This is the 2nd part of our blog series on Hydrogenators. At Amar, Hydrogenators are in our DNA. For 50 years our core business has been high pressure hydrogenator design.
The last blog post gave some tips on Hydrogenator design. We continue those tips in this post. Again, please contact our excellent team of chemical engineering experts for tailor-made advice on your hydrogenator design projects. Contact us
1. Loop Reactors: Hydrogenation via loop reactors has emerged as a process intensification alternative to traditional batch hydrogenator designs. A typical loop hydrogenator schematic is shown below (Courtesy: Buss, Switzerland). These are extremely versatile devices and can be operated in both batch and flow modes. They provide excellent reintrainment and mass transfer in addition to high heat transfer capabilities.
2. Scale up safety: Here’s an anecdotal example that is very common. A plant started 20 years ago with 50 tons per month of production which utilized batch hydrogenators of 10,000 Litre size at 8 bar pressure. Over the decades market size grew and now that same plant manufactures thousands of tons per month of product. You enter a hydrogenator section with dozens of 10,000-liter batch hydrogenators. This is inefficient! Even from a safety perspective, it is not the best idea to have dozens of high pressure hydrogenators in a small area running at high pressures. There are better ways to scale up. Switch to flow mode! Use better hydrogenator designs! Talk to us. Contact us
3. Design: Hydrogenators for particular processes have developed into unique designs. Be aware of what has been already done in the industry so you can use this knowledge for your processes. Perry’s Handbook is an excellent resource. The figure below shows a hollow shaft design for the hydrogenation of nitrocaprolactum. The next figure shows a continuous hydrogenator used for edible oils. A study of such designs will give ideas for your specific application. The chemistry may be new. But the engineering typically has already been done before! The third sketch shows a hydrogenator used for the continuous hydrogenation of fats.
4. Inerting: Hydrogen will react explosively in atmospheres of Oxygen or Air. Hence inerting is a crucial operation prior to any hydrogenation. Do not ignore this step, especially in pilot plants and labs. This error or negligence in inerting has been implicated in several accident reports. See the P&ID of a section of a hydrogenation pilot plant and note the Nitrogen and ancillaries devoted to inerting.
5. Solubilities of Hydrogen: Hydrogen has relatively low solubilities in many solvents. This can be the rate-determining step. Overcome this bottleneck by increasing pressures. At the lab scale, this means having high pressure reactors capable of doing high pressure hydrogenations. Of course, at plant scale high pressure will often mean a transition to flow mode designs to keep Capex under control.
6. Catalyst choice and screening: Most hydrogenators run in a catalytic mode in the fine chemical/pharma industry. A solid catalyst e.g. Raney Nickel or Palladium / Platinum on Carbon is an example. Remember that the right catalyst can make a huge difference. Both selectivity and reaction rate can be hugely influenced. It can often be the difference between a viable commercial process and a dead end. Spend time hunting for a good catalyst. A good catalyst design is still an art but parallelizing the process will help. Invest in a parallel catalyst screening reactor. One Amar model is shown below.
7. Safe venting of hydrogenators: Hydrogen needs to be very carefully vented. Some sites will add an inert gas such as steam or N2 to the vent. Think about these choices carefully. Also consider potential sources of ignition at the vent which could be friction, static, or lightning activity. Don’t skip a flame arrestor. It will prevent any ignition from back-propagating to your hydrogenator. Remember flame arrestors for H2 duty need to be specifically designed. Do not blindly use a flame arrestor from another duty on a hydrogen vent.
We hope these tips help you on your next hydrogenator project. Please contact our experts for more specific advice. Contact us