The crude oil in the refinery is distilled into its components and due to the difference in boiling points in different parts of the tower, the crude oil is separated from each other. In the initial distillation process (distillation at ambient pressure) some heavy material remains in the bottom of the tower which is transferred to the distillation towers in vacuum and its various components are separated by vacuum distillation. The rest of the tower, known as Vacuum Batum, is used to make bitumen.
In order to produce bitumen, the batons are aerated in the bitumen production unit (bitumen production tower). The temperature of the vacuum floor inside the tower is about 240 to 320 degrees Celsius, and the passage of air through the vacuum floor at this temperature causes the oxidation process to take place, and as a result of the aeration process, the remaining properties can be reduced. The most important effect of blowing air on vacuum batons is to convert Meltan molecules to heavier molecules, namely asphaltene. This conversion reduces the degree of penetration of bitumen and increases the smoothness of bitumen.
Vacuum bottom (VB) is the heaviest shear of crude oil extracted.
The bottom of the vacuum distillation column in oil refineries is the base material for bitumen production. Depending on the source of crude oil and the refining process, the composition of VB varies greatly and has a significant effect on the mechanical properties and microstructure of bitumen. The most common separation method divides the bitumen composition into four general groups (SARA): saturated, aromatic, resin (which make up the maltene fraction) and asphaltenes. Each SARA fraction is a mixture of complexity, aromatics, heteroatom content, and molecular weight that increases S <A <R <As, respectively.
In some refineries that use heavy crude oil and control the pressure and temperature in the vacuum distillation columns, bitumen can be obtained directly as the degree of penetration that can be used in paving. VB produced in Iranian refineries has a penetration> 300 dmm (at 25 ° C) and η near 600 cS (at 135 ° C), which is not suitable for pavement applications, except for the Shiraz refinery, which has a direct 60 carat / 70 produces. Blowing hot air into VB is an extensive process for obtaining bitumen. Unfortunately, due to the increase in traffic load, the clean bitumen obtained in the refinery (directly or by blowing) is not able to withstand the dynamic mechanical loads of traffic, which leads to permanent deformation (grooving) and its removal under prolonged loading. Fatigue and cracking occur under prolonged loading at medium and low temperatures due to thermal stresses, aging, and so on.
Due to these inherent weaknesses of bitumen, many studies have been performed to modify bitumen with various additives, so modified bitumen with improved mechanical properties has been developed. Addition of polymers to bitumen improves the degree of performance (increased softening point, reduced penetration and Frass break point). Pavements made using these polymer-modified bitumens are more resistant to grooves and heat cracking and reduce damage from fatigue and peeling.
With lower temperature sensitivity, many of these studies use virgin polymers such as PE, EVA, PET, SBS and SBR, which significantly increase production costs. Among these, there are many waste polymers from petrochemical industrial processes and post-consumption waste polymers are considered as environmental pollutants such as used tires, polyethylene parts, used latex gloves, etc., which are cheap and useful in bitumen modification.
The use of secondary (recycled) materials, instead of primary (raw), helps to reduce landfill pressures, reduce the need for extraction, protect the environment and minimize the consumption of primary resources. Addition of recycled rubber to asphalt mix using dry process can improve the engineering properties of asphalt mix and has a significant effect on the performance of permanent deformation resistance at high temperature and cracking at low temperature.
Bitumen is a natural black substance. Evaporation of volatile organic compounds and high levels of asphaltene make it hard and brittle, which can be used as a hardener.
The softening point of petroleum bitumen There are significant sources of natural bitumen in several regions of Iran such as Kermanshah, Behbahan, Moghan, etc., which are used as fuel in furnaces and if it can be used as a desirable additive for bitumen. , Be issued. Various polymers are used to improve the ductility of modified bitumen, and styrene-butadiene rubber (SBR) latex is used as a virgin polymer successfully in bitumen modification.
To mix the components with VB, first VB is melted in a furnace at 160 ° C for 1 hour and transferred to a pre-heated mixing chamber at 180 ° C. The mixing chamber is heated and controlled using a Haake oil circulation heater. Here, while the high-cut mixer is running at 8000 rpm, the modifiers enter the mixing chamber and the mixing continues for the next 90 minutes. At the end of mixing, the mixture is transferred inside.
Junapol model microscope. Viscoelastic properties of selected mixture, VB base, empty VB and 60/70 clean bitumen measured on Paar-Physica MCR300 rheometer in dynamic oscillation mode using 25 mm parallel plate geometry at 30 ° C and 1-500 Hz.
Results and discussion
The results of conventional experiments performed on bituminous mixtures prepared are summarized in the table
In this table, the physical properties of the base and control (bitumen without adding any modifiers under the mixing conditions) are given.
According to the Iranian Government Pavement Regulations and according to the climatic conditions of Iran, bitumen with a penetration grade of 50.40, 70.60 and 100.85 are recommended for dry, temperature and cold climates, respectively.
Modified bitumen is not self-sustaining and other properties of bitumen such as softening point, penetration, fracture point, morphology and rheological properties should be.
Standard ductility length is available for clean bitumen (usually more than 100 cm at 25 ° C) but this feature is not standard for modified bitumen. Therefore, these composites can be used in paving and other applications.
Clean bitumen obtained in the refinery (directly or by blowing) is not able to withstand dynamic mechanical loads and therefore must be modified. Waste polymers are considered as environmental pollutants after consumption and should be reused. There are also natural bitumen resources in several regions of Iran that can be used to improve bitumen. Recycled waste polyethylene, waste latex, CRM, NB and HVS are used to obtain bitumen from VB. The combination of 10% natural bitumen and 5% recycled latex with VB is suitable for obtaining 70/60 modified bitumen by improving the rheological behavior and thus reducing the possibility of cracking at low temperatures and cracking at high temperatures.