How to Invoke Async BPEL from Sync BPEL | Is it possible to add wait activity in Sync BPEL.?

Is it possible to invoke a Asynchronous BPEL from Synchronous BPEL.?
Yes. Its possible. 

Is it possible to add "Wait" activity in Sync BPEL.?
Yes. Its possible.

While you are trying to invoke a Async BPEL from Sync BPEL, you might notice that the invoke activity is success. But the receive activity will be in Pending state as show below.

Same for wait activity as well.

And also you might notice an error message in dashboard as below.

"Waiting for response has timed out. The conversation id is null. Please check the process instance for detail. "

To resolve this, you need to change the transaction property(in composite.xml) in Sync BPEL as,

<component name="BPELProcessXX" version="1.1">
<implementation.bpel src="BPELProcessXX.bpel"/>
<property name="bpel.config.transaction">requiresNew</property>
<property name="bpel.config.oneWayDeliveryPolicy" type="xs:string"
              many="false">async.persist</property>
</component>