TECHNOLOGY OF EXTRACTION OF DIMETHYL ETHER FROM METHANOL

ABSTRACT

In research work, the process of obtaining dimethyl ether (DME) consists of extracting methanol directly from natural gas and converting methanol to DME in a single apparatus. Consequently, the separation and purification step of methanol (CH₃OH) as an intermediate before it is recycled to DME is eliminated. New selective zeolite catalysts are used in the synthesis, and long-term stability tests of the selective zeolite catalyst were conducted during its operation for 1000 hours. At the same time, it was found that the catalyst almost does not lose its activity under working conditions of P=0.3 MPa and T=180 ℃. In a selective zeolite catalyst, methanol can be efficiently converted to DME at a volumetric rate of 0.6 h–1 in liquid CH₃OH to DME conversion using a TriStar II (3020) automatic gas adsorption analyzer model BJH (Barrett-Joyner-Halenda) "Crystal 5000" gas chromatograph was determined. The phase composition of the catalyst samples was studied by X-ray phase analysis (XRD) using a Shimadzu XRD-6000 diffractometer. It is planned to use 1 reactor together, each of which is loaded with 25 g of catalyst. In this case, even with a short-term recovery of one of their catalysts, it is possible to organize the continuous operation of obtaining motor fuels.

АННОТАЦИЯ

В исследовательской работе процесс получения диметилового эфира (ДМЭ) состоит из выделения метанола непосредственно из природного газа и превращения метанола в ДМЭ в одном аппарате. Следовательно, этап отделения и очистки метанола (CH₃OH) в качестве промежуточного продукта перед его рециркуляцией в ДМЭ исключается. В синтезе использованы новые селективные цеолитные катализаторы, а также проведены длительные испытания на стабильность селективного цеолитного катализатора при его работе в течение 1000 часов. При этом установлено, что катализатор практически не теряет своей активности в рабочих условиях Р=0,3 МПа и Т=180 ℃. Селективный цеолитный катализатор может эффективно преобразовывать метанол в ДМЭ с объемной скоростью 0,6 ч–1 в жидком CH₃OH для превращения в ДМЭ с использованием автоматического газоанализатора TriStar II (3020), модель BJH (Barrett-Joyner-Halenda) «Crystal 5000», газ определяли хроматографом. Фазовый состав образцов катализаторов изучали методом рентгенофазового анализа (РФА) на дифрактометре Shimadzu XRD-6000. Планируется использовать вместе 1 реактор, в каждый из которых загружено по 25 г катализатора. В этом случае даже при кратковременном восстановлении одного их катализаторов можно организовать непрерывный процесс получения моторных топлив.

Keywords: methanol (CH₃OH), dimethyl ether (DME), temperature, catalyst, selective zeolite catalyst.

Ключевые слова: метанол (CH₃OH), диметиловый эфир (DME), температура, катализатор, cселективный цеолитный катализатор.

Introduction

DME production technology has been developed by several foreign companies in the United States (Air Products and Chemicals), Great Britain (VR), Japan (NKK Corp), Denmark (Haldor Topsoe) and others [1]. Existing technologies for the production of motor fuels from natural gas have the following disadvantages: high material costs, high energy consumption and consumption standards for raw materials, and low quality of the target product. At the same time, due to the sharp increase in world prices for hydrocarbon raw materials, there is a tendency in different regions of the world to dramatically change the industrial demand for the main products of petrochemical synthesis (ethene, propene, butene, DME, benzene, alkyl aromatic hydrocarbons) [2,3]. In addition, there is a change in the prices of different brands of fuel (carburettor and diesel). Therefore, when creating new production facilities, it is necessary to develop such technologies that are flexible for different manufactured products [4,5]. The second situation, on the one hand, leads to the need to develop new types of production with high profitability, and on the other hand, the range of products produced by this enterprise will be less dependent on their efficiency in terms of price changes in world markets. [6].

Based on the above, new products should be focused not only on the production of environmentally friendly high-octane motor fuels but also on the production of the main products of petrochemical synthesis - olefins, benzene, and alkyl aromatics [7].

On the other hand, all the main technological stages of the production of motor fuel, DME, and methanol are exothermic. And although the heat effect of individual reactions is relatively small and amounts to 4-11 kcal/mol, about 98% of the total conversion of raw materials is achieved in industrial equipment [8,9].

It is proposed to use polytropic shell and tube reactors in the advanced technology of the fuel synthesis process. They are easy to manufacture and use the coolant boiling in the Intertubes of the reactor to dissipate heat. As the latter, organic high-boiling compounds, water, salt solutions can be chosen. Due to the choice of the cooling device, one or another thermal operation mode of the reactor is ensured. In addition, special attention should be paid to the stability of the operating mode of the device in question - with a rapid increase in the temperature of the reagents in the reaction zone, the rate of heat transfer to the coolant immediately increases, and vice versa, when the product flow is cooled, the reaction raw materials are heated by heat carriers. Consequently, it is possible to organize its stable, almost isothermal mode in such devices [10,11].

Experimental part

The process of obtaining DME in scientific research work consists of obtaining methanol directly from natural gas and converting methanol to DME in a single apparatus. Consequently, the step of separating and purifying methanol as an intermediate before recycling it to DME is eliminated. Since the DME synthesis reaction is exothermic, the heat released in the first reactor is used to generate medium pressure steam. After the second adiabatic reactor, the fixed gas is heated and cooled in the heat exchanger of the raw material (synthesis gas) and fed to the condenser, where the product (water-methanol-DME mixture) is separated from the synthesis gas. The gaseous phase is divided into two streams - recirculation gas and waste gas, in order to avoid accumulation of inertia in the stream.

Due to the low condensation capacity of dimethyl ether, the discharge gases are sent to the absorption column, where the residues of dimethyl ether are separated from it with methanol. Long-term stability tests of the selective zeolite catalyst were conducted during its operation for 1000 hours. At the same time, it was found that the catalyst almost does not lose its activity under operating conditions of P=0.3 MPa and T=180 ℃. In a selective zeolite catalyst, methanol can be efficiently converted to DME at a volumetric rate of 0.6 h–1 in liquid.

At the end of the research stage dedicated to the study of the chemical transformation process, we move on to its analysis in the catalyst grain and in the catalytic reactor. Values of efficiency factors for catalyst granules were calculated according to this model. It turns out that the values of efficiency factors for all substances are about 0.7. For normal operation of the reactor, the temperature increase from the reactor wall to the centre of the reactor tube should not exceed 6-8 ℃. According to the results of the modelling, a system of measures to control the catalytic process was developed, which ensures the stable operation of the stand reactor and the production of high-octane gasoline of the required quality.

DME synthesis process is carried out in separate reactors. This allows the catalyst to be used for a longer period of time. In addition, pure DME (99%) can be obtained as the final product. According to this technological scheme, 0.86 tons of gasoline or 1.2 tons of DME can be obtained from 0.5 tons of methanol. Synthesis of motor fuels from DME is carried out in two reactors. The catalyst is regenerated at different times and continuous production is achieved. Motor fuels are purified only from lower alkanes. The kinetic laws of the synthesis and process of DME from methanol were studied in the device shown in Figure 1 below. The main component of the device is an internal diameter of 45 mm and a length of 600 mm, filled with a 100 mm filler for heating the injected gas mixture at once, and equipped with a gas inlet nozzle (4) from the lower side to obtain DME from natural gas made of nickel. intended reactor is (1). In the central part of the reactor intended for obtaining DME from methanol (3) the catalyst intended for obtaining DME from methanol is placed (~15 mg). Heating of the reactor designed to obtain DME from methanol was carried out with an electric furnace, the temperature of which was controlled using (7).

Temperature control in the reactor designed for obtaining DME from methanol was carried out using a thermocouple (8) and a millivoltmeter (9) located inside the reactor (a). Synthesis gas (16) and argon (17) were used to create a gas environment in the reactor designed to obtain DME from methanol. Gases were sent to the reactor designed to obtain DME from methanol with taps (10, 11). Gas consumption was determined using rotameters (12, 13) and controlled by manometers (5, 6). A reducer (15) was used to control the gas pressure in the cylinder. Fig. 1.

Figure 1. An experimental setup for studying the kinetics of DME formation

1 – Reactor designed for obtaining DME from methanol; 2 – torsion balance; 3 – Catalyst for obtaining DME from methanol; 4 – nozzle; 5, 6 – manometer; 7 – autotransformer; 8 - thermocouple; 9 milli-voltmeter; 10, 11 – crane; 12, 13– rotameter; 14, 15 - reducers; 16, 17 – gas source.

In this reactor, an additional amount of hydrogen is introduced along with the feed stream, which allows the reactor to operate stably continuously for at least 3,000 hours. In this case, even with a short-term recovery of one of their catalysts, it is possible to organize continuous operation of obtaining motor fuels. In general, the whole system of previously described measures allows to obtain motor fuel that is 10-15% lower than conventional schemes. DME recovery during operation was determined using a Crystal 5000 gas chromatograph, StarTri II (3020) automatic gas adsorption analyzer model BJH (Joyner-Barrett-Halenda).

The phase composition of the catalyst samples was studied by X-ray phase analysis (XRD) using a Shimadzu XRD-6000 diffractometer. The surface morphology of the samples was studied by scanning electron microscope based on IILMU VEGA electron microscope and ENERGY INCA 350 energy dispersive microanalysis. Diffractometer (XRD Pan Analytical) was used to study the phase composition of the catalysts, and scanning electron microscopy (SEM) was used to study the surface characteristics.

Conclusion

New selective zeolite catalysts are used in the synthesis. A low-temperature process technology has been developed for the production of methanol-based DME, which, while reducing energy consumption, increases process productivity and the quality of produced DME compared to conventional industrial processes. A catalytic process has been created that provides more than 60% of the total amount of olefinic hydrocarbons in the reaction products of the conversion of methanol and DME to lower olefins in high-silicon zeolites. The latter can serve as an effective raw material for a new generation of motor fuel, which has been proven by experience.

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