by the inlet temperature of the asphalt binder in the high shear mill being between 150 ^° C and 180 ^° C. 06. Process according to claim 01, characterized by using a high shear homogenizing mixer with three stages of dispersion, composed of three sets of rotors and stators having teeth at an angle of approximately 45 ^Q and shaft drive speed of 1100 rpm. 07. Process according to claim 01, in which an H2S emission reducer is added to the mixture in the high shear mill.