To ensure the integrity of fossil evidence found at climatically unstable archeological sites, the immediate coating of newly exposed fossils with a specially formulated alkaline solution is as crucial, if not more crucial than, the prompt removal of the fossil from the site.
(B) crucial as, if not more crucial than, the
(E) crucial, if not more crucial, as the

I just need an explanation between option B and E, whether the placement of the word "as" or the presence of the comparative word "than" plays a role in the elimination of option E against option B. 

This question tests you on conjunctions. If you are thorough with the use of conjunctions, this question should not be a difficult nut to crack.

Co-relative conjunctions come in pairs, joining various sentence elements that should be treated as grammatically equal

Ex

• Neither.. nor
• either.. or
• as..so
• as..as
• hardly.. when etc

Please go through the recording of Conjunctions once again.

In the given sentence,

To ensure the integrity of fossil evidence found at climatically unstable archeological sites, the immediate coating of newly exposed fossils with a specially formulated alkaline solution is as crucial, if not more crucial than, the prompt removal of the fossil from the site.

….. is as crucial as.. This is the correct structure using the correct co-relative conjunctions.

E uses the comparative adjective- “more”. It should be followed by “than” and not “as”. 

If not more crucial than.. 

And not,

if not more crucial, as. Eliminate E.

Option B is correct.