Book binding glue can be removed without too much fuss but caution is advised.
My method is the microwave.
You can practise with what heat levels suit you but I use high as I'm impatient to move onto the next job.
With the cover removed place the naked book in the m/w on a piece of kitchen paper and let it warm up, being extremely careful not to leave it too long, as in... go off and make a cuppa !!!
This time depends on the thickness of the book, the thinner the faster it heats up.
Take the book out and either peel off individual chapters or if the glue is soft enough scrape that off with a knife.
I prefer section by section then the glue peels off easily and not so messy.
Remember the book continues to heat for a few moments once its left the m/w which helps the process but if too hot will burn your fingers.
I cannot stress enough that this method undertaken by the stupid can result in the book catching fire. And/or the glue being super hot and scalding you badly.
The secret is to do a little a lot. In and out of the m/w until its all gone.
If your a lil concerned that the m/w method may set fire to your kitchen then try method 2.
Super heated water.
Find a shallow dish a little narrower in diameter to the book you want to de-glue.
Fill this dish with water and some salt.
Place this in the micro wave and heat the water until it boils rapidly.
Remove the dish using a oven glove or dry cloth to prevent burning from the dish and scalding from the water.
Place it on a flat surface and rest the naked book to be de-glued spine down of course on the dish edges over the water.
After a moment use a knife and tease the glue a little if its soft quickly wipe it with a paper towel then return.
Once the glue is no longer viscous return the dish to the m/w and repeat proceedure.
Yes its a lil messy which is why I use method one.
Don't knock this idea until you've tried it.
If you are enjoying a warm sunny day then make the most of it by sitting outside in the sunshine with your naked book to be de-glued.
Use a magnifying glass to melt the glue off, being careful not to set ablaze this work of literature.
Place the book on a paper towl to catch the glue.
While away a few lazy minutes zapping that pesky glue.