I need to reduce the pressure in an existing 1" line to 1bar before it enters a column (feed). The source of the stream is at 20 bar. We have a iso container available to use as a buffer.
Are there standard reducers available?

From your post this is a column feed.  I assume some type of distillation column.  That said, it is a more complex issue than just a standard piece of pipe to install.  You need to look at temperatures and check for flashing.  If that is the case then you need to be careful about locating a device.  Maybe the first question should be why are you trying to reduce this streams pressure?

Yes it is a distillation column. The column operates just above atmospheric and the stream is 95% water with the balance being oxygenates.
We might not be able to use pumps and therefore the 20bar driving force will need to be sufficient to overcome the resistance in the line.
However we will still need to manipulate the pressure of the line before it enters the column. And if there is flashing, it will be some of the oxygenates which we want to take off at the top of the column.

In your case you have a downstream "pressure setter" i.e. then column. This means that you will get whatever flow the dP from your source to your termination will "create". Insert an obstruction (orifice, valve whatever) and you get less. Insert a flowmeter and a regulator and you can limit your flow to a specific flow rate. The downstream pressure is set by your column - assuming that it can handle any flow rate that you deliver.

If, In fact, you have 300 psi water (solution) at the point where the pipe arrives at the column, you will have cavitation, unless the temperature of the solution is such that its vapor pressure is higher than the atmospheric pressure in the column.  It's hard to say with confidence since you have not stated flowrate, temperature and the true composition of the solution, but I suspect strongly that a globe control valve with a single-stage anticavitation cage would be appropriate for the application.  If the solution is hot and it's Flashing, an eccentric rotary plug valve with the seat on the downstream side would be a viable choice.  

Look at the architecture of the column and verify that the nozzle is not directed at something expensive and/or difficult to repair.  You want the 2-phase flow to go in to free volume so it can slow by friction instead of by impacting upon a target.

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