The Catalans never wanted to be part of Spain in the first place. They were assimilated by conquest in the early 18th C. and have never really gotten over it. Now the Catalan President is planning to hold an election in November in which complete independence will be on offer.
Catalonia: "We want out!"
The Catalan autonomous region has its own language, a long coast line, a long border with France and is ideally placed to become an independent nation. Weakness in Madrid is all the excuse they need to ramp up the separatist movement.
Catalonia is the most industrialised part of Spain; the most able to look after itself. As an independent nation they could skip most of the austerity the rest are going to have to endure. As a nation in its own right Catalonia would be as rich as the UK - per capita, and decidedly richer than the rest of Spain, and richer than countries such as Greece or Portugal.
At the moment Spain is essentially a "Castilian Empire" based in central Spain with Madrid as its nexus. The outlying regions have had to be bribed (when the empire was weak) and bullied (when the empire was strong) since the eighteenth century to keep them onside. Now the empire is weaker than it has ever been before. This does not look good for Spain as a nation state.