Biphenyltetracarboxylic acid dianhydride and process for producing the same, and polyimide formed from the same and process for producing the same

1. A biphenyltetracarboxylic acid dianhydride, wherein a solution obtained by dissolving the dianhydride at a concentration of 0.05 g/ml in a 2N NaOH aqueous solution has a transmittance of light with a wavelength of 400 nm of at least 98%.

2. The dianhydride of claim 1 , which has a palladium content of not higher than 0.2 mass ppm.

3. A biphenyltetracarboxylic acid dianhydride, wherein a solution obtained by dissolving the dianhydride at a concentration of 0.05 g/ml in a 2N NaOH aqueous solution has a transmittance of light with a wavelength of 400 nm of at least 98%, obtained by heating and sublimation purification of biphenyltetracarboxylic acid,

wherein the heating is carried out at a pressure of from 1×10 2 Pa to 1.1×10 5 Pa to a maximum temperature in a range of from 210° C. to 250° C. in such a manner that a rate of temperature increase is higher than 50° C./hr for a period of at least ¼ of the time for a temperature rise from 60° C. to 210° C., and the temperature is maintained to be from 150° C. to 250° C. for from 0.5 to 10 hours.

4. The dianhydride of claim 1 , produced by a process comprising:

heating biphenyltetracarboxylic acid to produce biphenyltetracarboxylic acid dianhydride,

wherein the heating is carried out with a heating device which comprises, housed therein, a hollow rotary shaft comprising a plurality of hollow rotary heating members and which is designed to feed a heated heating medium to hollow portions of the rotary heating members via a hollow portion of the rotary shaft, to thereby supply an amount of heat required for reaction by heat transfer from each surface of the rotary shaft, rotary heating members,

wherein each of the hollow rotary heating members has a wedge shape as viewed from a side and a fan shape as viewed from a front and is secured at a neck portion of the fan shape to the hollow rotary shaft, and

wherein a biphenyltetracarboxylic acid powder is continuously supplied from a first end of the heating device as a starting material,

wherein the powder is heated as it is contacted with the hollow rotary heating members which are rotating,

wherein the powder is subjected to a dehydration reaction while it is transferred in an axial direction in the heating device, and

wherein biphenyltetracarboxylic acid dianhydride is continuously discharged as a product from a second end of the heating device.

5. The dianhydride of claim 4 , wherein, in the heating device, at least two such hollow rotary shafts are provided in a horizontal direction in parallel to one another; on each rotary shaft, rotary heating members disposed at two positions symmetrical about a point, as viewed from the front, are provided alternately in the axial direction in a predetermined number at equal distances; and the groups of rotary heating members provided on the adjacent rotary shafts take such spatial disposition that they are mutually free from contact with each other during rotation of both rotary shafts.

6. The dianhydride of claim 5 , wherein the heating device further comprises a heating jacket,

wherein the hollow rotary shaft is also designed to feed a heated heating medium to a hollow portion of the heating jacket via a hollow portion of the rotary shaft, and

wherein to the amount of heat required for the reaction is also supplied by heat transfer from each surface of the heating jacket.

7. The dianhydride of claim 4 , wherein the heating is followed by sublimation purification.

8. The dianhydride of claim 4 , wherein the sublimation purification is carried out at a temperature of at least 250° C.

9. The dianhydride of claim 3 , wherein the dianhydride obtained by the process is 3,4,3′,4′-biphenyltetracarboxylic acid dianhydride.