Dear Giri,

it depends on the environment in which nitrobenzene /NB/ is present. If it is in water emulsion, you may rid of it by extraction with chloroform, benzene and like. In the case of extraction of reaction mixture after NB oxidation of lignin in wood or of isolated lignin, the alkaline pH of reaction mixture during extraction should  be mentained, not to extract the finals /vaniline, syringaldehyde, p-hydroxibenzaldhyde and derived aromatic acids/ with NB. After extraction of NB, the finals may be extracted from the mixture acidified to pH 2-3.

If you need to remove NB from another mixture, e.g. after nitration of NB to dinitrobezenes,  the rotavap destilation in rather deep vacuum at temperatures approx. 100 to 140 oC could work well. This method can be used for separation of NB from any non volatile and thermostable compound in a mixture.

The steam distillation of NB from the mixture can be also used /solubility of NB in H2O at 20 oC is approx. 0.2 g/100 ml/ in case that other components in it are much less volatile and thermostable.

In general, you may extract NB from any water emulsion on condition that the moieties present in it are soluble in water and insoluble in benzene, chloroform, diethylether, CS2  .... etc.

Good luck.

If your target compound is non-volatile, you can try steam distillation.

This is a typical case when one really needs to know more about the other components.

Giving a specific advice can be irresponsible, e.g. in cases where the suggested solution could lead to highly exothermic events. Such events sometimes manifest themselves only upon scale up. Please be more specific.

If you know that your target compound is solid, then you can try to recrystallize your  compound from suitable solvents

Is there any specific reason why nitrobenzene has to be the solvent?

@ Daniel: sometimes there is; both as a reagent and a high-boiling solvent.

 see eg. skraup reaction.

Nitrobenzene from reaction mixture can be removed by extracting the reaction mixture with ether. But one must know from what type of reaction mixture you want to separate nitrobenzene(Acid/phenol/base). You can remove one component using qualitative analysis of the mixture containing  two/three components.

I agree with my colleagues above that without knowing anything about your reaction it is very difficult to give good advice for removing nitrobenzene.  For instance it would be helpful to know about your compounds volatility, solubility and potential hazards.  If your compound is soluble in aqueous media, then a simple extraction will suffice. If it is organic soluble, it is more difficult, and there is not a good way that I know of to extract NB.  You could try steam distillation (requiring approximately 125 mL of water for every 25 mL of NB).  However, I think the easiest way (and probably the quickest way) to remove nitrobenzene with common lab equipment is to put your solution in a  multi-neck roundbottom flask, put a rubber septum on every neck except one and attach the unused neck to a rotary evaporator.  Turn the heat up of  the water bath (70-75 should do the trick if you have a decent vacuum pump) and pull full vacuum.  Put a needle through one of the rubber septums and allow it to rotate like this until dry.  In the end, you will need to use a high vacuum pump to remove residual NB or run a column.  However, this will quickly get rid of the bulk amount of solvent.  Good luck.  

You can try vacuum distillation. 

how do separate nitro benzene and aniline in a mixture