I have a lot of experiences to change MDPV HCl salt to Freebase, with several methods.
At now the highest yield and easiest method is below;
a) Prepare something basic and hydrophilic substance, which pH must be higher than 12 (the higher pH the higher yield freebase due to existence the chemical equilibrium between MDPV-HCl, in other words ionised tertiary amine, hydrophilic style of MDPV, and MDPV freebase, in other words deionised lipophilic style of MDPV, and this balance depends on pH of aqueous layer.), for example, ammonia water NH4OH or if you could gain Sodium hydroxide solution, and non-polar solvent like hexane (Ether or methylene chloride is slightly polar and this polarity never be negligible in this case.) or pentane.
b) Put adequate amount of MDPV-HCl in a flask or a testing tube, and then pour basic aqueous liquid that is prepared. Never use hot water over 40 degree celsius because MDPV freebase is unstable, especially in the high temperature. You can confirm the changing at this time for colour turns while to yellow. MDPV freebase is white (not tan) in solid style though yellow in liquid style.
c) Pour adequate amount of non-polar solvent, and shake it. MDPV freebase is moving to non-polar layer, so this layer shows yellow, and disappears the yellow-colour substance from aqueous layer. MDPV freebase immediately decomposes in aqueous layer so hurry up. If residue substance exists in aqueous layer you have to pour non-polar solvent more amount, and do it again. At this time it must be two separated layer exist in a flask, upper is yellow organic layer and bottom is aqueous layer, this is ammonium chloride solution if you succeeded.
d) Put Non-polar layer on a dish or something, and throw aqueous layer away.
e) Wait till solvent completely volatilised. Never use heat for volatilisation, if you did MDPV would be decomposed easily and you would gain nothing. It's better to conserve lower than 10 degree Celsius temperature the environment around this step, then MDPV freebase easily appears in solid style.
f) MDPV freebase is solid at 40 degree celsius in fact, but this point it may be in oily liquid with yellow colour, then cooling the dish whole.
g) After about 12 hours MDPV freebase has turned to solid. It's white if not decomposed, so the solid is coloured at this point, you should do again with attention to temperature.
P.S.
MDPV HCl is harmful to smoke because it's close to the vaporise point and decompose point and decomposed substance is strong adrenergic toxicity. MDPV freebase, if you made properly, is almost no harm at all to smoke, but again, never forget to attention to decompose when smoked.