Continuous Equipment Is Not Continuous Manufacturing

Continuous Manufacturing (CM) has become an increasingly important objective in biopharmaceutical manufacturing. As enabling technologies have advanced, we now have continuous chromatography, continuous filtration, inline buffer preparation, continuous concentration, PAT, and increasingly sophisticated automation and control systems.

But this raises a fundamental question:

If we install continuous processing equipment, do we actually have a continuous manufacturing process?

Not necessarily.

This distinction may appear semantic at first, but it goes to the heart of how continuous bioprocesses should be designed.

A Continuous Unit Operation Does Not Make a Continuous Process

Consider a conventional downstream process consisting of several operations:

Harvest clarification → Capture chromatography → Virus inactivation → Polishing chromatography → Virus filtration → UF/DF

Suppose conventional batch capture chromatography is replaced with multi-column continuous chromatography.

The chromatography operation itself may now accept feed continuously and generate product over an extended period.

But what happens next?

If the chromatography product enters a holding vessel, waits there until the chromatography campaign is complete, and is then transferred as a batch into the next operation, we have certainly intensified one unit operation.

But have we created continuous manufacturing?

The answer depends on where we draw the process boundary.

At the chromatography equipment boundary, the operation may be continuous.

At the overall downstream process boundary, the manufacturing process remains largely time-dependent.

That distinction is extremely important.

We Need to Define Continuity at the Right Boundary

Traditionally, downstream processes have been designed around individual unit operations.

Each step has its own equipment.

Each has its own operating procedure.

Each starts and stops according to its own schedule.

Intermediate vessels connect the steps.

From an equipment perspective, this architecture makes perfect sense.

But continuous manufacturing requires us to look at the process differently.

Instead of asking:

"Is this equipment continuous?"

we should ask:

"Is material moving continuously through the manufacturing process?"

Those are very different questions.

A continuous chromatography system feeding a batch holding tank may be continuous equipment.

A continuous TFF system processing material from another holding tank may also be continuous equipment.

Connecting several such systems through intermediate batch storage does not automatically create a continuous manufacturing process.

The individual technologies may be continuous.

The process architecture may not be.

Continuous Manufacturing Is a System-Level Property

This leads to an important principle:

Continuity should be evaluated at the process level, not merely at the equipment level.

Imagine three unit operations.

Process A operates continuously.

Process B operates continuously.

Process C operates continuously.

If A finishes into a holding vessel, B later processes that vessel, and its output subsequently waits for C, then A, B, and C may individually use continuous technologies while the overall manufacturing sequence remains discontinuous.

This illustrates something fundamental:

Continuous Manufacturing is not simply the sum of continuous unit operations.

It is a property of the overall manufacturing architecture.

The Holding Vessel Tells Us Something Important

Intermediate holding vessels perform extremely useful functions in conventional batch manufacturing.

They decouple unit operations.

If upstream finishes before downstream is ready, material can wait.

If one operation processes material faster than another, the vessel absorbs the difference.

If equipment needs cleaning or preparation, the downstream process can start later.

That is precisely why they are so useful in batch manufacturing.

But it is also why they deserve special attention when designing connected and continuous processes.

The more important question is:

Which process boundaries are necessary, and which exist primarily because of traditional batch process architecture?

That is a process design question.

Process Integration, Connected Processing and Continuous Manufacturing Are Different

This is why Lisure believes several concepts frequently grouped under Process Intensification should be distinguished.

Process Integration

Process Integration asks:

Can multiple process functions be combined?

For example, can one processing technology perform functions that traditionally required two or more separate operations?

The objective may be to eliminate equipment, reduce processing time, decrease material handling, or simplify the process.

This is the first level of architectural thinking.

Connected Processing

Connected Processing asks a different question:

Can material move directly from one unit operation into another without conventional intermediate batch storage?

Here the challenge becomes synchronization.

Upstream and downstream operations must interact.

Flow rates matter.

Processing durations matter.

Equipment states matter.

Automation becomes increasingly important.

We are no longer simply optimizing individual unit operations. We are designing the relationship between them.

Continuous Manufacturing

Continuous Manufacturing goes further still.

The fundamental question becomes:

Can the manufacturing process be designed so that product-containing material continuously enters the process and product-containing material continuously exits it?

This moves the definition of continuity away from individual equipment and toward the boundary conditions of the manufacturing process itself.

That is a fundamentally different way of thinking about CM.

Not Every Unit Operation Needs to Be Intrinsically Continuous

This distinction leads to another interesting consequence.

If Continuous Manufacturing is defined at the manufacturing-system level, does every unit operation inside the system need to operate continuously in exactly the same way?

Perhaps not.

Many biopharmaceutical operations are inherently time-dependent.

Chromatography columns undergo loading, washing, elution, regeneration, and equilibration.

Certain chemical or biochemical operations require defined reaction or residence times.

Filters may require replacement.

Equipment may need cleaning or preparation.

Trying to eliminate every time-dependent behavior inside every unit operation may unnecessarily constrain process design.

A more useful engineering question may be:

Can time-dependent unit operations be organized within an overall architecture that satisfies continuous manufacturing boundary conditions?

That shifts the problem dramatically.

Instead of forcing every piece of equipment to become continuous, we design the process to operate continuously.

This is where Process Design becomes more important than individual equipment technology.

The Difference Between Technology and Architecture

The biopharmaceutical industry has developed many powerful enabling technologies for Process Intensification.

Multi-column chromatography can increase resin utilization.

SPTFF can provide continuous concentration.

Inline dilution can reduce buffer preparation requirements.

Advanced sensors and PAT can provide increasingly rich process information.

Automation can coordinate increasingly complex operations.

All of these technologies are important.

But technologies are building blocks.

Architecture determines how the building blocks work together.

A collection of sophisticated continuous technologies does not automatically create a well-designed continuous manufacturing process, just as purchasing advanced laboratory instruments does not automatically create a well-designed laboratory.

The relationships between the components matter.

The boundaries matter.

Material flow matters.

Time matters.

Control matters.

That is why Process Intensification ultimately becomes a Process Design problem.

Start With the Process, Not the Equipment

A common approach to Process Intensification is to begin by identifying continuous equipment.

Can we replace this chromatography skid with continuous chromatography?

Can we add SPTFF?

Can we introduce inline dilution?

Those can all be valuable improvements.

But there is another way to approach the problem.

Start with the process itself.

Ask:

What material needs to move through this manufacturing process?

Which process functions must occur?

Which functions can be integrated?

Where are the necessary process boundaries?

Where is intermediate storage truly required?

Which operations need to be synchronized?

What should the inlet and outlet conditions of the overall process look like?

Only after answering those questions do we determine what equipment architecture is needed.

This reverses the conventional sequence.

Instead of allowing available equipment to define the process architecture, the desired process architecture defines the equipment requirements.

This Is the PI Process Design Framework

This distinction sits at the center of Lisure's PI Process Design Framework.

Process Development determines the process science.

Process Intensification asks how that science can be executed more efficiently.

Process Integration simplifies the process.

Connected Processing removes unnecessary boundaries between operations.

Continuous Manufacturing establishes continuity at the manufacturing-process level.

Equipment, automation, control strategy, PAT, and digital systems then provide the technologies necessary to execute that architecture.

This hierarchy matters because it prevents us from confusing an enabling technology with the manufacturing objective itself.

Continuous chromatography is a technology.

Continuous filtration is a technology.

Inline conditioning is a technology.

Continuous Manufacturing is a process architecture.

The More Important Question

Perhaps we should therefore change one of the questions we commonly ask about Continuous Manufacturing.

Instead of asking:

"Which unit operations can we make continuous?"

we should ask:

"How should the overall process be designed so that manufacturing can operate continuously?"

The difference between those two questions may seem small.

It is not.

The first question begins with equipment.

The second begins with process architecture.

And that may ultimately be the difference between installing continuous equipment and actually achieving Continuous Manufacturing.

The future of Continuous Manufacturing will not be defined by how many continuous technologies we install. It will be defined by how intelligently we design the process around them.

That is the premise behind the Lisure PI Process Design Framework (PDF).

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Lisure Technology Co.

2559 US-130

Cranbury, NJ 08512