Another 230 million passwords tried using the brainflayer tool, using the tool really don't take up too much time, compiling the wordlists is another matter, haha... 
https://share.xboxlife.dk/file/mmq1zwe3ytdlmdc4m2i4yzc2ndeyn2yxzjhjy2y5owq.png
https://share.xboxlife.dk/file/mmq1zwe3ytdlmdc4m2i4yzc2ndeyn2yxzjhjy2y5owq.png
I think you are in the wrong way. the answer of this puzzle in not a brainwallet. let me explain:
each 64 byte hexadecimal number can be a bitcoin private key. for generating a bitcoin private key from a 32 character plain text we have 2 options:
option 1: a brainwallet: we calculate sha256 hash of text. the result is 64 byte hexadecimal number. in fact result of calculation of hsa256 of any text with any length always is a 64 byte hex. then in this option the length of text is not necessary be 32 character.
option 2: we convert each letter to its ascii code. the result of converting each English letter to its ascii code is a 2 byte hexadecimal number. then converting a 32 character text to its ascii code is a 64 byte hexadecimal number.
according to the OP post I think the option 2 is the right way.
I believe it is option 2 as well. (Except I believe you meant 32 bytes, not 64. A private key is 256 bits which is 32 bytes, or 64 characters in the range 0-9 or A-F in hexadecimal.)
It could also be sha256 of a .txt which could be formated in unicode/bigendian or utf8 (edit, but then the puzzle is not correct by saying the 32 characters string is the private key).
yes, you are right. a private key is 32 byte and 64 hexadecimal digit.