No, you can not claim your son in 2018.
The special rule for a noncustodial parent (you) to claim a child only applies if the child is considered as living with either of you for at least 1/2 of the year.
However, when a child is emancipated, for this purpose (the special rule for divorces) he is no longer considered as living with either parent after his emancipation.
Because he was emancipated in April, he is not considered as living with either parent for more than 1/2 of they year (at least for this purpose), the special rule for a noncustodial parent (you) to claim the child no longer applies.
https://www.irs.gov/publications/p501#en_US_2018_publink1000226258