Method for the quantitative determination of Al4C3 and apparatus for carrying out the method

Abstract

The invention relates to a method for quantitatively determining Al.sub.4C.sub.3 and a device for carrying out the method.

Claims

1. Method for the quantitative determination of Al.sub.4C.sub.3, comprising the following steps: A. providing a gas-tight sealable chamber; B. providing a substance comprising Al.sub.4C.sub.3, wherein the substance comprising Al.sub.4C.sub.3 is provided in the form of a refractory product; C. providing at least one aqueous liquid that reacts with Al.sub.4C.sub.3 to form at least one gas; D. placing the substance comprising Al.sub.4C.sub.3 and the at least one aqueous liquid in the chamber; E. sealing the chamber in a gas-tight manner; F. reacting the Al.sub.4C.sub.3 of the substance comprising Al.sub.4C.sub.3 and the at least one aqueous liquid in the chamber to form the at least one gas; G. quantitatively determining the at least one gas formed; H. quantitatively determining Al.sub.4C.sub.3 in the substance comprising Al.sub.4C.sub.3 based on the quantitative determination of the at least one gas formed.

2. The method according to claim 1, wherein the at least one gas comprises methane.

3. The method according to claim 1, wherein the at least one aqueous liquid comprises water.

4. The method according to claim 1, wherein the substance comprising Al.sub.4C.sub.3 and the at least one aqueous liquid are mixed together.

5. The method according to claim 1, wherein the substance comprising Al.sub.4C.sub.3 is carbon bonded.

6. The method according to claim 1, wherein the substance comprising Al.sub.4C.sub.3 is provided in bulk.

7. The method according to claim 1, wherein the chamber is under positive pressure during the reaction of the substance comprising Al.sub.4C.sub.3 with the at least one aqueous liquid in the chamber.

8. The method according to claim 1, wherein the chamber is subjected to temperature during the reaction of the substance comprising Al.sub.4C.sub.3 with the at least one aqueous liquid in the chamber.

9. The method according to claim 1, wherein the chamber is provided by an autoclave.

10. The method according to claim 1, wherein the quantitative determination of the formed at least one gas is performed only after complete reaction of the substance comprising Al.sub.4C.sub.3 and the at least one aqueous liquid in the chamber to form the at least one gas.

11. The method according to claim 1, wherein the at least one gas is quantitatively determined by means of an infrared optical gas sensor.

12. The method according to claim 1, wherein the at least one gas is quantitatively determined by means of a pressure sensor.

13. Apparatus for carrying out the method according to claim 1, comprising: 13.1 a gas-tight sealable chamber (3); 13.2 means (7; 206) for quantitatively determining gas formed in the chamber (3).

14. The apparatus according to claim 13, wherein the chamber (3) is provided by an autoclave (2).

15. The apparatus according to claim 13, comprising at least one of the following means for quantitative determination of gas formed in the chamber: infrared-optical gas sensor (206) or pressure sensor (7).

Description

[0062] FIG. 1 a highly schematized embodiment of an apparatus for carrying out the method according to the invention;

[0063] FIG. 2 measurement results for the determination of the methane concentration and the hydrogen concentration when carrying out the exemplary embodiment of the method according to the invention; and

[0064] FIG. 3 measurement results for the pressure measurement when carrying out the exemplary embodiment of the method according to the invention.

EXEMPLARY EMBODIMENT OF THE APPARATUS

[0065] In its entirety, the apparatus in FIG. 1 is designated with the reference sign 1.

[0066] The apparatus 1 comprises an autoclave 2, which comprises a chamber 3 that can be sealed in a gas-tight manner. The autoclave 2 further comprises a stirrer 4, by means of which substances present in the chamber 3 can be stirred and mixed, and an electrical heating device for applying temperature to the chamber 3. The autoclave 2 has a lid 6, by means of which the chamber 3 can be sealed in a gas-tight manner. The autoclave 2 further has a pressure sensor 7 for measuring the pressure in the chamber 3.

[0067] A first gas conduit 100 is guided through the wall of the autoclave 2 and extends from a first end 101, at which the first gas conduit 100 opens into the chamber 3, to a second end 102. At its second end 102, the first gas conduit is connected to a nitrogen tank 103 containing nitrogen. A first gas conduit path is defined by the first gas conduit 100, through which gas can be conducted along the first gas conduit 100 from the second end 102 to the first end 101. The first gas conduit 100 can be closed by a valve 104.

[0068] A second gas conduit 200 is passed through the wall of the autoclave 2, extending from a first end 201, where the second gas conduit 200 opens into the chamber 3, to a second end 202. A second gas conduit path is defined by the second gas conduit 200, through which gas can be conducted along the second gas conduit 200 from the first end 201 to the second end 202. Along the second gas conduit 200, in the direction of flow of the second gas conduit path from the first end 201 to the second end 202, the following components are arranged: A valve 203, a gas wash bottle 204 arranged fluidically therebehind, a gas conditioning pump 205 arranged fluidically therebehind, a gas sensor 206 arranged fluidically therebehind, and a conductivity detector 207 arranged fluidically therebehind. Finally, the second gas conduit 200 opens into a gas vent 208 at the second end 202 arranged fluidically downstream of the conductivity detector 207. The second gas conduit 200 can be shut off by the valve 203. The gas wash bottle 204 includes a bath of 10% sulfuric acid through which the second gas conduit path is passed. A gas flowing along the second gas conduit path is coolable to 5 C. by the gas conditioning pump 205. To control the gas flow rate along the second gas conduit path downstream of the gas conditioning pump 205, the gas volume flow rate through the gas conditioning pump 205 can be adjusted. The gas sensor 206 is an infrared optical gas sensor, through which the concentration of gaseous methane conducted along the second gas conduit path can be measured. The conductivity detector 207 is a thermal conductivity detector through which the concentration of gaseous hydrogen conducted along the second gas conduit path is measurable.

[0069] A third gas conduit 300 extends from a portion of the first gas conduit 100 between the second end 102 and the valve 104 to a portion of the second gas conduit 200 between the valve 203 and the gas wash bottle 204. A third gas conduit path is defined by the third gas conduit 300, through which gas can be conducted along the third gas conduit 300 from the protruding portion of the first gas conduit to the protruding portion of the second gas conduit 200. The third gas conduit 300 can be closed by a valve 301.

[0070] On the conduit portion of the first gas conduit 100 between the nitrogen tank 103 and the branch of the first gas conduit 100 into the third gas conduit 300, the first gas conduit 100 includes a flow meter 105 for measuring the volume of gas of nitrogen gas flowing through the first gas conduit 100.

[0071] A fourth conduit 400 is routed through the lid 6 of the autoclave 2, extending from a first end 401, where the fourth conduit 400 opens into the chamber 3, to a second end 402. At its second end 402, the fourth conduit is connected to a water tank 403 containing water. A conduit path is defined by the fourth conduit 400, through which water can be conducted along the fourth conduit 400 from the second end 402 to the first end 401. The fourth conduit 400 can be closed by a valve 404.

Exemplary Embodiment of the Method

[0072] In practical application, according to a first exemplary embodiment, the method according to the invention is carried out on the apparatus 1 as follows, wherein the quantitative determination of the formed at least one gas, in the exemplary embodiment methane, is carried out by means of a gas analytical quantitative determination of the methane.

[0073] The aforementioned apparatus 1 is provided. By means of the autoclave 2, a gas-tight sealable chamber 3 is thus provided.

[0074] Further, an aqueous liquid in the form of water is provided by the water tank 403.

[0075] To provide a substance comprising Al.sub.4C.sub.3, a magnesia carbon brick was first prepared from 88.5 by mass of MgO, 8% by mass of C, 2.5% by mass of phenolic resin binder and 1% by mass of Al. To simulate a used condition of this magnesia carbon brick, the magnesia carbon brick was coked for 6 hours at 1,000 C. in a reducing atmosphere, and portions of Al.sub.4C.sub.3 formed from portions of the Al and C of the magnesia carbon brick. Portions of the Al in the magnesia carbon brick further reacted with nitrogen from the air during carbonization to form AlN (aluminum nitride). The coked magnesia carbon brick was crushed to a grain size below 1 mm. In this form, the appropriately used magnesia carbon brick crushed to bulk was provided as a substance comprising Al.sub.4C.sub.3.

[0076] With lid 6 lifted, 10 g of the magnesia carbon brick crushed into bulk material was introduced into chamber 3 of autoclave 2, and chamber 3 was then closed by lid 6. Valve 404 still remained closed during this process.

[0077] Valves 104 and 203 were then opened and gaseous nitrogen was introduced from nitrogen tank 103 into chamber 3 through first gas conduit 100, displacing air present in chamber 3 and escaping from chamber 3 through second gas conduit 200. Subsequently, valves 104 and 203 were closed again.

[0078] With the valve 404 open, 70 ml of water from the water tank 403 was then introduced into the chamber 3 via the fourth line 400, and the chamber 3 was subsequently sealed gas-tight by closing the valve 404. The stirrer 4 was then activated, so that the crushed magnesia carbon brick located in the chamber 3 and the water located in the chamber 3 were intimately mixed together.

[0079] At the same time, the heating device 5 was activated and the room 3 was uniformly heated from room temperature to a temperature of 150 C. within a period of 30 minutes and held at this temperature for a period of 5 minutes. After the holding time of 5 minutes at 150 C., the heating device 5 was deactivated and the autoclave 2 was cooled from the outside with water, whereupon the temperature in the room 3 dropped again.

[0080] During this temperature application to chamber 3 and mixing of the crushed magnesia carbon brick with the water in chamber 3, the Al.sub.4C.sub.3 of the magnesia carbon brick reacted with the water according to the following reaction equation (I):

Al.sub.4C.sub.3+12H.sub.2O.fwdarw.4Al(OH).sub.3+3CH.sub.4(I)

[0081] Furthermore, the AlN of the magnesia carbon brick and residues of Al unreacted during carbonization reacted with the water according to the following reaction equations (II) and (III):

AlN+3H.sub.2O.fwdarw.Al(OH).sub.3+NH.sub.3(II)

2Al+6H.sub.2O.fwdarw.2Al(OH).sub.3+3H.sub.2(III)

[0082] Due to the temperature impact on the chamber 3 and the gases methane (CH.sub.4), ammonia (NH.sub.3) and hydrogen (H.sub.2) produced according to the above reaction equations (I) to (III), the nitrogen gas introduced into the chamber 3 and the water vapor produced, the pressure in the chamber 3 increased to about 4 bar overpressure while the magnesia carbon brick and the water reacted with each other.

[0083] Before the subsequent opening of valve 203, valve 301 was still opened first and gaseous nitrogen was fed from nitrogen tank 103 through first gas conduit 100 and third gas conduit 300 into second gas conduit 200 to calibrate gas sensor 206 and conductivity detector 207. Gas conditioning pump 205 was activated to support this line of nitrogen gas.

[0084] After the temperature in room 3 dropped to 45 C., valve 203 was opened to allow the gases (methane, ammonia, hydrogen, water vapor, and nitrogen) located in room 3 to be conveyed along the second gas conduit path defined by second gas conduit 200.

[0085] To convey these gases located in the chamber 3 along the second gas conduit path defined by the second gas conduit 200, valve 104 was opened and nitrogen was fed from the nitrogen tank 103 via the first gas conduit 100 into the chamber 3. The nitrogen captured the gases located in the chamber 3, left the chamber via the first end 201 of the second gas conduit 200 and, as a carrier gas, subsequently conveyed the gases along the second gas conduit path. The gas volume of the gas conveyed in this process was determined using the flow meter 105. It is true that a portion of the gas present in the chamber 3 already flows into the second gas conduit path when the valve 203 is opened; however, the volume of this gas portion is negligible in relation to the total volume conveyed by the carrier gas, so that the gas volume can be reliably determined by the flow meter 105.

[0086] When the gases were conveyed through the bath of 10% sulfuric acid of the gas wash bottle 204, the ammonia was first washed out.

[0087] Furthermore, the gases were cooled to 5 C. during their subsequent conveyance through gas processing pump 205, causing water vapor to condense out.

[0088] The remaining gases methane, hydrogen and nitrogen were conveyed along the gas sensor 206, and the concentration of methane in the gas was continuously determined by the gas sensor 206.

[0089] Subsequently, the remaining gases were conveyed along the conductivity detector 207, with the concentration of hydrogen in the gas being continuously determined by the conductivity detector 207.

[0090] FIG. 2 shows the results of the measurement of the concentration of methane in ppm determined by the gas sensor 206 and the concentration of hydrogen in % by volume determined by the conductivity detector 207, each over the measurement time in seconds.

[0091] Finally, the gases were vented to the outside through the gas vent 208.

[0092] Of the gases formed during the reaction of the magnesia carbon brick and the water, methane was quantitatively determined by gas analysis, and then the amount of Al.sub.4C.sub.3 in the magnesia carbon brick was quantitatively determined based on this quantitative determination of methane.

[0093] First, according to the equation

V(.sub.CH4)[I]=CH.sub.4 [ppm]*10.sup.6*N.sub.2[I/min]*1 [sec]

the total volume of the extracted methane was determined.

[0094] From the measurement results for the concentration of methane according to FIG. 2, the concentration of methane was first determined over the entire measurement period, which corresponds to the integral over time CH.sub.4 dt. Then the sum of the concentration of methane over the entire measurement period was determined as CH.sub.4 [ppm]=1.312*10.sup.6 ppm.

[0095] Then, from the averaged flow rate over the measurement period of 1.00/60 [I/sec] set at flow meter 105, the total volume of methane pumped was calculated as follows:

V(.sub.CH4)[I]=1.312*10.sup.6 ppm*10.sup.6*1.00/60[I/sec]*1 [sec]=0.022 [I]

[0096] To obtain the amount of substance (in moles) of methane, the calculated volume must be divided by the molar volume of methane under standard conditions. The molar volume under standard conditions is calculated according to the general gas equation

V.sub.mol[I/mol]=(R*T)/p

with [0097] R=8,314 [(kg*m.sup.2)/(s.sup.2*mol*K)] [0098] T=273.15 [K] [0099] p=101325 [Pa]=101325 [kg/(m*s.sup.2)] [0100] as follows:

V.sub.mol=(8,314[(kg*m.sup.2)/(s.sup.2*mol*K)]*273.15 [K])/101325 [kg/(m*s.sup.2)]=0.022413 [m.sup.3/mol]=22.413 [I/mol]

[0101] The quantitative determination of the amount of methane was finally carried out according to the equation

n CH.sub.4 [mol]=V(.sub.CH4)[I]/Vmol[I/mol]

as follows:

n CH.sub.4 [mol]=0.022 [I]/22.413 [I/mol]=9.8*10.sup.4 [mol]

[0102] For the subsequent quantitative determination of the amount of substance of Al.sub.4C.sub.3 in the magnesia carbon brick was then based on this amount of substance determination for methane according to the reaction equation (I):

Al.sub.4C.sub.3+12H.sub.2O.fwdarw.4Al(OH).sub.3+3CH.sub.4(I),

after which 1 mole of Al.sub.4C.sub.3 reacts to form 3 moles of CH.sub.4 (reaction ratio ), calculated back stoichiometrically according to the following equation:

Al.sub.4C.sub.3[g]=n CH.sub.4 [mol]**M(.sub.Al4C3)[g/mol]

with

M(.sub.Al4C3)=molar mass Al.sub.4C.sub.3 [g/mol]

[0103] This allowed the amount of substance of Al.sub.4C.sub.3 in the magnesia carbon brick to be quantitatively determined as follows:

Al.sub.4C.sub.3[g]=9.8*10.sup.4 [mol]**143.96 [g/mol]=0.0471 g

[0104] The amount of Al.sub.4C.sub.3 in the magnesia carbon brick was thus quantitatively determined to be g.

[0105] With respect to the sample amount of 10 g, this corresponded to a concentration of Al.sub.4C.sub.3 in the sample magnesia carbon brick of 4710 ppm.

Exemplary Embodiment 2 of the Method

[0106] According to a second exemplary embodiment, the method according to the invention was carried out on the apparatus 1 as follows, wherein the quantitative determination of the formed at least one gas, in the exemplary embodiment methane, was carried out by means of a pressure measurement.

[0107] The method according to the second exemplary embodiment was carried out essentially according to the method according to exemplary embodiment 1. However, when the method was carried out, during heating of the chamber 3 in the temperature interval of 50 to 85 C. and during cooling of the chamber 3 in the temperature interval of 89 to 50 C., the overpressure was measured by means of the pressure sensor 7. Furthermore, the method was carried out twice, once with the sample according to exemplary embodiment 1 and another time with a magnesia carbon brick (zero sample), which differed from the magnesia carbon brick according to embodiment example 1 only in that no Al had been added to it, so that no Al.sub.4C.sub.3 could form during its coking.

[0108] FIG. 3 shows the measurement results for these pressure measurements. The solid line shows the measurement results for the pressure measurement of the zero sample, while the dashed line shows the measurement results for the pressure measurement of the magnesia carbon brick according to embodiment example 1.

[0109] Of the gases formed during the reaction of the magnesia carbon brick and the water, methane was quantitatively determined by means of the pressure measurement in order to subsequently quantitatively determine the amount of Al.sub.4C.sub.3 in the magnesia carbon brick based on this quantitative determination of methane.

[0110] For this purpose, the overpressure p was first measured with pressure sensor 7 (relative pressure measurement) at 50 C. during heating and during cooling and determined as follows:

p.sub.(Heating up 50 C.)=0.2745 [bar]

p.sub.(Cooling down 50 C.)=0.65 [bar]

[0111] Taking into account a correction factor to account for the expansion of the air, the following is obtained:

Correction factor p.sub.corr=p.sub.(zero sample cooling down 50 C.)p.sub.(zero sample heating up 50 C.)=0.1928 [bar]0.076 [bar]=0.1168 [bar]

and thus

p.sub.(corr cooling down 50 C.)=p.sub.(cooling down 50 C.)p.sub.corr=0.65 [bar]0.1168 [bar]=0.5332 [bar]

[0112] Then the absolute pressure p [bar] was calculated according to:

p[bar]=p.sub. corr[bar]+1.013 [bar]

which is therefore

p.sub.(absolute 50 C.cooling)=p.sub. corr+1.013 [bar]=0.5332 [bar]+1.013 [bar]=1.5462 [bar]=154620[kg/(m*s.sup.2)]

and on cooling

p.sub.(absolute 50 C.cooling)=p.sub. corr+1.013 [bar]=0.5332 [bar]+1.013 [bar]=1.5462 [bar]=154620 [kg/(m*s.sup.2)]

[0113] By measuring the hydrogen concentration using the conductivity detector 207 (for measurement results, see FIG. 2), the reaction kinetics could be determined. This allows the assignment of the course of the pressure signal to the reaction products H.sub.2 and CH.sub.4. This means that the pressure change during heating is mainly due to H.sub.2 and during cooling mainly to CH.sub.4.

[0114] According to the general gas equation

p*V/(R*T)=n

with

Free volume V[I]=0.1[I]=0.0001 [m.sup.3]

Density of air .sub.air[kg/m.sup.3 ]=1.1877 [kg/m.sup.3]=1.1877 [g/I]

Molar mass air M M.sub.air [g/mol]=28.949 [g/mol]

R=8.314 [(kg*m.sup.2)/(s.sup.2*mol*K)]

T.sub.50 C.=273.15 [K]+50 [K]=323.15 [K]

with the mass of air

Mass of air m.sub.air [g]=V [I]*.sub.air=0.1 [I]*1.1877 [g/I]=0.11877 [g]

and thus the mole of air

n.sub.air [mol]=m.sub.air/M.sub.air=0.11877 [g]/28.949 [g/mol]=0.0041027 [mol]

results for the mole of hydrogen

n.sub.H2 (Heating up 50 C.)=p.sub.absolute (50 C. heating up)*V/(R*T)n.sub.air 128750 [kg/(m*s.sup.2)]*0.0001 [m.sup.3]/(8.314 [(kg*m.sup.2)/(s.sup.2*mol*K)]*323.15 [K])0.0041027 [mol]=0.00068947 [mol].

[0115] Thus, the amount of substance of methane could be quantitatively determined as follows:

n.sub.CH4 50 C. [mol]=p.sub.(absolute 50 C. cooling down)*V/(R*T.sub.50 C.)n.sub.airn.sub.H2 heating up 50 C. 154620 [kg/(m*s.sup.2)]*0.0001 [m.sup.3]/(8.314 [(kg*m.sup.2)/(s.sup.2*mol*K)]*323.15 [K])0.0041027 [mol]0.00068947 [mol]=0.00096291 [mol].

[0116] For the subsequent quantitative determination of the amount of substance of Al.sub.4C.sub.3 in the magnesia carbon brick, it was then stoichiometrically calculated back on the basis of this substance amount determination for methane according to the reaction equation (I), according to which 1 mol of Al.sub.4C.sub.3 reacts to 3 mol of CH.sub.4 (reaction ratio ), as follows:

Al.sub.4C.sub.3 [g]=n CH.sub.4 (50 C.) [mol]**M(.sub.Al4C3) [g/mol]=9.6291*10.sup.4 [mol]**143.96 [g/mol]=0.0462 g

[0117] The amount of Al.sub.4C.sub.3 in the magnesia carbon brick was thus quantitatively determined to be g.

[0118] With respect to the sample amount of 10 g, this corresponded to a concentration of Al.sub.4C.sub.3 in the sampled magnesia carbon brick of 4620 ppm.

Evaluation of the Quantitative Determination of Al.SUB.4.C.SUB.3 .According to Embodiments 1 and 2

[0119] The embodiment examples 1 and 2 show that the method according to the invention allows a reliable, simple and safe quantitative determination of Al.sub.4C.sub.3.

[0120] The reliability follows in particular also from a comparison of the results for the determination according to exemplary embodiments 1 and 2, according to which the relative deviation of the measurement results for the quantitative determination on Al.sub.4C.sub.3 was only about 1.9%.

[0121] The simplicity of the method follows in particular also from the simple performance of the method, in which, among other things, a quantitative determination of the methane does not have to be performed during the entire reaction time due to the reaction in a gas-tight sealed room, as well as the simple quantitative determination of Al.sub.4C.sub.3 by means of calculation based on the quantitative determination of the methane.

[0122] The safety of the method also results in particular from the use of water for the reaction of the Al.sub.4C.sub.3.