STUDY THE PROCESS OF RECEIVING HYDROCARBONS FROM RUBBER WASTE

ABSTRACT

The prospects of recycling used rubber tires and obtaining a secondary fuel resource are considered. The results of the study of the process of obtaining hydrocarbons from rubber tires are presented. As a result of the conducted research, it was found that the most promising process for obtaining fuel distillates from rubber waste is pyrolysis without air access. The optimal parameters of the process of obtaining hydrocarbons from used rubber tires are determined.

АННОТАЦИЯ

Рассмотрены перспективы утилизации отработанных резиновых покрышек и получения вторичного топливного ресурса. Представлены результаты исследования процесса получения углеводородов из резиновых покрышек. В результате проведенных исследований установлено, что наиболее перспективным процессом получения топливных дистиллятов из отходов резины является пиролиз без доступа воздуха. Определены оптимальные параметры процесса получения углеводородов из отработанных резиновых покрышек.

Keywords: automobile tires, rubber, recycling, energy, chemical methods, physical methods, natural resources, pyrolysis, fuel distillates, pyrogas.

Ключевые слова: автомобильные шины, каучук, утилизация, энергия, химические методы, физические методы, природные ресурсы, пиролиз, топливные дистилляты, пирогазы.

Introduction. At present, in Republic of Uzbekistan and in many other countries of the world, a large amount of hydrocarbon-containing waste, such as worn tires and plastics, is accumulated every year.

Spent tires are one of the main types of environmental pollutants, because they are difficult to biodegradable and non-destructive waste. During combustion, poisonous gases decompose, and waste products are considered a favorable environment for the life of rodents and insects [1-3].

Most of leading countries of the world are intensively working on improving and creating new technologies for recycling tire waste, as well as on improving the performance of individual stages of developed processes, which significantly increases the efficiency of the method. At the same time, much attention is paid to the environmental aspects of processing, namely, the creation of waste-free and low-waste resource-saving technologies [4-7].

In spite of the existence of many ways of tire processing and the use of waste products, the volume of processed tires currently does not exceed 30%. This is mainly due to significant material costs, the organization of additional production and the lack of efficiency of the known processes [8].

Processing of worn tires and plastic waste is one of the urgent tasks for the Republic of Uzbekistan [9].

Based on the scientific, environmental and technical problem associated with the disposal of rubber waste and the production of a secondary fuel resource, the purpose of this work was to study the process of processing worn automobile tires by pyrolysis without air access to obtain fuel distillates.

Objects and methods of research. Worn automobile tires were used as the object of research.

To carry out experiments, we developed a technology for pyrolysis of worn automobile tires without air access, and on its basis, we assembled a laboratory setup, the diagram of which is shown in the figure.

Figure 1. Diagram of a laboratory installation for pyrolysis without air access of worn out car tires:

1 – balloon He; 2 – rheometer; 3 – tubular reactor; 4,10 – thermocouple tubes; 5 – autotransformer; 6 – ЛАТР; 7 – Pressure gauge; 8,14 – thermocouple; 9 – steam generator; 11 – condensate collector; 12 – gas meter 13 - refrigerator; 15 – water tank

By the method of thermogravimetry in crucible without air access, the temperature range of decomposition of rubber from tires was determined. At the same time, the temperature of the beginning of decomposition is set, which is equal to 285 °С, the maxima of decomposition are in the region of 350-425 °С, and the temperature at the end of the process was 535 °С. Based on the obtained thermogravimetric data, the pyrolysis process was carried out at a temperature of 200-500 °C, which was controlled using a thermocouple located in the middle of the reactor. The temperature rise rate was 7-10 °C per minute. Upon reaching the required temperature of the experiment, the sample was kept in the reactor for 1-2 hours. Overheated steam required for pyrolysis was obtained in a steam generator. The flow rate of water vapor going into the reactor was controlled by amount of water entering the steam generator by changing the rate of its outflow in the capillary depending on the pressure above the water created in the dosing tank using nitrogen. From the steam generator, water vapor, and from the cylinder, helium, purified from oxygen, is blown into the reactor. Water vapor is overheated to 500-600 °C. The evolved gaseous pyrolysis products were evacuated from the reactor through a gas outlet tube and sent to cooled condenser for condensation of vapors of a hydrocarbon mixture and a condensate collector.

Flow rates of water vapor and helium were measured with rheometers. The experiments were carried out in the following sequence: the reactor was preheated to the process temperature, and then helium was blown through it for several minutes. The helium supply was stopped and steam was blown into the reactor. After loading the crumb rubber into the reactor, the temperature dropped to 300 °C. After 7-10 minutes, crumb rubber was heated to the optimum temperature of the pyrolysis process, which was maintained constant throughout the operation. At the end of the process, the supply of water vapor was stopped, the carbon residue was cooled with helium, and the necessary parameters were determined regarding the properties of the pyrolysis products.

Results of research. During the research, the following pyrolysis products were obtained and their yield according to the results of four experiments is:

• pyrolysis gas - 6.8 - 8.2%;
• resin + water - 61.4 - 62.8%;
• solid residue - 29.0 - 30.8%.

The gases released at the initial stage of pyrolysis (up to 300 °C) are mainly nitrogen and carbon dioxide. After 300 °C, in the absence of oxygen at the reflux temperature, non-condensable light hydrocarbon gases, which have flammable properties, increase.

Pyrolysis resin is a dark brown liquid containing 2-3% water, does not decompose during prolonged standing. The following parameters have been determined for the pyrolysis resin:

• boiling point - 180 °С;
• heat of combustion - 35 MJ/kg;
• content of aliphatic compounds - 5.3%;
• content of aromatic compounds - 95.8%;
• content of sulfur - 1.5%.

The resulting pyrolysis resin can be recommended for use as boiler fuel without additional treatment.

Solid carbonaceous residue is black carbon with ash content of 7-8%.

For black carbon, the following parameters are correspond:

• bulk density - 477.0 g/dm³;
• adsorption activity on benzene - 142.0 g/dm³;
• sulfur content - 2.3%;
• calorific value - 24.5 MJ/kg.

Black carbon can be used as raw material for the production of activated carbon, pyrocarbon, as well as fuel in special combustion devices. In addition, now in all over the world there is an acute problem of finding new effective substitutes for expensive metallurgical cokes and the carbon black obtained because of pyrolysis, if it is properly processed, can serve as a raw material for the production of carbon reducing agents. However, a serious obstacle to this decision may be the contamination of the pyrolysis residue with sulfur, the content of which in metallurgical cokes is unacceptable.

Conclusion. Thereby, because of the experiments carried out, it can be concluded that worn rubber tires have high-energy characteristics and, by subjecting them to high-temperature deep destruction without oxygen access (pyrolysis), they can be used to obtain unconventional energy carriers in the form of liquid and gaseous fuels, as well as black carbon, i.e. promising raw material for receiving high-efficient sorbents.

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