Carbon Black: Promise and Potential

Carbon Black is a commercial form of solid carbon that is manufactured in highly controlled processes to produce specifically engineered aggregates of carbon particles that vary in particle size, aggregate size, shape, porosity and surface chemistry. Carbon Black typically contains more than 95 % pure carbon with minimal quantities of oxygen, hydrogen and nitrogen.

In the manufacturing process, Carbon Black particles range from 10 nm to approximately 500 nm in size. These fuse into chain-like aggregates, which define the structure of individual Carbon Black grades.

What is Carbon Black

Carbon Black is used in a diverse group of materials in order to enhance their physical, electrical and optical properties. Its largest volume use is as a reinforcement and performance additive in rubber products.

In rubber compounding, natural and synthetic elastomers are blended with Carbon Black, elemental sulphur, processing oils and various organic processing chemicals, and then heated to produce a wide range of vulcanized rubber products. In these applications, Carbon Black provides reinforcement and improves resilience, tear-strength, conductivity and other physical properties.

Carbon Black is the most widely used and cost effective rubber reinforcing agent (typically called Rubber Carbon Black) in tire components (such as treads, sidewalls and inner liners), in mechanical rubber goods (“MRG”), including industrial rubber goods, membrane roofing, automotive rubber parts (such as sealing systems, hoses and anti-vibration parts) and in general rubber goods (such as hoses, belts, gaskets and seals).

Applications of Carbon Black

Besides rubber reinforcement, Carbon Black is used as black pigment and as an additive to enhance material performance, including conductivity, viscosity, static charge control and UV protection. This type of Carbon Black (typically called Specialty Carbon Black) is used in a variety of applications in the coatings, polymers and printing industries, as well as in various other special applications.

Actually, after oil removal and ash removal processing from tire pyrolysis, we can get high-purity commercial carbon black, which can be used to make color master batch, color paste, oil ink and as addictive in plastic and rubber products. Besides, after activation treatment, the carbon black will become good materials to produce activated carbon.

In the coatings industry, treated fine particle Carbon Black is the key to deep jet black paints. The automotive industry requires the highest black intensity of black pigments and a bluish undertones.

Carbon Black has got a wide array of applications in different industries

Small particle size Carbon Blacks fulfill these requirements. Coarser Carbon Blacks, which offer a more brownish undertone, are commonly used for tinting and are indispensable for obtaining a desired grey shade or color hue.

In the polymer industry, fine particle Carbon Black is used to obtain a deep jet black color. A major attribute of Carbon Black is its ability to absorb detrimental UV light and convert it into heat, thereby making polymers, such as polypropylene and polyethylene, more resistant to degradation by UV radiation from sunlight. Specialty Carbon Black is also used in polymer insulation for wires and cables. Specialty Carbon Black also improves the insulation properties of polystyrene, which is widely used in construction.

In the printing industry, Carbon Black is not only used as pigment but also to achieve the required viscosity for optimum print quality. Post-treating Carbon Black permits effective use of binding agents in ink for optimum system properties. New Specialty Carbon Blacks are being developed on an ongoing basis and contribute to the pace of innovation in non-impact printing.

Pyrolysis of Scrap Tires

scrap-tires-pyrolysisPyrolysis of scrap tires offers an environmentally and economically attractive method for transforming waste tires into useful products, heat and electrical energy. Pyrolysis refers to the thermal decomposition of scrap tires either in the absence or lack of oxygen. The principal feedstocks for pyrolysis are pre-treated car, bus or truck tire chips. Scrap tires are an excellent fuel because of their high calorific value which is comparable to that of coal and crude oil. The heating value of an average size passenger tire is between 30 – 34MJ/kg.

Pyrolysis is the most recommended alternative for the thermochemical treatment of waste tires and extensively used for conversion of carbonaceous materials in Europe and the Asia-Pacific. Pyrolysis is a two-phase treatment which uses thermal decomposition to heat the rubber in the absence of oxygen to break it into its constituent parts, e.g., pyrolysis oil (or bio oil), synthetic gas and char. Cracking and post-cracking take place progressively as the material is heated to 450-500°C and above.

Process Description

The pyrolysis method for scrap tires recycling involves heating whole or halved or shredded tires in a reactor containing an oxygen free atmosphere and a heat source. In the reactor, the rubber is softened after which the rubber polymers disintegrate into smaller molecules which eventually vaporize and exit from the reactor. These vapors can be burned directly to produce power or condensed into an oily type liquid, called pyrolysis oil or bio oil. Some molecules are too small to condense and remain as a gas which can be burned as fuel. The minerals that were part of the tire, about 40% by weight, are removed as a solid. When performed well a tire pyrolysis process is a very clean operation and has nearly no emissions or waste.

The heating rate of tire is an important parameter affecting the reaction time, product yield, product quality and energy requirement of the waste tire pyrolysis process. If the temperature is maintained at around 450oC the main product is liquid which could be a mixture of hydrocarbon depending on the initial composition of waste material. At temperature above 700oC, synthetic gas (also known as syngas), a mixture of hydrogen and carbon monoxide, becomes the primary product due to further cracking of the liquids.

Schematic for Pyrolysis of Scrap Tires

Schematic for Pyrolysis of Scrap Tires

The nature of the feedstock and process conditions defines the properties of the gas, liquid and solid products. For example, whole tires contain fibers and steel while shredded tires have most of the steel and sometimes most of the fiber removed. Processes can be either batch or continuous. The energy required for thermal decomposition of the scrap tires can be in the form of directly-fired fuel, electrical induction and or by microwaves (like a microwave oven). A catalyst may also be required to accelerate the pyrolysis process.

Useful Products

The high acceptance of pyrolysis for the treatment of scrap tires is due to the fact that the derived oils and syngas can be used as biofuels or as feedstock for refining crude oil or chemical products. The pyrolysis oil (or bio oil) has higher calorific value, low ash, low residual carbon and low sulphur content.

The use of pyrolysis oil in cement kilns, paper mills, power plants, industrial furnaces, foundries and other industries is one of the best uses of scrap tires.  Pyrolysis of scrap tyres produces oil that can be used as liquid fuels for industrial furnaces, foundries and boilers in power plants due to their higher calorific value, low ash, residual carbon and sulphur content.

The solid residue, called char, contains carbon black, and inorganic matter. It contains carbon black and the mineral matter initially present in the tire. This solid char may be used as reinforcement in the rubber industry, as activated carbon or as smokeless fuel.