Venus has a much too dense atmosphere with sulfric acid and the surface is extremely hot and dry, how shall a colonization take place under these circumstances?

In about 50 km height, air pressure and temperature are relatively similar as those on Earth's surface.

The suggestion is therefore to produce Oxygen and water in this height. The factory that has to do that must float.

chemical reactions

picture: the most important chemical reactions

Bosch-reaction

CO₂ + 2 H₂ -> C + 2 H₂O

photosynthesis

At Photosynthesis carbon dioxyde and water is transformed into glucose and oxygen. Glucose is the raw material for all plant matter, for example cellulose

6 H₂O + 6 CO₂ -> C₆H₁₂O₆ + 6 O₂

oxyhydrogen reaction

H₂ + 2 O₂ -> 2 H₂O

The only thing missing is hydrogen. Very few of that is available on Venus, but enormous amounts can be found on the gas giants.

Hydrogen and oxygen are currently the preferred rocket fuel. So when you take oxygen from Venus and hydrogen from Jupiter, you can run a space ship between these planets.

The spacecraft would fly by Jupiter, scrape the atmosphere and fill it's tanks with hydrogen. On Venus a part of the hydrogen can be used with the Bosch-reaction to create oxygen, which is then used as rocket fuel.

If this spacecraft can be made efficient enough, it can be used to transport hydrogen from Jupiter to Venus to create water and oxygen on Venus. As a waste-product carbon would be created, too, which could be dropped to the surface or used as building material.

advantages

This way of transforming Venus has many advantages:

No new technology necessary

This plan does not need any new technology, all elements are available - for decades. The biggest parts (hydrogen/oxygen rocket engine, heat shild for re-entry) are available since the 1960's and were successfully used numerous times.

No time pressure

It's irrelevant wether the transformation is done in 100 or 100,000 years. In case of a crisis on earth, the transformation could be slowed without endangering the mission.

Once started, the process can run alone. The used energy is fully self-created. Earth is only needed for spare-parts, repairs and calculations. After a couple of decades it may even be possible to continue without any help from earth.

A lifeboat for all life

This independence is also the reason why this colony would be an excellent lifeboat in case of a planet-wide catastrophy on earth. On Venus a small number of colonists would have the basic requirements for life: Water, food, oxygen and energy. Of course you will need many other elements in small amounts which may not be obtainable locally (for example phosphorus). However with sufficient storage and efficient recycling, it might be possible to survife for hundreds of years.

problems

In comparison to so many other suggestions about Venus which often contain far-fetched elements like planet-sized mirrors or shades, changes of orbit or other huge feats, this plan is implementable very easily. In theory, the technology is readily available - in praxis, there are of course some problems which have to be solved:

Overheating and compression of the rocket fuel

To transport oxygen and hydrogen efficiently, it is necessary to keep them in fluid form and very cold. The near sun could be a problem in achieving that.

A problem is also the re-entry into the atmosphere, when much hydrogen has to be transported. The fraction during re-entry creates a lot of heat, which can be problematic.

Aggressivity of Venus' atmosphere

Possibly the biggest problem may be the acids in Venus' atmosphere. Even though the floating factory should in general be above the sulfur clouds and most much sulfuric acid, some contact will probably be inevitable in the course of the years.

Especially the produced materials (carbon fiber, cellulose, etc.) are very sensitive to acids and may be coated or protected in some other way which may need imports from earth.

Reliability and lifetime of pendler spacecraft and shuttle

To design spacecraft which run for decades or even centuries is of course a big challenge. Repairs of the shuttle could be done on Venus, but the pendler-spacecraft should not needs any repairs at all.

Therefore only parts with absolutely no wear can be used - even if this means worse efficiency. This request is contrary to most of today's rockets, which are mostly throw-away designs. Only the Space Shuttle is designed to be reusable and even that needs lots of maintainance before each start. Nevertheless, the Space Shuttle has proven that it is possible to reuse heat-shield and rocket-engines.