A method for producing a solid material from a solution containing one or more dissolved species or products dissolved in solvent, comprises providing the solution to one side of a porous material, the porous material having at least a layer comprising an inorganic layer having mesoporous pores and/or a carbon layer having mesoporous pores, or a mixed matrix having mesoporous pores comprising carbon and another material, and evaporating at least part of the solvent from the other side of the porous material, characterised in that a solid material is crystallised and recovered from the other side of the porous material. The porous material may comprise a layer having porosity such that it retains molecules having a molecular weight of greater than 100, 000 Daltons and the layer has pores of larger than 2nm. Unlike previous crystallization methods using membranes in which crystals are recovered from the retentate side of the membrane, crystals are recovered from the permeate side of the porous material in the present invention.