**4. Effect of process parameters on pyrolytic products**

Specifically, pyrolysis reactor selection is the principal factor to decide the quality and quantity of final products [34]. From the studies, it is observed that fixed bed reactor (slow pyrolysis) is mostly used to produce biofuels as it is simple in operation and maintenance as well easy in construction. However, advanced pyrolytic techniques such as plasma pyrolysis, microwave pyrolysis, ultrasonic pyrolysis, solar-based pyrolysis are being explored and they will likely emerge as significant concepts in the future.

From tabulated studies, it is observed that biochar yield increases at slow pyrolysis rate, i.e., approximately 350–400°C at 5°C/min for 30 minutes of holding time. Whereas, bio-oil and bio-gas occur at little higher temperatures and higher heating rates (>500°C for 20°C/min). The above phenomenon clarifies that slower heating rate provides enough time to settlement of volatiles during thermal treatment, but not in higher heating rates [35]. Similarly, pyrolysis of safflower seed cake occurs at 400–600°C at 50°C interval and at 10, 30, and 50°C/min. The authors claimed that with increasing heating rates, bio-oil yield increases, but with increase in temperature from 400 to 600°C, yield of bio-oil decreases. Because, at higher temperatures, secondary reactions occur and lead to an increase in the content of gases rather than bio-oil. However, biochar yield decreases with increment in both heating rate and temperature [22]. In **Table 2**, the effect of different thermal process parameters and their influence on pyrolytic output are listed.


#### **Table 2.**

*Process parameters of pyrolysis process.*
