CS209386B1 - A method of preventing the explosion of dimethyl terephthalate vapor - Google Patents

Abstract

The invention relates to a method of preventing the explosion of dimethyl terephthalate vapors by the action of available phlegmatizers from the group of carbon dioxide or its mixture with nitrogen. The phlegmatization conditions are selected with respect to the critical content of the oxidant. The invention can be used for protection against explosion in the production of dimethyl terephthalate, or in its further processing at higher temperatures.

Description

(54) Method for preventing the explosion of dimethyl terephthalate vapors

The invention relates to a method of preventing the explosion of dimethyl terephthalate vapors by the action of available phlegmatizers from the group of carbon dioxide or its mixture with nitrogen. The phlegmatization conditions are selected with respect to the critical content of the oxidant.

The invention can be used for explosion protection during the production of dimethyl terephthalate, or during its further processing at higher temperatures.

The invention relates to a method of preventing the explosion of dimethyl terephthalate vapors with oxygen-containing gas using available phlegmatizers.

The potential explosion hazard of dimethyl terephthalate vapors may be encountered when processing this substance at elevated temperatures, e.g. during melting.

Published knowledge in the available literature regarding the explosiveness of dimethyl terephthalate vapors and explosion prevention is insufficient.

In practice, it is possible to use devices with good hermeticity and exclusion of potential ignition sources. However, these measures do not guarantee the required safety. These shortcomings are often solved by the use of pure nitrogen.

A higher effect of preventing the explosion of dimethyl terephthalate vapors is achieved by the method of the present invention.

According to the present invention, the method of preventing the explosion of dimethyl terephthalate vapors by the action of a phlegmatizing agent is carried out in such a way that carbon dioxide or its mixture with nitrogen is used as the phlegmatizing agent under conditions corresponding to the oxygen content in the system in the range of 9 to

11.7% vol.

The advantage of the method of preventing the explosion of dimethyl terephthalate vapors according to the present invention is the fact that work safety is increased by increasing the possible critical oxygen content in dimethyl terephthalate vapors, as well as the economy of the process, especially when using purified furnace gases or combustion gases, which can be treated by removing oxygen, but the presence of a small amount of oxygen or rare gases is not a defect of phlegmatization. For example, in the case of combustion gases obtained by burning fuel with a limited amount of air, the oxygen content in them is around 0.5% by volume. The advantage is the use of furnace and/or other waste gases.

The addition of the phlegmatizer can be a single or gradual process, possibly in conjunction with the transport of dimethyl terephthalate.

It is advantageous to store the phlegmatizer in a gas tank, from which it is fed into the protected space through a control valve controlled by a signal from the oxygen analyzer.

; The safety of embodiment ¹ and the advantages of the invention are represented by the following embodiment examples and figures 1 and 2, where figure 1 shows the dependence between the explosiveness of dimethyl terephthalate on the concentration of added nitrogen or carbon dioxide at a temperature of 250 °C and atmospheric pressure. The concentration of dimethyl terephthalate (% vol.) is plotted on the x-axis and the concentration of added nitrogen or carbon dioxide (% vol.) is plotted on the y-axis.

Curve 1 in the figure defines the explosive region of the dimethyl terephthalate-air-nitrogen system and curve 2 the explosive region of the dimethyl terephthalate-air-carbon dioxide system.

Figure 2 shows the explosive range of the dimethyl terephthalate-air-nitrogen system and the dimethyl terephthalate-air-carbon dioxide system at 250 °C and atmospheric pressure. The x-axis shows the concentration of dimethyl terephthalate (% vol.) and the y-axis shows the total inert content of the system (% vol.). Line 1 determines the critical oxygen content of the dimethyl terephthalate-air-nitrogen system, line 2 determines the critical oxygen content of the dimethyl terephthalate-air-carbon dioxide system and line 3 determines the dimethyl terephthalate-air system.

Example 1

Into the explosion chamber in the shape of a ball made of stainless steel with a volume of 5.58 l, equipped with jacket heating and a separately heated dispenser, further in the upper part with a thermocouple T _t and in the lower part with a thermocouple T ₂ made of NiCr — Ni with a diameter of 0.5 mm so that the measuring ends are 1/4 of the diameter away from the chamber wall and an initiation source in the form of a spiral, which forms one thread (3 mm) made of kanthal with a thickness of 0.6 mm and a capacitive pressure sensor, after three times of evacuation at a temperature of 250 °C, the partial pressure stage is dosed directly into the explosion chamber from a dispenser with a needle valve according to a mercury manometer. The dispenser is heated to a temperature of 250 °C. Next, a phlegmatizer is dosed. The explosion chamber is aerated through the needle valve with atmospheric air. After its closure, the mixture is initiated by a heated spiral, through which a current of I = 16 A passes for 4 s. Temperature changes delta tj and delta _t2 are indicated by thermocouples and recorded by recorders.

For comparison, the resulting overpressures indicated by the pressure sensor are also monitored, with oscillographic recording.

An explosion is considered to be a sudden increase in temperature immediately after initiation of more than 15 °C (60 d) indicated by a thermocouple located in the lower half of the explosion chamber. The explosion limit is determined as the arithmetic mean of the concentration of dimethyl terephthalate in systems for which a positive and negative result is found in the explosion tests.

The calculated explosion limits are rounded to 0.1 vol. %. The explosive areas of the systems are shown in the right-angled triangular diagrams in Fig. 1 according to Tables 1 and 2. The critical oxygen content according to Fig. 2 for phlegmatization with nitrogen is 9.0 vol. % and with carbon dioxide 11.7 vol. %.

Table 1. Explosive zone of the DMT — air — nitrogen system at a temperature of 250 °C and atmospheric pressure

Concentration (% vol.) Explosion ··. was + was not - Explosive limits (% vol.) Pressure rise after initiation (kPa) Note DMT added n ₂ air total N ₂ content 1 2 3 4 5 6 7 8 0.8 0 99.2 78.4 0.8 0 DMV 0.9 0 99.1 78.3 + 174. air 6.3 0 93.7 74.0 + 6.4 61 HMVvo 6.4 0 93.6 73.9 - 0 air 6.1 2.5 91.4 74.7 - 5.9 • 0 HMV 5.7 2.5 91.8 75.0 + 69 5.2 5.0 89.8 75.9 + 5.2 61 HMV 5.3 5.0 89.7 75.9 — 0 4.5 10.0 85.5 77.5 + 4.6 55 HMV 4.7 10.0 85.3 77.4 — 0 3.4 25.0 71.6 81.6 — 3.3 0 HMV 3.2 25.0 71.8 81.7 + 51 2.1 40.0 57.9 85.7 + 2.2 61 HMV 2.3 40.0 57.7 85.6 — 0 1.6 50.0 48.4 88.2 1.6 0 HMV 1.5 50.0 48.3 88.3 + 97 1.3 55.0 43.7 89.5 — 1.2 0 HMV 1.2 55.0 43.8 89.6 + 62 1.3 56.0 42.7 89.7 - 1.2 0 DMV=HMV 1.2 56.0 42.8 89.8 + 47 1.1 57.0 41.9 90.1 0 ' 1.1 55.0' 43.9 89.7 + 65 1.0 56.0 43.0 90.0 - 0 0.9 55.0 44.1 89.8 — 1.0 0 DMV 1.0 55.0 44.0 89.0 + 62 0.8 50.0 49.2 88.9 + 0.8 108 DMV 0.7 50.0 49.3 88.9 — 0 0.7 40.0 59.3 86.8 — 0.8 0 DMV 0.8 40.0 59.2 86.8 + 132

Table 2 Explosive zone of the DMT — air — CO ₂ system at a temperature of 250 °C and atmospheric pressure

Concentration (% vol.) The explosion was + not — Explosive limits (% vol.) Pressure rise after initiation (kPa) Notes DMT added every ₂ air total content n ₂ + co ₂ 0.94 40 59.06 86.66 - 1.0 0 DMV 1.06 40 58.94 86.56 + 1.2 45 53.8 87.50 - , 1>2 0 DMV 1.2 44 54.8 87.29 + 1.6 42.5 55.9 86.66 vacuum 0 1.5 42.5 56.0 86.74 + 1.6 78 HMV 1.45 39.6 58.95 86.17 + 85 2.0 35.0 63.0 84.77 + 2.0 98 HMV 2.0 36.0 62.0 84.98 — 0 3.1 20 76.9 80.75 + - 181 HMV 4.98 5 90.02 76.12 + 5.0 76 HMV 5.00 10 85.0 77.15 — 0

Explanations: DMT — dimethyl terephthalate

DM V — lower explosion limit HMV — upper explosion limit

Example 2

Inert gas (phlegmatizer) is obtained by burning a propane-butane mixture and air in a furnace lined with high-alumina bricks. From the furnace, the gases are led to a water-sprayed scrubber, where they are washed and cooled to a temperature of 325 °C. The hydrocarbon gases used contained no more than 5 mg/m ³ of hydrogen sulfide. In order to reduce the combustion temperature in the furnace and protect the lining from premature failure, the hydrocarbon gas is diluted in a mixer with combustion products before the nozzles. From the scrubber, the combustion products proceed to a heat exchanger, where they are cooled to 200 °C while heating the gas directed to the drying section for adsorbent regeneration. Oxygen removal is carried out by hydrogenation on a platinum-

Claims (1)

SUBJECT A process for preventing the explosion of dimethyl terephthalate by the action of a phlegmatizing agent, characterized in that a new catalyst at 250 ° C and atmospheric pressure is used as phlegmatizing agent. After cooling to 30 ° C in a scrubber, some of the gases are proceeded to be mixed with hydrocarbon gases. The remaining gas is compressed to a pressure of 1000 kPa, proceed for drying with active clay and further to the manifold. The production rate of the equipment used was 30 m ³ / h of dry gas containing 0.1% by volume. oxygen in the residual gas based on chromatographic analysis. Distribution gas was used to meter the dimethyl terephthalate powder into a 5 L melter in which the oxygen content was monitored by a paramagnetic analyzer at 9% v / v. above the melt, and at a system temperature of 170 ° C and deliberate initiation, no explosive conversion occurred in 10 attempts. OF THE INVENTION Carbon dioxide or a mixture thereof with nitrogen under conditions corresponding to an oxygen content of the system in the range of 9 to 11.7% by volume.