As other have mentioned the value of a warrant is based on its intrinsic value + a time value (equivalent to a future option). 

Right now the intrinsic value of PTA B warrants are : - $0.05   (Stock price minus conversion value  $0.30-$0.35)

Its time value is equal to its market price minus its intrinsic value : $0.10 - (-) $0.05 = $0.15

Over the previous weeks the time value has been between $0.15 to almost $0.20 with an average of about $0.18

The time value will decrease over time to reach zero,  2 -3 months before the warrants expiry date.

At a PTA stock price of $0.35, the B warrants should be traded between $0.15  to $0.20  

At $0.40, between $0.20 to $0.25

At $0.45, between $0.25 to $0.30

In 6 months from now the time value will likely decline to around 10 to 15 cent.

For a company that is expected to double production in the next 6 months, its B warrants should be traded now at a higher value, around 13 to 15 cents, under more rational markets conditions.