Joseph's comment is certainly right. Either tomcat is still running and listening on port 50500, or something else is listening on port 50500. In either case, alfresco won't start.
You can do: sudo netstat -anp | grep 50500 | grep LISTEN
that'll show you what process is listening on that port. You could then do, e.g.,
ps auxw | grep 12345 (if in the netstat it was process 12345 listening on that port). That's either another alfresco instance or possibly just something else listening on 50500. Stop that processes (and moving forward, make sure it doesn't start, maybe remove it via sudo apt-get remove or configure it to listen on another port).
Also, there's this:
SEVERE: An incompatible version 1.1.22 of the APR based Apache Tomcat Native library is installed, while Tomcat requires version 1.1.24
If you fix the 50500 issue and tomcat still won't start, look into this.