Reduction in benzothiazole emissions when heating benzothiazole-containing rubber
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-08
- Publication Date
- 2026-03-25
AI Technical Summary
The use of recycled tire rubber as a bitumen modifier in asphalt production is hindered by the release of benzothiazole emissions when heated, posing environmental and toxicological concerns due to additives used in tire production, particularly at temperatures above 100°C.
The method involves heating rubber containing benzothiazole in the presence of polyphosphoric acid (PPA), which reduces benzothiazole emissions by mixing PPA with the rubber before heating, typically to temperatures between 100°C and 160°C, with PPA concentrations of 0.5 to 20% by weight, to suppress the release of benzothiazole during the production of asphalt.
This approach effectively reduces benzothiazole emissions, with at least 6% by weight of PPA completely suppressing benzothiazole release at 120°C and 160°C, as demonstrated by Purge and Trap GC-MS technology, improving the environmental safety of the asphalt production process.
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Abstract
Description
[0001] Reduction of benzothiazole emissions when heating rubber containing benzothiazole
[0002] For decades, scrap tire rubber has been recycled as a modifier for binders (bitumen) in asphalt-based road surfaces. While the use of natural rubber as a bitumen modifier dates back to the 19th century, ground rubber granulate from scrap tires was first used in this context in 1960.
[0003] Rubber, whether of natural or synthetic origin, or recycled from scrap tires, serves as a polymeric modifier for bitumen. Polymers extend the temperature range at which bitumen exhibits sufficiently good properties as a binder in road surfaces (including prevention of permanent deformation and cracking). Scrap tire rubber is proving to be a sustainable alternative to synthetic polymers, as the material is generated as waste, thus avoiding landfill storage or thermal recycling with the associated CO2 emissions.
[0004] However, scrap tire rubber exhibits several disadvantages that may hinder its widespread use. For example, as a vulcanized material, it is poorly miscible with bitumen due to crosslinking via sulfur bridges. This can be facilitated with the help of additives, as described, for example, in WO2017032661 and WO2021028290.
[0005] Rubber, in particular rubber from used tires, can contain benzothiazole if it was added as an additive during production. Furthermore, substances which can release benzothiazole when heated, such as 2-mercaptobenzothiazole or amides of benzothiazole or 2-mercaptobenzothiazole, can have been added to the rubber during production. In the context of the invention, substances which can release benzothiazole when heated are preferably understood to mean compounds which release benzothiazole at 160°C, particularly preferably at a temperature of 120°C to 160°C and most preferably at a temperature of 100°C to 120°C. The use of benzothiazole or substances which release benzothiazole when heated as additives for rubber varies greatly from region to region and is, for example, much more common in Europe than in Asia or the USA.These additives are mostly used in the production of passenger car tires, but can also be used in truck tires.
[0006] The release of benzothiazole when rubber is heated to temperatures above 100°C is problematic. Concerns about emissions from road construction have recently come into focus, as described in Patrik T Nilsson et al., Annals of Work Exposures and Health, Vol. 62, Issue 7, August 2018, Pages 828-839. Although rubber as a modifier does not significantly increase, and in some cases even reduces, the emission of volatile, hydrocarbon-based components of bitumen, the presence of benzothiazole poses both an olfactory and toxicological threat to the environment, particularly when used with scrap tire rubber.
[0007] Another additive already used to modify bitumen is polyphosphoric acid (PPA). The latter has occasionally been used as a modifier for the flow behavior and setting point of bitumen or asphalt to reduce cracking in winter or to suppress rutting in hot summers. While its use in combination with ground rubber or shredded scrap tires has been disclosed, e.g., in G. Yadollahi et al., Construction and Building Materials 25 (2011) 3108-3116, it has not been used in combination with rubber containing benzothiazole and / or substances that release benzothiazole upon heating.
[0008] There was therefore a need for a process for reducing benzothiazole emissions during heating of benzothiazole and / or during heating of rubber containing benzothiazole-releasing substances, in particular in the process for producing asphalt by heating asphalt binder (bitumen) and benzothiazole and / or during heating of rubber containing benzothiazole-releasing substances.
[0009] Surprisingly, it has now been found that a reduction in benzothiazole emission when heating rubber containing benzothiazole and / or benzothiazole-releasing substances can be achieved by heating in the presence of polyphosphoric acid (PPA).
[0010] The present invention thus relates to a process for reducing benzothiazole emissions when heating rubber containing benzothiazole and / or benzothiazole-releasing substances, wherein the heating is carried out in the presence of polyphosphoric acid (PPA).
[0011] Preferably, the method is used to reduce benzothiazole emissions when heating rubber containing benzothiazole.
[0012] Heating is typically carried out to a temperature of at least 100°C, preferably between 100°C and 190°C, and particularly preferably between 120°C and 160°C. Shredded used tires, particularly rubber powder from used tires, is preferred as the rubber. The rubber powder can be hot-ground or cryogenically ground, as offered, for example, by MRH Mülsener Rohstoff und Handelsgesellschaft mbH.
[0013] In a preferred embodiment, the phosphoric acid and the gum containing benzothiazole and / or substances releasing benzothiazole during heating are mixed before heating.
[0014] Preferably, the polyphosphoric acid is applied homogeneously to the surface of the rubber. Any type of mixer suitable for producing a homogeneous solid mixture can be used to apply the PPA to the rubber surface. This could be, for example, an Ultra Turrax stirrer or a plowshare mixer, regardless of whether it has a horizontal or vertical design. Alternatively, a spraying process can be used, in which heated, liquid polyphosphoric acid is atomized through a nozzle to form a mist, which then precipitates on the surface of the rubber.
[0015] Polyphosphoric acids of the PPA 95% to PPA 124% type can be used, preferably of the PPA 100% to PPA 118% type, and particularly preferably of the PPA 105% to 115% type. The figures refer to the concentration of the polyphosphoric acid. Concentrations greater than 100% are possible because the proportion of P2O5 in H3PO4 is included.
[0016] Polyphosphoric acids (PPA), for example, are formed by the partial hydrolysis of phosphorus pentoxide with substoichiometric amounts of water. In addition to partially hydrolyzed cyclic compounds, polyphosphoric acids essentially consist of linear molecules of the general formula H( n +2)O(3n+i)Pn, as described, for example, in Brief review of the chemistry of polyphosphoric acid (PPA) and bitumen, J.-F. Masson Energy & Fuels, v. 22, no. 4, June 2008, pp. 2637-2640.
[0017] Typically, the polyphosphoric acid is used in an amount of 0.5 to 20 wt%, preferably 3 to 10 wt% and most preferably 5 to 7 wt% based on the rubber.
[0018] Ideally, the process for reducing benzothiazole emissions is used in the production of asphalt from rubber and bitumen. The present invention thus relates to a process for producing asphalt with reduced benzothiazole emissions, comprising mixing and heating: a) rubber containing benzothiazole and / or substances that release benzothiazole upon heating, b) bitumen, c) polyphosphoric acid (PPA).
[0019] The process is preferably used in the production of asphalt using rubber containing benzothiazole.
[0020] The preferred rubber material is shredded old tires, especially rubber powder from old tires. The rubber powder can be hot-ground or cryogenically ground.
[0021] The heating is typically carried out to a temperature of at least 100°C, preferably between 100°C and 190°C and particularly preferably between 120°C and 160°C.
[0022] In a preferred embodiment, the phosphoric acid and the rubber containing benzothiazole and / or substances releasing benzothiazole during heating are mixed before heating and then mixed with the bitumen which has already been heated to a temperature of at least 100°C, preferably between 100°C and 190°C and particularly preferably between 120°C and 160°C.
[0023] Preferably, the polyphosphoric acid is applied homogeneously to the surface of the rubber.
[0024] Polyphosphoric acids of the type PPA 95% to PPA 124%, preferably of the type PPA 100% to PPA 118% and particularly preferably of the type PPA 105% to 115% can be used as polyphosphoric acid.
[0025] Typically, the polyphosphoric acid is used in an amount of 0.5 to 20 wt.%, preferably 3 to 10 wt.% and particularly preferably 6 to 8 wt.% based on the rubber.
[0026] The present invention further relates to the use of polyphosphoric acid for reducing benzothiazole emissions when heating rubber containing benzothiazole and / or benzothiazole-releasing substances when heating, as well as the use of polyphosphoric acid for reducing benzothiazole emissions in the production of asphalt from rubber containing benzothiazole and / or benzothiazole-releasing substances and bitumen when heating these substances, in particular in the embodiments shown above.
[0027] The present invention further relates to asphalt containing: a) rubber containing benzothiazole and / or substances that release benzothiazole upon heating, b) bitumen c) polyphosphoric acid (PPA). The present invention further relates to asphalt obtainable by applying the process according to the invention for reducing benzothiazole emissions upon heating of rubber or by the process according to the invention for producing asphalt.
[0028] To demonstrate the reduction of emissions and odor-forming components, the so-called Purge and Trap GC-MS technology[6] was used, which allows the assignment of individual molecules via their mass spectrum, as well as the determination of the content of volatile components in the circulating air via the peak areas in the GC spectrogram.
[0029] In one example, cryogenically ground rubber powder from European truck tires, with a grain size of 0.2–0.4 mm, was mixed with various amounts of polyphosphoric acid PPA 118%, PPA 115%, PPA 108%, and PPA 105% and thoroughly mixed using an Ultra Turrax stirrer (T 25 Basic homogenizer). Rubber powder from car tires can be treated in a similar manner.
[0030] In another example, the cold-ground rubber powder mm was mixed with various amounts of polyphosphoric acid PPA 118%, PPA 115%, PPA 108% and PPA 105% and thoroughly mixed using a standard paddle stirrer for laboratory use.
[0031] In both cases, 0 to 10 wt.% PPA based on rubber powder was used and thoroughly mixed for approximately 30–45 minutes. All samples were then heated to 120°C or 160°C, respectively, and the volatile components were completely expelled from the cold-ground rubber powder. The volatile components were condensed and collected in a cold trap. The trap was then heated, and the analytes were collected and fed to the GCMS spectrometer.
[0032] A reduction in the amount of benzothiazole released was observed in all samples containing at least 0.5 wt.% PPA relative to the rubber powder. When at least 6 wt.% PPA was added to the rubber powder, the emission of benzothiazole was completely suppressed in all cases at both 120°C and 160°C.
[0033] Figure 1 illustrates the suppressive effect of PPA on benzothiazole using cryogenically ground rubber powder without PPA, cryogenically ground rubber powder with 2% PPA (115%), cryogenically ground rubber powder with 5% PPA (115%), and cryogenically ground rubber powder with 6% PPA (115%) at 120°C. The data were determined by P&T GCMS and show sections at the typical retention time of benzothiazole at approximately 22.45 min. The extraction of the benzothiazole peak is shown on the right.
Claims
1. A process for reducing benzothiazole emissions during heating of rubber containing benzothiazole and / or benzothiazole-releasing substances, wherein the heating is carried out in the presence of polyphosphoric acid (PPA).
2. The method according to claim 1, wherein the heating is carried out to a temperature of at least 100°C, preferably between 100°C and 190°C and particularly preferably between 120°C and 160°C.
3. Process according to claim 1 or 2, wherein the phosphoric acid and the gum containing benzothiazole and / or substances releasing benzothiazole during heating are mixed before heating.
4. Process according to one or more of claims 1 to 3, wherein polyphosphoric acids of the type PPA 95% to PPA 124%, preferably of the type PPA 100% to PPA 118% and particularly preferably of the type PPA 105% to 115% are used as polyphosphoric acid.
5. Process according to one or more of claims 1 to 4, wherein the polyphosphoric acid is used in an amount of 0.5 to 20 wt.%, preferably 3 to 10 wt.% and particularly preferably 6 to 8 wt.%, based on the rubber.
6. Process according to one or more of claims 1 to 5, wherein shredded old tires, preferably rubber powder from old tires, are used as rubber.
7. Process for the production of asphalt with reduced benzothiazole emission, comprising mixing and heating: a) rubber containing benzothiazole and / or substances which release benzothiazole upon heating, b) bitumen c) polyphosphoric acid (PPA).
8. The method according to claim 7, wherein the heating is carried out to a temperature of at least 100°C, preferably between 100°C and 190°C and particularly preferably between 120°C and 160°C.
9. The process according to claim 7 or 8, wherein the phosphoric acid and the gum containing benzothiazole and / or substances releasing benzothiazole during heating are mixed prior to heating.
10. Process according to one or more of claims 7 to 9, wherein polyphosphoric acids of the type PPA 95% to PPA 124%, preferably of the type PPA 100% to PPA 118% and particularly preferably of the type PPA 105% to 115% are used as polyphosphoric acid.
11. Process according to one or more of claims 7 to 10, wherein the polyphosphoric acid is used in an amount of 0.5 to 20 wt.%, preferably 3 to 10 wt.% and particularly preferably 6 to 8 wt.%, based on the rubber.
12. The method according to one or more of claims 7 to 11, wherein shredded old tires, preferably rubber powder from old tires, are used as rubber.
13. Use of polyphosphoric acid to reduce benzothiazole emissions when heating rubber containing benzothiazole and / or substances releasing benzothiazole when heated.
14. Use of polyphosphoric acid to reduce benzothiazole emissions in the production of asphalt from rubber containing benzothiazole and / or when heating benzothiazole-releasing substances and bitumen while heating these substances.
15. Use according to claim 13 or 14, wherein the polyphosphoric acid is used in an amount of 0.5 to 20 wt.%, preferably 3 to 10 wt.% and particularly preferably 6 to 8 wt.%, based on the rubber.
16. Asphalt preserving: a) Rubber containing benzothiazole and / or substances which release benzothiazole when heated, b) Bitumen c) Polyphosphoric acid (PPA).