A plentiful source of cellulose, hemicellulose, and lignin is agricultural waste biomass, which can be used sustainably in the pyrolysis process. The quality and yield of pyrolysis products are dependent on the thermal decomposition and degradation of the lignocellulosic biomass. To improve the susceptibility of lignocellulosic matter to degradation, various pretreatment techniques are used: i) mechanical (grinding, cutting); ii) chemical (treatment with alkali and acids); iii) thermal (steam and hot water), and biological (digestion). Maize cob as a representative of agricultural biomass was selected for investigation in this work. First, the biomass was ground and divided into two batches (raw and subjected to chemical pretreatment). The hydrogen chloride-rich gas released in the polyvinyl chloride thermal dehydrochlorination process was used for the pretreatment of maize cob. The raw and pre-treatment maize cob was then pyrolyzed in drop-tube rector at 500 C in a nitrogen atmosphere. To capture chlorides formed in the pyrolysis process and reduce the CO2 content in the pyrolysis gas, the reactor was equipped with a CaO bed. The experimental results showed that the pretreatment of maize cob influenced the yield and composition of pyrolysis products. The char obtained from the pretreatment maize cob contained more carbon (77%) than the char from the untreated biomass (72%). A positive effect on bio-oil yield was also observed, in the case of pretreatment maize cob, which increased to 38% (for untreated biomass it was 33%). Unfortunately, pyrolysis of biomass after pretreatment with hydrogen chloride promotes the formation of CO2 in pyrolysis gases. The CO2 content in the pyrolysis gas increased from 39% to 57% in the nitrogen-free state. Thus, the use of a CaO bed was applied and proved to be effective in reducing CO2 (up to 8% for the pretreatment of biomass with hydrogen chloride) and also showed catalytic activity by promoting hydrogen formation.