Separating sodium sulfate from chromium trioxide solution
The overall reaction is:
$$\ce{H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O}$$

How to separate chromium trioxide and sodium sulfate from solution?

Since chromium trioxide is soluble, it exist as chromic acid in the solution. So, in the reaction pot, there are compounds like  $\ce{H2CrO4, H2Cr2O7}$ along with our target compound $\ce{CrO3}$, all in equilibrium. But with the addition of a large excess of concentrated sulfuric acid, water is withdrawn from the hydrated forms and the chromium trioxide separates from the solution in the shape of red needles. Successively, the reaction pot is made to stand overnight for the chromium trioxide to precipitate slowly in form of needles and then filtered off from the solution using Buchner filter. The synthesis procedure of chromium trioxide can be found in prepchem.com:

100 grams of sodium dichromate are dissolved in 250 ml of water and
the obtained solution is filtered. 200 ml of concentrated sulfuric
acid are dropwise added with constant stirring until a slight
permanent precipitate of chromium trioxide is formed. The mixture is
cooled for half an hour or longer, then slowly, while stirring, 200 ml
of concentrated sulfuric acid are added dropwise. The reaction mixture
is left to stand over night in order that the crystal meal may become
somewhat coarser. The larger crystals (and purer) of chromium trioxide
could be obtained by heating the solution with crystal meal with
stirring to $\pu{100 ^{\circ}C}$ and allowing to cool slowly. If this process is
repeated once or twice, a more satisfactory product will be obtained.
The obtained crystals of chromium trioxide are filtered with a Buchner
funnel with a sintered glass disc instead of the usual paper filter
(chromium trioxide is a strong oxidizing agent and will oxidize
organic material).  After draining the crystals completely and
pressing the surface and treating with 15 ml of concentrated (65-70%)
nitric acid. The nitric acid is removed by suction and the operation
is repeated twice with 10 ml of nitric acid each time. Finally, the
red crystals of chromium trioxide are dried by suction as much as
possible, transferred in a dry evaporating dish and by gentle heating
the remaining nitric acid is removed. Dried product is stored in a
stoppered bottle. Yield is 60%.

Note: chromium trioxide is toxic, corrosive, a powerful oxidizer and a potent carcinogenic. Sulfuric acid is corrosive and can burn your skin if you are careless. Handle those chemicals with care. Perform this synthesis only after you become a qualified chemist. This answer is only for educational purpose only.