I breastfeed my baby for 2 years now i am expecting my second is it true that formula keeps them satisfied for longer or is it a myth ?

By 2 years old, your child shouldn’t be nursing that often. He should be eating mostly regular food. If he’s crying for milk all the time, it’s not about him being hungry. You should consider trying to wean him off the breast milk so you can focus on feeding the new baby. Most toddlers only nurse occasionally as a comfort thing, like before bedtime. They don’t actually need the milk for nutrition. He should be drinking regular milk at his age. 

Most newborns need to eat every two hours, whether formula fed or not. When your baby is a few months old, and your milk supply is well established, you can supplement with formula if you like.

It isn't quite clear what you're asking or trying to do.  Here are some thoughts:

1. Your 2-year-old can and "should" be weaned if he isn't already -- unclear from your post. Many kids self-wean, but some enjoy the comfort of the processes long after their need for the nutrients has passed. 

2. Each baby is different, but breastfeeding is a 24/7 job in the first couple of months -- but generally well worth the effort.  

3. Most babies had a difficult time switching between bottle and breast.  If your newborn adapts to a bottle, you may end up having to express/pump your milk to feed in a bottle.  

4. Discuss this with your ob/gyn and pediatrician.