Keyword extraction from the text field in Excel file

I’m new to RapidMiner and would appreciate you help in setting up the process to extract the Keywords from the text field in Excel file (Survey results).
I could extract the KWs using the MonkeyLearn KW extraction extension, but free of charge access allows to make only a certain number of queries each month.
Could anyone suggest an alternative and free of charge way to extract the KWs (which are compounded by one or more words) from an Excel file?
 
Thank you in advance